Search PubMed⌕ Search

Biomedical subjects

C W Chan

Publications and source records attributed to C W Chan.

At least 55 records · Page 3Linked to original sources
PubMed1997

Studies of melatonin effects on epithelia using the human embryonic kidney-293 (HEK-293) cell line.

The expression of melatonin receptors (MR) of the Mel1a subtype in basolateral membrane of guinea pig kidney proximal tubule suggests that melatonin plays a role in regulating epithelial functions. To investigate the cellular basis of melatonin action on epithelia, we sought to establish an appropriate in vitro culture model. Epithelial cell lines originating from kidneys of dog (MDCK), pig (LLC-PK1), opossum (OK), and human embryo (HEK-293) were each tested for the presence of MR using 2-[125I]iodomelatonin (125I-MEL) as a radioligand. The HEK-293 cell line exhibited the highest specific 125I-MEL binding. By intermediate filament characterization, the HEK-293 cells were determined to be of epithelial origin. Binding of 125I-MEL in HEK-293 cells demonstrated saturability, reversibility, and high specificity with an equilibrium dissociation constant (Kd) value of 23.8 +/- 0.5 pM and a maximum number of binding sites (Bmax) value of 1.17 +/- 0.11 fmol/mg protein (n = 5), which are comparable with the reported Kd and Bmax values in human kidney cortex. Coincubation with GTPgammaS (10 microM) and pertussis toxin (100 ng/ml) provoked a marked decrease in binding affinity (Kd was increased by a factor of 1.5-2.0), with no significant difference in Bmax. Melatonin (1 microM) decreased the forskolin (10 microM) stimulated cAMP level by 50%. HEK-293 cells do not express dopamine D1A receptor. Following transient transfection of HEK-293 cells with human dopamine D1A receptor (hD1A-R), exposure of the cells to dopamine stimulated an increase in the level of cAMP. Similarly, transient transfection of HEK-293 cells with rat glucagon-like peptide-1 (GLP-1), glucose-dependent insulinotropic peptide (GIP), and PTH type 1 receptors, each resulted in an hormone inducible increase in cAMP levels. Surprisingly, only the stimulatory effect of dopamine could be inhibited by exposure to melatonin. The inhibitory effect of melatonin on dopamine D1-induced increase in cAMP was completely inhibited by pertussis toxin (100 ng/ml, 18 h). Immunoblot and immunocytochemical studies were carried out using two polyclonal antibodies raised against the extra and cytoplasmic domains of Mel1a receptor. Immunoblot studies using antibody against the cytoplasmic domain of Mel1a receptor confirmed the presence of a peptide blockable 37 kDa band in HEK-293 cells. Indirect immunofluorescent studies with both antibodies revealed staining predominantly at the cell surface, but staining with the antibody directed against the cytoplasmic domain required prior cell permeabilization. By RT-PCR, HEK-293 cells express both Mel1a and Mel1b messenger RNAs, but the messenger RNA level for Mel1b is several orders of magnitude lower than for Mel1a. We conclude that HEK-293 cells express MR predominantly of the Mel1a subtype. Our evidence suggests that one of the ways that melatonin exerts its biological function is through modulation of cellular dopaminergic responses.

Animals↗
PubMed1996

Concanavalin A-induced apoptosis in murine macrophages through a Ca(2+)- independent pathway.

Concanavalin A (ConA), normally a mitogen of T lymphocytes, was found to induce apoptosis or programmed cell death in murine peritoneal macrophages. The following observations support this assertion: 1) incubation of peritoneal macrophages or cultured PU5-1.8 macrophage cells with ConA caused a dose- and time-dependent reduction of mitochondrial dehy-drogenase activity as measured by 3-(4,5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT) assay, 2) treatment of cells with ConA induced formation of apoptotic bodies as seen under the confocal laser scanning microscope, 3) challenge of cells with ConA produced a considerable amount of cell debris with DNA content next to G0 phase as revealed by flow cytometry and 4) ConA was able to elicit DNA fragmentation in these cells. The involvement of Ca(2+) in mediating the apoptosis was studied in single cells by confocal laser scanning microscope using the Ca(2+) fluorescence dye, fluo-3. Our results show that ConA induced an immediate rise of intracellular free Ca(2+) concentration as well as opening of Ca(2+) channels on cell surface. But when the cells were treated with 1,2-bis(o-aminophenoxy) ethane-N, N, N', N'-tetraacetic acid/AM (BAPTA/AM), a Ca(2+) chelator, to buffer the rise of internal Ca(2+), ConA still caused DNA fragmentation. Furthermore, injection of Ca(2+) into the cell with ionomycin had no stimulatory effect on DNA fragmentation. These results suggest that Ca(2+) changes induced by ConA are not a prerequisite for apoptosis in macrophages.

Journal Article↗
PubMed1995

Comparison of [125I]iodomelatonin binding sites in infant cerebellum of sudden infant death syndrome and non-sudden infant death syndrome.

[125I]Iodomelatonin bindings sites in human infant cerebellum were studied by radioligand receptor binding assay and in vitro quantitative autoradiography. The binding sites characterized in membrane preparations revealed saturable, reversible and highly specific binding sites with a Kd value of 21.2 +/- 8.33 pM and a Bmax value of 2.02 +/- 0.52 fmol/mg protein. 10 microM of GTP gamma S significantly reduced the binding capacity, suggesting the possible G-protein coupling of the binding sites. Autoradiographic study showed that the labelling was mainly located in the cerebellar cortex. On comparison of the binding parameters from cerebellum of sudden infant death syndrome (SIDS) and non-SIDS infants, no significant change in binding capacity and binding affinity was detected. These findings suggest that the binding sites in cerebellum may not be related to the etiology of SIDS.

Analysis of Variance↗
PubMed1995

Functional reconstitution of ion channels from Paramecium cortex into artificial liposomes.

Toward isolating channel proteins from Paramecium, we have explored the possibility of functionally reconstituting ion channels in an artificial system. Proteins from Paramecium cortex reconstituted with soybean azolectin retained several channels whose activities were readily registered under patch clamp. The most commonly encountered activities were three: (i) a 71-pS cation channel that opens at all voltages unless di- or trivalent cations were added to close them, (ii) a 40 pS monovalent cation channel, and (iii) a large-conductance channel that prefers anions and exhibits many subconductance states. These channels survived mild detergent treatments without observable functional alterations. The possible origin of these channels from internal membranes, the possible role of 71-pS channel in internal Ca2+ release, and the prospects of their purification are discussed.

Animals↗
PubMed1995

A simple and efficient treatment for fingertip injuries.

We have developed a simple, cheap and efficient method of management of fingertip injuries using an occlusive dressing--the fingertip cap (Hyphecan). The results of 156 fingertip injuries treated with this method demonstrate recovery to a near normal fingertip.

Adolescent↗
PubMed1994

Foot biomechanics during walking and running.

OBJECTIVE: To describe the anatomy and biomechanics of the foot and to explain how movement and gait are integrated in the foot during walking and running. DESIGN: We review the anatomy and the biomechanical adaptations of the foot during walking and running. MATERIAL AND METHODS: Illustrations are presented to depict these biomechanics. RESULTS: The human foot is an intricate mechanism that cushions the body and adapts to uneven surfaces. It provides traction for movement, awareness of joint and body position for balance, and leverage for propulsion. CONCLUSION: With an understanding of the factors discussed herein, clinicians will have more knowledge to evaluate foot problems.

Biomechanical Phenomena↗
PubMed1993

The pain drawing and Waddell's nonorganic physical signs in chronic low-back pain.

Pain drawings were obtained from a group of 651 patients who had chronic low-back pain. Pain drawings were rated in four grades according to the degree of organic and nonorganic pain. Experienced and inexperienced evaluators were used. The reliability was excellent with an interevaluator reliability between 73% and 78%. A correlation between pain drawings and Waddell's nonorganic physical signs demonstrated that a large proportion of patients with high Waddell scores had nonorganic pain drawings. No significant differences were noted in the distribution of Waddell scores and pain drawings based on patient gender or payment status (i.e., medicolegal or workers' compensation). Pain drawings afford an important adjunct in the physician's assessment of chronic low-back pain.

Female↗
PubMed1993

Contents of fructose, citric acid, acid phosphatase, proteins and electrolytes in secretions of the accessory sex glands of the male golden hamster.

Secretions were collected from the ampullary gland, dorsolateral prostate, ventral prostate, coagulating glands and seminal vesicles of male golden hamsters aged 15-20 weeks. The concentrations of total protein, citric acid, fructose, acid phosphatase, chloride, sodium, potassium, calcium, magnesium and zinc were determined. The ampullary gland secreted predominantly citric acid, sodium and acid phosphatase. Zinc was secreted only by the prostatic complex, with the largest quantity coming from the coagulating gland. The highest concentrations of potassium, calcium and magnesium were found in secretions of the ventral prostate. The coagulating gland and dorsolateral prostate were the principal contributors to total protein. The hamster appears to be more related to the mouse than to the rat in terms of the secretory functions of its accessory sex glands.

Acid Phosphatase↗
PubMed1992

Extent of nasopharyngeal carcinoma involvement inside the nasopharynx. Lack of prognostic value on local control.

A study on the use of fiberscopic examination and multiple biopsy specimens taken from the nasopharynx in the assessment of the extent of nasopharyngeal carcinoma (NPC) involvement inside the nasopharynx found that the involvement often was more extensive than the detected with conventional methods. In the current study, 247 patients with NPC were studied with the use of fiberscopic examination, and multiple biopsy specimens were taken from the superior wall, posterior wall, and lateral wall of the nasopharynx on both sides. It was confirmed that the tumor often involved the nasopharynx extensively. Also, the extent of primary tumor involvement inside the nasopharynx was correlated with the American Joint Committee (AJC) T stage and the degree of paranasopharyngeal extension of the tumor (P = 0.0100 and 0.0009, respectively), as well as with the size of the largest node and the lowest neck level involved by the node in the ipsilateral neck (P = 0.0005 and 0.005, respectively). However, the extent of primary tumor involvement inside the nasopharynx, expressed as either the number of the six standard sites or the number of the AJC subsites that were involved, had no predictive value on the control of the primary tumor (P = 0.3773 and 0.7794, respectively) at a median follow-up time of 27 months. Except when salvage brachytherapy is contemplated for persistent or recurrent NPC, the extent of primary tumor involvement inside the nasopharynx should not be routinely studied.

Actuarial Analysis↗
PubMed1992

Radiation therapy for nasopharyngeal carcinoma: histologic appearances and patterns of tumor regression.

Nasopharyngeal carcinoma is a common malignancy in Hong Kong and is treated by external radiotherapy. After 6.5 weeks of radiotherapy, the nasopharynx of 100 patients was examined and biopsy specimens were taken. All patients had repeated examination and biopsies done every 2 weeks until exophytic tumor was not seen and biopsy samples were negative on more than one examination of the nasopharynx. The interval between the cessation of therapy and biopsy ranged from 1 day to 11 weeks. Twenty-three patients had atypical findings and five of these had residual tumor requiring gold grain implantation brachytherapy. We identified a number of distinct pathologic changes in the post-biopsy material. Most of these changes disappeared 8 weeks after the cessation of therapy, but the presence of residual tumor after this time was an indication for subsequent therapy. If the date of the first biopsy was delayed until 6 weeks after the completion of radiotherapy, the percentage of atypical biopsies containing residual tumor rose from 21% to 55%. The posttreatment biopsy should be performed twice, as four patients had negative biopsy findings due to sampling error.

Adolescent↗
PubMed1992

Thermoregulation and fever in normal persons and in those with spinal cord injuries.

Thermoregulation and fever are primarily mediated through the hypothalamus and its effector mechanisms. In persons with complete spinal cord injuries above T-6, thermoregulation is substantially impaired because of the interruption of neuronal pathways to and from the hypothalamus. These same pathways are important in the production of fever in response to infections, and injury to these pathways in patients with high-level spinal cord injuries should diminish their ability to mount a febrile response. In clinical practice, however, measurements of body temperature are used to make decisions in patients with spinal cord injuries in a manner similar to that in patients without spinal cord injuries. In this article, we review the literature on thermoregulation and fever in normal persons and in those with complete spinal cord injuries and propose possible mechanisms for fever in persons with high-level spinal cord injuries.

Body Temperature↗
PubMed1992

Nasopharyngeal carcinoma in situ in nasopharyngeal carcinoma.

AIMS: To assess the presence of carcinoma in situ (CIS) in patients with nasopharyngeal carcinoma (NPC) and to see if the number of biopsy sites facilitates detection of CIS. METHODS: Formalin fixed, paraffin wax embedded biopsy specimens (n = 285) from 187 patients with NPC in 1987 were studied for the presence of CIS as well as for the histological assessment of the subtype of CIS. RESULTS: Fifteen (8.0%) patients had CIS, representing 8.3% of all new patients with NPC and 11.6% of patients with persistent disease or relapse. CIS was undifferentiated or poorly differentiated, no cases of well differentiated squamous cell CIS were identified. There was no significant difference in the incidence of CIS when multiple endoscopic biopsy specimens were taken rather than single forceps biopsy specimens. CONCLUSIONS: CIS can only be identified in a few patients with NPC largely because of late presentation with advanced disease at the time of diagnosis and the focal nature of the dysplastic process. The presence of dysplasia in relapses of NPC suggests that these tumours may be second growths rather than regrowths of a primary tumour.

Carcinoma in Situ↗
PubMed1992

Epstein-Barr virus DNA in nasopharyngeal carcinomas from Chinese patients in Hong Kong.

AIMS: To investigate the presence of Epstein-Barr virus (EBV) in cases of nasopharyngeal carcinoma (NPC) in Chinese patients living in Hong Kong. METHODS: Nasopharyngeal biopsy specimens, formalin fixed and paraffin wax embedded, from 24 patients, eight with undifferentiated nasopharyngeal carcinoma, eight with well differentiated squamous carcinoma, and eight showing normal tissue histology, were analysed for the presence of Epstein-Barr virus (EBV) DNA by slot-blot hybridisation on extracted unamplified DNA, and also after amplification of EBV specific sequences by the polymerase chain reaction (PCR). RESULTS: DNA slot-blot analysis showed viral DNA in all the undifferentiated, five of the well differentiated tumours, and none of the normal biopsy specimens. PCR studies confirmed positivity in the eight undifferentiated tumours, but six of the well differentiated tumours and three of the normal biopsy specimens showed viral DNA by this method, illustrating its greater sensitivity. CONCLUSIONS: EBV genome is present in appreciable copy number in most cases of well differentiated NPC in Chinese patients in Hong Kong.

Base Sequence↗
PubMed1992

Effect of feeding palmitic, oleic, and linoleic acids to Japanese quail hens (Coturnix coturnix japonica). 2. Maternal diets and stage of incubation on the lipid metabolism of quail embryos.

An experiment was conducted to evaluate the effects of diets containing 3% of either palmitic acid (Diet PA), oleic acid (Diet OA), or linoleic acid (Diet LA) and three stages of development (Days 11, 13, and 15 of incubation) on 1) weights of yolk plus yolk sac membrane (TY), yolk sac membrane (YSM), yolk, liver, and extrahepatic tissue (ET); and 2) the fatty acid composition of phospholipid, triglyceride, and cholesterol ester fractions of YSM and ET of quail embryos. Embryos from birds fed Diet LA had the highest (P less than .05) weights of TY and yolk followed by those from birds fed Diet OA and Diet PA. The weight of ET was highest (P less than .05) in embryos from birds fed Diet PA followed by those from birds fed Diet LA and Diet OA. The weights of YSM and liver were not affected by the maternal diet (P greater than .05). The weight of TY decreased whereas the weights of liver and ET increased as incubation progressed (P less than .05). The weight of YSM was maximum at Day 13 of incubation. In the phospholipid, triglyceride, and cholesterol ester fractions of both YSM and ET of embryos, the fatty acid present at the highest level, except palmitic acid, was the one added to the maternal diet. In phospholipids of both YSM and ET the oleic acid content decreased and linoleic acid increased as incubation progressed. In triglycerides and cholesterol esters of both YSM and ET, the levels of palmitic acid increased, but oleic and linoleic acids decreased, with advancing embryonic development. The results of the present study indicate that embryos from birds fed Diet PA mobilize more yolk material and produce heavier ET than embryos from birds fed Diet OA and Diet LA. The fatty acid profiles of phospholipid, triglyceride, and cholesterol esters of embryonic tissues are consistently influenced by dietary fatty acid and the stage of development.

Animals↗
PubMed1991

Visual disability and major causes of blindness in NSW: a study of people aged 50 and over attending the Royal Blind Society 1984 to 1989.

Visual disability in individuals aged 50 years and over seeking services of the Royal Blind Society in the years 1984 to 1989, was studied with respect to changes in frequency of major causes together with age and sex of those affected. The results mirror statistics in the UK. Age-related macular degeneration (AMD) accounts for an increasing proportion of visual disability (34% in 1984 to 43% in 1989). Of particular interest was the frequency of disability attributed to cataract. While decreasing (24% in 1984 to 19% in 1989), cataract still represents a significant cause of potentially treatable disability. The authors conclude that there is a changing prevalence of visual disability caused mainly by an increase in AMD and a subgroup of patients attending for services who appear to have a potentially remediable disability. These conclusions affirm the need for close liaison between ophthalmological practitioners and agencies for the blind.

Aged↗