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Biomedical subjects

C Chan

Publications and source records attributed to C Chan.

At least 73 records · Page 4Linked to original sources
PubMed2000

Comparison of a live attenuated and an inactivated varicella vaccine to boost the varicella-specific immune response in seropositive people 55 years of age and older.

Healthy, varicella-zoster virus (VZV)-seropositive subjects, aged 55-89 years (mean age 66 years), received either 4000 PFU of live, attenuated VZV vaccine (n=85) or an equal volume of this vaccine that was heat-inactivated (n=82). Both vaccines significantly boosted VZV antibody (enzyme immunoassay) and gamma-interferon production by peripheral blood mononuclear cells stimulated by VZV antigen. These responses returned to baseline by 12 months. Circulating mononuclear cells that proliferated in response to VZV antigen were significantly more numerous (responder cell frequency assay) after either vaccine, and persisted with a half-life of 17. 5-21.3 months. There were no differences in immune response to either vaccine in this older age cohort.

Aged↗
PubMed2000

Nuclear factor-kappaB activation is involved in LMP1-mediated transformation and tumorigenesis of rat-1 fibroblasts.

The mechanism of latent membrane protein LMP1 of EBV in inducing cell transformation and tumorigenesis was investigated in Rat-1 fibroblasts. A plasmid encoding a site-specific mutant of LMP1 defective in binding to tumor necrosis factor receptor-associated death domain protein was constructed. This LMP1(TRADD) gene is 75% defective in nuclear factor (NF)-kappaB activation and 100% defective in activator protein-1 activation. When introduced into Rat-1 cells through retrovirus, the Rat-1-LMP1(TRADD) cells showed a significant reduction of focus formation and decreased tumor growth in nude mice as compared with Rat-1-LMP1 cells, suggesting that NF-kappaB or activator protein-1 activation may be important for LMP1-induced cell transformation. To further delineate the determinants of LMP1-mediated cellular transformation, a retrovirus with a dominant-negative I kappaB alpha was introduced into the transformed Rat-1-LMP1 cells. The presence of I kappaB alpha significantly suppressed both focus formation and tumorigenicity of Rat-1-LMP1 cells. Our results suggest that the activation of NF-kappaB may play an important role in LMP1-mediated cell transformation and tumorigenesis.

Animals↗
PubMed2000

Optimization of rat hepatocyte culture in citrated human plasma.

BACKGROUND: Maintenance of liver-specific functions in hepatocyte cultures during plasma exposure is critical for the clinical application of bioartificial liver assist systems. Sodium citrate is a common anticoagulant but has been shown to be cytotoxic to hepatocytes. We have tested the effect of various supplements on the viability and function of adult primary rat hepatocytes exposed to citrated plasma. MATERIALS AND METHODS: Freshly isolated rat hepatocytes were cultured in the collagen gel sandwich configuration in culture medium for 6 days followed by exposure to citrated human plasma with various supplements for 1 week. Controls were left in culture medium throughout. Viability and synthetic functions were evaluated. RESULTS: Hepatocytes exposed to unsupplemented citrated plasma lost significant viability and function within the first 2 days. Cells cultured in plasma supplemented with a fivefold concentrate of standard hepatocyte culture medium maintained urea (1. 2-2.1 micromol/day/10(6) cells) and albumin (51-62 microg/day/10(6) cells) synthesis rates equal to or higher than those of controls. Among the various components of the concentrated medium supplement, calcium chloride (1.8 mM), magnesium sulfate (0.8 mM), amino acids (fourfold Basal Medium Eagle amino acids including 4 mM glutamine), and glucagon (14 ng/ml) were found to be essential in maintaining urea synthesis. Maintenance of a high albumin synthesis rate also required the addition of hydrocortisone (7.5 microg/ml) and insulin (0.5 U/ml). CONCLUSIONS: Appropriate metabolic and hormonal supplementation of citrated human plasma prevents its cytotoxic effects and may be used in conjunction with in vivo use of bioartificial liver assist systems.

Albumins↗
PubMed2000

Is decompressive craniectomy for acute cerebral infarction of any benefit?

BACKGROUND: Acute occlusion of the major cerebral arteries results in ischaemic changes to the brain, without time for reperfusion by the collateral circulation. The subsequent cellular events lead to a breakdown of the blood-brain barrier, causing malignant cerebral edema manifested clinically by a rapid neurological deterioration. The aim of this study was to determine the value of surgical decompression in patients who present with acute cerebral infarction. METHODS: Retrospective review of patients with deteriorating consciousness level from massive cerebral ischemia and secondary edema, treated by decompressive craniectomy. RESULTSThere were 10 patients over a 2-year period from 1997-99, consisting of seven male and three female patients (mean age 47.56 years) with a mean preoperative Glasgow Coma Scale (GCS) score of 6/15. Three patients had dominant middle cerebral artery (MCA) infarction, four had nondominant MCA infarction, one had posterior cerebral artery infarction, and the remaining two had cerebellar infarction. At a mean follow-up period of 7 months, two patients had died (20% mortality), four patients (40%) were vegetative or severely disabled, and the remaining four patients (40%) had mild disability or good outcome. Favorable prognostic factors were younger age (less than 50 years) and good initial GCS score (14 or better). CONCLUSION: Decompressive craniectomy in the setting of acute brain swelling from cerebral infarction is a life-saving procedure and should be considered in younger patients who have a rapidly deteriorating neurologic status.

Adult↗
PubMed2000

Designing an amperometric thick-film microbial BOD sensor.

Thick film oxygen electrodes manufactured by screen print method have been used as a transducer for a biochemical oxygen demand (BOD) sensor. The kinetics of the immobilized yeast, Arxula adeninivorans (Arxula) has been studied. The apparent KM of immobilized Arxula (> 100 microM) is higher than free cells of Arxula (70 microM). The increase in KM caused by the effect of immobilization extends the linear range of the sensor. End-point measurement and quasi-kinetic measurement have been studied comparatively as measurement procedures with a good correlation. The Vmax for end-point measurement is 790.7 microM/s and that for quasi-kinetic measurement is 537.3 microM/s. The limit of detection is calculated 1.24 mg/l BOD. Using the quasi-kinetic measurement, instead of end-point measurements, the measuring time can be reduced from 5-30 min to 100 s. The sensor layer thickness or increase in the layer of covering gel can increase the KM that is accompanied with the extension of the linear range of the sensor. Nevertheless, increase in the layer of covering gel will not increase the saturation signal. Domestic wastewater was checked by the thick film BOD sensor and the results are satisfactory.

Bacteria↗
PubMed2000

An evaluation of whole blood testing for Helicobacter pylori infection in the Chinese population.

BACKGROUND: Near patient tests for Helicobacter pylori were developed to assist in the management of dyspepsia patients in general practice. Most studies were performed in western populations. AIM: To evaluate the rapid whole blood test (Flexpack HP) for H. pylori in the Chinese population. METHODS: Consecutive dyspeptic patients referred for upper endoscopy were recruited. During upper endoscopy, biopsies were taken from the antrum and corpus for rapid urease test (CLO test) and histological examination. After endoscopy, the whole blood test (FlexPack HP) was performed according to the manufacturer's instruction. Patients then received a 13C-urea breath test. Results of the whole blood test were compared with the gold standard (CLO test, histology and 13C-urea breath test). RESULTS: A total of 294 consecutive patients gave a valid Flexpack HP result for interpretation. The mean age of patients was 47.7 (range 15-85) years. Analysis showed a sensitivity, specificity, positive predictive value, negative predictive value and accuracy of 58%, 92%, 91%, 63% and 73% respectively. CONCLUSION: The FlexPack HP whole blood test showed good specificity but lacked sensitivity. It is not sensitive enough to be used in a general practice setting for the test-and-treat approach in the Chinese population.

Adult↗
PubMed2000

Amino acid supplementation improves cell-specific functions of the rat hepatocytes exposed to human plasma.

Maintaining hepatocyte function during plasma exposure is critical for the successful development of hepatocyte-based bioartificial liver assist systems. Past attempts to culture hepatocytes in plasma yielded discouraging results. Using a stable culture model based on sandwiching hepatocytes between two layers of collagen gel, we investigated the effect of hormone and amino acid supplementation during exposure of rat hepatocytes to heparin-treated human plasma for 1 week. Morphology and hepatocyte-specific functions were evaluated for hepatocytes cultured in Dulbecco's Modified Eagle medium (DMEM), nonsupplemented plasma, plasma supplemented with hormones, or with hormones plus amino acids. Amino acids were supplemented at four-fold concentration of Basal Medium Eagle with 4 mM glutamine, whereas hormones included 7.5 microg/mL of hydrocortisone and 50 microU/mL of insulin. Cuboidal structure and bile canaliculi formation were observed throughout the 1-week exposure period for control hepatocytes in DMEM and for hepatocytes cultured in hormone supplemented plasma. Albumin and urea synthesis rates of hepatocytes in hormone plus amino acid supplemented plasma during the last day of plasma exposure were 60.4 +/- 13.7 and 75.6 +/- 6.5 (microg/day per 1 x 10(6) cells, mean +/- SD), respectively, comparable to cultures in standard culture medium. On the other hand, hepatocytes exposed to nonsupplemented plasma suffered significant morphological and functional damage. The results of this study indicate that hormone plus amino acid supplementation help to restore function in hepatocytes exposed to plasma.

Albumins↗
PubMed2000

A comparative study of the elective treatment of variceal hemorrhage with beta-blockers, transendoscopic sclerotherapy, and surgery: a prospective, controlled, and randomized trial during 10 years.

OBJECTIVE: To compare three options for the elective treatment of portal hypertension during a 10-year period. METHODS: Patients included in the trial were 18 to 76 years old, had a history of bleeding portal hypertension, and had undergone no prior treatment. Treatment options were beta-blockers (propranolol), sclerotherapy, and portal blood flow-preserving procedures (selective shunts and the Sugiura-Futagawa operation). RESULTS: A total of 119 patients were included: 40 in the pharmacology group, 46 in the sclerotherapy group,and 33 in the surgical group. The three groups showed no differences in terms of age, Child-Pugh classification, and cause of liver disease. The rebleeding rate was significantly lower in the surgical group than in the other two groups. The rebleeding rate was only 5% in the Child A surgical group, compared with 71% and 68% for the sclerotherapy and pharmacotherapy groups, respectively. Survival was better for the low-risk patients (Child A) in the three groups, but when the three options were compared, no significant difference was found. CONCLUSIONS: Portal blood flow-preserving procedures offer the lowest rebleeding rate in low-risk patients undergoing elective surgery.

Adolescent↗
PubMed2000

Dynamics of flow, resistance, and intramural vascular volume in canine coronary circulation.

Varying coronary volume will vary vascular resistance and thereby have an effect on coronary hemodynamics. Six ventricular septa were isolated from anesthetized dogs, dispersed in a biaxial stretch apparatus at diastolic stress, and perfused artificially with an oxygenated perfluorochemical emulsion at maximal vasodilation. Flow and thickness were measured continuously by an electromagnetic flow probe and sonomicrometer. Pressure was varied sinusoidally around 30, 50, and 70 mmHg with an amplitude of 7.5 mmHg; frequencies ranged between 0.015 and 7 Hz. Bode plots of admittance (flow/pressure) and capacitance (scaled thickness/pressure) were constructed. A two-compartment model was used in which the resistances vary with volume. Realistic values of microvascular compliance ( approximately 0.3 ml x mmHg(-1) x 100 g(-1)) were found. Values 10 times higher were then found when resistances were forced to be constant. We concluded that volume dependence of resistances have to be taken into account when dynamic or static pressure-flow relations are studied and conceal the effect of a large intramyocardial compliance on arterial hemodynamics.

Animals↗
PubMed2000

An unusual case of traumatic intracranial hemorrhage caused by wakeboarding.

Wakeboarding is a relatively new and exciting sporting activity which is similar to water-skiing. While there have been several reports of water-skiing-related injuries, there has been nothing reported in the literature so far concerning injuries in wakeboarding. We present the case of a 14-year-old male who sustained an unusual intracranial subdural hemorrhage while wakeboarding and postulate on the mechanisms which could have resulted in the injury.

Adolescent↗
PubMed2000

A new preadmission staging system for predicting inpatient mortality from HIV-associated Pneumocystis carinii pneumonia in the early highly active antiretroviral therapy (HAART) era.

A common severe complication of human immunodeficiency virus (HIV) infection has been Pneumocystis carinii pneumonia (PCP). Recently, with increasing use of PCP prophylaxis and multidrug antiretroviral therapy, the clinical manifestations of HIV infection have changed dramatically and the predictors of inpatient mortality for PCP may have also changed. We developed a new staging system for predicting inpatient mortality for patients with HIV-associated PCP admitted between 1995 and 1997. Trained abstractors performed chart reviews of 1,660 patients hospitalized with HIV-associated PCP between 1995 and 1997 at 78 hospitals in seven metropolitan areas in the United States. The overall inpatient mortality rate was 11.3%. Hierarchically optimal classification tree analysis identified an ordered five-category staging system based on three predictors: wasting, alveolar-arterial oxygen gradient (AaPO(2)), and serum albumin level. The mortality rate increased with stage: 3.7% for Stage 1, 8.5% for Stage 2, 16.1% for Stage 3, 23.3% for Stage 4, and 49.1% for Stage 5. This new staging system may be useful for severity of illness adjustment in the current era while exploring current variation in HIV-associated PCP inpatient mortality rates among hospitals and across cities.

AIDS-Related Opportunistic Infections↗
PubMed2000

Ceramide path in human lung cell death.

Lung epithelium plays a significant role in modulating the inflammatory response to lung injury. Airway epithelial cells are targeted by hydrogen peroxide (H(2)O(2)) and oxygen radicals, which are agents commonly produced during inflammatory processes. The mechanisms and molecular sites affected by H(2)O(2) are largely unknown but may involve the induction of sphingomyelin (SM) hydrolysis to generate ceramide, which serves as a second messenger in initiating an apoptotic response. Here we show that exposure of human airway epithelial (HAE) cells to 50 to 100 microM H(2)O(2) induces within 5 to 10 min a greater than 2-fold activation of neutral sphingomyelinase activity with concomitant SM hydrolysis, ceramide generation, and apoptosis. On the other hand, activation of protein kinase C (PKC) by 12-O-tetradecanoylphorbol-13-acetate inhibits both H(2)O(2)-induced ceramide production and apoptosis. The apoptotic response could be restored by the addition of 25 microM cell-permeant C6-ceramide. These findings indicate that ceramide, the product of SM hydrolysis, plays an important role in H(2)O(2)-induced apoptosis in HAE cells, and that PKC counteracts ceramide-mediated apoptosis in these cells. We suggest that the mediation of epithelial cell apoptosis by ceramide and its inhibition by PKC constitute a central mechanism by which inflammatory processes are modulated in the epithelium of the lung.

Apoptosis↗
PubMed2000

Psychiatric morbidity and illness experience of primary care patients with chronic fatigue in Hong Kong.

OBJECTIVE: The authors' goal was to examine the prevalence and experience of psychiatric morbidity among primary care patients with chronic fatigue in Hong Kong. METHOD: One hundred adult patients with medically unexplained fatigue for 6 or more months were assessed with the Explanatory Model Interview Catalogue, psychopathological rating scales, and an enhanced version of the Structured Clinical Interview for DSM-III-R. RESULTS: The lifetime prevalence of DSM-III-R depressive and anxiety disorders was 54%. Current depressive and anxiety disorders were identified in 28 patients, who exhibited more psychopathology and functional impairment than other patients. Thirty-three patients had somatoform pain disorder, and 30 had undifferentiated somatoform disorder, but most of them could also be diagnosed as having shenjing shuairuo (weakness of nerves) and, to a lesser extent, ICD-10 neurasthenia. Chronic fatigue syndrome diagnosed according to the 1988 Centers for Disease Control criteria was rare (3%) and atypical. Generally, patients mentioned fatigue if asked, but pains (36%), insomnia (20%), and worries (13%) were the most troublesome symptoms. Most patients attributed illness onset to psychosocial sources. CONCLUSIONS: Psychiatric morbidity was common among primary care patients with chronic fatigue. Subthreshold psychiatric morbidity was very common and was more validly represented by the disease construct of shenjing shuairuo or neurasthenia than somatoform disorder.

Adolescent↗
PubMed2000

Applications of immunohistochemistry in the evaluation of immunosuppressive agents.

Immunohistochemistry (IHC) can be a valuable endpoint to evaluate lymphocyte subpopulations in tissues following exposure to presumptive immunosuppressive agents. IHC is more sensitive than conventional histology in detecting subtle differences in lymphocyte numbers and distribution in tissue. In combination with flow cytometric analysis of peripheral lymphocyte subpopulations, IHC can determine if alterations detected in the peripheral blood are a result of trafficking or reflective of changes in tissue distribution. These techniques can be used to evaluate adult animals as well as to evaluate the effects of immunosuppressive agents on fetal tissues in reproductive toxicology studies. While IHC can enhance the detection of subtle changes in lymphocyte subpopulations in tissue, the evaluation of additional endpoints of immune function must be done to further assess the biological or clinical significance of these changes.

Animals↗
PubMed2000

A study of health services for the Chinese minority in Manchester.

This article describes a small-scale study which examined the views of both users and providers of primary healthcare services for the Chinese minority in Manchester. Thirty Chinese mothers of pre-school children were selected from immunization records and interviewed face-to-face at their homes using structured questionnaires and unstructured discussions. Thirty-eight GPs who had the largest number of Chinese patients (n = 10) registered with them, and 26 health visitors who worked with these GPs were also interviewed, using semi-structured questionnaires. The findings indicate that a discrepancy exists between the views of GPs, health visitors and Chinese mothers on the use of primary healthcare services. The health professionals' awareness of the effects of socio-economic characteristics, demographic profile and indigenous health beliefs and attitudes on the quality of primary healthcare services for Chinese families in Manchester is discussed.

Adult↗
PubMed2000

Postexposure effectiveness of varicella vaccine.

OBJECTIVE: 1) To describe the postexposure effectiveness of varicella vaccine in a homeless shelter; and 2) to demonstrate an effective public health intervention and its implications. DESIGN: A prospective observational study. SETTING: A women and children's shelter in Philadelphia with 2 cases of varicella before intervention. OUTCOME MEASURES: Varicella in vaccinated and unvaccinated shelter residents; vaccine effectiveness for prevention of varicella when administered after exposure among children <13 years of age. RESULTS: Sixty-seven shelter residents received varicella vaccine after exposure, including 42 children <13 years of age. One child who was unvaccinated developed varicella, but no vaccinated child developed typical disease. Vaccine effectiveness was 95.2% (95% CI, 81.6%-98.8%) for prevention of any disease and 100% for prevention of moderate or severe disease among the children <13 years of age. CONCLUSION: When used within 36 hours after exposure to varicella in a setting where close contact occurred, varicella vaccine was highly effective in preventing further disease. This study provides support for the recent recommendation by the Advisory Committee on Immunization Practices to administer varicella vaccine after exposure: this practice should minimize the number of moderate or severe cases of disease and prevent prolonged outbreaks.

Chickenpox↗