Biomedical subjects

W Chan

Publications and source records attributed to W Chan.

At least 73 records · Page 4Linked to original sources

PubMed1997

Inhibition of transforming growth factor beta 1 induction by dietary vitamin E in unilateral ureteral obstruction in rats.

Free radical species associated with bilateral ureteral obstruction (BUO) are considered important in the pathogenesis of the glomerular and tubulointerstitial injury in BUO rats. We seek to test the hypothesis that the use of an easily administered antioxidant, vitamin E, at sufficient plasma concentrations, can decrease this release of free oxygen radicals in kidney tissue and ameliorate the increase of the fibrogenic cytokine, transforming growth factor beta-1 (TGF beta-1). We used the unilateral ureteral obstruction (UUO) rat model, because the presence of the uninjured contralateral kidney provides a nonuremic internal milieu, in contrast to the uremic, acidotic, and hypercholesterolemic BUO model. Compared to sham controls, the UUO animals showed a dramatic increase in renal cortical TGF beta-1 mRNA, as quantitated by Northern blot analysis with cyclophilin internal standards. This increase in TGF beta-1 mRNA was reversed in UUO rats treated with vitamin E. The plasma malondialdehyde (MDA) concentration, an index of lipid peroxidation and an indirect index of free radical release, was significantly elevated in UUO animals compared to sham animals. The vitamin E-treated UUO animals showed a significant decrease in both plasma and renal cortical tissue MDA content. Taken together, these findings provide evidence of the important biological role of reactive free radical species in the tubulointerstitial injury of UUO and the novel role of vitamin E in modulating the mRNA of the fibrogenic TGF beta-1 in obstructive uropathy.

Administration, Oral↗

PubMed1997

Empyema thoracis in children: a 26-year review of the Montreal Children's Hospital experience.

The appropriate management of pediatric empyema thoracis remains controversial. The authors reviewed 47 cases of empyema thoracis over a 26-year period. The management of empyema included initial diagnostic thoracentesis and classification as acute, fibropurulent, or chronic. If the empyema was "acute," therapeutic tap, tube thoracostomy, or no surgical intervention was performed. "Fibropurulent" empyemas were uniformly treated with tube thoracostomy. The lung was decorticated when the empyema was encased by a thick peel, had recurred and was multiloculated, was refractory and the patient remained clinically unwell, or had occurred as a complication of previous thoracotomy. All patients with acute empyemas responded to antibiotics irrespective of drainage (average duration of fever, 17 days; average stay in hospital, 27 days). Of the fibropurulent empyemas in our review, complete drainage was attained in seven of 39 (18%), and decortication was not required in any empyema that was completely drained. Loculations persisted in 25 of 39 (64%) after tube thoracostomy but nonetheless resolved. The remaining seven of 39 (18%) with persistent loculations required formal decortication. Of the patients with fibropurulent empyemas that responded to tube thoracostomy, the average duration of fever was 13 days and hospitalization, 23 days. Of those requiring decortication the average duration of fever was 24 days and hospitalization, 40 days. These results will allow a baseline for comparison of new strategies (fibrinolytics and early thoracoscopy) that may reduce days of fever, hospitalization, and risk of formal decortication.

Adolescent↗

PubMed1997

The effects of running stress on plasma vitamin A levels in rats.

The plasma concentrations of vitamin A, zinc and proteins and the hepatic level of vitamin A were determined in rats subjected to running as a model for stress and which were receiving standard or vitamin-A free diets. All rats showed a decrease in plasma vitamin A with running compared with non-running control animals. Hepatic levels of vitamin A were higher in these two test groups than in their weight- and age-matched non-running controls. The data support that running, like other forms of stress, decreases plasma vitamin A, consistent with the retention of vitamin A in the liver.

Animals↗

PubMed1997

Buthionine sulphoximine alone and in combination with melphalan (L-PAM) is highly cytotoxic for human neuroblastoma cell lines.

Buthionine sulphoximine (BSO) selectively inhibits glutathione (GSH) synthesis and may enhance the antineuroblastoma activity of melphalan (L-PAM). We determined the cytotoxicity of BSO (dose range 0-1000 microM) alone and in combination with L-PAM (dose range 0-0 microM) in a panel of 18 human neuroblastoma cell lines. BSO alone was highly cytotoxic with 16/18 neuroblastoma cell lines having IC90 values (range 2.1- > 1000 microM) below the clinically achievable steady-state plasma level of 500 microM BSO. Maximal cell killing correlated with GSH levels decreased to less than 10% baseline, and was partially reversed by the addition of exogenous anti-oxidants (GSH, vitamin E and ascorbate). Fluorocytometric analysis of DNA fragments by the Tunnel method detected 92% of a BSO sensitive cell line in apoptosis after a 48 h exposure to 500 microM BSO. The combination of L-PAM and BSO synergistically enhanced the cell killing of L-PAM alone by > 1-3 logs (combination index < 1). We conclude that BSO has significant single-agent cytotoxicity against neuroblastoma and enhances cell killing when combined with L-PAM.

Antineoplastic Agents↗

PubMed1997

Blood pressure reactivity in urban youth during angry and normal talking.

Distinctions between male and female adult patterns of cardiovascular disease are well established. Although risk for cardiovascular disease begins early in life, little research has been focused on the beginning of gender difference patterns. This pilot study examined blood pressure reactivity, gender, and biologic maturity in adolescents talking about angry life circumstances and the usual progression of their day. Systolic and diastolic blood pressure increased during talking, and the addition of biologic maturity to the analysis distinguished males from females. Males had higher systolic blood pressures than did females throughout the protocol, and, generally, mature subjects had higher systolic and diastolic blood pressures than did less mature subjects. These pilot data confirm the effects of talking on blood pressure. The data suggest that biologic maturity enhances understanding of gender differences in adolescent blood pressure reactivity and continued study of the gender-blood pressure reactivity distinctions in adolescents may further understanding of adult patterns of gender differences in cardiovascular disease.

Adolescent↗

PubMed1997

Murine gastrulation requires HNF-4 regulated gene expression in the visceral endoderm: tetraploid rescue of Hnf-4(-/-) embryos.

Immediately prior to gastrulation the murine embryo consists of an outer layer of visceral endoderm (VE) and an inner layer of ectoderm. Differentiation and migration of the ectoderm then occurs to produce the three germ layers (ectoderm, embryonic endoderm and mesoderm) from which the fetus is derived. An indication that the VE might have a critical role in this process emerged from studies of Hnf-4(-/-) mouse embryos which fail to undergo normal gastrulation. Since expression of the transcription factor HNF-4 is restricted to the VE during this phase of development, we proposed that HNF-4-regulated gene expression in the VE creates an environment capable of supporting gastrulation. To address this directly we have exploited the versatility of embryonic stem (ES) cells which are amenable to genetic manipulation and can be induced to form VE in vitro. Moreover, embryos derived solely from ES cells can be generated by aggregation with tetraploid morulae. Using Hnf-4(-/-) ES cells we demonstrate that HNF-4 is a key regulator of tissue-specific gene expression in the VE, required for normal expression of secreted factors including alphafetoprotein, apolipoproteins, transthyretin, retinol binding protein, and transferrin. Furthermore, specific complementation of Hnf-4(-/-) embryos with tetraploid-derived Hnf-4(+/+) VE rescues their early developmental arrest, showing conclusively that a functional VE is mandatory for gastrulation.

Animals↗

PubMed1997

Prevalence of sleep-disordered breathing in diastolic heart failure.

OBJECTIVE: Sleep-disordered breathing (SDB) is common in congestive heart failure. While isolated diastolic heart failure (DHF) accounts for up to a third of all cases of congestive heart failure, the prevalence of SDB in DHF is unknown. We aim to determine the prevalence and characteristics of SDB in a group of patients with symptomatic DHF. METHODS: Twenty subjects with symptomatic DHF (New York Heart Association class II or III) and isolated diastolic dysfunction on echocardiography were assessed with lung function tests, modified sleep and health questionnaire, and overnight polysomnography. Significant SDB was defined as an apnea/hypopnea index (AHI) > 10. RESULTS: Thirteen female and seven male subjects (mean age, 65+/-6.0 years; mean body mass index (BMI), 28+/-3.2) were evaluated, of whom 17 (85%) had a diagnosis of hypertension. Overall sleep quality was poor, with fragmentation and frequent arousals associated with respiratory events. Fifty-five percent of the patients had significant SDB, mainly obstructive apneas. BMI and the prevalence of hypertension were similar in patients with and without SDB. The deceleration time, an index of diastolic dysfunction, was more prolonged in the group with SDB (236+/-40 ms vs 282+/-31 ms; p<0.05). As a group, a lower minimum percentage arterial oxygen saturation during sleep, but not the AHI was associated with more severe degree of diastolic dysfunction on echocardiogram, including a lower ratio between the early peak transmittal flow velocity and the late peak atrial systolic velocity (rho=0.57; p<0.05) and a prolonged isovolumic relaxation time (rho=-0.54; p<0.05). CONCLUSIONS: SDB is common in patients with DHF. Patients with DHF and SDB may be associated with worse diastolic dysfunction than those without SDB, although a causal relationship remains to be established.

Aged↗

PubMed1997

Giardiasis in ringed seals from the western arctic.

Sixteen beluga whales (Delphinapterus leucas) and fifteen ringed seals (Phoca hispida) from the western arctic region of Canada were examined for giardiasis and cryptosporidiosis. Intestinal contents from the rectum and colon were collected from animals slaughtered by Inuit hunters. A fluorescent monoclonal antibody identified Giardia sp. cysts in three of 15 (20%) seals. Thus, ringed seals are implicated as a potential reservoir for this zoonosis in the arctic.

Animals↗

PubMed1997

Review of the first 50 cases completed by the RACR mammography QA programme: phantom image quality, processor control and dose considerations.

The Mammography Quality Assurance Programme, recently established by the Royal Australasian College of Radiologists, has processed the first 50 applications. This programme, which closely follows the programme of the American College of Radiology (ACR), utilizes phantom film images, thermoluminescent dosimetry measurement of mean glandular dose, processor control charts, clinical images, equipment reports and required survey information to establish that a centre conforms to a minimum standard in mammography. The present paper describes the initial results of the first phantom images, dose measurements, processor control and survey information. A film review panel of six members has been trained in phantom film reading. Their evaluation of phantom films was compared with film readings by members of the ACR and was found to be in close agreement. Fifty films have been evaluated up to the present time with a failure rate of 26%. The major causes of failure were unacceptable film artefacts and poor contrast (as indicated by reduced fibre and mass visibility). A surprising result was the high failure in processing, where 23% of units reviewed had significant problems, including failure to keep the processor within required control limits. Only one centre recorded a mean glandular dose above 2 mGy with no centre over the 3 mGy limit. A review of the frequency of the quality control testing shows that the acceptance of quality assurance in mammography, while greater than in the initial stages of the ACR programme, is less than current US practice. These initial results for the accreditation process probably reflect an initial period of adjustment, as seen by the high pass rate achieved by centres that have resubmitted material to gain accreditation.

Accreditation↗

PubMed1996

The novel anticonvulsant SB 204269 binds to a stereospecific site in the mouse brain.

The novel compound SB 204269 (trans-(+)-6-acetyl-4S-(4-fluorobenzoylamino)- 3,4-dihydro-2,2-dimethyl-2H-benzo[b]pyran-3R-ol, hemihydrate) shows potent anticonvulsant activity in the mouse maximal electroshock seizure threshold test. The binding of [3H]SB 204269 to mouse forebrain membranes is saturable (Bmax 217 fmol/mg protein, Kd 32 nM) and stereospecific. The excellent anticonvulsant profile of SB 204269, combined with the identification of a unique binding site for the compound, suggest that it has potential clinical utility as a novel treatment for epilepsy.

Animals↗

PubMed1996

Seeding of A beta fibril formation is inhibited by all three isotypes of apolipoprotein E.

Apolipoprotein E is immunochemically localized to amyloid plaque in Alzheimer's brains, and the allelic distribution of ApoE in individuals is associated with a disposition toward Alzheimer's disease. We show here that all three ApoE isotypes exhibit a strong and specific ability to inhibit both nucleation and seeding of fibril formation by the A beta peptide in vitro. A beta (1-40) depleted of aggregates requires long incubation times before the onset of fibril formation, but addition of very low levels of A beta fibrils to such reactions is sufficient to reduce or eliminate this lag time. ApoE added to such seeded reactions extends the lag time in a dose-dependent manner, so that higher levels of seeding require higher levels of ApoE to achieve a given delay time to reaction onset. This effect is observed with all three isotypes produced in Escherichia coli, as well as with plasma-derived ApoE and the N-terminal domain of ApoE3 produced in E. coli. In contrast, bovine serum albumin and the four-helix bundle protein interleukin-4 are poor inhibitors of seeding. ApoE3 can also inhibit fibril formation by A beta (1-42). The three full-length isotypes of ApoE produced in E. coli are equipotent at inhibition. It is therefore possible that the genetics of ApoE and AD may fundamentally depend on the ability of ApoE to inhibit seeding but that the trends in the genetics must be related to something other than the specific activities of the native ApoE isoforms used in these studies. The data show ApoE to be the first member of a new class of fibril formation inhibitor that acts by blocking the seeding of fibril growth.

Alzheimer Disease↗

PubMed1996

Native complex formation between apolipoprotein E isoforms and the Alzheimer's disease peptide A beta.

To explore whether the genetic linkage between apolipoprotein E (ApoE) alleles and susceptibility to Alzheimer's disease might be attributable to a direct molecular interaction between ApoE and the amyloid peptide A beta, we have produced ApoE variants in Escherichia coli and studied their interactions with A beta under native conditions. When incubated with A beta at 20-40 microM concentrations, all three isoforms of ApoE (2, 3, and 4) readily form complexes with A beta which can be isolated by gel filtration in native buffer. Freshly mixed ApoE and A beta generate a complex that co-migrates in gel filtration with the main A280 peak, which migrates identically to the ApoE tetramer alone. After several hours incubation, an additional, high molecular weight, soluble aggregate appears which also contains both ApoE and A beta. Neither ApoE nor A beta incubated by themselves produces high molecular weight aggregates under these conditions. Incubation of A beta with control proteins bovine serum albumin and immunoglobulin generates negligable binding in the gel filtration assay. Similar results were obtained whether A beta (1-40) or A beta (1-42) was used, and plasma-derived ApoE gave similar results to E. coli-produced material. The data are consistent with a role for ApoE-A beta interactions in modulating the development of AD. Since no major differences were observed in the behavior of the three ApoE isotypes, however, the molecular basis of the genetic trend between ApoE alleles and AD cannot be attributed to specific activity differences between the molecular forms of ApoE characterized in this study.

1-Propanol↗

PubMed1996

Tenascin-C expression by angiogenic vessels in human astrocytomas and by human brain endothelial cells in vitro.

The expression of the extracellular matrix glycoprotein tenascin-C (TN) is enhanced in human astrocytomas and correlates with angiogenesis. To determine whether vascular cells are able to synthesize TN, we investigated the expression of TN protein and mRNA in nine astrocytomas. Immunogold electron microscopy in two glioblastomas multiforme detected the presence of TN in an extracellular perivascular location and to a lesser extent among tumor cells, confirming light microscopy immunohistochemical findings. In situ hybridization of astrocytomas using a digoxigenin-labeled antisense riboprobe detected strong staining for TN mRNA in vascular cells, especially in hyperplastic vessels, including those at the invasive edge of the tumors but not in vessels of normal brains. We observed weaker staining in tumor cells indicating a higher level of TN mRNA in vascular than in tumor cells. No staining was detected with the sense probe. Moreover, we investigated the ability of human brain microvessel endothelial cells (HBMECs) in primary culture to synthesize TN in vitro. Western blot analysis of the culture supernatants from HBMECs detected large amounts of TN. Immunogold silver staining demonstrated the presence of TN on the surface of HBMECs and in the subendothelial matrix. The distribution of TN mRNA in vascular cells of astrocytomas and the ability of HBMECs to synthesize TN in vitro demonstrate that vascular cells, including endothelial cells, are a major source of TN associated with angiogenesis. Furthermore, our results suggest that TN expression may be associated with endothelial cell activation and may play an important role in angiogenesis.

Astrocytoma↗

PubMed1996

Evaluation of serum and tissue levels of alpha-tocopherol.

This study was designed to test the effect of supplementation of several antioxidants, including alpha-tocopherol, on the clinical reduction of premalignant oral lesions. Samples of oral mucosa and serum were taken from baseline to 9 months of supplementation from patients with premalignant oral lesions and analyzed for alpha-tocopherol by HPLC. Statistical increases in both serum and tissue alpha-tocopherol were found after supplementation. There was no statistical relationship between alpha-tocopherol and beta-carotene levels.

Female↗

PubMed1996

An ApoE-Abeta inhibition complex in Abeta fibril extension.

BACKGROUND: Literature reports differ dramatically in showing that apolipoprotein E either facilitates or inhibits Abeta aggregate formation in vitro. Resolution of the nature of the ApoE-Abeta interaction is critical for progress towards understanding its possible role in the modulation of Alzheimer's disease. RESULTS: Here, we show that purified ApoE-Abeta co-aggregate is a poor seed of fibril formation. We also demonstrate ApoE inhibition of Abeta fibril growth in four independent aggregation assays, arguing that the poor fibril formation observed under these conditions is real and not an analytical artifact. We also directly show ApoE binding to immobilized Abeta fibrils by surface plasmon resonance. CONCLUSIONS: The results suggest a unifying model in which ApoE binds to Abeta fibril seeds and nascent nuclei to generate stable complexes that inhibit the rapid extension of mono-component Abeta fibrils but at the same time can foster continued slow growth of mixed ApoE-Abeta aggregates. In vivo co-aggregate formation may be important in many examples of pathological protein misassembly.

Amyloid beta-Peptides↗

PubMed1996

Mutational effects on inclusion body formation in the periplasmic expression of the immunoglobulin VL domain REI.

BACKGROUND: Inclusion body (IB) formation in bacteria is an important example of protein misassembly, a phenomenon which also includes folding-dependent aggregation in vitro and amyloid deposition in human disease. Previous studies of mutational effects in other systems implicate the stability of a folding intermediate-rather than the native state-as playing a key role in IB formation. To contribute to an understanding of the comparative biophysics of VL misassembly in different biological settings, we have studied mutation-dependent periplasmic IB formation by the VL domain REI in Escherichia coli. RESULTS: A series of mutants were produced in periplasmic IBs, where, in all cases, the signal peptide was removed. In addition, the intradomain disulfide was clearly formed before deposition into IBs. IB formation in these mutants does not correlate with monomer/dimer equilibrium constants, but does correlate with the thermodynamic stability of the native state. CONCLUSIONS: The results implicate a late, equilibrium folding intermediate in IB formation, in contrast to the apparent involvement of transient folding intermediates in other IB systems described to date. As equilibrium unfolding intermediates have also been implicated in light chain amyloidosis and deposition diseases, IB formation may prove a useful model for these human diseases.

Amino Acid Sequence↗

PubMed1996

beta-Adrenoceptors and dexamethasone synergistically stimulate the expression of the angiotensinogen gene in opossum kidney cells.

We transiently co-transfected opossom kidney (OK) cells with the plasmid containing the cDNA for beta 1-adrenoceptor (pBC-beta 1 AR) or beta 2-adrenoceptor (pBC-beta 2 AR) and a fusion gene with the 5'-flanking region of the angiotensinogen (ANG) gene linked to a bacterial chloramphenicol acetyl transferase (CAT) coding sequence as a reporter, pOCAT (ANG N-1498/ +18). Co-transfection of plasmid pBC-beta 1 AR or pBC-beta 2 AR alone enhanced the expression of pOCAT (ANG N-1498/+18). The addition of isoproterenol further stimulated the expression of pOCAT (ANG N-1498/ +18) when co-transfected with pBC-beta 1AR, but not with pBC-beta 2AR. Moreover, the addition of a combination of dexamethasone and isoproterenol synergistically stimulated the expression of pOCAT (ANG N-1498/+18) when co-transfected with pBC-beta 1AR, but not when cotransfected with pBC-beta 2AR. The synergistic effect of dexamethasone and isoproterenol was inhibited by the presence of RU 486 (an antagonist of glucocorticoid) or Rp-cAMP (an inhibitor of cAMP-dependent protein kinase A I and II). To localize the putative cAMP-responsive element (CRE) and glucocorticoid responsive element (GRE) in the ANG gene, we constructed the fusion gene by inserting the DNA fragment, ANG N-806 to N-465 upstream of the thymidine kinase (TK) promoter fused to a CAT gene and introduced them with pBC-beta 1AR into OK cells. The addition of dexamethasone or isoproterenol alone stimulated the expression of pTKCAT (ANG N-806/-465). The addition of isoproterenol and dexamethasone synergistically stimulated the transcriptional activity of pTKCAT (N-806/-465). These studies demonstrate that the beta 1-adrenoceptor and dexamethasone act synergistically to stimulate the expression of the ANG gene in OK cells via the putative CRE and GREs in the 5'-flanking region of the rat ANG gene. These data should aid in the understanding of the molecular mechanism(s) of the stimulatory effect of catecholamines/glucocorticoid induced expression of the ANG gene in the kidney.

Adrenergic beta-Agonists↗

PubMed1996

Reproducibility of a self-administered diet history questionnaire administered three times over three different seasons.

The reproducibility of the widely used Health Habits and History Questionnaire (HHHQ) for estimating "usual past-year" nutrient intake was examined. The HHHQ was self-administered on three occasions during three different seasons; 68 women (avg age 43 yrs) provided usable data for all three questionnaires in the appropriate seasons. Intraclass correlations (ICC) among the three administrations ranged from 0.56 (carotene) to 0.82 (fat as percentage of energy), with a median of 0.72. Thus, reliability was moderate to good, and season of administration/ordinality generally had little impact on ranking of individuals. The point estimates of intake of energy and a number of nutrients were higher in the first administration (winter). Except for dietary fiber and possibly carotene, most differences disappeared when adjusted for energy using a nutrient density approach, as well as using repeated-measures regression models. The higher intake in the first administration may be due more to either learning or fatigue effect rather than an effect of seasonal food availability on perceptions of "usual" intake. These data should be used in conjunction with validity data in the future to help evaluate the gain in precision of group means (and changes in these means) and improved estimates of odds ratios and correlations between nutrients and factors such as serum values, if a questionnaire is administered more than once.

Adult↗