Biomedical subjects

H Chan

Publications and source records attributed to H Chan.

At least 55 records · Page 3Linked to original sources

PubMed1999

Sputum eosinophils and exhaled nitric oxide during late asthmatic reaction in patients with western red cedar asthma.

Examination of sputum for eosinophils and measurement of exhaled nitric oxide have been proposed as noninvasive methods of assessing airway inflammation in asthma. The use of these tests in the evaluation of patients with occupational asthma has not been reported. This study investigated the changes in sputum eosinophils and exhaled NO before and at intervals after inhalation challenge with plicatic acid in patients with suspected western red cedar asthma. Of 17 subjects who underwent challenge, nine had a positive bronchoconstrictor reaction (responders) and eight had a negative reaction (nonresponders). At 6 and 24 h after plicatic acid challenge, there was a significant increase in sputum eosinophils among responders, which was inversely related to the fall in forced expiratory volume in one second (FEV1) at 6 h. An increase in sputum eosinophils was also found in three nonresponders. Levels of exhaled NO increased at 24 h after challenge with plicatic acid in both responders and nonresponders, being significant only in nonresponders. No correlation was found between the increase in nitric oxide and the magnitude of the functional changes in the airways. There were significant correlations between the degree of sputum eosinophilia and the level of exhaled NO before and after methacholine and plicatic acid challenge. In conclusion, the late asthmatic reaction induced by plicatic acid in patients with western red cedar asthma is associated with an increase in sputum eosinophils. The usefulness of measuring sputum eosinophils and exhaled nitric oxide in the clinical evaluation of patients with suspected occupational asthma caused by low molecular weight compounds has yet to be determined.

Adult↗

PubMed1999

Cyclic-AMP induction of gap junctional intercellular communication increases bystander effect in suicide gene therapy.

The phenomenon of the "bystander effect" (BE) observed in suicide gene therapy studies leads to the intriguing possibility that cytotoxicity can be achieved even in tumor cells that have not themselves been targeted with novel genetic material. There is considerable data suggesting the role of gap junction-mediated intercellular communication (GJIC) in the BE. Transfer of connexin (Cx)-encoding genes, the building blocks of GJIC, has been shown both in vitro and in vivo to increase the BE. Since the loss of GJIC is a common feature of cancer cells, we examined the consequence of GJIC up-regulation on the BE in suicide gene therapy. We used 8-bromo-cyclic-AMP to induce Cx43 and GJIC. In mixing assays, using various proportions of cells containing viral thymidine kinase delivered by an adenoviral delivery system or stably transduced by a retrovirus vector, 8-bromo-cyclic-AMP enhanced the BE of cell killing using ganciclovir. The induction in cell killing was more significant when a low percentage of the cell population was infected, which is the relevant clinical situation. We have demonstrated that this is not due to an effect on infectivity or suicide gene expression. Since decreased GJIC is part of the transformed phenotype, induction of Cxs provides an element of selectivity to suicide gene therapy. Our study adds strength to the rationale to develop clinically tolerable GJ inducers to potentiate the effect of suicide gene therapy via the BE.

8-Bromo Cyclic Adenosine Monophosphate↗

PubMed1998

Expression and characterization of human tissue kallikrein variants.

Human tissue kallikrein is a serine protease implicated in the pathology of various inflammatory disorders. As one of the two principal enzymes that generate proinflammatory kinin peptides in vivo, tissue kallikrein represents an attractive target for therapeutic intervention in diseases such as asthma, pancreatitis, and rheumatoid arthritis. Three distinct human tissue kallikrein variants, differing in one or two amino acid substitutions, are predicted to exist based on genomic or cDNA nucleotide sequences derived from different tissues. The effects of these substitutions on the biochemical properties of tissue kallikrein are unknown but could, in principle, confer tissue-specific functions on the enzyme or affect the clinical utility of specific kallikrein inhibitors. All three variants, as well as a deglycosylated derivative, were expressed in high yield as recombinant proteins in Pichia pastoris. The recombinant kallikrein variants and natural urinary kallikrein all hydrolyzed synthetic peptides with similar specificity and efficiency and released kallidin from kininogen at comparable rates. Similarly, no significant differences were observed in the interactions between kallikrein variants and protein inhibitors such as SBTI, alpha1-PI, and aprotinin. We conclude that the known tissue kallikrein variants represent allelic variants and are not likely to have tissue-specific activity related to the amino acid substitutions.

Amino Acid Sequence↗

PubMed1998

The health consequences of vertebral deformity in elderly Chinese men and women.

The following health consequences of vertebral deformity in Hong Kong elderly Chinese men and women were studied: the prevalence of back pain, disability due to back pain, and low morale. Lateral X-ray films were taken of the thoracic and lumbar spine of 796 community-dwelling Chinese subjects (396 men, 400 women) (aged 70-79). Subjects with one or more definitely deformed vertebra (reduction in vertebral height 3 SD or more below the mean) were classified as definite cases, those with one or more mildly deformed vertebra (reduction in vertebral height 2-2.99 SD below the mean) as mild cases, and the rest as controls. The prevalence and consequences of back pain were measured by a standardized questionnaire, and morale was measured by the Geriatric Morale Score. The relative risk (RR) and 95% confidence interval (CI) of having back pain and being depressed were calculated by logistic regression. Classifications included 16% of men and 30% of women as definite cases, 37% of men and 35% of women as mild cases, and 47% of men and 35% of women as controls. The relative risk (RR) of back pain was 2.3 (95% CI 1.4-3.9) (P < 0.05) in women with definite deformity and 1.5 (95% CI 0.9-2.5) (P > 0.05) in women with mild deformity, as compared with controls. Sixty-four percent of all men had back pain. This prevalence was much higher than figures obtained in a previous survey on low back pain. The prevalence of back pain did not differ by deformity status, but more men with vertebral deformity were on analgesic. There was no significant association between disability due to back pain and vertebral deformity in women. The RR for having a low morale score (of 5 and below) was 2.3 (95% CI 1.3-4.1) (P < 0. 05) in women with mild deformity; men with vertebral deformity did not have a low morale. It was concluded that vertebral deformity was associated with significant back pain and psychological morbidity in elderly Chinese women. Although men with vertebral deformity did not report more back pain, more were on analgesics than controls.

Aged↗

PubMed1998

Use of adjuvant ICE chemotherapy in the treatment of anaplastic ependymomas.

Despite the improved outcome for patients with ependymoma treated by surgery and radiotherapy, their prognosis remains relatively poor. To assess the impact of adjuvant chemotherapy, we reviewed the overall survival of consecutive patients with anaplastic ependymoma treated over a 10-year period with surgery and ICE (ifosfamide+ VP 16+carboplatin) chemotherapy with or without radiation at our institution. There were 11 patients (6 male, 5 female), with a median age of 3.4 years (range 1.2-1 1.1): 4 under 2 years and 7 were over 2 years old. Overall, 5 had gross total resections: 4 are alive, 2 in continuous complete remission and 2 in second complete remission. One patient who was less than 2 years old died. Among the 6 with subtotal resection, 2 achieved a complete remission after chemotherapy. However, 5 of the 6 patients have since died of progressive disease, with a median overall survival of 75 months. Overall survival was 24% and progression-free survival was 39%. In 2 of 6 patients with residual postoperative disease a temporary objective response was noted with adjuvant ICE chemotherapy. This regimen did not confer an overall survival advantage.

Aging↗

PubMed1998

Comparison of survival outcomes in patients with intracranial germinomas treated with radiation alone versus reduced-dose radiation and chemotherapy.

Concern about long-term sequelae of irradiation has led to the use of adjuvant chemotherapy with lower dose irradiation in the treatment of intracranial germinomas. To assess the feasibility of this approach versus radiation only, the survival of 16 evaluable patients (13 boys, 3 girls) with biopsy-proven intracranial germinomas treated at the Hospital for Sick Children was assessed. Between 1977 and 1988, 8 patients were treated with radiation only: 7 received tumour doses between 4000 and 5100 cGy and spinal prophylaxis; 1 received 3060 cGy to the tumour with no prophylaxis. After a median follow-up of 84 months, 7 are in continuous first CR and 1 is in second CR. Between 1988 and 1996, 8 patients received adjuvant platinum- and etoposide-based chemotherapy for two or three cycles followed by local irradiation to the tumour (2500-3500 cGy). After a median follow-up of 40 months, 6 are in continuous first CR and 1 in second CR; 1 has died of progression. Survival outcomes in the two groups are similar. Prospective trials to assess event-free survivals, neurocognitive and neuroendocrine outcomes are needed before definitive treatment recommendations can be made.

Adolescent↗

PubMed1998

T-lymphocyte responses to plicatic acid-human serum albumin conjugate in occupational asthma caused by western red cedar.

BACKGROUND: T cells are known to play a major role in the pathogenesis of atopic allergic asthma, but it is less clear whether they are involved in occupational asthma caused by low molecular weight chemicals such as plicatic acid. OBJECTIVES: We sought to determine whether peripheral blood T cells from patients with western red cedar asthma (WRCA) recognize plicatic acid (PA) conjugated to human serum albumin (HSA) as judged by proliferation or cytokine production and to analyze the response to PA inhalation with flow cytometry. RESULTS: Significant proliferative responses to PA-HSA were observed in eight of 33 patients with WRCA, none of 10 exposed nonasthmatic cedar workers, and one of 18 nonasthmatic control subjects. Two of 25 patients with WRCA also showed proliferative responses to unconjugated PA. All the WRCA responders were either currently exposed to cedar or had ceased exposure within the preceding 2 years. None of the four patients receiving oral steroids responded, but inhaled steroids did not seem to influence responsiveness. No correlations were found between the maximum stimulation response and any of the current FEV1 values, the current PC20 methacholine values, or the magnitude of the late asthmatic response to PA. Peripheral blood T-cell subset proportions and their degree of activation were similar in patients with WRCA and exposed control subjects. There was no change in T-cell phenotypes or their activation markers after PA inhalation challenge. In vitro, PA-HSA stimulation did not affect subset ratios but led to release of small amounts of IL-5 and IFN-gamma, with no detectable increase in IL-4. CONCLUSIONS: PA-HSA-specific T lymphocytes seem to be present in small numbers in the peripheral blood of patients with WRCA and may respond to antigenic exposure by producing IFN-gamma and IL-5. However, the proportion of responding cells would appear to be lower than in comparable studies of atopic asthma.

Adult↗

PubMed1998

Immunoisolation and characterization of a subdomain of the endoplasmic reticulum that concentrates proteins involved in COPII vesicle biogenesis.

Rubella virus E1 glycoprotein normally complexes with E2 in the endoplasmic reticulum (ER) to form a heterodimer that is transported to and retained in the Golgi complex. In a previous study, we showed that in the absence of E2, unassembled E1 subunits accumulate in a tubular pre-Golgi compartment whose morphology and biochemical properties are distinct from both rough ER and Golgi. We hypothesized that this compartment corresponds to hypertrophied ER exit sites that have expanded in response to overexpression of E1. In the present study we constructed BHK cells stably expressing E1 protein containing a cytoplasmically disposed epitope and isolated the pre-Golgi compartment from these cells by cell fractionation and immunoisolation. Double label indirect immunofluorescence in cells and immunoblotting of immunoisolated tubular networks revealed that proteins involved in formation of ER-derived transport vesicles, namely p58/ERGIC 53, Sec23p, and Sec13p, were concentrated in the E1-containing pre-Golgi compartment. Furthermore, budding structures were evident in these membrane profiles, and a highly abundant but unknown 65-kDa protein was also present. By comparison, marker proteins of the rough ER, Golgi, and COPI vesicles were not enriched in these membranes. These results demonstrate that the composition of the tubular networks corresponds to that expected of ER exit sites. Accordingly, we propose the name SEREC (smooth ER exit compartment) for this structure.

Animals↗

PubMed1998

Is tyrosine kinase activation involved in basophil histamine release in asthma due to western red cedar?

Occupational asthma due to western red cedar is associated with histamine release from basophils and mast cells on exposure to plicatic acid (PA), but the mechanisms underlying this response remain unclear. Specific kinase inhibitors were used to study the role of tyrosine and serine/threonine kinases in PA-induced histamine release from human basophils. Pretreatment with the tyrosine kinase inhibitor methyl 2,5-dihydroxy-cinnamate (MDHC) attenuated histamine release from basophils triggered by anti-IgE (29.8% inhibition; n = 15; P < 0.01) or grass pollen (48% inhibition; n = 6; P < 0.01). Inhibition was concentration-dependent and could be reversed by washing the cells in buffer, while the inactive stereoisomer of MDHC did not affect histamine release. In contrast, the protein kinase C inhibitor staurosporine did not affect histamine release by either anti-IgE or grass pollen. Pretreatment with MDHC partially inhibited PA-induced histamine release from basophils of 6/9 patients with red cedar asthma (25.4% vs 33.8%; P = NS). Staurosporine gave a similar level of inhibition of PA-induced histamine release (25.3% vs 33.8%; P = NS). Thus, signal transduction of the human basophil Fc epsilon RI appears to depend upon tyrosine kinase activation, but not on protein kinase C (serine/threonine kinase) activation. The lack of specific effect on plicatic acid-induced histamine release in basophils obtained from patients with occupational asthma due to western red cedar suggests that tyrosine kinases are not as important in this disease as in atopic asthma, and is consistent with the view that histamine release in red cedar asthma is largely IgE-independent.

Allergens↗

PubMed1997

A novel tetrodotoxin-sensitive, voltage-gated sodium channel expressed in rat and human dorsal root ganglia.

Dorsal root ganglion neurons express a wide repertoire of sodium channels with different properties. Here, we report the cloning from rat, dorsal root ganglia (DRG), cellular expression, and functional analysis of a novel tetrodotoxin-sensitive peripheral sodium channel (PN), PN1. PN1 mRNA is expressed in many different tissues. Within the rat DRG, both the mRNA and PN1-like immunoreactivity are present in small and large neurons. The abundance of sodium channel mRNAs in rat DRG is rBI > PN1 >/= PN3 >>> rBIII by quantitative reverse transcription-polymerase chain reaction analysis. Data from reverse transcription-polymerase chain reaction and sequence analyses of human DRG and other human tissues suggest that rat PN1 is an ortholog of the human neuroendocrine channel. In Xenopus oocytes, PN1 exhibits kinetics that are similar to rBIIa sodium currents and is inhibited by tetrodotoxin with an IC50 of 4.3 +/- 0.92 nM. Unlike rBIIa, the inactivation kinetics of PN1 are not accelerated by the coexpression of the beta-subunits.

Amino Acid Sequence↗

PubMed1997

An improved method of flexible endoscopic creation of tracheoesophageal fistula for voice restoration.

We present improvements of a previously reported method of tracheoesophageal puncture for voice restoration in postlaryngectomy patients. Our method utilizes a flexible endoscope to enable the tracheoesophageal puncture to be made under direct visualization using only local anesthesia and intravenous sedation. After 3 days, the created tracheoesophageal fistula tract is mature enough to allow placement of a voice prosthesis in the office. This allows the entire procedure to be performed in an outpatient setting with minimal risk.

Carcinoma, Squamous Cell↗

PubMed1997

The syndrome of inappropriate secretion of antidiuretic hormone (SIADH) as a consequence of neck dissection.

The syndrome of inappropriate secretion of antidiuretic hormone (SIADH) can have multiple causes. Surgical neck dissections may have an association with this syndrome and represent the basis for this study. A retrospective review of 50 patients undergoing neck dissections was performed to evaluate for the development of hyponatraemia as a consequence of SIADH. Based on the results of this review, a prospective study of 20 consecutive patients undergoing 22 neck dissections was performed to determine the incidence of SIADH. A control group of 25 consecutive patients undergoing major non-neck dissection surgery was also studied. SIADH developed in nine of 50 patients (18 per cent) of our retrospective group with a high incidence of development in those who had jugular vein ligation (JVL) (22 per cent), pre-operative radiation therapy (25 per cent) or squamous cell cancers (32 per cent). SIADH developed in six patients undergoing 22 neck dissections (27 per cent) in our prospective group. A high incidence was also noted for those with JVL (42 per cent), pre-operative radiation therapy (67 per cent) or squamous cell cancer (40 per cent). No patients developed symptomatic hyponatraemia. No patients in the prospective control group developed SIADH. Neck dissection surgery is associated with a significant risk for the development of SIADH. Factors such as jugular vein ligation (JVL), pre-operative radiotherapy and squamous cell cancer appear to increase this risk.

Adolescent↗

PubMed1997

Bladder management in acute care of stroke patients: a quality improvement project.

A follow-up evaluation of the effectiveness of bladder management in stroke patients with voiding difficulty was conducted during the period of May-August 1995. The results of this study showed 84% of all stroke patients successfully achieved urinary continence within the first month of stroke. This promising result supports the idea that uncomplicated bladder problems in the acute phase of stroke may be addressed by a management protocol using bladder scanning to estimate volume, intermittent catheterizations/post-void residual regimens, noninvasive voiding strategies and drug therapy to facilitate effective bladder emptying.

Aged↗

PubMed1997

Stringent structural and sequence requirements of the human herpesvirus 6B lytic-phase origin of DNA replication.

The lytic-phase origin of DNA replication from human herpesvirus 6B (HHV-6B oriLyt) contains two binding sites for the origin-binding protein (OBPH6B), both of which are required for DNA replication and which are separated by an AT-rich spacer. We have tested the functional significance of the structural, spatial and sequence characteristics of this spacer element by constructing a series of mutated origin sequences and analysing their replication efficiency. Changes in the sequence composition of length of the spacer resulted in dramatic decreases in replication efficiency. Furthermore, in contrast to what has been observed for herpes simplex virus type 1 (HSV-1) oriS, insertion of a complete helical turn of DNA into the spacer also resulted in abrogation of origin function. These data suggest that the arrangement of OBP sites in HHV-6B oriLyt is stringently constrained in terms of spacing and intervening sequence.

Base Sequence↗

PubMed1997

Prostanoid action on the human pulmonary vascular system.

1. Four types of prostanoid receptor are present on pulmonary arterial vessels of man. Thromboxane (TP) receptors mediate constriction and are blocked by antagonists such as BAY u-3405, GR 32,191 and EP 169. Prostaglandin (PG) EP3 receptors also mediate constriction, the agonist potency ranking being SC 46,275 > sulprostone > misoprostol > or = PGE2; this action needs to be borne in mind when PGE analogues are used therapeutically. 2. Prostaglandin E2 causes relaxation in a few pulmonary artery preparations: an EP2 receptor may be involved. Prostacyclin, acting through i.p. receptors, consistently produces relaxation and studies are in progress to determine the contribution made by K(+)-channel opening. Agonist potencies of stable prostacyclin analogues and non-prostanoid prostacyclin mimetics, such as BMY 45,778 and the novel diphenylindole CU 23, on human pulmonary artery and platelets are well correlated. Interestingly, the non-prostanoid mimetics show persistent relaxant effects in vitro, which may be related to their high lipophilicities. 3. Prostacyclin and iloprost are being used to treat severe pulmonary hypertension; further study of the pharmacodynamic and pharmacokinetic properties of other i.p. receptor agonists could produce improved therapy.

Humans↗

PubMed1996

Expression of human dopamine beta-hydroxylase in Drosophila Schneider 2 cells.

Human dopamine beta-hydroxylase (DBH) has been expressed in transformed Drosophila Schneider 2 (S2) cells with yields of > 16 mg/l. Most of the activity was found in the culture fluid. Similarly, human neuroblastoma cells also secrete native DBH into the medium, but at a much lower level than recombinant Drosophila cells. We have purified native and recombinant human DBH by a modified purification procedure using SP-Sepharose, lentil lectin-Sepharose and gel-filtration chromatography and carried out studies to compare the two enzymes. Two variants of human DBH that differ by a single amino acid (either serine or alanine) at position 304 were expressed in Drosophila cells, purified, and found to have no significant difference in enzyme activity. The molecular mass of human DBH monomer has been determined from SDS/PAGE to be 73 kDa, but the recombinant DBH from Drosophila is smaller at 66 kDa. The difference may be due to glycosylation as deglycosylated enzymes from both sources are identical in size (61 kDa). The Km of tyramine for native and recombinant human enzymes are virtually the same but higher than bovine DBH by about 3-fold. Likewise, the inhibition of native and recombinant human DBH by fusaric acid and SKF102698 is not significantly different but IC50 values are 2-3-fold higher than that for the bovine enzyme. These results strongly support the conclusion that recombinant human DBH from Drosophila S2 cells can be used in place of human neuroblastoma-derived DBH for drug screening, characterization of the enzyme's physicochemical properties, and determination of structure-function relationships. The Drosophila expression system has thus provided a convenient source for large quantities of human DBH enzyme.

Amino Acid Sequence↗

PubMed1996

A case of bronchial obstruction by metastatic renal cell carcinoma.

A 68-year-old Chinese male with a history of renal cell carcinoma presenting with increasing shortness of breath and hemoptysis was found to have subtotal left main bronchial obstruction secondary to a metastatic endobronchial tumor. The mass was completely resected through a rigid ventilating bronchoscope, and a silicone stent was placed over the tumor bed in the left main bronchus. He remained asymptomatic with no evidence of bronchoscopic recurrence 4 months after the procedure. Obstructive endobronchial metastases from nonpulmonary primaries are rare. Endoluminal resection with stent placement can provide good palliation in this group of patients with limited survival.

Aged↗

PubMed1996

In vitro T-lymphocyte response and house dust mite-induced bronchoconstriction.

BACKGROUND: There is considerable evidence that T cells may play an important role in asthma. The purpose of this study was to determine whether the responsiveness of T lymphocytes to mite allergen stimulation in vitro is a determinant of bronchial response to house dust mite (HDM) allergen challenge in subjects who are allergic to HDM. METHODS: Peripheral blood was taken from seven healthy nonatopic subjects and 23 subjects with positive skin test reactions to HDM. Of the subjects in the latter group, 16 had an asthmatic reaction on inhalation challenge with HDM extract (HDM-responders), whereas the remaining seven had a negative reaction (HDM allergic). The proportion of subsets of T lymphocytes and their activation and the amount of IL-2, IL-4, IL-5, and interferon-gamma released in the supernatants with and without stimulation with the HDM extract were determined. RESULTS: Without stimulation, the proportions of subsets of T lymphocytes and their activation were similar between groups. When stimulated with the HDM allergen, the proportion of CD4+CD25+ cells from HDM responders was significantly higher than those in the control group. Comparison within groups of cell cultures with and without stimulation with the mite allergen showed that the proportion of CD4+, CD4+CD25+, CD4+/CD8+, and CD3+HLADR+ cells were significantly increased in HDM responders with stimulation; there was a trend for CD4+CD25+ cells to be increased in the HDM-allergic subjects; no increase in any T-lymphocyte subsets was found in the control subjects. The release of IL-5 was significantly greater in HDM responsers than in the other two groups. The severity of the immediate asthmatic reaction was significantly associated with the degree of nonallergic bronchial hyperresponsiveness and the amount of IL-5 released but not with the level of specific IgE to the mite allergen or subsets of T lymphocytes with and without stimulation. CONCLUSION: The findings suggest that responsiveness of T lymphocytes to allergen challenge in vitro may play a role in determining the bronchial response to the allergen in vivo.

Animals↗