Search PubMed⌕ Search

Biomedical subjects

K H Chan

Publications and source records attributed to K H Chan.

At least 19 recordsLinked to original sources
PubMed2007

Vascular delivery of c-myc antisense from cationically modified phosphorylcholine coated stents.

c-Myc is involved in the formation of neointimal hyperplasia. We investigated in vitro, ex vivo and in vivo release of antisense c-myc from cationically modified phosphorylcholine-coated stents, as well as the effects on c-Myc expression and neointima formation in a porcine coronary stent model. In vitro experiments were performed to determine optimal loading of stents with antisense. Stents loaded with labelled antisense were deployed in porcine arteries ex vivo and in vivo. Antisense was detected in the vessel wall directly surrounding the stent of pig carotid and coronary artery up to 48 h after stent deployment. Nuclear uptake was observed in endothelial and vascular smooth muscle cells. Labelled antisense within peripheral tissues in vivo was <1.0% of that within stented arterial segments. Control and antisense loaded stents implanted into 10 pig coronary arteries and analysed at 28 days post-stenting showed that lumen area within the antisense stents was significantly increased (i.e. 30.5% greater, P<0.01), whilst both neointimal area and neointimal thickness were significantly reduced (17.5% and 19.5%, respectively, P<0.01) compared to control stents. Cationically modified phosphorylcholine coated stent-based delivery of c-myc antisense is feasible with minimal systemic delivery and is associated with a reduction of in-stent neointimal hyperplasia in pig coronary arteries.

Animals↗
PubMed2006

Comparative analytical sensitivities of six rapid influenza A antigen detection test kits for detection of influenza A subtypes H1N1, H3N2 and H5N1.

BACKGROUND: Rapid and simple methods for diagnosing human influenza A (H5N1) disease urgently needed. The limited data so far suggest that the currently available rapid antigen detection kits have poor clinical sensitivity for diagnosis of human H5N1 disease. OBJECTIVES: To compare the analytical sensitivity of six commercially available rapid antigen detection kits for the detection of "human" (subtypes H1N1, H3N2) and "avian" (subtype H5N1) influenza A viruses. STUDY DESIGN: Six commercially available test kits for the detection of influenza A were investigated. Analytic sensitivity for the detection of two contemporary H1N1, two H3N2 and three H5N1 viruses was determined using virus culture as a reference method. RESULTS AND CONCLUSIONS: Each test kit detected the H5N1 virus subtypes as efficiently as they detected conventional human viruses of subtypes H1N1 or H3N2. However, limits of detection of influenza viruses of all subtypes by antigen detection kits were >1000-fold lower than virus isolation. Thus, the reportedly poor clinical sensitivity of these antigen detection kits for diagnosis of patients with H5N1 disease is not due to a difference of sensitivity for detecting avian influenza H5N1 compared to human influenza viruses.

Animals↗
PubMed2006

Degradation of atrazine by modified stepwise-Fenton's processes.

The removal of atrazine (ATZ) by stepwise Fenton's processes (stepwise-FP) was studied and the system models were developed through the examination of reaction kinetics. The study compared the performance of the removal of ATZ by conventional FP with stepwise-FP, where the total dose of H(2)O(2) was split and inputted into the system at different times and/or quantities. The performance of stepwise-FP was found to be better than that of conventional FP. This was probably due to the minimization of the peak concentration of H(2)O(2) in the solution, which reduced the probability that valuable H(2)O(2) and hydroxyl radicals would be consumed in forming weaker radicals. The reaction kinetics of the decay of ATZ in stepwise-FP was found to be a two-stage process; and in each stage, fast decay followed by stagnant decay was observed. Two characterized constants (the initial decay rate and the oxidative capacity) were introduced and were found to be useful in quantifying the stepwise-FP. The models for predicting stepwise-FP with respect to different dosing times and/or asymmetrical doses were developed, and were found to be very useful for evaluating the system performance and/or for process design.

Atrazine↗
PubMed2006

Three Indonesian clusters of H5N1 virus infection in 2005.

BACKGROUND: Since 2003, the widespread ongoing epizootic of avian influenza A (H5N1) among poultry and birds has resulted in human H5N1 cases in 10 countries. The first case of H5N1 virus infection in Indonesia was identified in July 2005. METHODS: We investigated three clusters of Indonesian cases with at least two ill persons hospitalized with laboratory evidence of H5N1 virus infection from June through October 2005. Epidemiologic, clinical, and virologic data on these patients were collected and analyzed. RESULTS: Severe disease occurred among all three clusters, including deaths in two clusters. Mild illness in children was documented in two clusters. The median age of the eight patients was 8.5 years (range, 1 to 38). Four patients required mechanical ventilation, and four of the eight patients (50%) died. In each cluster, patients with H5N1 virus infection were members of the same family, and most lived in the same home. In two clusters, the source of H5N1 virus infection in the index patient was not determined. Virus isolates were available for one patient in each of two clusters, and molecular sequence analyses determined that the isolates were clade 2 H5N1 viruses of avian origin. CONCLUSIONS: In 2005 in Indonesia, clusters of human infection with clade 2 H5N1 viruses included mild, severe, and fatal cases among family members.

Adult↗
PubMed2006

Avian influenza H5N1 in viverrids: implications for wildlife health and conservation.

The Asian countries chronically infected with avian influenza A H5N1 are 'global hotspots' for biodiversity conservation in terms of species diversity, endemism and levels of threat. Since 2003, avian influenza A H5N1 viruses have naturally infected and killed a range of wild bird species, four felid species and a mustelid. Here, we report fatal disseminated H5N1 infection in a globally threatened viverrid, the Owston's civet, in Vietnam, highlighting the risk that avian influenza H5N1 poses to mammalian and avian biodiversity across its expanding geographic range.

Animals↗
PubMed2006

Immune response to influenza vaccination in community-dwelling Chinese elderly persons.

We investigated the immune antibody response to influenza vaccine in community-dwelling Chinese elderly persons in Hong Kong. One hundred and twenty-eight subjects were recruited in a single-blind, randomized, and placebo-controlled trial. There was no significant baseline difference between the vaccine and placebo groups regarding the seroprotection rates (PR) (haemagglutination inhibition [HI] titre>or=1:40) and geometric mean titres (GMT) of the HI antibody titers. The PR, GMTs and serological response rates increased significantly in the vaccinated versus placebo groups in A-H1N1 at both weeks 4 and month 6. The GMTs and serological response rates but not the PR for A-H3N2 and influenza B increased significantly in vaccinated versus placebo group at week 4 and month 6 post-vaccination. Multivariate logistic regression analyses of the seroconversion rate for A-H3N2 within the vaccinated group showed that gender, coronary heart disease and the serum albumin level were significant predictors (p=0.018, 0.009 and 0.025, respectively). Influenza vaccination provoked a protective HI antibody response in community-living Chinese elderly persons. The mean number of unplanned hospital admissions per subject over 6 months was significantly lower in the vaccinated than in the placebo groups. Hospitalized elderly persons had poorer nutrition, 4-week post-immunization HI antibody titres and lower mini-mental state examination (MMSE) score than non-hospitalized elderly persons. Logistic regression analyses showed that chronic obstructive airway disease significantly increased the risk of hospitalization while the serum albumin level and 4-week A-H3N2 PR (HI>or=40) were independent predictors of a decreased risk of hospitalizations.

Aged↗
PubMed2006

Enhancement of ozone oxidation and its associated processes in the presence of surfactant: degradation of atrazine.

In this study, the degradation of atrazine (ATZ) by ozone (O3) oxidation and its associated processes (i.e. UV, UV/O3) in the presence and absence of surfactant was investigated and compared. A non-ionic surfactant, Brij 35, was selected. It was found that the presence of a low concentration of surfactant could improve the removal of ATZ by increasing the dissolution of ozone and the indirect generation of hydroxyl radicals. The saturated ozone level and the reaction rate constants were increased with increasing the concentration of surfactant and then decreased at higher surfactant doses at pH level of 2.5. A similar trend was observed at pH level of 7.0 in the presence of bicarbonate ion, because it is capable of deactivating the hydroxyl radicals generating at higher pH level. However, when the radical reactions become dominant in the ozonation (at pH 7.0 without bicarbonate), the saturated ozone level was higher than that with bicarbonate and the kinetic rate constants were increased first and levelled off with increasing of the dose of surfactant. Through the examining of a proposed unit performance index, the low concentration of surfactant is surely beneficial to the ozonation process. Besides, the direct photolysis and photo-assisted ozonation were compared to the ozonation. A significant enhancement on the decay rate of ATZ was resulted exclusively by adding the surfactant. An enhancement index for quantifying the improvement of the various processes was developed.

Atrazine↗
PubMed2006

Myopia as a latent phenotype of a pleiotropic gene positively selected for facilitating neurocognitive development, and the effects of environmental factors in its expression.

Myopia has become an almost pandemic problem in many populations. There are compelling evidence to suggest that myopia is a hereditary condition. However, myopia would constitute a definite selection disadvantage during most stages of human evolution, which is incompatible with its moderate to high prevalence in most modern populations. The rapid upsurge of myopia over just a few decades also implies that its inheritance does not follow any of the usual patterns, and environmental factors may have an important role in precipitating its occurrence in those who are genetically predisposed. Previous studies showed that myopes were, on average, more intelligent than non-myopes, and this association had been attributed to a biological link between eye growth and brain development. We propose a pleiotropic genetic model to explain the atypical epidemiologic and inheritance pattern of myopia and its relationship with neurocognitive development. This pleiotropic gene was positively selected for its facilitation of human intelligence. The myopic component is a latent phenotype; myopia will not be expressed unless some novel external factors are encountered (i.e. a "quirk" phenomenon). Therefore, the myopic component was selectively neutral in our ancestral environment. The net gain in Darwinian fitness enables the pleiotropic gene to attain a high frequency in the human population, as reflected by our current prevalence of myopia.

Animals↗
PubMed2006

The partitioning and modelling of pesticide parathion in a surfactant-assisted soil-washing system.

Soil sorption of organic pollutants has long been a problematic in the soil washing process because of its durability and low water solubility. This paper discussed the soil washing phenomena over a wide range of parathion concentrations and several soil samples at various fractions of organic content (foc) levels. When parathion dosage is set below the water solubility, washing performance is stable for surfactant concentrations above critical micelle concentration (cmc) and it is observed that more than 90% of parathion can be washed out when dosage is five times lower than the solubility limit. However, such trends change when non-aqueous phase liquids (NAPL) is present in the system. Parathion extraction depends very much on the surfactant dosage but is not affected by the levels of foc in the system. In between the extreme parathion dosage, a two-stage pattern is observed in these boundary regions. Washing performance is first increased with additional surfactant, but the increase slows down gradually since the sorption sites are believed to be saturated by the huge amount of surfactant in the system. A mathematical model has included foc to demonstrate such behavior and this can be used as a prediction for extraction.

Adsorption↗
PubMed2006

Clinical phenotypes of a large Chinese multigenerational kindred with autosomal dominant familial ALS due to Ile149Thr SOD1 gene mutation.

About 10% of amyotrophic lateral sclerosis (ALS) cases are familial. We identified a five-generation Chinese family with autosomal dominant familial ALS (FALS). We performed a detailed family study, clinical and electromyographic validation, and SOD1, VEGF and CNTF mutation analyses. Forty-five living members (16 affected) were studied and DNA samples collected. Genealogical data were collected for deceased members. Based on the duration between symptom onset to ventilator dependence, they were divided into rapidly progressive (range 1-18 months, mean (SD) duration = 12.08 (+/-6.10) months, mean (SD) age of symptom onset = 39.75 (+/-9.84) years) and slowly progressive groups (>18 months; mean (SD) age of onset = 37.25 (+/-5.32) years old). We identified a heterozygous mutation of ATT to ACT of SOD1 gene at codon 149 in exon 5 resulting in substitution of isoleucine to threonine. It co-segregated with all affected members and 11 non-symptomatic members. We report a large multigenerational Chinese FALS kindred with I149T mutation in SOD1. No polymorphisms or mutations were found to date in two known modifier genes, namely, VEGF and CNTF, which were associated with heterogeneity in the phenotype within this kindred. Follow-up of the family will be helpful to explore any potential disease markers.

Adult↗
PubMed2006

Coronaviruses in bent-winged bats (Miniopterus spp.).

A novel group 1 coronavirus was previously identified in bent-winged bats (Miniopterus spp.). Here, results are described from our ongoing surveillance of these bats for coronaviruses. These findings show that group 1 coronaviruses are endemic in these bat populations in Hong Kong. Genetic analysis of these viruses indicates that there are at least four different, but closely related, group 1 coronaviruses (bat-CoV 1A, 1B, HKU7 and HKU8) circulating in bent-winged bats. Phylogenetic analysis revealed that these group 1 bat coronaviruses have descended from a common ancestor and that these viruses have been established in these bats for a long period of time. These data provide a better understanding of the emergence and evolution of coronaviruses. Bat-CoV 1A and 1B were detected in apparently healthy Miniopterus magnater and Miniopterus pusillus, respectively, on repeated sampling occasions at a single habitat, suggesting that these viruses have established a persistent infection in these populations.

Amino Acid Sequence↗
PubMed2006

Idiopathic inflammatory demyelinating disorders after acute transverse myelitis.

Acute transverse myelitis (ATM) is commonly para-infectious. Recurrent ATM occurs in connective tissue diseases (CTD), infective myelitis and idiopathic inflammatory demyelinating disorders (IIDD) including multiple sclerosis (MS) and neuromyelitis optica (NMO). Previous studies might include NMO and idiopathic recurrent transverse myelitis (IRTM) as MS. The aim was to study the outcome of patients after a first attack of idiopathic ATM. Idiopathic ATM patients over a 6-year period were retrospectively studied. Known causes of myelopathy were excluded. Among 32 patients studied, 20 (63%) had single ATM attack upon follow up for 39-93 months, three developed recurrent ATM related to CTD (two systemic lupus erythematosus and one anti-Ro antibody positive) and nine (28.1%) developed recurrent neuroinflammation compatible with IIDD. Among IIDD patients, three had NMO, two restricted variant of NMO, three IRTM and one classical MS. NMO, its variant and IRTM had mean spinal MRI abnormality of 3.7, 2.1 and 3.9 vertebral segments respectively while non-recurrent ATM had 1.6 vertebral segments. Four (80%) of the five patients with NMO or its variant had poor neurological prognosis versus only one (5%) of non-recurrent ATM patients. IRTM patients had advanced mean onset age, 62 years vs. 43 years for non-recurrent ATM patients. In IIDD patients presenting with ATM as first attack of neuroinflammation, NMO and its variant (56%) were most frequent, then IRTM (33%), with classical MS (11%) the rarest. As long-term treatments for NMO are different from MS, early recognition of NMO and its variant is important for prevention of serious neurological deficits.

Adult↗
PubMed2006

Nissen fundoplication and gastrostomy in severely neurologically impaired children with gastroesophageal reflux.

OBJECTIVES: To study the effect of Nissen fundoplication and gastrostomy in severely neurologically impaired children. DESIGN: Prospective observational study. SETTING: Developmental Disabilities Unit of a regional medical centre in Hong Kong. PATIENTS: Children with severe neurological impairment and gastroesophageal reflux who were institutionalised between 1999 and 2004 inclusive. MAIN OUTCOME MEASURES: Incidence of vomiting, gastro-intestinal bleeding, and pneumonia in the baseline year and consecutive years following surgery; 24-hour oesophageal pH monitoring; recurrence rate (determined by 24-hour oesophageal monitoring); body weight; complications of surgery; and mortality. RESULTS: Twenty children, with a mean age at surgery of 8.5 (standard deviation, 3.5) years, were recruited. Nissen fundoplication was performed in nine children and 11 children underwent laparoscopic fundoplication. Children were monitored for 1.3 to 5.7 years (median, 3.5 years) after surgery. The incidence of vomiting and gastro-intestinal bleeding was significantly decreased following surgery (P < 0.001 and P = 0.001, respectively; Friedman's test). There was no difference between the preoperative and postoperative incidence of pneumonia (P = 0.973, Friedman's test). The median reflux index was reduced from 5.7% to 0.15% after surgery but six (30%) patients had recurrent gastroesophageal reflux. The mean body weight was 17.4 kg (standard deviation, 4.7 kg) at baseline and 22.8 kg (standard deviation, 4.4 kg) at the end of follow-up (P < 0.05, Student's t test). One patient had mild dumping syndrome soon after fundoplication. One patient had one episode of intestinal obstruction. Four patients died 1.9 to 5.0 years following surgery due to respiratory disease. CONCLUSION: Our results indicate that in severely neurologically impaired children with gastroesophageal reflux, vomiting, gastro-intestinal bleeding, and reflux indices based on 24-hour oesophageal pH monitoring were significantly reduced following fundoplication and gastrostomy. The incidence of pneumonia was unchanged. The recurrence rate of reflux was 30% and mortality rate was 20%.

Adolescent↗
PubMed2005

Acceleration and quenching of the photolysis of PCB in the presence of surfactant and humic materials.

The photodecay of a polychlorobiphenyl (PCB) congener, 2,3,4,5-tetrachlorobiphenyl (TeCB), in a surfactant-aided soil-washing process was investigated. The surfactant was found to be a useful hydrogen source in improving the TeCB photodecay via photoreduction process, while the light attenuation effect resulted from the nontarget compounds in the solution, and the impact of humic materials that co-extracted from the soil played important roles in the process of photolytic destruction of TeCB. A well-defined sediment, EPA-11, was used as the source of humic materials in examining the acceleration and quenching effects in the photolysis process. Experimental results indicated that the low dose of humic materials mainly acted as a supplementary hydrogen source to improve the photodegradation rate, while at a higher dose its amphoteric property of being a photochemical quencher become perceptible gradually, thus retarding the reaction. These effects were inspected and the dominant rate constants were quantified through the examination of possible sub-reactions in the assistant of proposed linear models in this study. The models under three different conditions at zero, low, and high humic levels associated with a light attenuation model were successfully developed to solve the dominant rate constants of the process. The good correlations between the experimental data and the models verify that the proposed reaction mechanisms of rate acceleration (resulting from the hydrogen source characteristics of the surfactant and humic material) and rate retardation (high levels of humic materials) coexist in the process.

Humic Substances↗
PubMed2005

A study of kinetic modelling and reaction pathway of 2,4-dichlorophenol transformation by photo-fenton-like oxidation.

The degradation of 2,4-dichlorophenol (2,4-DCP) by the photo-Fenton-like (Fe3+/H2O2/UVC) process under various reaction conditions was investigated. It was interesting to find that the reaction kinetics of 2,4-DCP in Fe3+/H2O2/UVC systems varied depending on the initial [Fe3+] concentration. A pseudo first-order kinetic and a non-conventional kinetic were discovered at low and higher [Fe3+] concentrations, respectively. A model was used to simulate the non-conventional kinetic process, where two character parameters (the initial decay rate and the final decay fraction) were found to be critical in determining the process. The two parameters successfully quantify the photo-Fenton-like oxidation under different concentrations of [Fe3+] and [H2O2] and the corresponding ratios of Fe(III)/H2O2. The reaction intermediates were identified by an LC/MS analysis and a reaction mechanism was proposed.

Chlorophenols↗