PubMed Health⌕ Search

Biomedical subjects

K L Chan

Publications and source records attributed to K L Chan.

At least 19 recordsLinked to original sources
PubMed2001

Inhibin binding sites and proteins in pituitary, gonadal, adrenal and bone cells.

Activin signals via complexes of type I (50-55 kDa) and II (70-75 kDa) activin receptors, but the mechanism of inhibin action is unclear. Proposed models range from an anti-activin action at the type II activin receptor to independent actions involving putative inhibin receptors. Two membrane-embedded proteoglycans, betaglycan and p120, have recently been implicated in inhibin binding, but neither appears to be a signalling receptor. The present studies on primary cultures of rat pituitary and adrenal cells, and several murine and human cell lines were undertaken to characterise inhibin binding to its physiological targets. High affinity binding of inhibin to the primary cultures and several of the cell lines, like that previously described for ovine pituitary cells, was saturable and reversible. Scatchard analysis revealed two classes of binding sites (K(d) of 40-400 and 500-5000 pM, respectively). Affinity labelling identified [125I]inhibin binding proteins with apparent molecular weights of 41, 74, 114 and >170 kDa in all cell types that displayed high affinity, high capacity binding of inhibin. Additional labelling of a 124 kDa species was evident in gonadal TM3 and TM4 cell lines. In several cases, activin (> or =20 nM) competed poorly or not at all for binding to these proteins. The 74, 114 and >170 kDa inhibin binding proteins in TM3 and TM4 cells were immunoprecipitated by an anti-betaglycan antiserum. These three proteins correspond in size to the activin receptor type II and the core protein and glycosylated forms of betaglycan, respectively, that have been proposed to mediate anti-activin actions of inhibin, but the identity of the 74 kDa species is yet to be confirmed. Studies of [125I]inhibin binding kinetics and competition for affinity labelling of individual binding proteins in several cell lines suggest these three species and the 41 and 124 kDa proteins form a high affinity inhibin binding complex. In summary, common patterns of inhibin binding and affinity labelling were observed in inhibin target cells. Novel inhibin binding proteins of around 41 and 124 kDa were implicated in the high affinity binding of inhibin to cells from several sources.

Activin Receptors↗
PubMed2001

Cytotoxic activity of Typhonium flagelliforme (Araceae).

The plant Typhonium flagelliforme (Araceae), commonly known as the 'rodent tuber', is often included as an essential ingredient in various herbal remedies recommended for cancer therapies in Malaysia. Various extracts prepared from either the roots, tubers, stems or leaves were tested for cytotoxic activity on murine P388 leukaemia cells using the MTT assay method. Both the chloroform (IC50 = 6.0 microg/mL) and hexane (IC50 = 15.0 microg/mL) extract from the 'roots and tubers' exhibited weak cytotoxic activity. The hexane extract (IC50 = 65.0 microg/mL) from the 'stems and leaves' exhibited weaker cytotoxic activity than the chloroform extract (IC50 = 8.0 microg/mL). Although the juice extract from the 'roots and tubers' is frequently consumed for cancer treatment, it exhibited poor cytotoxic activity. Further analysis using an amino acid analyser revealed that the juice extract contained a high concentration of arginine (0.874%). A high tryptophan content (0.800%) was confirmed by NMR and HPLC analysis.

Amino Acids↗
PubMed2001

Population data for 12 STR loci in Hong Kong Chinese.

The allele distributions at the 12 short tandem repeat (STR) loci D3S1358, HUMvWA, HUMFIBRA/FGA, HUMTHO1, HUMTPOX, HUMCSF1P0, D5S818, D13S317, D7S820, D8S1179, D21S11 and D18S51 have been determined for 284 unrelated Chinese in Hong Kong. The combined probability of identity for the 12 STR loci was about 4.1 x 10(-14) and the overall probability of excluding paternity 0.999978. None of the 12 loci were found to deviate from Hardy-Weinberg expectations according to the results of the exact test. There was also little evidence for association of alleles between loci. The results demonstrate that the loci are useful for forensic human identification and parentage testing for the Chinese population in Hong Kong.

China↗
PubMed2001

Reproductive impairment of sea urchins upon chronic exposure to cadmium. Part I: Effects on gamete quality.

Successful reproduction is a determining factor for species survival. Pollution may impair reproductive success of adults through effects on gamete quality. Reproductive impairment of the sea urchin Anthocidaris crassispina upon chronic (4 weeks) exposure to 0.01 and 0.1 mg l-1 Cd2+ was investigated. Criteria used for assessing gamete quality included sperm motility, egg morphology, fertilization rate and dynamics of first cleavage. A dose-response relationship was found between Cd2+ levels and changes in sperm motility, and percentage fertilization. Sperm motility, measured by computer-assisted sperm analysis, indicated that percent motile sperm, velocities, and percent sperm with normal trajectory were significantly affected by chronic exposure to > or = 0.1 mg l-1 Cd2+. A decline in sperm motility was also accompanied by a decrease in fertilization success of sea urchin sperm. Width/height ratio of sea urchin eggs was not affected by cadmium, but larger egg sizes were found when sea urchins were exposed to 0.1 mg l-1 Cd2+. Male sea urchins exposed to Cd2+ produced poorer quality sperm, as indicated by a lower percent fertilization and lower cleavage rate, implying that male sea urchins were more sensitive than females to chronic Cd2+ exposure. Results of the present study provide an explanation of reproductive impairment in marine invertebrates upon chronic exposure to Cd2+.

Animals↗
PubMed2001

Role of CD4+ and CD8+ T cells in early and late acute rejection of small bowel allograft.

BACKGROUND/PURPOSE: Results of small bowel transplantation remain unsatisfactory because of severe immune rejection. The current study aims to elucidate the role of activation of CD4+ and CD8+ T cells in early and late acute rejection of small bowel allograft and, hence, provide the immunologic basis for developing new therapeutic strategies. METHODS: We used an MHC fully mismatched (DA to Lewis) heterotopic rat small bowel transplant model and a unique FK506-based immunosuppressive regimen, which suppresses early acute rejection but does not prevent late acute rejection. Flow cytometric analysis was used to quantitate the number of activated CD4+ and CD8+ T cells in graft and host mesenteric lymph nodes. RESULTS: The survival (mean +/- SD) of intestinal allograft was significantly prolonged, from 6.6 +/- 0.84 days for the untreated group to 40.7 +/- 14.1 days for the FK506-treated group. Activation of CD4+ cells was suppressed significantly in the FK506-treated group on postoperative day 7 compared with the untreated group (29.4% +/- 3.55% v 52.83% +/- 11.9%; P <.01). Activation of CD8+ cells was similarly suppressed (31.5 +/- 10.34% v 48.53 +/- 14.34%; P <.05). Interestingly, at late acute rejection, activated CD4+ and CD8+ T cells remained at almost the same low levels as those on postoperative day 7 in the FK506-treated group. The spleen to body weight ratio was significantly increased in the untreated group (0.53 +/- 0.07), and slightly increased in the FK treated group (0.27 +/- 0.07, on postoperative day 7; 0.24 +/- 0.07 at late acute rejection) compared with the syngeneic group (0.18 +/- 0.02). CONCLUSION: The activation of CD4+ and CD8+ T cells was suppressed effectively by early potent immunosuppressive treatment resulting in prolonged survival of intestinal allograft. At late acute rejection, the CD4+ and CD8+ T cells remained at low-level activation status, in contrast to the surge of CD4+ and CD8+ activation during early acute rejection. This suggests that persistent T cell activation even at low level is sufficient to cause the late acute rejection eventually. A therapeutic strategy targeting these cells is needed for long-term engraftment.

Animals↗
PubMed2001

A prospective study of a one-week nonbismuth quadruple therapy for childhood Helicobacter pylori infection.

PURPOSE: In the eradication of Helicobacter pylori infection, a 1-week therapy improves patient compliance, but drug resistance may limit its efficacy. The effectiveness of the 1-week nonbismuth quadruple therapy was studied prospectively in children with proven H pylori infection in a population with a high rate of metronidazole resistance. METHODS: All pediatric patients who presented to our institutions with acute and chronic upper gastrointestinal conditions requiring endoscopy from June 1997 to February 2000 were investigated prospectively for H pylori infection. Gastric biopsy specimens were analyzed with rapid urease test and histopathology, H pylori-positive children were treated with omeprazole, clarithromycin, amoxicillin, and metronidazole for 7 days. The result of treatment was assessed 1 month after treatment with endoscopy and biopsy. The same treatment was repeated for 2 weeks if H pylori was still present. In patients who needed a third endoscopy, their biopsy specimens were cultured to determine antibiotic sensitivity. Results were correlated with patients' symptoms and endoscopic findings. RESULTS: Thirty-three children with acute (severe epigastric pain, n = 14; gastrointestinal bleeding, n = 9) and chronic (recurrent abdominal pain, n = 7; anemia, n = 3) conditions were treated for H pylori. Thirty-one (94%) were confirmed to have H pylori eradicated by a 1-week therapy, whereas 1 patient had eradication after a further 2-we'ek therapy (3.3%). The only unresponsive patient had H pylori resistant to both clarithromycin and metronidazole. All ulcers and erosions healed after the eradication of H pylori. Three patients had persistent recurrent abdominal pain despite H pylori eradication. CONCLUSIONS: The 1-week therapy with omeprazole, clarithromycin, amoxicillin, and metronidazole is an effective treatment of H pylori in children in a population with a high incidence of metronidazole resistant strain of H pylori. Peptic ulcers and erosions healed with the eradication of the bacteria.

Adolescent↗
PubMed2001

Identification of specific inhibin A-binding proteins on mouse Leydig (TM3) and sertoli (TM4) cell lines.

The binding of human inhibin A to cell surface binding proteins of mouse Leydig (TM3) and Sertoli (TM4) cell lines was investigated. Scatchard analysis identified two classes of inhibin A-binding sites on TM3 (K(d(1)) = 85 pM and 4,160 sites/cell; K(d(2)) = 520 pM and 12,500 sites/cell) and TM4 (K(d(1)) = 61 pM and 2,620 sites/cell; K(d(2)) = 520 pM and 10,400 sites/cell) cells. Compared with inhibin A, inhibin B only partially competed [(125)I]inhibin A binding (6-8%), whereas activin A competed weakly (<0.01%). Chemical cross-linking of [(125)I]inhibin A to both cell lines identified five [(125)I]inhibin A binding complexes with apparent molecular masses of 70, 95, 145, 155, and more than 200 kDa. Inhibin A displacement of [(125)I]inhibin A from each of these cross-linked species (ED(50) = 60-110 pM) closely resembled displacement from intact TM3 (ED(50) = 97 +/- 32 pM) and TM4 (ED(50) = 75 +/- 28 pM) cells, suggesting that all of these proteins are involved in the high affinity inhibin A binding complex. Immunoprecipitation of iodinated inhibin A complexed to TM3 and TM4 cells with an antibody against human betaglycan identified protein complexes of more than 200, 145, and 95 kDa. It is concluded that the high affinity binding complex for inhibin A found in these cell lines consists of betaglycan and several proteins of unknown identity and may represent the putative inhibin receptor complex.

Activins↗
PubMed2001

Using gadolinium-infusion MR venography to show the impalpable testis in pediatric patients.

UNLABELLED: OBJECTIVE; This study evaluated the adjunctive value of gadolinium-infusion MR venography to locate the impalpable testis. SUBJECTS AND METHODS: Routine MR imaging and MR venography were performed in 34 patients presenting with impalpable testis. MR venography was performed by dynamic injection of gadopentetate dimeglumine bismethylamide with images taken at delayed venous phases. The site of the testis was determined by detection of the contrast-enhanced pampiniform venous plexus. RESULTS: A total of 44 impalpable testes were examined. Twenty-six hypoplastic canalicular testes, two testes at pelvic skinfold, four atrophic testes in the scrotum, and five intraabdominal testes were detected on both routine MR imaging and MR venography. Five "vanishing" testes in the scrotum and two at the groin region were detected by MR venography but not on MR imaging. CONCLUSION: Gadolinium-infusion MR venography is superior to MR imaging in the detection of atrophic testes. The method is a useful adjunct in patients with negative MR imaging findings.

Adolescent↗
PubMed2001

Prosthetic valve fungal endocarditis due to histoplasmosis.

Fungal endocarditis is associated with severe patient morbidity and mortality. Unfortunately, fungal endocarditis is difficult to diagnose because fungal pathogens are uncommonly isolated from routine blood cultures. Histopathological examination of surgically excised cardiac valves, peripheral emboli and systemic ulcers may be useful in identifying pathogens as etiological agents of culture-negative endocarditis. The authors describe a 63-year-old man who had culture-negative endocarditis. Multiple echocardiograms showed progression of the vegetations with valve stenosis despite treatment with multiple antimicrobials. He had multiple peripheral emboli before surgery. Disseminated histoplasmosis was diagnosed by bone marrow culture. Yeast organisms consistent with histoplasma were shown in the vegetations of his excised mitral valve prosthesis. The patient was treated with amphotericin and has been doing well in the two years since his surgery. The diagnosis and management of fungal endocarditis are emphasized.

Anti-Bacterial Agents↗
PubMed2000

The statistical variability of blood alcohol concentration measurements in drink-driving cases.

Like many other places in the world, Hong Kong has drink-driving legislation which prohibits a driver from having in his blood alcohol exceeding a prescribed limit while in control of a motor vehicle. The accuracy of measuring this alcohol concentration is obviously of prime concern as an erroneous result can avert the administration of justice. The common practice is to deduct all errors from the measured value and compare the deducted value with the prescribed limit, so that the benefit of all errors of the measurement is given to the driver. It is therefore important for any laboratory responsible for measuring blood alcohol concentrations to identify and quantify all errors associated with the measurement. The present study examined 900 blood alcohol determinations carried out by the Hong Kong Government Laboratory (HKGL) on cases of suspected drink driving. The determinations were performed by 5 different analysts with two different sets of instruments during 1995-1997. Statistical analysis indicated that the instruments had no bearing on the random error or variability and that even though analyst was a significant factor on variability, the deviation from the mean so caused was only 0.3% and of no practical significance. When the systematic error introduced by the tolerance limits of the certified alcohol standards (purchased from the Laboratory of Government Chemists, UK) was taken into account, the total uncertainty (random plus systematic errors) of an alcohol determination at 99.5% confidence level was found to be 4%. It is recommended that laboratories engaged in blood alcohol determination should adopt similar statistical treatment of their analytical results to find out the error and to ensure that the results are independent of analyst and instrument used.

Automobile Driving↗
PubMed2000

Measurements of the dielectric properties of peripheral blood mononuclear cells and trophoblast cells using AC electrokinetic techniques.

The separation of trophoblast cells from the maternal circulation could provide a valuable diagnostic tool for prenatal diagnosis of genetic abnormalities. This has been attempted using antibody methods, but due to non-specificity of the antibodies, maternal cell contamination remains a problem. We have investigated the potential of dielectrophoretic separation methods as a means of isolating trophoblast cells from mixed peripheral blood mononuclear cells. To determine the potential of this method the dielectric properties of trophoblast cells and mixed peripheral blood mononuclear cells were measured using dielectrophoretic crossover and single cell electrorotation methods. Both dielectrophoretic crossover data and electrorotation data gave an average specific membrane capacitance of the peripheral blood mononuclear cells of 11.5 mF m(-2). Trophoblast cells prepared using three different methods had a higher average specific membrane capacitance in the range 13-18 mF m(-2). The differences in capacitance between the cell types could be exploited as the basis of an AC electrokinetic-based system for the separation of trophoblast cells from peripheral blood mononuclear cells.

Cell Membrane↗
PubMed2000

18S rRNA secondary structure and phylogenetic position of Peloridiidae (Insecta, hemiptera).

A secondary structure model for 18S rRNA of peloridiids, relict insects with a present-day circumantarctic distribution, is constructed using comparative sequence analysis, thermodynamic folding, a consensus method using 18S rRNA models of other taxa, and support of helices based on compensatory substitutions. Results show that probable in vivo configuration of 18S rRNA is not predictable using current free-energy models to fold the entire molecule concurrently. This suggests that refinements in free-energy minimization algorithms are needed. Molecular phylogenetic datasets were created using 18S rRNA nucleotide alignments produced by CLUSTAL and rigorous interpretation of homologous position based on certain secondary substructures. Phylogenetic analysis of a hemipteran data matrix of 18S rDNA sequences placed peloridiids sister to Heteroptera. Resolution of affiliations between the three main euhemipteran lineages was unresolved. The peloridiid 18S RNA model presented here provides the most accurate template to date for aligning homologous nucleotides of hemipteran taxa. Using folded 18S rRNA to infer homology of character as morpho-molecular structures or nucleotides and scoring particular sites or substructures is discussed.

Animals↗