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Biomedical subjects

H T Chan

Publications and source records attributed to H T Chan.

12 recordsLinked to original sources
PubMed2005

Excess injury mortality among smokers: a neglected tobacco hazard.

OBJECTIVE: To assess the mortality risks from injuries for smokers and ex-smokers and to quantify the mortality burden of smoking from injury in Taiwan. METHODS: Smokers' (and ex-smokers') mortality risks from injuries were compared with that of non-smokers in a merged cohort from Taiwan. A total of 64,319 male subjects were followed up for 12-18 years. Relative risks (RR) (adjusted for age and alcohol use) and 95% confidence intervals (CI) for cause specific injury deaths were calculated using the Cox proportional hazard model. Relative risks of injury mortality were also calculated to assess the presence of dose-response relations with daily smoking quantity. RESULTS: Alcohol use adjusted relative mortality risks for all injuries (RR 1.69, 95% CI 1.39 to 2.05) including those from motor vehicle accidents (RR 1.88, 95% CI 1.44 to 2.45) and non-motor vehicle accidents (RR 1.48, 95% CI 1.11 to 1.99) were significantly higher for smokers than non-smokers. Mortality was also increased for most subtypes of non-motor vehicle injuries including falls, fires, and job related injuries. Furthermore, these increases were dose dependent, with the heaviest smokers having the highest risk and the lightest smokers the lowest risk, and ex-smokers, no increase. In 2001, over one fifth (23%) of all male injury deaths in Taiwan was associated with smoking. CONCLUSION: This study demonstrated the significant association between fatal injuries and smoking. This relation adds further weight to smoking cessation campaigns.

Accidental Falls↗
PubMed2002

An autologous blood donation program for paediatric scoliosis patients in Hong Kong.

A retrospective audit was conducted to determine the safety, efficacy and patient satisfaction related to a preoperative autologous blood donation program for children and teenagers undergoing corrective surgery for scoliosis. Forty-five of the 77 patients donated the requested amount of blood. These 45 compliant patients had been requested to donate fewer units of blood than noncompliant patients (mean 4.0 vs 4.6 respectively, P = 0.02). Twelve patients required allogeneic blood transfusion. Two patients had surgery delayed making the collected autologous blood unavailable. The extent of the operation was associated with the need for allogeneic blood transfusion. Six and a half percent of all donated units of blood were discarded. No major complications were reported. Overall, 93% of patients were satisfied with the program. With careful patient selection, good inter-departmental coordination and teamwork, preoperative autologous blood donation in paediatric patients undergoing extensive corrective surgery for scoliosis is safe and effective.

Adolescent↗
PubMed2001

nef-deleted HIV-1 inhibits phagocytosis by monocyte-derived macrophages in vitro but not by peripheral blood monocytes in vivo.

OBJECTIVE: HIV-1 infection impairs a number of macrophage effector functions, but the mechanism is unknown. We studied the role of HIV-1 Nef in modulating phagocytosis by human monocytes and monocyte-derived macrophages (MDM). DESIGN AND METHODS: Using a flow cytometric assay, phagocytosis of Mycobacterium avium complex (MAC) by monocytes in whole blood of Sydney Blood Bank Cohort (SBBC) members infected with a nef-deleted (Delta nef) strain of HIV-1 was compared with that of monocytes from uninfected or wild-type (WT) HIV-infected subjects. The specific impact of Nef on phagocytosis by MDM was determined by either infecting cells in vitro with Delta nef strains of HIV-1 or electroporating Nef into uninfected MDM. RESULTS: MAC phagocytic capacity of monocytes from SBBC members was equivalent to that of cells from uninfected individuals (P = 0.81); it was greater than that of cells from individuals infected with WT HIV-1 (P < 0.0001), irrespective of CD4 counts and HIV viral load. In contrast, in vitro infection of MDM with either Delta nef or WT strains of HIV-1 resulted in similar levels of HIV replication and equivalent impairment of phagocytosis via Fc gamma and complement receptors. Electroporation of Nef into MDM did not alter phagocytic capacity. CONCLUSIONS: This study provides evidence demonstrating the complex indirect effect of Nef on phagocytosis by peripheral blood monocytes (infrequently infected with HIV-1) in vivo. Conversely, the fact that MDM infected with either Delta nef or WT HIV-1 in vitro (high multiplicity of infection) show comparably impaired phagocytosis, indicates that HIV-1 infection of macrophages can directly impair function, independent of Nef.

CD4 Lymphocyte Count↗
PubMed2001

Quantifying complement-mediated phagocytosis by human monocyte-derived macrophages.

The present study demonstrates that SRBC can be opsonized with untreated human serum such that lysis by active complement components is minimal but sufficient opsonization occurs to permit high rates of complement-mediated phagocytosis. Phagocytosis of SRBC opsonized with 2% whole human serum by human monocyte-derived macrophages was quantified in a colourimetric assay. Ingestion of SRBC was shown to occur solely via complement receptors because no phagocytosis was observed when SRBC were coated with heat- inactivated human serum, phagocytosis was augmented by the phorbol ester, PMA, and phagocytosis was inhibited by a protein kinase C (PKC)-specific inhibitor RO 31-8220. This method was used to demonstrate directly that HIV-1 infection of human monocyte-derived macrophages inhibits complement-mediated phagocytosis and will provide a useful tool for pharmacological investigations on complement-mediated phagocytosis by adherent macrophages.

Animals↗
PubMed1999

CD40 antibody evokes a cytotoxic T-cell response that eradicates lymphoma and bypasses T-cell help.

CD40 is essential in enabling antigen-presenting cells to process and present antigen effectively to T cells. We demonstrate here that when antibody against CD40 is used to treat mice with syngeneic lymphoma, a rapid cytotoxic T-cell response independent of T-helper cells occurs, with tenfold expansion of CD8+ T cells over a period of 5 days. This response eradicates the lymphoma and provides protection against tumor rechallenge without further antibody treatment. Thus, it seems that by treating mice with monoclonal antibody against CD40, we are immunizing against syngeneic tumors. The phenomenon proved reproducible with two antibodies against CD40 (3/23 and FGK-45) in three CD40+ lymphomas (A20, A31 and BCL1) and gave partial protection in one of two CD40- lymphomas (EL4 and Ten1). Although the nature of the target antigens on these lymphomas is unknown, CD8+ T cells recovered from responding mice showed powerful cytotoxic activity against the target B-cell lymphoma in vitro.

Animals↗
PubMed1998

Deep vein thrombosis and pulmonary embolism in the Chinese population.

Deep vein thrombosis and pulmonary embolism is a well-recognised major health problem in the West. There is a deep-rooted belief among clinicians that deep vein thrombosis is rare in Asians, particularly in the Chinese population. However, it appears that the incidence of venous thrombosis and pulmonary embolism is increasing in Chinese patients. Prophylaxis reduces the incidence of venous thrombosis by 66% and of pulmonary embolism by 50%--- prophylaxis should therefore be considered for Chinese patients who have a high risk of developing postoperative deep vein thrombosis. This report reviews the current literature on this subject.

Journal Article↗
PubMed1995

Hawaiian tephritid fruit flies (Diptera): integrity of the infestation-free quarantine procedure for 'Sharwil' avocado.

In 1990, the infestation-free quarantine procedure for 'Sharwil' avocados grown in Kona, HI, was approved based on the assumption that fruits on trees are not hosts of tephritid fruit flies. In February 1992, the infestation-free quarantine procedure was suspended because of discovery of oriental fruit fly, Bactrocera dorsalis (Hendel), larval infestation in fruits on trees in certified orchards. Subsequently, an intensive field study was conducted to determine the level of tephritid fruit fly infestations in 'Sharwil' fruits. Results gathered negated two assumptions of the infestation-free quarantine procedure. First, the procedure assumed that only immature and mature green fruits are attached on trees; our data showed that, although most fruits on trees were either immature or mature green, a few ripe fruits occurred during the fruiting season. Second, the procedure assumed that mature green fruits have absolute resistance to tephritid fruit flies occurring in Hawaii; our field data showed that mature green 'Sharwil' avocados are suitable hosts of oriental fruit fly, albeit poor hosts. We present several hypotheses that may explain the failure of the infestation-free quarantine procedure for 'Sharwil' avocados. Morphological, physical, and chemical attributes of maturing 'Sharwil' fruits that may be useful in developing indices of fruit maturity and quality are also presented.

Animals↗
PubMed1995

The development of anti-CD79 monoclonal antibodies for treatment of B-cell neoplastic disease.

The B-cell antigen receptor (BCR) consists of cell surface IgM associated with the CD79 alpha/beta heterodimer. In this paper we describe a panel of monoclonal antibodies (mAbs) recognising the extracellular regions of human CD79 alpha and beta. FACS analysis demonstrated that the mAbs bind to a range of Burkitt's lymphoma lines, a mouse B-cell line (JO-72) transfected with human CD79 alpha and beta, and tumour biopsies from NHL patients. The specificity of the mAbs was confirmed by immunoprecipitation. The Ka for the binding of IgG from the anti-CD79 alpha mAbs to cell surface CD79 alpha on Ramos cells was 3 x 10(8) M-1, and their maximum level of binding, 1.7-2 x 10(5) molecules/cell, matched that obtained with anti-Fc mu and anti-Fd mu mAbs. All four anti-CD79 beta mAbs were of lower affinity. Interestingly, in growth arrest studies, we found that while all anti-Fc mu mAbs caused profound inhibition of proliferation of Ramos cells, a range of other anti-BCR mAbs, which included the anti-CD79, anti-Fab mu, anti-gamma and anti-idiotype reagents, all performed poorly giving a maximum of 25% inhibition. These differences in performance are believed to relate to the ability of anti-BCR mAbs to cross-link neighbouring surface BCR and suggest that, unlike anti-Fc mu which favours cross-linking, most of these mAbs are binding in a monogamous, non-cross-linking, union with the BCR.

Animals↗
PubMed1992

The mechanism of inhibition by EDTA and EGTA of methanol oxidation by methylotrophic bacteria.

Ethyleneglycol (aminoethylether) tetra-acetic acid (EGTA) was shown to be a potent competitive inhibitor of electron transfer between methanol dehydrogenase (MDH) and its electron acceptor cytochrome cL. Addition of Ca2+ ions relieved the inhibition by removal of the inhibitory EGTA. Removal of EGTA by gel filtration completely relieved the inhibition. EGTA did not remove the tightly bound Ca2+ present in the MDH. Indo-1, a fluorescent analogue of EGTA, bound tightly to MDH in a 1:1 ratio but not to cytochrome cL; binding was prevented by EGTA. It was concluded that EGTA inhibits methanol oxidation by binding to lysyl or arginyl residues on MDH thus preventing docking with cytochrome cL.

Alcohol Oxidoreductases↗
PubMed1991

The interaction of methanol dehydrogenase and cytochrome cL in the acidophilic methylotroph Acetobacter methanolicus.

The quinoprotein methanol dehydrogenase (MDH) of Acetobacter methanolicus has an alpha 2 beta 2 structure. By contrast with other MDHs, the beta-subunit (approx. 8.5 kDa) does not contain the five lysine residues previously proposed to be involved in ionic interactions with the electron acceptor cytochrome cL. That electrostatic interactions are involved was confirmed by the demonstration that methanol:cytochrome cL oxidoreductase activity was inhibited by high ionic strength (I), the strength of interaction being inversely related to the square root of I. Specific modifiers of arginine residues on MDH inhibited this reaction but not the dye-linked MDH activity. Modification of lysine residues on MDH that altered its charge had no effect on the dye-linked activity but inhibited reaction with cytochrome cL. When the charge was retained on modification of lysine residues, little effect on either activity was observed. Cross-linking experiments confirmed that lysine residues on the alpha-subunit, but not the beta-subunit, are involved in the 'docking' process between the proteins.

Acetobacter↗