Biomedical subjects

E C Chan

Publications and source records attributed to E C Chan.

At least 55 records · Page 3Linked to original sources

PubMed1999

Enhanced role for the opening of potassium channels in relaxant responses to acetylcholine after myocardial ischaemia and reperfusion in dog coronary arteries.

1. Anaesthetized dogs were subjected to 1 h occlusion of the left circumflex coronary artery followed by 2 h of reperfusion. Relaxant responses were examined in coronary artery rings removed proximal (nonischaemic) or distal (ischaemic) to the site of occlusion. 2. Relaxant responses to acetylcholine (ACh) were similar in nonischaemic and ischaemic artery rings. In addition ACh-induced relaxation of nonischaemic and ischaemic artery rings was equally susceptible to inhibition of nitric oxide (NO) synthase using L-N(G)-nitroarginine (L-NOARG, 10(-4) M), or to inhibition of soluble guanylate cyclase using 1H-[1,2,4]oxadiazolo[4,3-a]quinoxaline-1-one (ODQ, 10(-5) M). 3. In nonischaemic arteries, the relaxation to ACh was unaffected by high K+ (67 mM) but in ischaemic arteries, the maximum relaxation to ACh was significantly reduced from 113+/-6 to 60+/-2% (ANOVA, P<0.05). Tetraethylammonium (TEA, 10(-3) M), an inhibitor of large conductance calcium activated potassium (BK(Ca)) channels did not inhibit the response to ACh in nonischaemic arteries but in ischaemic arteries TEA significantly shifted the concentration response curve to ACh to the right (pEC(50); nonischaemic, 7.07+/-0.25; ischaemic, 6.54+/-0.21, P<0.01, ANOVA) without decreasing the maximum relaxation. TEA did not affect the responses to sodium nitroprusside in either nonischaemic or ischaemic arteries. 4. In conclusion, ischaemia/reperfusion did not change the sensitivity of endothelium-dependent relaxation to L-NOARG or ODQ indicating that ischaemia did not affect the contribution of NO or cyclic GMP to ACh-induced relaxation. However, in ischaemic arteries the opening of the BK(Ca) channels contributed to relaxation caused by ACh whereas TEA had no effect in nonischaemic arteries. The factor responsible for the opening of this potassium channel was a factor other than NO and may be endothelium derived hyperpolarizing factor (EDHF).

Acetylcholine↗

PubMed1999

Carcinosarcoma of the parotid gland: ultrasound and computed tomography findings.

Carcinosarcoma is a rare tumour of the salivary gland. The ultrasound and CT appearances of a rapidly enlarging carcinosarcoma in the parotid are described. Both modalities revealed a 4-cm tumour with relatively benign features and no evidence of lymphadenopathy. Ultrasound showed a well-defined mass of homogeneous low echogenicity and posterior acoustic enhancement. Computed tomography showed a parotid mass of homogeneous attenuation similar to muscle, and homogeneous enhancement following contrast. The clue to the malignant nature of the lesion was a short indistinct superficial margin with tumour extension into the adjacent subcutaneous tissues.

Adult↗

PubMed1999

In vitro elution of antibiotic from antibiotic-impregnated biodegradable calcium alginate wound dressing.

OBJECTIVE: The authors investigated the calcium alginate dressing as a drug-delivery system for the treatment of various surgical infections. METHODS: Cytotoxicity of the calcium alginate dressing to fibroblasts and HeLa cells was evaluated by the 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H tetrazolium bromide (MITT) colorimetric assay. The calcium alginate dressing was mixed with vancomycin, and lyophilized or not lyophilized to form two types of antibiotic dressings. The antibiotic dressings were placed in 2 mL of phosphate buffered saline (PBS) or in PBS containing 0.01% calcium ions, and incubated at 37 degrees C. The PBS was changed daily, and the removed solutions were stored at -70 degrees C until the antibiotic concentration in each sample was determined by high performance liquid chromatography assay. RESULTS: The results suggested that the antibiotic dressings present no obvious toxic risk to their use as a drug-delivery system. The concentration of vancomycin in each sample was well above the breakpoint sensitivity concentration (the antibiotic concentration at the transition point between bacterial kill. ing and resistance to the antibiotic) for more than 14 days. The release was most marked during the first 48 hours. The concentration of calcium ions in PBS and the lyophilization of the manufacture process of antibiotic dressings prolonged the antibiotic diffusion duration. The diameter of the sample inhibition zone ranged from 10 to 11 mm, and the relative activity of vancomycin ranged from 62.88% to 92.18%. CONCLUSION: All antibiotic dressings released bactericidal concentrations of the antibiotics in vitro for the period of time needed to treat surgical infections. This study offers a convenient method to meet the specific antibiotic requirement for different patients.

Alginates↗

PubMed1999

Signaling pathway and pepsinogen secretion in Helicobacter pylori-infected human gastric adenocarcinoma.

Although in vitro studies have suggested that Helicobacter pylori not only attaches to cultured cells but also induces signal transduction events in host cells, the underlying mechanism of H. pylori action has yet to be fully investigated. In the present study, a cytotoxin-positive H. pylori was used to infect and examined for its effect on the stimulation of second messengers in human gastric adenocarcinoma (AGS). Results showed that H. pylori increased cytosolic free calcium concentration [Ca2+]i in host cells in a dose-dependent manner. The increase of [Ca2+]i was due to release from the intracellular Ca2+ store as well as entry to the extracellular Ca2+. H. pylori infection on host cells was also found to induce the generations of inositol phosphates, adenosine 3', 5'-cyclic monophosphate, and guanosine 3',5'-cyclic monophosphate, and to stimulate the secretion of pepsinogen.

Adenocarcinoma↗

PubMed1999

Development of a biodegradable antibiotic delivery system.

Antibiotic beads have been used as a drug delivery system for the treatment of various surgical infections. In this study, the copolymer 50:50 poly(DL-lactide):co-glycolide was mixed with vancomycin powder and hot compressing molded at 55 degrees C to form five types of biodegradable antibiotic beads. The beads were placed in 1 mL of phosphate buffered saline and incubated at 37 degrees C. The phosphate buffered saline was changed daily, and the removed buffer solutions were stored at -70 degrees C until the antibiotic concentration in each sample was determined by high performance liquid chromatography system assay. The concentration of vancomycin in each sample was well above the breakpoint sensitivity concentration (the antibiotic concentration at the transition point between bacterial killing and resistance to the antibiotic) for more than 32 days. The release was most marked during the first 48 hours. All copolymer 50:50 poly(DI lactide):co-glycolide biodegradable beads released high concentrations of the antibiotics in vitro for the time needed to treat bone infections (4 to 6 weeks). The diameter of the sample inhibition zone ranged from 6.5 mm to 10 mm, and the relative activity of vancomycin ranged from 12.5% to 100%. Copolymers with low heat of formation temperatures are required for making a controlled release system to prevent antibiotic decomposition, which occurs when using the hot compressing molded method. The rate and duration of release from the antibiotic beads can be adjusted by varying the diameter of the beads. This offers a convenient method to adjust the release rate to meet the specific antibiotic requirements for different patients.

Absorbable Implants↗

PubMed1998

Identification of novel genes that are differentially expressed in human colorectal carcinoma.

By using mRNA differential display technology, we have identified three cDNA clones, myl 3, myl 4, and myl 6, to show significant changes in expression between human colorectal tumor and paired normal tissue. Northern blot analysis indicated that clone myl 3 expression was elevated in normal tissue, and clone myl 4 expression was elevated in tumor tissue. Nucleotide sequence analysis revealed that clones myl 3 and myl 4 have not been previously identified. However, clone myl 6 appears to be the human homolog of the 3' end region of tissue inhibitor of metalloproteinase 3 (TIMP-3). Northern blot analysis showed that a 2.5 kb TIMP-3 transcript was expressed at a much higher level in normal tissue than the colorectal tumor.

Aged↗

PubMed1998

Authentic cell-specific and developmentally regulated expression of pro-opiomelanocortin genomic fragments in hypothalamic and hindbrain neurons of transgenic mice.

The pro-opiomelanocortin (POMC) gene is expressed in a subset of hypothalamic and hindbrain neurons and in pituitary melanotrophs and corticotrophs. POMC neurons release the potent opioid beta-endorphin and several active melanocortins that control homeostasis and feeding behavior. POMC gene expression in the CNS is believed to be controlled by distinct cis-acting regulatory sequences. To analyze the transcriptional regulation of POMC in neuronal and endocrine cells, we produced transgenic mice carrying POMC27*, a transgene containing the entire 6 kb of the POMC transcriptional unit together with 13 kb of 5' flanking regions and 8 kb of 3' flanking regions. POMC27* was tagged with a heterologous 30 bp oligonucleotide in the third exon. In situ hybridization studies showed an accurate cell-specific pattern of expression of POMC27* in the arcuate nucleus and the pituitary. Hypothalamic mRNA-positive neurons colocalized entirely with beta-endorphin immunoreactivity. No ectopic transgenic expression was detected in the brain. Deletional analyses demonstrated that neuron-specific expression of POMC transgenes required distal 5' sequences localized upstream of the pituitary-responsive proximal cis-acting elements that were identified previously. POMC27* exhibited a spatial and temporal pattern of expression throughout development that exactly paralleled endogenous POMC. RNase protection assays revealed that POMC27* expression mimicked that of POMC in different areas of the CNS and most peripheral organs with no detectable ectopic expression. Hormonal regulation of POMC27* and POMC was identical in the hypothalamus and pituitary. These results show that distal 5' sequences of the POMC gene located between -13 and -2 kb target expression into the CNS of transgenic mice in a precise neuron-specific, developmentally and hormonally regulated manner.

Animals↗

PubMed1998

Enantiomeric separation of tramadol hydrochloride and its metabolites by cyclodextrin-mediated capillary zone electrophoresis.

The enantiomeric separation of tramadol hydrochloride and its major metabolites, O-demethyltramadol (M1) and N-demethyltramadol (M2) was studied using cyclodextrin (CD)-mediated capillary zone electrophoresis (CZE). Influence of the choice of type and concentration of CD, capillary temperature, length of capillaries, buffer pH and the addition of polymer modifier on the chiral separation of tramadol and its metabolites was evaluated. It was found that the drug and the metabolites can be baseline-separated simultaneously by using 50 mM phosphate buffer (pH 2.5) containing 75 mM methyl-beta-CD, 220 mM urea and 0.05% (w/v) hydroxypropylmethyl cellulose.

Analgesics, Opioid↗

PubMed1998

Identification of neutral and acidic sphingomyelinases in Helicobacter pylori.

We demonstrated for the first time the presence of sphingomyelinase (SMase) in Helicobacter pylori. Activation of SMase has been implicated as the cause of elevation of cellular ceramide levels and consequently of apoptosis. The data indicate that there are two classes of SMase, defined by their optimal pHs and cellular locations, existing in H. pylori. One is an Mg(2+)-dependent membrane-bound enzyme with an optimal activity at pH 7, and the other is an Mg(2+)-independent cytosolic enzyme with an optimal activity at pH 5. Bisalumin, a bismuth salt, was found to inhibit the activities of both forms of SMase regardless of the presence of Mg2+. By Western blot analysis, the membrane-bound SMases of H. pylori and Bacillus cereus were shown to be antigenically related and to have a similar denatured molecular mass of 28 kDa.

Bismuth↗

PubMed1998

Two-dimensional electrophoretic analysis of membranous protein from human thyroid tissues and cancer cell lines.

Thyroid neoplasm is the most commonly encountered neoplastic disorder in endocrine clinics. Thyroid scan, ultrasonography, and fine needle aspiration cytology (FNAC) are used as diagnostic tools to differentiate a malignant nodule from a benign lesion. There are certain limitations and pitfalls in FNAC, especially in the diagnosing of follicular tumors. The lack of characteristic findings or a specific tumor marker are the most common problems in the preoperative diagnosis of thyroid follicular carcinoma. Although serum thyroglobulin level has been used as a tumor marker for post-operative, well-differentiated thyroid cancer, the assay cannot be used for preoperative diagnosis of thyroid carcinoma. In this study, various thyroid tissues and cancer cell lines including CGTH W-1, CGTH W-3, RO 82 W-1, SW 579 cell lines were used for the investigation of tumor markers. Specific spots were identified in the area near the 60 kDa molecular mass protein and isoelectric point (pI) 5.9 of the CGTH W-1 cell line. These spots could not be found in the papillary or anaplastic thyroid cancer cell lines. Another spot with a molecular weight of about 9.8 kDa with a low pI of 4.8 was present in the CGTH W-1 and RO 82 W-1 cell lines. This spot appeared to be a tumor marker of follicular cancer cells. This spot could not be found in the papillary and anaplastic cancer cell lines and other benign thyroid tissues. Specific proteins that were identified in this study may be useful as tumor markers for follicular thyroid carcinoma.

Electrophoresis, Gel, Two-Dimensional↗

PubMed1998

What should men know about prostate-specific antigen screening before giving informed consent?

PURPOSE: Since prostate-specific antigen (PSA) screening is controversial, some authorities recommend that patients give informed consent before testing. We identified and compared what facts experts and patients thought men should know. SUBJECTS AND METHODS: We recruited a Delphi panel of national experts (6 urologists and 6 non-urologists) and conducted 6 focus groups of couples (48 subjects) with 24 screened and unscreened men from a university hospital. We ranked key facts that experts and couples thought men ought to know before consenting to PSA screening and conducted a multidisciplinary focus group to help interpret the findings. RESULTS: All participants would disclose that false positive and false negative results can occur and that it is not known whether PSA screening reduces prostate cancer mortality. The 12 experts would disclose the uncertain benefits of treating early, localized prostate cancer. All 24 couples would disclose that the PSA test is a blood test and that patients may worry about results. The 6 urologists would disclose that prostate cancer is often incurable when symptoms appear; the 6 non-urologists, that it can be asymptomatic. The 12 couples with screened men would disclose that the PSA test can detect cancer sooner than the digital rectal examination; the 12 couples with unscreened men, that PSA testing is controversial. CONCLUSIONS: Physicians and patients agree upon some facts that men should know about PSA screening before giving informed consent. However, physicians fail to emphasize other facts that patients find important. Physicians may differ by expertise; patients, by experience. Our findings provide content for informed consent for PSA screening, and our method may be useful for other controversial tests.

Delphi Technique↗

PubMed1998

Lack of S-adenosylmethionine results in a cell division defect in Escherichia coli.

The enzyme S-adenosylmethionine (SAM) synthetase, the Escherichia coli metK gene product, produces SAM, the cell's major methyl donor. We show here that SAM synthetase activity is induced by leucine and repressed by Lrp, the leucine-responsive regulatory protein. When SAM synthetase activity falls below a certain critical threshold, the cells produce long filaments with regularly distributed nucleoids. Expression of a plasmid-carried metK gene prevents filamentation and restores normal growth to the metK mutant. This indicates that lack of SAM results in a division defect.

Bacterial Proteins↗

PubMed1998

A corticotropin-releasing hormone type I receptor antagonist delays parturition in sheep.

In sheep, corticotropin-releasing hormone (CRH) can stimulate the fetal release of ACTH to produce a cortisol surge which leads to the onset of parturition. We tested the hypothesis that fetal CRH is a primary factor in the onset of parturition in sheep by using a Type I CRH receptor antagonist, antalarmin, to block the endogenous action of CRH. Pregnant ewes were cannulated at 130-135 days of gestation. Five catheters were placed into the amniotic sac, fetal femoral artery, fetal tarsal vein, maternal jugular vein and carotid artery. After 5 days' recovery, blood samples from maternal and fetal vessels were collected at the following times: a day before the start of infusion, at [-1, 0, 1, 2, 4, 8 and 24]h, on the first day of infusion, and thereafter daily throughout a 10-day infusion. Animals (n=6 per group) received infusions into a fetal vein of either a vehicle comprising 1:1 mixture of ethanol and polyethoxylated castor oil (Cremophor EL) or antalarmin (50 g/L) in the vehicle at a rate of 0.3 mL/h. The plasma samples were assayed for ACTH and cortisol using commercial RIA kits. Fetuses infused with vehicle delivered at a mean gestational age of 141.8 +/- 0.9 days compared with antalarmin-infused sheep at 148.8 +/- 1.6 days (P = 0.0036, unpaired Student's t-test). Fetal ACTH and cortisol did not change in the antalarmin-infused sheep after 3 days' infusion compared to significant increases in vehicle-infused sheep (P=0.004 and P = 0.016 respectively, ANOVA). These data show that CRH receptor antagonism in the fetus can delay the onset of parturition. It supports the hypothesis that hypothalamic CRH drives fetal production of ACTH and is essential for the onset of parturition triggered by a surge in fetal cortisol.

Adrenocorticotropic Hormone↗

PubMed1998

Corticotropin-releasing hormone directly and preferentially stimulates dehydroepiandrosterone sulfate secretion by human fetal adrenal cortical cells.

Estrogens produced by the placenta play a pivotal role in the endocrine control of pregnancy and induce many of the key changes involved in parturition. The placentae of humans and higher primates use the C19 androgen dehydroepiandrosterone sulfate (DHEA-S) supplied by the fetal adrenals as the principal substrate for estrogen synthesis. Thus, secretion of androgens by the fetal adrenals may be central to the process of primate parturition. The timing of human parturition also is correlated with placental CRH concentrations in the maternal circulation. Because the mechanisms that regulate DHEA-S production by the fetal adrenals are incompletely understood, we examined whether there is a functional relationship between CRH and steroid production by human fetal adrenal cortical cells. Using Northern blot analysis, we detected messenger RNA transcripts (2.7 kb) encoding the type-1 CRH receptor in total RNA extracted from midgestation human fetal adrenals, suggesting that the fetal adrenal cortex may be directly responsive to CRH. To test this, primary cultures of human fetal adrenal cortical cells were exposed to human CRH. Human CRH increased DHEA-S production by cultured human fetal adrenal cortical cells in a dose-dependent fashion, with an ED50 of 10-100 pmol/L. Human CRH was as effective as ACTH at stimulating DHEA-S production; however, it was 70% less potent than ACTH at stimulating cortisol production, indicating that its actions were preferentially directed toward increasing DHEA-S synthesis. Consistent with this thesis, we found that CRH increased abundance of messenger RNA encoding cytochrome P450 cholesterol side-chain cleavage and 17alpha-hydroxylase/17,20 lyase but not 3beta-hydroxysteroid dehydrogenase in adrenal cells. CRH did not alter cell number, indicating that it is not mitogenic for fetal adrenal cortical cells. These data demonstrate a direct functional interaction between CRH and the fetal adrenal. Therefore, placental CRH production, which rises exponentially during human pregnancy, may play a key role in promoting DHEA-S production by the fetal adrenals, which could lead to increasing placental estrogen synthesis and contribute to the process of parturition in humans.

Adrenal Cortex↗

PubMed1998

Elimination of microorganisms from dental operatory compressed air.

Compressed air is used to power high-speed handpieces, as well as to dry and clean surfaces in the oral cavity during patient treatment, in all dental operatories. The compressed air used in the dental operatories located in large institutions such as universities or hospitals is generally obtained from a central source, and is produced by continually running compressors. In operatories located in private practice settings, compressed air is obtained from small on-site air compressors, which may be run less frequently. A survey was made of operatories in the Montreal area to determine the microbial load of the compressed air produced by air compressors. An air sampler was used to collect compressed air and impinge it on a rotating agar medium surface. Compared to the air produced from compressors in constant use, the air collected from compressors that ran intermittently had a very high microbial load. The efficacy of an apparatus designed to sterilize the contaminated air produced by small, on-site compressors was tested. Called a Purilair, this device heats every particle of inflowing compressed air to 250 degrees C and then forces it through a fine-pore ceramic filter. In three private practice operatories, an in-line Purilair effectively sterilized the air being delivered by small compressors. The same result was obtained in the laboratory when lyophilized spores and cells of Bacillus stearothermophilus and conidia of Penicillium notatum and Aspergillus niger were sprayed into the intake line of the apparatus.

Academic Medical Centers↗

PubMed1997

Visualization of an extracellular mucoid layer of Treponema denticola ATCC 35405 and surface sugar lectin analysis of some Treponema species.

Slime layers and capsules are common amongst medically relevant bacteria. We herein report that Treponema denticola, which has been associated with periodontitis, synthesizes or acquires an extracellular polysaccharide layer that we have observed through electron microscopy using the polysaccharide-specific dye Alcian blue and phosphotungstate. We have also visualized this extracellular layer by dark-field microscopy of Alcian blue-stained spirochete cells. A representative strain of each of the oral spirochete species T. denticola, Treponema vincentii and Treponema socranskii were differentiated by concanavalin A, phaseolus, lotus A and arachis lectins in a microtiter plate immunoassay for the detection of surface sugars.

Bacterial Capsules↗

PubMed1997

An inexpensive solid medium for obtaining colony-forming units of oral spirochetes.

A method for the enumeration of colony-forming units of oral anaerobic spirochetes in new oral spirochete agarose (NOS-A) medium was described recently. However, the high cost of agarose limits the extent to which large assays can be carried out. Accordingly, a search for an inexpensive gelling agent that remains molten at 37 degrees C and gels at 25 degrees C was undertaken. Varying amounts of Noble agar or Bacto agar (0.5 to 1.5%, w/v) were mixed with varying amounts of gelatin (0.5 to 1.0%, w/v) in NOS medium. NOS medium containing 0.5% gelatin-0.5% Noble agar (NOS-GN) or 0.5% gelatin-0.5% Bacto agar (NOS-GB) met the above criteria. NOS-GN and NOS-GB media yielded higher colony-forming units with Treponema denticola than NOS-A medium in that order. However, all three media, NOS-GN, NOS-GB and NOS-A, performed equally well in the recovery of viable counts of T. vincentii. The NOS-GN medium was not liquefied by subgingival bacteria or two gelatinase-producing species of bacteria, Bacillus subtilis and Staphylococcus aureus. Thus NOS-GN medium is the recommended medium both in cost and performance for obtaining colony counts of spirochetes.

Bacillus subtilis↗

PubMed1997

Nitric oxide inhibits corticotropin-releasing hormone exocytosis but not synthesis by cultured human trophoblasts.

Nitric oxide (NO) plays an important role in many cell-cell signaling systems, but its mechanism of action is variable. We have previously reported that NO reduces secretion of the peptide hormone, CRH, from cultured placental cells and the perfused placenta. Because placental CRH production seems linked to human parturition, we wished to explore the mechanism of action of NO in this setting in more detail. We report here that in the placenta, NO specifically inhibited CRH exocytosis, not synthesis, and that endogenous NO affects this process. Cytotrophoblasts were prepared from term human placentas and cultured as monolayers. CRH immunoreactivity in the cell supernatants and cell extracts were measured by RIA. CRH messenger RNA was determined by Northern blot analysis. Sodium nitroprusside (SNP; 1-100 mumol/L) and S-nitroso-N-acetyl-penicillamine (SNAP; 1-100 mumol/L), NO donors, significantly reduced basal CRH concentration in the media, while increasing the concentration of CRH in the cells (P < 0.01), suggesting that exocytosis of CRH was inhibited. These effects could be attenuated by the NO scavenger hemoglobin (20 micrograms/mL). KCl (45 mmol/L), which causes exocytosis by depolarizing the cell membrane, increased CRH release by 2- to 3-fold, and this was inhibited by SNP. Basal release of CRH was augmented by the NO synthase competitive inhibitor N omega-L-arginine methyl ester (1 mmol/L; P < 0.01) and the guanylate cyclase inhibitor, LY83583 (1 mumol/L; P < 0.01). The inhibitory effect of SNP was also blocked by LY83583. CRH messenger RNA content did not change when the placental cells were incubated with SNP, N omega-L-arginine methyl ester, and LY83583 for 6 and 24 h, and this was consistent with studies showing that total CRH immunoreactivity (cells plus media) did not change in the presence of SNP. These studies indicate that exogenous NO inhibits CRH exocytosis, rather than biosynthesis, by human trophoblasts and that endogenous NO has tonic inhibitory effects on CRH release by these cells. The inhibitory effect of NO on basal and stimulated CRH release by placental trophoblasts seems to be a guanylate cyclase-mediated inhibition of exocytosis.

Adult↗