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Biomedical subjects

K Chan

Publications and source records attributed to K Chan.

At least 55 records · Page 3Linked to original sources
PubMed2001

Electrically driven microseparation methods for pesticides and metabolites: VI. Surfactant-mediated electrokinetic capillary chromatography of aniline pesticidic metabolites derivatized with 9-fluoroenylmethyl chloroformate and their detection by laser-induced fluorescence.

In this report, we describe a surfactant-mediated electrokinetic capillary chromatography (SM-EKC) system for the separation of 9-fluoroenylmethyl chloroformate (FMOC)-derivatized anilines by capillary electrophoresis (CE). The SM-EKC system consisted of dioctyl sulfosuccinate (DOSS)/acetonitrile mixtures and was suited for the CE separation of the relatively hydrophobic FMOC-aniline analytes and other neutral compounds, e.g. alkylphenyl ketones. While the organic modifier acetonitrile (ACN) allowed the solubilization of the hydrophobic solutes and maintained the DOSS surfactant in its monomeric form by inhibiting micellization, the DOSS surfactant associated with the FMOC anilines to a varying degree thus leading to their differential migration and separation. Under these conditions, the FMOC-anilines were readily detected at the 10(-6) M level by UV at 214 nm and at the 10(-8) M level by laser-induced fluorescence (LIF) using a solid-state UV laser operating at 266 nm line as the excitation wavelength. The FMOC precolumn derivatization was also readily performed in lake water spiked with anilines at near the limit of detection (LOD) level. The lake water matrix showed no significant effects on the extent of derivatization at the LOD level as well as on the detection of the analytes due to the selectivity of the FMOC derivatization. The derivatization and detection of spiked lake water necessitated only the removal of microparticles by microfiltration prior to derivatization and detection.

Aniline Compounds↗
PubMed2001

Enzymes active in the areas undergoing cartilage resorption during the development of the secondary ossification center in the tibiae of rats aged 0-21 days: II. Two proteinases, gelatinase B and collagenase-3, are implicated in the lysis of collagen fibrils.

In the transformation of the cartilaginous epiphysis into bone, the first indication of change in the surfaces destined for resorption is the cleavage of aggrecan core protein by unidentified matrix metalloproteinases (MMPs) (Lee et al., this issue). In cartilage areas undergoing resorption, the cleavage leaves as superficial, 6-microm-thick band of matrix, referred to as "pre-resorptive layer." This layer harbors G1-fragments of the aggrecan core protein within a framework of collagen-rich fibrils exhibiting various stages of degeneration. Investigation of this layer in every resorption area by gelatin histozymography and TIMP-2 histochemistry demonstrates the presence of an MMP whose histozymographic activity is inhibited by such a low dose of the inhibitor CT1746 as to identify it as gelatinase A or B. Attempts at blocking the histozymographic reactions with neutralizing antibodies capable of inhibiting either gelatinase A or B reveals that only those against gelatinase B do so. Immunostaining of sections with anti-gelatinase B IgG confirms the presence of gelatinase B in every pre-resorptive layer, that is, at the blind end of excavated canals (stage I; 6-day-old rats), at sites along the walls of the forming marrow space (stage II; 7days), at sites within the walls of this space as it becomes the ossification center (stage III; 9 days) and along the wall of the maturing center (stage IV; 10-21 days). We also report the presence of collagenase-3 in precisely the same sites, possibly as active enzyme, but this remains to be proven. Because the results reveal that collagenase-3 is present beside gelatinase B in every pre-resorptive layer and, because these sites exhibit various signs of degradation including fibrillar debris, reduction in fibril number, or overt loss, we propose that gelatinase B and collagenase-3 mediate the lysis of this pre-resorptive layer-most likely through a cooperative attack leading to the disintegration of the collagen fibril framework.

Animals↗
PubMed2001

Enzymes active in the areas undergoing cartilage resorption during the development of the secondary ossification center in the tibiae of rats ages 0-21 days: I. Two groups of proteinases cleave the core protein of aggrecan.

The formation of a secondary ossification center in the cartilaginous epiphysis of long bones requires the excavation of canals and marrow space and, therefore, the resorption of cartilage. On the assumption that its resorption requires the lysis of the major cartilage component aggrecan, it was noted that the core protein may be cleaved in vitro by proteinases from two subfamilies: matrix metalloproteinases (MMPs) and aggrecanases. Such cleavage results in aggrecan being replaced by a fragment of itself referred to as a "G1-fragment." To find out if this cleavage occurs in the developing epiphysis of the rat tibia, the approach has been to localize the G1 fragments. For this purpose two neoepitope antisera were applied, one capable of recognizing the MMP-generated G1-fragment that bears the C-terminus ...FVDIPEN341 and the other capable of recognizing the aggrecanase-generated G1-fragment that carries the C-terminus ...NITEGE373. With the aid of these antisera, we report here that aggrecan cleavage is localized to newly developed sites of erosion. Thus, at 6 days of age, canals allowing the entry of capillaries are dug out from the surface of the epiphysis in a radial direction (stage I), whereas immunostaining indicative of aggrecan cleavage by MMPs appears at the blind end of each canal. The next day, the canal blind ends fuse to create a marrow space in the epiphysis (stage II), whereas immunostaining produced by MMPs occurs along the walls of this space. By 9 days, clusters of hypertrophic chondrocytes are scattered along the marrow space wall to initiate the formation of the secondary ossification center (stage III), where the resorption sites are unreactive to either antiserum. From the 9th to the 21st day, the center keeps on enlarging and, as the distal wall of the marrow space recedes, it is intensely immunostained with both antisera indicating that both MMPs and aggrecanases are involved in this resorption. We conclude, that both enzyme subfamilies contribute to the lysis of aggrecan. However, the results suggest that the respective subfamilies target different sites and even stages of development in the tissue, suggesting some diversity in the mode of aggrecan lysis during the excavation of a secondary ossification center.

Aggrecans↗
PubMed2001

Sequence verification of oligonucleotides by electrospray quadrupole time-of flight mass spectrometry.

The combination of electrospray ionization (ESI) and quadrupole time-of-flight (Q-Tof) mass spectrometry presents a powerful tool to verify/determine the sequence of oligonucleotides. An ESI-Q-Tof instrument provides better sensitivity and much higher resolution compared with either ESI-triple quadrupole or ESI-ion trap devices. With high-resolution capability, the quadrupole time-of-flight instrument can provide an isotope pattern to support the charge state assignment. This will improve the reliability of the assignments of sequence-related w or a-Base series ions and lead to accurate determination of the oligonucleotide sequence.

DNA↗
PubMed2001

Pelvic instability after bone graft harvesting from posterior iliac crest: report of nine patients.

OBJECTIVE: To report the imaging findings in nine patients who developed pelvic instability after bone graft harvest from the posterior aspect of the iliac crest. DESIGN AND PATIENTS: A retrospective study was performed of the imaging studies of nine patients who developed pelvic pain after autologous bone graft was harvested from the posterior aspect of the ilium for spinal arthrodesis. Plain films, bone scans, and CT and MR examinations of the pelvis were reviewed. Pertinent aspects of the clinical history of these patients were noted, including age, gender and clinical symptoms. RESULTS: The age of the patients ranged from 52 to 77 years (average 69 years) and all were women. The bone graft had been derived from the posterior aspect of the iliac crest about the sacroiliac joint. All patients subsequently developed subluxation of the pubic symphysis. Eight patients had additional insufficiency fractures of the iliac crest adjacent to the bone graft donor site, and five patients also revealed subluxation of the sacroiliac joint. Two had insufficiency fractures of the sacrum and one had an additional fracture of the pubic ramus. CONCLUSIONS: Pelvic instability is a potential complication of bone graft harvesting from the posterior aspect of the iliac crest. The pelvic instability is manifested by insufficiency fractures of the ilium and subluxation of the sacroiliac joints and pubic symphysis.

Aged↗
PubMed2001

Cathepsin k is a critical protease in synovial fibroblast-mediated collagen degradation.

Synovial fibroblasts (SFs) play a critical role in the pathogenesis of rheumatoid arthritis (RA) and are directly involved in joint destruction. Both SF-resident matrix metalloproteases and cathepsins have been implicated in cartilage degradation although their identities and individual contributions remain unclear. The aims of this study were to investigate the expression of cathepsin K in SFs, the correlation between cathepsin K expression and disease severity, and the contribution of cathepsin K to fibroblast-mediated collagen degradation. Immunostaining of joint specimens of 21 patients revealed high expression of cathepsin K in SFs in the synovial lining and the stroma of synovial villi, and to a lesser extent in CD68-positive cells of the synovial lining. Cathepsin K-positive SFs were consistently observed at sites of cartilage and bone degradation. Expression levels of cathepsin K in the sublining and vascularized areas of inflamed synovia showed a highly significant negative correlation with results derived from the Hannover Functional Capacity Questionnaire (r = 0.78, P = 0.003; and r = 0.70, P = 0.012, respectively) as a measure of the severity of RA in individual patients. For comparison, there was no correlation between Hannover Functional Capacity Questionnaire and cathepsin S whose expression is limited to CD-68-positive macrophage-like synoviocytes. The expression of cathepsin K was also demonstrated in primary cell cultures of RA-SFs. Co-cultures of SFs on cartilage disks revealed the ability of fibroblast-like cells to phagocytose collagen fibrils whose intralysosomal hydrolysis was prevented in the presence of a potent cathepsin K inhibitor but not by an inhibitor effective against cathepsins L, B, and S. The selective and critical role of cathepsin K in articular cartilage and subchondral bone erosion was further corroborated by the finding that cathepsin K has a potent aggrecan-degrading activity and that cathepsin K-generated aggrecan cleavage products specifically potentiate the collagenolytic activity of cathepsin K toward type I and II collagens. This study demonstrates for the first time a critical role of cathepsin K in cartilage degradation by SFs in RA that is comparable to its well-known activity in osteoclasts.

Adult↗
PubMed2001

Anti-inflammatory and anti-ulcer activity of Calligonum comosum in rats.

The 10% ethanol extract of the aerial parts of Calligonum comosum (50--400 mg/kg, i.p.) significantly reduced the increase in hind paw oedema induced by carrageenan in rats. Following sub-acute oral administration of the extract (50 and 100 mg/kg, daily for 14 days), a significant anti-inflammatory activity in the cotton pellet model was observed. Pre-treatment with the extract (100, 200 and 400 mg/kg) produced a significant and dose-dependent inhibition to the acute gastric ulcers induced by phenylbutazone, indomethacin, 0.2 N NaOH and 80% ethanol.

Animals↗
PubMed2001

Anti-nociceptive and anti-inflammatory properties of Caralluma arabica.

In the present study, a 10% ethanolic extract of Caralluma arabica at the doses of 200 and 400 mg/kg was evaluated for the antinociceptive activity using the hot plate and acetic acid induced abdominal constrictions in mice and tail flick method in rats. Oral and topical application of C. arabica extract was assessed in the present study for anti-inflammatory properties using carrageenan-induced rat paw oedema. Anti-inflammatory activity was also evaluated using cotton pellet granuloma method. C. arabica extract showed significant Anti-nociceptive properties in all the models studied. C. arabica extract significantly reduced the increase in hind paw volume induced by carrageenan injection when used orally or topically. Results of the present study confirm the use of C. arabica traditionally for the treatment of painful and inflammatory conditions and indicate transdermal absorption of the plant extract.

Administration, Oral↗
PubMed2001

Neuropharmacological actions of Portulaca oleraceae L v. sativa (Hawk).

Portulaca oleracea L v. sativa (family: Portulacaceae) is a warm-climate annual, cultivated in the Arabian peninsula and used traditionally for alleviating pain and swelling. It was observed that a 10% ethanolic extract of this plant produced restriction of movement in animals during the routine screening studies. Therefore the effects of the extract on the locomotor activity, threshold to noxious stimulus, anti-convulsant activity and relaxant effects on the skeletal muscle were studied. The extract, on intraperitoneal administration, showed a significant reduction in the locomotor activity in mice, anti-nociceptive activity in rats using Tail Flick Method, an increase in the onset time of pentylenetetrazole-induced convulsions in mice and muscle relaxant activity in in vitro (rat hemidiaphragm) and in vivo (grip strength) experiments. The anti-nociceptive activity of the extract in rats was attenuated by naloxone pre-treatment indicating the involvement of opioid receptors in its anti-nociceptive effects. It is indicated from the results of the present study that P. oleracea v. sativa possesses varied effects on both the central and peripheral nervous system and the plant should be exhaustively studied for other neuropharmacological effects.

Analgesics↗
PubMed2001

Distinction between relaxations induced via prostanoid EP(4) and IP(1) receptors in pig and rabbit blood vessels.

1. Our study shows that the prostacyclin analogues AFP-07 and cicaprost are moderately potent agonists for prostanoid EP(4) receptors, in addition to being highly potent IP(1) receptor agonists. Both activities were demonstrated on piglet and rabbit saphenous veins, which are established EP(4) preparations. 2. On piglet saphenous vein, PGE(2) was 6.1, 24, 96, 138, 168 and 285 times respectively more potent than AFP-07, cicaprost, PGI(2), iloprost, carbacyclin and TEI-9063 in causing relaxation. Another prostacyclin analogue taprostene did not induce maximum relaxation (21 - 74%), and did not oppose the action of PGE(2). The EP(4) receptor antagonist AH 23848 (30 microM) blocked relaxant responses to PGE(2) (dose ratio=8.6+/-1.3, s.e.mean) to a greater extent than cicaprost (4.9+/-0.7) and AFP-07 (3.8+/-0.8), had variable effects on TEI-9063-induced relaxation (3.7+/-1.5), and had no effect on taprostene responses (<2.0). 3. On rabbit saphenous vein, AH 23848 blocked the relaxant actions of PGE(2), AFP-07, cicaprost, iloprost and carbacyclin to similar extents. 4. AFP-07, cicaprost and TEI-9063 showed high IP(1) relaxant potency on piglet carotid artery, rabbit mesenteric artery and guinea-pig aorta, with AFP-07 confirmed as the most potent IP(1) agonist reported to date. AH 23848 did not block cicaprost-induced relaxation of piglet carotid artery. EP(3) contractile systems in these preparations can confound IP(1) agonist potency estimations. 5. Caution is urged when using AFP-07 and cicaprost to characterize IP(1) receptors in the presence of EP(4) receptors. Taprostene may be a lead to a highly selective IP(1) receptor agonist.

Alprostadil↗
PubMed2001

Survival, morbidity, and resource use of infants of 25 weeks' gestational age or less.

OBJECTIVE: The objective of this study was to examine survival, morbidity, and resource use in a large cohort of extremely preterm infants. STUDY DESIGN: We examined all (n = 754) neonatal intensive care unit admissions born at < or =25 weeks' gestation and inborn deliveries (n = 949) between 22 and 25 weeks' gestation at 17 Canadian neonatal intensive care units. RESULTS: The overall survival rate was 63%, with a range from 14% at 22 weeks' gestation to 76% at 25 weeks' gestation. There was a high incidence of chronic lung disease (33%-51%), > or =grade 3 intraventricular hemorrhage (0%-16%), necrotizing enterocolitis (0%-14%), > or =stage 3 retinopathy of prematurity (27%-55%), nosocomial infection (25%-39%), and multiple gestation (18%-46%). Extremely preterm infants comprise 4% of neonatal intensive care unit admissions but account for 22% of deaths, 20%-60% of major morbidities, 11% of patient days, and 10%-35% of major procedures. Outborn infants had a higher incidence of chronic lung disease, severe retinopathy of prematurity, and intraventricular hemorrhage. CONCLUSION: Extremely preterm infants have a high incidence of mortality and morbidity and consume disproportionate amounts of neonatal intensive care unit resources.

Canada↗
PubMed2001

Sex trade involvement and rates of human immunodeficiency virus positivity among young gay and bisexual men.

BACKGROUND: Susceptibility to human immunodeficiency virus (HIV) infection is of particular concern for marginalized populations. The objective of this study was to determine risk factors associated with sex trade work among young gay and bisexual men. Further, we aimed to compare HIV prevalence and incidence among men involved and not involved in sex trade work. METHODS: The study is based upon data obtained from a prospective cohort study of young gay and bisexual men. Participants had completed a baseline questionnaire which elicited information on demographic information, sexual behaviours, and substance use. Sex trade involvement was defined as the exchange of money, drugs, goods, clothing, shelter or protection for sex within the one year prior to enrollment. Contingency table and multivariate logistic regression analyses were used to identify risk factors associated with involvement in the sex trade. RESULTS: Of the 761 eligible participants, 126 (16%) reported involvement in sex trade work. Multivariate logistic regression analysis revealed regular alcohol use (Odds Ratio [OR] = 3.6, 95% CI : 1.8-7.2), aboriginal ethnicity (OR = 3.7, 95% CI : 1.6-8.7), unemployment (OR = 3.9, 95% CI : 2.1-7.3), history of residence in a psychiatric ward (OR = 4.2, 95% CI : 1.8-9.8), bisexual activity (OR = 7.0, 95% CI : 3.5-14.1) and the use of crack (OR = 7.4, 95% CI : 3.0-18.7) to be independently associated with sex trade work. Sex trade workers had a significantly higher HIV prevalence at baseline compared with non-sex trade workers (7.3% versus 1.1%, P < 0.001). As well, HIV incidence was found to be significantly higher for sex trade workers compared with non-sex trade workers (4.7% versus 0.9%, P = 0.011). CONCLUSION: Our study reveals that for male sex trade workers in this setting increased vulnerability to HIV infection is related to unfavourable living conditions, substance use and sexual risk behaviour.

Adult↗
PubMed2001

Imputing physical health status scores missing owing to mortality: results of a simulation comparing multiple techniques.

BACKGROUND: Having missing data complicates the statistical analysis of health-related quality-of-life (HRQOL) data and, depending on the extent and nature of missing data, can introduce significant bias in treatment comparisons. OBJECTIVE: We evaluated the bias associated with 4 different imputation methods for estimating physical health status (PHS) scores missing as a result of mortality. METHODS: A simulation study was conducted in which we systematically varied mortality rates from 0% to 30% and change in PHS scores from -20 to 20 on a 100-point scale for a 2-group clinical trial with follow-up over 18 months. The 4 imputation methods were last value carried forward (LVCF), arbitrary substitution (ARBSUB), empirical Bayes (BAYES), and within-subject modeling (WSMOD). Pseudo-root mean square residuals (RMSRs) and differences between true and estimated slopes were used to evaluate how well the imputation methods reproduced the true characteristics of the simulated population data. RESULTS: ARBSUB and BAYES methods have the smallest RMSRs compared with LVCF and WSMOD across all mortality rates. As the rate of missing data resulting from mortality increased, all imputation techniques deviated more from population data. The BAYES technique was best at reproducing group slopes in cases with differential mortality rates or when mortality rates exceeded 15%. WSMOD and LVCF significantly underestimated changes in PHS. CONCLUSIONS: The different imputation methods produced comparable results when there were few missing data. The BAYES approach most closely estimated true population differences and change in PHS regardless of missing data rates. These findings are limited to physical health and functioning measures.

Analysis of Variance↗
PubMed2001

Efficient conversion of normal prion protein (PrP) by abnormal hamster PrP is determined by homology at amino acid residue 155.

In the transmissible spongiform encephalopathies, disease is closely associated with the conversion of the normal proteinase K-sensitive host prion protein (PrP-sen) to the abnormal proteinase K-resistant form (PrP-res). Amino acid sequence homology between PrP-res and PrP-sen is important in the formation of new PrP-res and thus in the efficient transmission of infectivity across species barriers. It was previously shown that the generation of mouse PrP-res was strongly influenced by homology between PrP-sen and PrP-res at amino acid residue 138, a residue located in a region of loop structure common to PrP molecules from many different species. In order to determine if homology at residue 138 also affected the formation of PrP-res in a different animal species, we assayed the ability of hamster PrP-res to convert a panel of recombinant PrP-sen molecules to protease-resistant PrP in a cell-free conversion system. Homology at amino acid residue 138 was not critical for the formation of protease-resistant hamster PrP. Rather, homology between PrP-sen and hamster PrP-res at amino acid residue 155 determined the efficiency of formation of a protease-resistant product induced by hamster PrP-res. Structurally, residue 155 resides in a turn at the end of the first alpha helix in hamster PrP-sen; this feature is not present in mouse PrP-sen. Thus, our data suggest that PrP-res molecules isolated from scrapie-infected brains of different animal species have different PrP-sen structural requirements for the efficient formation of protease-resistant PrP.

Amino Acids↗
PubMed2001

Deletion of beta-strand and alpha-helix secondary structure in normal prion protein inhibits formation of its protease-resistant isoform.

A fundamental event in the pathogenesis of transmissible spongiform encephalopathies (TSE) is the conversion of a normal, proteinase K-sensitive, host-encoded protein, PrP-sen, into its protease-resistant isoform, PrP-res. During the formation of PrP-res, PrP-sen undergoes conformational changes that involve an increase of beta-sheet secondary structure. While previous studies in which PrP-sen deletion mutants were expressed in transgenic mice or scrapie-infected cell cultures have identified regions in PrP-sen that are important in the formation of PrP-res, the exact role of PrP-sen secondary structures in the conformational transition of PrP-sen to PrP-res has not yet been defined. We constructed PrP-sen mutants with deletions of the first beta-strand, the second beta-strand, or the first alpha-helix and tested whether these mutants could be converted to PrP-res in both scrapie-infected neuroblastoma cells (Sc(+)-MNB cells) and a cell-free conversion assay. Removal of the second beta-strand or the first alpha-helix significantly altered both processing and the cellular localization of PrP-sen, while deletion of the first beta-strand had no effect on these events. However, all of the mutants significantly inhibited the formation of PrP-res in Sc(+)-MNB cells and had a greatly reduced ability to form protease-resistant PrP in a cell-free assay system. Thus, our results demonstrate that deletion of the beta-strands and the first alpha-helix of PrP-sen can fundamentally affect PrP-res formation and/or PrP-sen processing.

Animals↗
PubMed2001

Studies of epidermal growth factor receptor inhibition in breast cancer.

Until recently, there has been little knowledge on the growth control of oestrogen receptor (ER)-negative ductal carcinoma in situ (DCIS) and invasive breast cancer. The recent development of DCIS models, such as transgenic mice, cell-line xenograft models and, importantly, in vivo human DCIS xenograft models has facilitated the investigation and understanding of the control of growth of early pre-invasive breast lesions. Recent studies have shown that ER-negative DCIS, unlike ER-positive DCIS, is hormone independent and does not respond to anti-oestrogen treatment. Moreover, DCIS of the comedo type utilises type I tyrosine kinase growth factors, such as epidermal growth factor receptor (EGFR) and c-erbB-2, in receptor signalling for growth. New data underscore the importance of EGFR as the major modulating growth factor receptor in the control of proliferation in the breast. Pre-clinical studies performed on human DCIS xenografts in nude mice suggest a potential role for EGFR tyrosine kinase inhibitors (EGFR-TKIs). More specifically, ZD1839, a novel orally active and selective EGFR-TKI, has been shown to produce a response in DCIS through a decrease in epithelial proliferation. These findings have enhanced our knowledge of signal transduction pathways in cancer and indicate that tyrosine kinase blockade of EGFR has potential for the treatment and chemoprevention of DCIS. It is hoped that further advances in this area and evaluation of EGFR-TKIs in Phase II/III clinical trials will allow their therapeutic potential as anticancer agents to be appreciated.

Animals↗
PubMed2000

Identification and purification of an intrinsic human muscle myogenic factor that enhances muscle repair and regeneration.

The limited ability of damaged muscle to regenerate after gross injuries is a major clinical problem. To date, there is no effective therapeutic treatment for muscle injuries. In the present study, we have examined the ability of crude and fractionated human skeletal muscle extracts to promote myogenic cell proliferation and differentiation. It was found that the crude muscle extract could significantly stimulate BrdU incorporation in C2C12 myogenic cell line. In addition, the extract also promoted myogenic cell alignment and fusion. Using electrophoresis techniques, in conjunction with in vitro refolding technique, a protein with molecular weight of approximately 40 kDa was identified that could produce the same effects as the crude muscle exdtract. We also tested the ability of semipurified (30-50 kDa) muscle extract to promote muscle repair in adult rats. Surgical intervention was used to induce muscle damage in the tibialis anterior. The semipurified muscle extract (fraction H) was injected subcutaneously over the tibialis anterior for a period of 5 days. It was found that the damaged muscle fibers were replaced by newly regenerated muscle fibers. These newly regenerated fibers originated from the fusion of differentiated satellite cells as revealed by BrdU-labeling analysis. In contrast, the injury site of muscles treated with BSA control protein contained mainly fibroblasts.

Adult↗