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Biomedical subjects

G Thomas

Publications and source records attributed to G Thomas.

At least 307 records · Page 17Linked to original sources
PubMed1997

A spray management valve for hand-compression sprayers.

The commercially available spray management valve provided consistent flow rates when used with hand-compression sprayer systems. The 15-psi spray management valve maintained a constant flow rate of 180, 150, and 155 ml/min in combination with a fine 45 degrees flat fan nozzle and Hudson. B&G, and Chapin hand-compression sprayers, respectively. The 30-psi spray management valve maintained a constant flow rate and adequate spray-on time when combined with the coarse flat fan nozzle for each of the 3 hand-compression sprayers tested.

Mosquito Control↗
PubMed1997

[Localization of a tumor suppressor gene distal to D22S270 in colorectal cancers].

Recurrent allelic losses on chromosome 22q have been reported in colorectal cancer, distal to the NF2 gene, suggesting that another tumor suppressor gene might be involved. We report here the typing of 256 sporadic colorectal tumors and 18 colonic cancer cell lines using a set of chromosome 22 polymorphisms, ranging from 20 to 45. A panel of somatic cell hybrids, that allows to distinguish 11 bins in the 22q13 region, was used to localize 19 of the 45 selected markers and the putative tumor suppressor gene BZRP. Allelic-loss was observed in 43% of tumors. The minimal region of deletion that could be determined, telomeric to locus D22S270, refines significantly the position of the gene. The localization of the BZRP gene in this region led to a systematic screening for somatic point mutation. Direct sequencing of its coding sequence in 36 tumors hemizygous for chromosome 22 allowed the identification of three polymorphisms but failed to detect somatic mutation.

Adenocarcinoma↗
PubMed1997

Occupational health and safety in Canadian health care facilities.

Numerous authors have expressed concern about the employee health and safety services offered by health care facilities in Canada. More than perhaps any other type of employer, these facilities are well equipped to provide extensive occupational health programs and should be sensitive to the need, but in reality too few facilities offer too little in the way of services. Compounding the problem are the strains resulting from nationwide cutbacks in health care spending, which have seriously deteriorated the quality of working life in Canadian health care facilities. Occupational health and safety programs are correspondingly more important, but are still too rare.

Canada↗
PubMed1997

Erythrocyte adenylate kinase isoenzyme as a marker for hemolysis.

The presence in serum of adenylate kinase isoenzyme originating from erythrocyte can be useful as a marker for detecting hemolysis. We have presented preliminary evidence for identifying hemolytic anemia patients earlier by determining erythrocyte AK isoenzyme activity in serum (or plasma) rather than using measurement of plasma hemoglobin concentration. This test being quite specific for hemolysis should find use as a quick method for estimating the extent of in vivo hemolysis in hemolytic patients earlier than heretofore possible.

Adenylyl Cyclases↗
PubMed1997

Abnormal phospholipid molecular species of erythrocytes in sickle cell anemia.

As the lipid composition of cell membranes has significant effects upon cellular function, we hypothesized that the membranes of sickle cells might have a distorted lipid composition. Accordingly, we analyzed the molecular species of the choline and ethanolamine glycerophospholipids, the fatty acid composition of the total phospholipids and of the five major individual phospholipids of erythrocytes from 8 patients with sickle cell anemia and from 14 normal subjects. Of the 31 molecular species identified for each subclass of the glycerophospholipids, 12 were found to be distinctly abnormal. Sickle cells contained more molecular species with saturated and monounsaturated fatty acid at the sn-2 position and fewer molecular species with polyunsaturated fatty acids at the sn-2 position. The values ranged from 20 to 60% above or below normal values. In diacyl choline glycerophospholipids (outer membrane leaflet), sickle erythrocytes contained lower amounts of the 16:0-18:2 species and higher 16:0-18:1 and 16:0-16:0 species. In diacyl ethanolamine glycerophospholipid (inner membrane leaflet), sickle erythrocytes had lower amounts of 18:0-22:6; 16:0-22:4; 18:0-18:2; 18:1-18:2; and 18:1-20:3. In phosphatidylcholine and phosphatidylethanolamine, sickle erythrocytes contained less linoleic acid, less docosahexaenoic acid (30-40%) and more oleic and palmitic acids (20-30%) compared to normal erythrocytes. These same differences were seen also in the total phospholipids. Our data demonstrated distinct abnormalities of the phospholipid molecular species composition in the membrane lipids of sickle erythrocytes. These defects might have a role in one or more known metabolic abnormalities of sickle cell disease including cation imbalance, dehydration, disturbed membrane phospholipid asymmetry, and hypercoagulability. Furthermore, detailed information of the phospholipid molecular species composition of normal erythrocytes was provided.

Anemia, Sickle Cell↗
PubMed1997

[Internal quality assurance or Hawthorne effect?].

The tendency of study participation per se to affect outcome is described by the term Hawthorne effect. This process defines the first step for internal quality assurance. However, whenever an attempt is made to describe the effects of quality assurance in more detail specific mathematical tools are required, including a database system that allows the calculation of clinical profiles, problem profiles, time-related variance of variables, univariate and multivariate statistics, calculation of scores and application of the hazard function. However, it has to be considered that any mathematical model is a way to present a hypothesis and not a proof. Whenever a proof is required, one should not ask for internal quality assurance, but design a randomized study.

Cardiac Surgical Procedures↗
PubMed1996

Inverse correlation between RER+ status and p53 mutation in colorectal cancer cell lines.

The high point mutation rate of replication error-prone (RER+) cells could theoretically lead to inactivation of the p53 gene by polyclonal mutations, which might explain the conflicting results that have been published on the p53 status of RER+ colon cancers. To address this issue, we tested the p53 status of 21 human colorectal cancer cell lines, including four showing microsatellite instability (RER+ phenotype). Denaturing gradient gel electrophoresis (DGGE) followed by sequencing showed that all four RER+ cell lines were wild type for p53 while 15 of the 17 RER- cell lines contained p53 mutations (P=0.001). Eight cell lines (four RER+ and four RER-) were analysed using three complementary methods to test more rigorously the polyclonal mutation hypothesis. (i) Of 87 single-cell clones (seven to 14 per cell line) examined by DGGE, only those derived from known p53 mutant cell lines showed altered profiles. (ii) Antibody DO-7 stained more than 80% of nuclei from the p53 mutant cell lines, but only 15% of nuclei from the RER+ cell lines. (iii) A yeast functional assay which can simultaneously detect polyclonal mutations at over 500 different sites in the p53 cDNA scored all four RER+ cell lines as containing only transcriptionally active p53. These data thus do not support the polyclonal mutation hypothesis and instead suggest that mismatch repair deficiency provides a p53-independent pathway for development of colorectal cancers.

Colorectal Neoplasms↗
PubMed1996

Identification of new members of the Gas2 and Ras families in the 22q12 chromosome region.

Monitoring of loss of heterozygosity in human tumors has suggested that the 22q12 region may contain another tumor suppressor gene(s) in addition to the NF2 gene. The genomic sequencing of a 40-kb region bounded by the EWS and BAM22 genes and containing a CpG-rich region has identified two new genes in the q12 region of chromosome 22. One of them, GAR22, is closely related to mouse Gas2, a gene isolated as being negatively regulated by serum and growth factors and exhibiting a high expression in growth arrested mouse fibroblasts. The other, RRP22, belongs to the Ras superfamily, in which it defines a new subgroup. Its expression appears to be strictly limited to the central nervous system. Growth-arrest-specific and Ras-related genes are likely candidates to be involved in tumorigenic processes. Although no mutation was observed in a small set of meningiomas and schwannomas, alteration of these new genes should now be searched in other tumors with frequent allelic losses on chromosome 22 not associated with NF2 mutation.

Amino Acid Sequence↗
PubMed1996

17 beta-Estradiol prevents dysfunction of canine coronary endothelium and myocardium and reperfusion arrhythmias after brief ischemia/reperfusion.

BACKGROUND: Brief myocardial ischemia is associated with myocardial and coronary endothelial dysfunction caused by oxygen free radicals released during reperfusion. Estrogen, known to have antioxidant activity, may prevent these complications. METHODS AND RESULTS: We assessed the effect of 2 weeks of treatment with 17 beta-estradiol (E, 100 micrograms.kg-1.d-1, n = 12) or placebo (P, n = 15) on myocardial and coronary endothelial function during the first 2 hours of reperfusion in dogs subjected to 15 minutes of ischemia induced by occlusion of the left anterior descending coronary artery (LAD). Our results show that the incidence of ventricular arrhythmias significantly decreased in E (3 of 12) compared with P (11 of 15). Systolic shortening, significantly depressed in P during early reperfusion, was maintained at preischemic levels in E. During reperfusion, the increase in LAD flow to acetylcholine, attenuated in P (60 +/- 6%), was preserved in E endothelium. (151 +/- 28%) and was associated with increased serum nitrite/nitrate concentration. n-Pentane in exhaled gas in vivo, an index of lipid peroxidation, increased significantly during early reperfusion in P (from 9.1 +/- 1.9 to 41.6 +/- 13.0 ppb, P < .05) but not in E (23.0 +/- 6.9 ppb). In vitro, arterial segments from E generated significantly less superoxide anion after hypoxia/reoxygenation than those from P. Ischemic/reperfused LAD segments from E also revealed a better preservation of endothelium-dependent relaxation in vitro (maximum relaxation, 42 +/- 4% versus 24 +/- 4% in P; P < .05). CONCLUSIONS: Estrogen protects against endothelial and myocardial dysfunction resulting from brief ischemia/reperfusion. This protection may relate to an antioxidant effect of estrogen.

Acetylcholine↗
PubMed1996

Phosphatidylinositol 3-kinase signals activate a selective subset of Rac/Rho-dependent effector pathways.

BACKGROUND: Phosphatidylinositol 3'-hydroxyl kinase (PI 3-kinase) is activated by many growth factor receptors and is thought to exert its cellular functions through the elevation of phosphatidylinositol (3,4,5)-triphosphate levels in the cell. PI 3-kinase is required for growth-factor induced changes of the actin cytoskeleton which are mediated by the GTPases Rac and Rho. Recently, a role for Rac and Rho in regulating gene transcription has become evident. RESULTS: Here, we show that membrane targeting of the p110 catalytic subunit, but not the p85 regulatory subunit, of PI 3-kinase generates a constitutively active enzyme that allows us to assess the relative contribution of PI 3-kinase activation to a particular cellular response. Expression of this active PI 3-kinase induced actin reorganization in the form of Rac-mediated lamellipodia and focal complexes, and Rho-mediated stress fibres and focal adhesions. However, expression of active PI 3-kinase did not induce the Ras/Rac/Rho signalling pathways that regulate gene transcription controlled by the c-fos promoter, the c-fos serum response element or the transcription factors Elk-1 and AP-1. CONCLUSIONS: Our results demonstrate that PI 3-kinase induces a selective subset of cellular responses, but is not sufficient to stimulate the full repertoire of Rac- or Rho-mediated responses.

3T3 Cells↗
PubMed1996

The Drosophila p70s6k homolog exhibits conserved regulatory elements and rapamycin sensitivity.

The protein p70s6k/p85s6k lies on a mitogen-stimulated signaling pathway and plays a key role in G1 progression of the cell cycle. Activation of this enzyme is mediated by a complex set of phosphorylation events, which has largely contributed to the difficulty in identifying the upstream kinases that mediate p70s6k activation. Genetics has proved a powerful complementary approach for such problems, providing an alternative means to identify components of signaling cascades and their functional end targets. As a first step toward implementing such an approach, we have cloned cDNAs encoding the Drosophila melanogaster p70s6k homolog (Dp70s6k). Dp70s6k is encoded by a single gene, which generates three mRNA transcripts and exhibits an overall identity of 78% in the catalytic domain with its mammalian counterpart. Importantly, this high identity extends beyond the catalytic domain to the N terminus, linker region, and the autoinhibitory domain. Furthermore, all the critical phosphorylation sites required for mammalian p70s6k activation are conserved within these same domains of Dp70s6k. Chief amongst these conserved sites are those associated with the selective rapamycin-induced p70s6k dephosphorylation and inactivation. Consistent with this observation, analysis of total S6 kinase activity in fractionated Drosophila Schneider line 2 cell extracts reveals two peaks of activity, only one of which is rapamycin sensitive. By employing a monospecific polyclonal antibody generated against Dp70s6k, we show that the cloned DP70s6k cDNA has identity with only the rapamycin sensitive peak, suggesting that this biological system would be useful in determining not only the mechanism of p70s6k activation, but also in elucidating the mechanism by which rapamycin acts to inhibit cell growth.

Amino Acid Sequence↗
PubMed1996

An EWS/ERG fusion with a truncated N-terminal domain of EWS in a Ewing's tumor.

As a result of chromosome translocations, the EWS gene is fused to a variety of transcription factors in human solid tumors. Up to now, gene fusions of EWS with 6 different partners have been described. In all fusions presently reported the entire N-terminal domain of EWS (NTD-EWS) composed of 265 amino acids encoded by the first 7 exons of EWS was always included in the chimeric proteins, suggesting that the integrity of this domain was mandatory for the oncogenic property of the fusion proteins. We report the molecular characterization of a Ewing tumor demonstrating a reciprocal t(21;22)(q22;q12) translocation. No EWS/ERG fusion transcript could be detected with previously reported RT-PCR primers. However, Southern-blot experiments demonstrated that the EWS gene was disrupted within a 2-kb PstI genomic fragment including exon 7. PCR amplification and sequence of the translocation junction fragments indicated that the breakpoint was localized within exon 7 of EWS. The resulting fusion gene encoded a chimeric protein in which a truncated NTD-EWS was linked, in frame, to the ETS DNA-binding domain of ERG. This observation indicates that, to avoid false negative results, RT-PCR-based diagnosis of tumors with EWS fusion transcripts should now include the search for such rare variants. It also suggests that the amino-terminal portion of the NTD-EWS, but not its carboxy terminal part, might be fundamental for the oncogenicity of the chimeric proteins.

Adolescent↗
PubMed1996

ARF and PITP restore GTP gamma S-stimulated protein secretion from cytosol-depleted HL60 cells by promoting PIP2 synthesis.

BACKGROUND: In many cell types, including neutrophils and HL60 cells, there is an absolute requirement for a GTP-dependent step to elicit Ca(2+)-regulated secretion. Neutrophils and HL60 cells secrete lysosomal enzymes from azurophilic granules; this secretion is inhibited by 1% ethanol, indicating that phosphatidate (PA) produced by phospholipase D (PLD) activity may be involved. PLD can use primary alcohols in preference to water during the hydrolytic step, generating the corresponding phosphatidylalcohol instead of PA, its normal product. As ARF (ADP-ribosylation factor) proteins regulate PLD activity and are implicated in constitutive vesicular traffic, we have investigated whether ARF is also required for GTP-dependent secretion in HL60 cells. RESULTS: We have used a cell-permeabilization protocol that allows HL60 cells to become refractory to stimulation with GTP gamma S plus 10 microM Ca2+ with regard to secretion and PLD activity. Permeabilization with streptolysin O for 10 minutes permitted the loss of freely diffusable cytosolic proteins, including ARF proteins. Fractions derived from brain cytosol, enriched in ARF proteins, restored secretory function and PLD activity. The major contaminating protein present in these ARF-enriched fractions was identified as phosphatidylinositol transfer protein (PITP). Unexpectedly, PITP was also found to restore GTP gamma S-dependent secretion. Restoration of secretory function was characterized using recombinant proteins, rARF1 and rPITP alpha and rPITP beta. The rARF1 protein restored both secretory function and PLD activity, whereas PITP only restored secretory function. However, both ARF and PITP were capable of stimulating phosphatidylinositol bis phosphate (PIP2) synthesis. CONCLUSIONS: ARF and PITP restore secretory function in cytosol-depleted cells when stimulated with GTP gamma S plus Ca2+. We have previously shown that PITP participates in the synthesis of PIP2. In comparison, ARF1 activates PLD, producing PA, which is a known activator of phosphatidylinositol-4-phosphate 5 kinase, the enzyme responsible for PIP2 synthesis. We propose that ARF and PITP both restore exocytosis by a common mechanism-promoting PIP2 synthesis.

ADP-Ribosylation Factor 1↗
PubMed1996

4E-BP1 phosphorylation is mediated by the FRAP-p70s6k pathway and is independent of mitogen-activated protein kinase.

It has previously been argued that the repressor of protein synthesis initiation factor 4E, 4E-BP1, is a direct in vivo target of p42mapk. However, the immunosuppressant rapamycin blocks serum-induced 4E-BP1 phosphorylation and, in parallel, p70s6k activation, with no apparent effect on p42mapk activation. Consistent with this finding, the kinetics of serum-induced 4E-BP1 phosphorylation closely follow those of p70s6k activation rather than those of p42mapk. More striking, insulin, which does not induce p42mapk activation in human 293 cells or Swiss mouse 3T3 cells, induces 4E-BP1 phosphorylation and p70s6k activation in both cell types. Anisomycin, which, like insulin, does not activate p42mapk, promotes a small parallel increase in 4E-BP1 phosphorylation and p70s6k activation. The insulin effect on 4E-BP1 phosphorylation and p70s6k activation in both cell types is blocked by SQ20006, wortmannin, and rapamycin. These three inhibitors have no effect on p42mapk activation induced by phorbol 12-tetradecanoate 13-acetate, though wortmannin partially suppresses both the p70s6k response and the 4E-BP1 response. Finally, in porcine aortic endothelial cells stably transfected with either the wild-type platelet-derived growth factor receptor or a mutant receptor bearing the double point mutation 740F/751F, p42mapk activation in response to platelet-derived growth factor is unimpaired, but increased 4E-BP1 phosphorylation is ablated, as previously reported for p70s6k. The data presented here demonstrate that 4E-BP1 phosphorylation is mediated by the FRAP-p70s6k pathway and is independent of mitogen-activated protein kinase.

3T3 Cells↗
PubMed1996

Simultaneous purification of influenza haemagglutinin and neuraminidase proteins by immunochromatography.

A new and rapid method for co-purification of haemagglutinin (HA) and neuraminidase (NA) proteins from influenza A/H3N2 viruses is described. Surface glycoproteins were first solubilized using a non-ionic detergent under high ionic strength conditions, then they were separated by chromatography on sepharose previously bound to monoclonal antibodies (MAbs) directed either against HA (IaH-chromatography) or against NA (IaN-chromatography). Depending on the protein specificity of the MAb immobilized on the column, HA or NA was bound to sepharose and the counterpart protein was free in the flow-through volume. IaH-chromatography and IaN-chromatography proved equally efficient in term of recoveries (> 75%) and purity (> or = 99%) of both HA and NA but differences appeared when considering functional and antigenic properties of pure proteins. Those properties were highly retained in IaH- and IaN-derived HA as well as in IaH-derived NA while IaN-NA was partially degraded. IaH-chromatography allowed the co-purification of HA and NA proteins in heterologous antigen-antibody system with a 50% rate of cross reactivity. IaH-HA and IaH-NA may be suitable for immunity studies, standardization of influenza vaccine and for diagnostic purposes.

Animals↗
PubMed1996

Clinical relevance of loss heterozygosity of the short arm of chromosome 1 in neuroblastoma: a single-institution study.

Neuroblastoma is characterized by a wide variability of its clinical course, and considerable effort has been made to identify factors determining outcome in this disease. In a series of 82 patients from a single institution, we have investigated the prognostic impact of multiple clinical, biological and genetic parameters. Univariate testing showed that advanced stage of disease, abdominal localization of the primary tumor, elevated urinary dopamine levels, N-myc amplification (NMA) and loss of heterozygosity of chromosome lp (LOH lp) were related to a poor outcome. Most of these parameters were strong indicators of treatment failure in children younger than 12 months of age but none of them, apart from stage, had a significant prognostic impact in patients older than 12 months at diagnosis. Interestingly, the shorter survival time associated with the presence of lp deletions or NMA appears to be more strongly linked to a poorer outcome after relapse or progression than to a shorter progression-free interval. Although different types of LOH lp have been described in neuroblastoma and may be associated with different biological features, as suggested by a different pattern of catecholamine secretion, tumors with LOH lp present an aggressive clinical behavior, regardless of the type of LOH lp. In this study, LOH lp is an indicator of poor prognosis and identifies a larger population at risk than NMA alone.

Chromosomes, Human, Pair 1↗
PubMed1996

beta-Amyloid-mediated vasoactivity and vascular endothelial damage.

Deposits of beta-amyloid are apparent in ageing and Alzheimer's disease, but the role of this peptide in neurodegeneration is unclear. The free-radical theory of ageing may also account for Alzheimer-type degeneration and consequently links between free-radical generation and beta-amyloid have been sought. We demonstrate here that beta-amyloid interacts with endothelial cells on blood vessels to produce and excess of superoxide radicals, with attendant alterations in endothelial structure and function. The superoxide radical can scavenge endothelium-derived relaxing factor and produce potent oxidizing agents, which can cause lipid peroxidation and other degenerative changes. The alterations in vascular tone and endothelial damage are prevented by the oxygen-radical-scavenging enzyme superoxide dismutase. These observations suggest a normal vasoactive role for beta-amyloid as well as a mechanism by which beta-amyloid may play a role in vascular abnormalities and neurodegeneration mediated by free radicals.

Acetylcholine↗