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Biomedical subjects

G Thomas

Publications and source records attributed to G Thomas.

At least 325 records · Page 18Linked to original sources
PubMed1996

Comparative cellular processing of the human immunodeficiency virus (HIV-1) envelope glycoprotein gp160 by the mammalian subtilisin/kexin-like convertases.

We present here the pulse and pulse-chase analysis of the biosynthesis of the envelope glycoprotein gp160 and its intracellular processing by the subtilisin/kexin-like convertases furin, PACE4, PC1, PC5 and its isoform PC5/6-B. We demonstrate that furin and to a much lesser extent PACE4, PC5/6-B and PC1 are candidate enzymes capable of processing gp160 intracellularly. Furthermore we show that furin can also process gp160/gp120 into gp77/gp53 products by cleavage at the sequence RIQR/GPGR just preceding the conserved GPGR structure found at the tip of the hypervariable V3 loop. The results show that processing into gp120 could occur at or before the trans-Golgi network (TGN) where sulphation of the oligosaccharide moieties of gp160 was detected. In contrast, the formation of gp77/gp53 by furin is a late event occurring after exit from the TGN. Our data also revealed that the alpha glucosidase I inhibitor N-butyldeoxynojirimycin, although affecting the oligosaccharide composition of gp160, does not impair the processing of either gp160 or gp120 by either furin or PACE4. Finally, the co-expression of the [Arg355, Arg358]-alpha-1-antitrypsin Portland variant was shown to potently inhibit the processing of both gp160 and gp120 by these convertases.

Animals↗
PubMed1996

Mapping of a susceptibility locus for Crohn's disease on chromosome 16.

Crohn's disease (CD) and ulcerative colitis are the major forms of chronic inflammatory bowel diseases in the western world, and occur in young adults with an estimated prevalence of more than one per thousand inhabitants. The causes of inflammatory bowel diseases remain unknown, but genetic epidemiology studies suggest that inherited factors may contribute in part to variation in individual susceptibility to Crohn's disease. A genome-wide search performed on two consecutive and independent panels of families with multiple affected members, using a non-parametric two-point sibling-pair linkage method, identified a putative CD-susceptibility locus on chromosome 16 (P less than 0.01 for each panel). The localization was centered around loci D16S409 and D16S419 by using multipoint sibpair analysis (P less than 1.5x10(-5)). This region of the genome contains candidate genes which may be relevant to the pathogenic mechanism of inflammatory bowel diseases.

Alleles↗
PubMed1996

Synergistic effect of interleukin-1 beta and tumor necrosis factor alpha on PGE2 production by articular chondrocytes does not involve PLA2 stimulation.

This study investigates the ways in which two proinflammatory cytokines, tumor necrosis factor alpha (TNF) and interleukin-1 beta (IL1), cause increased production of prostaglandin E2 (PGE2) in rabbit articular chondrocytes (RAC). Rabbit articular chondrocytes in primary culture were incubated with IL1, TNF, or both. Arachidonic acid (AA) release, PGE2 production, and the activities of cytosolic phospholipase A2 (cPLA2), secreted phospholipase A2 (sPLA2), and cyclooxygenase (COX) were measured. The mRNA levels of cPLA2, sPLA2, and COX-2 were also measured by Northern blotting, using specific complementary DNA probes. Incubation of IL1-stimulated RAC with TNF further increased PGE2 production. This synergy did not involve PLA2 stimulation, as there were no increases in AA release, cPLA2 and sPLA2 activities, or mRNA. In contrast, TNF increased the effect of IL1 on COX-2 activity and mRNA level. These results show that TNF and IL1 act in synergy in PGE2 production in articular chondrocytes. As sPLA2 and cPLA2 do not seem to be involved, COX-2 appears to be the best target for a specific anti-inflammatory strategy against cartilage degradation.

Animals↗
PubMed1996

Lysis of intravascular thrombus prior to coronary stenting using the dispatch infusion catheter.

The presence of angiographic evidence of thrombus is generally thought to be a contraindication to coronary stent placement. This report describes four patients in whom angiographic thrombus was lysed using the Dispatch infusion catheter prior to coronary stenting. Urokinase was infused via the Dispatch catheter with resolution of angiographic evidence of thrombus in all cases. No complications were encountered using this technique, and all patients had excellent angiographic results after stenting. We conclude that lysis of intracoronary thrombus using the Dispatch infusion catheter is feasible and appears safe in this small study. Further trials are needed to determine if this technique reduces the acute stent thrombosis rate compared to other techniques for stent deployment in the presence of angiographic evidence of thrombus.

Angioplasty, Balloon, Coronary↗
PubMed1996

Endometrial carcinoma--relative effectiveness of adjuvant irradiation vs therapy reserved for relapse.

Fifty-four patients with recurrent endometrial carcinoma were identified from a retrospective review of charts of 304 endometrial cancer patients seen between 1983 and 1989 at our center. A review was undertaken to identify the patterns of relapse, to determine the outcome of salvage treatment, to examine the factors predictive of effective salvage, and, if salvage is effective, to assess an alternative strategy to routine adjuvant postoperative pelvic radiotherapy. Forty percent of the entire recurrent population are long-term survivors. Of the 54 relapsing patients, primary therapy had been surgery alone in 32 and surgery and adjuvant radiotherapy (rt) in 22. Isolated pelvic recurrence was the predominate relapse site in those who had not received adjuvant pelvic RT as primary therapy (23 of 32 or 72%). Distant relapse predominated in those who received adjuvant RT (17 or 22 or 77%). Twenty-eight (54%) failed in the pelvis alone, and 26 (46%) had a component of distant failure. Of the 28 with isolated pelvic relapse, 16 had vaginal mucosal disease involvement only and 12 had disease in the parametrium and/or the pelvic sidewall. With a minimum follow-up for the survivors of 5 years, 21 of the 28 with isolated pelvic relapse received radical radiotherapy and 14 or 67% had maintained pelvic control until death or last follow-up. Eleven of 14 (79%) with disease confined to the mucosa had pelvic control, whereas only 3 of 7 (43%) with extramucosal disease were controlled. No patient experienced major treatment-related toxicity. Tumor size, anatomic extent of pelvic recurrence, RT dose, and disease-free interval were examined for prognostic significance for pelvic control and survival by univariate analysis. Only anatomic extent of pelvic recurrence showed a nonstatistically significant trend as a predictor for control with P = 0.08. In conclusion, a significant proportion of patients with disease recurrence confined to the pelvis can be rendered disease-free long-term with maintained pelvic control. A reexamination of the role of routine adjuvant pelvic RT is therefore undertaken in light of these data.

Aged↗
PubMed1996

Investigation of different ontogenetic stages of Raillietiella sp. (Pentastomida: Cephalobaenida). Structure of the foregut and considerations about the feeding process.

The foregut of Raillietiella sp. was investigated ultrastructurally in different ontogenetic stages: the embryo prior to hatching, the first-stage larva, the infective fourth-stage larva from the intermediate host, and juveniles and adults from the definitive host. As early as at the embryo stage the chitinous mouth armature is highly specialized. During postembryogenesis this structure is modified until it reaches its final shape in the juvenile. The most important changes occur during the period of development from the infective larva to the juvenile, which is related to the change from the intermediate to the definitive host; only stages inhabiting the definitive host can use their mouth as a suction pump. Therefore, only juveniles and adults are capable of sucking blood, whereas larvae are dependent on accessible liquid food. The remaining foregut represents a conveyor tube, growing in width toward the midgut. From the juvenile stage onward the transition to the midgut is formed as a cardiac valve.

Animals↗
PubMed1996

N-MYC amplification, loss of heterozygosity on the short arm of chromosome 1 and DNA ploidy in retinoblastoma.

Recurrent genetic alterations different from the alteration of the RB1 gene on chromosome 13q14 have been described in retinoblastoma, including structural alterations on the short arm of chromosome 1 and amplification of the N-MYC oncogene. These two genetic alterations are major prognostic factors in neuroblastoma, another embryonic neuro-ectodermal tumour. In order to assess the frequency of these alterations and their possible association with clinical parameters in retinoblastoma, we studied a series of 46 retinoblastoma tumour samples. Ploidy was assessed by flow cytometry, N-MYC copy number was evaluated by a spot-blot procedure using the pNb-1 probe and loss of heterozygosity was investigated by PCR analysis at mini- and microsatellites located on the short arm of chromosome 1. Most tumours were in the diploid or near diploid range; only one case exhibited tetraploidy. N-MYC amplification was observed in only one of the 45 tumours. Loss of heterozygosity on the short arm of chromosome 1 was observed in 9/43 tumours (21%); in particular, its incidence was higher in metastatic than in localised disease (P < 0.05). We suggest that alterations of one or several genes on chromosome 1p might play a role in the oncogenesis or progression of retinoblastoma. Analysis of the long term follow-up of these and additional patients should determine the prognostic value of this parameter.

Child, Preschool↗
PubMed1996

A hidden Markov model approach to neuron firing patterns.

Analysis and characterization of neuronal discharge patterns are of interest to neurophysiologists and neuropharmacologists. In this paper we present a hidden Markov model approach to modeling single neuron electrical activity. Basically the model assumes that each interspike interval corresponds to one of several possible states of the neuron. Fitting the model to experimental series of interspike intervals by maximum likelihood allows estimation of the number of possible underlying neuron states, the probability density functions of interspike intervals corresponding to each state, and the transition probabilities between states. We present an application to the analysis of recordings of a locus coeruleus neuron under three pharmacological conditions. The model distinguishes two states during halothane anesthesia and during recovery from halothane anesthesia, and four states after administration of clonidine. The transition probabilities yield additional insights into the mechanisms of neuron firing.

Action Potentials↗
PubMed1996

Escherichia coli K-12 genes essential for the synthesis of c-type cytochromes and a third nitrate reductase located in the periplasm.

The 'aeg46.5' operon was originally detected as an 'anaerobically expressed gene' located at minute 46.5 on the Escherichia coli linkage map. Subsequent results from the E. coli Genome Sequencing Project revealed that the 'aeg46.5' promoter was located in the centisome 49 (minute 47) region. Downstream from this promoter are 15 genes, seven of which are predicted to encode a periplasmic nitrate reductase and eight encode proteins homologous to proteins essential for cytochrome c assembly in other bacteria. All of these genes, together with the 'aeg46.5' promoter, have been subcloned on a 20kb EcoRI fragment from Kohara phage 19D1. Evidence is presented that, as predicted, the region includes structural genes for two c-type cytochromes of mass 16kDa and 24 kDa, which are transcribed from the previously described 'aeg46.5' promoter, and that the first seven genes encode a functional nitrate reductase. We, therefore, propose that they should be designated nap (nitrate reductase in the periplasm) genes. Plasmids encoding the entire 20kb region, or only the downstream eight genes, complemented five mutations resulting in total absence of all five known c-type cytochromes in E coli, providing biochemical evidence that these are ccm (for cytochrome c maturation) genes. The ccm region was transcribed both from the FNR-dependent, NarL- and NarP-regulated nap promoter (formerly the 'aeg46.5' promoter) and from constitutive or weakly regulated promoters apparently located within the downstream nap and ccm genes.

Amino Acid Sequence↗
PubMed1996

Isolation of a novel gene from the DiGeorge syndrome critical region with homology to Drosophila gdl and to human LAMC1 genes.

DiGeorge syndrome, and more widely the CATCH 22 syndrome, are associated with microdeletions in chromosomal region 22q11.2. A critical region of 500 kb has been delimited within which maps the breakpoint of a balanced translocation associated with mild CATCH 22 phenotypes. We report the isolation from this critical region of a novel gene, DGCR6, which maps 115 kb centromeric to the balanced translocation breakpoint. The DGCR6 gene product shares homology with the Drosophila melanogaster gonadal protein, which participates in gonadal and germ-line cells development, and with the human laminin. gamma-1 chain, which upon polymerization with alpha- and beta- chains forms the laminin molecule. Laminin binds to cells through interaction with a receptor and has functions in cell attachment, migration and tissue organization during development. DGCR6 could be a candidate for involvement in the DiGeorge syndrome pathology by playing a role in neural crest cell migration into the third and fourth pharyngeal pouches, the structures from which derive the organs affected in DiGeorge syndrome.

Amino Acid Sequence↗
PubMed1996

In vivo rearing and development of Wohlfahrtia magnifica (Diptera: Sarcophagidae).

Wohlfahrtia magnifica (Schiner, 1862) has a seasonal cycle from May to September. The main objective of the current study is the rearing and development in the laboratory, outside its natural life cycle. The free and obligate parasite phases were reared in the laboratory during 7 mo, from 16 September to 26 March. Between 97.49 and 98.27% of the third instars reached the pupal stage (at 24 degrees C and under natural light cycle). Between 73.98 and 92.24% of the pupae developed into adults (at 70% RH and 22 degrees C). In the induced cycle the ratio of females to males was between 1.87:1.00 and 1.40:1.00, at 70% RH and 24 degrees C. In the trials involving the diapause pupae, 35.29% emerged as adults during a period of 53 d (from 23 January to 20 March), when held at an average storage temperature of 18 degrees C. Eighty-five percent emerged during 2 d (23 and 24 February) when the storage temperature was 4 degrees C.

Animals↗
PubMed1996

Solution structure of the phosphorylated sites of ribosomal protein S6 by 1H NMR spectroscopy.

An increase in the rate of protein synthesis is found to be accompanied by phosphorylation of the 40S ribosomal protein S6. Treatment of S6 by cyanogen bromide produced three fragments, and one of the fragments of S6, which is a C-terminal portion of S6 (M(r) approximately 4,000), contains all phosphorylation sites of S6. The C-terminal fragment of S6 contains seven serines. S6 kinase phosphorylates S6 specifically, i.e. five serines in the C-terminal of S6 are phosphorylated. The three-dimensional structure of S6 peptide was studied in 50% trifluoroethanol/50% H2O solution by 1H NMR with combined use of distance geometry and restrained molecular dynamics calculations. NMR results indicated that it takes an alpha-helix between Glu5 and Arg21 and a distorted helical structure for the following three residues, but no rigid structure was present from Ser25 through the C-terminus and for the N-terminal region (Lys1-Lys4). The specificity of the phosphorylation of the peptide is discussed from a structural aspect.

Amino Acid Sequence↗
PubMed1996

Testing candidate loci on chromosomes 1 and 6 for genetic linkage to Peutz-Jeghers' disease.

Peutz-Jeghers' syndrome (PJS) is a disease with autosomal dominant inheritance, which is characterised by gastrointestinal hamartomata and characteristic melanin pigmentation. Three candidate sites for a PJS locus have recently been proposed, chromosomes 1p31-p32, 6q25 and 6p11-cen. At the first of these sites, a multipoint LOD score of 4.00 had been found, strongly suggesting genetic linkage to PJS. The last two candidate sites were suggested by the chromosomal breakpoints of a patient with an inv(6) and PJS. We have analysed up to 34 families in order to test each of the three candidate sites for linkage to PJS. No evidence was found in support of a Peutz-Jeghers' syndrome locus on chromosome 1p31-p32. The candidate region on 6q25 was also excluded. The region close to the centromere of chromosome 6 has not been excluded and there is some evidence of linkage to a marker near 6cen, although genetic heterogeneity in PJS must be proposed to account for a gene at this site.

Chromosomes, Human, Pair 1↗
PubMed1996

Modification of Ca2+ metabolism in the rabbit aorta as a mechanism of spasmolytic action of warifteine, a bisbenzylisoquinoline alkaloid isolated from the leaves of Cissampelos sympodialis Eichl. (Menispermaceae).

The regulation of intracellular Ca2+ as a mechanism of spasmolytic activity of a bisbenzylisoquinoline alkaloid, warifteine, isolated from the leaves of Cissampelos sympodialis, Eichl (Menispermaceae) was studied in the rabbit aorta. Warifteine (pD2' 4.12 +/- 0.09) similar to verapamil (pD2' 6.89 +/- 0.05) antagonized, in a noncompetitive and reversible manner, KCl-induced contractions, mediated by Ca2+ entry through voltage-operated channels. Noradrenaline-induced sustained contractions mediated by Ca2+ entry through receptor-operated channels were also inhibited by warifteine (IC50 6.03 x 10(-5) M) and the standard agent sodium nitroprusside (IC50 1.9 x 10(-8) M). In Ca(2+)-free medium, the alkaloid reduced the intracellular Ca(2+)-dependent transient contraction to noradrenaline by inhibiting the release of Ca2+ (IC50 2.6 x 10(-5) M) from the stores and the refilling (IC50 1.9 x 10(-5) M) of the intracellular stores. The standard agent, procaine, also inhibited the release of Ca2+ (IC50 3.2 x 10(-5) M) but had no significant effect on Ca2+ uptake into the stores. Warifteine failed to affect intracellular Ca2+ stores sensitive to caffeine, while procaine inhibited (IC50 7.9 x 10(-4) M) the release of Ca2+ from these stores. The results indicate that warifteine may cause muscle relaxation by inhibiting Ca2+ channels and by modifying the intracellular Ca2+ stores sensitive to noradrenaline.

Alkaloids↗
PubMed1996

The principal rapamycin-sensitive p70(s6k) phosphorylation sites, T-229 and T-389, are differentially regulated by rapamycin-insensitive kinase kinases.

Mitogen-induced activation of p70(s6k) is associated with the phosphorylation of specific sites which are negatively affected by the immunosuppressant rapamycin, the fungal metabolite wortmannin, and the methylxanthine SQ20006. Recent reports have focused on the role of the amino terminus of the p85(s6k) isoform in mediating kinase activity, with the observation that amino-terminal truncation mutants are activated in the presence of rapamycin while retaining their sensitivity to wortmannin. Here we show that the effects of previously described amino- and carboxy-terminal truncations on kinase activity are ultimately reflected in the phosphorylation state of the enzyme. Mutation of the principal rapamycin-targeted phosphorylation site, T-389, to an acidic residue generates a form of the kinase which is as resistant to wortmannin or SQ20006 as it is to rapamycin, consistent with the previous observation that T-389 was a common target of all three inhibitors. Truncation of the first 54 residues of the amino terminus blocks the serum-induced phosphorylation of three rapamycin-sensitive sites, T-229 in the activation loop and T-389 and S-404 in the linker region. This correlates with a severe reduction in the ability of the kinase to be activated by serum. However, loss of mitogen activation conferred by the removal of the amino terminus is reversed by additional truncation of the carboxy-terminal domain, with the resulting mutant demonstrating phosphorylation of the remaining two rapamycin-sensitive sites, T-229 and T-389. In this double-truncation mutant, phosphorylation of T-229 occurs in the basal state, whereas mitogen stimulation is required to induce acute upregulation of T-389 phosphorylation. The phosphorylation of both sites proceeds unimpaired in the presence of rapamycin, indicating that the kinases responsible for the phosphorylation of these sites are not inhibited by the macrolide. In contrast, activation of the double-truncation mutant is blocked in the presence of wortmannin or SQ20006, and these agents completely block the phosphorylation of T-389 while having only a marginal effect on T-229 phosphorylation. When the T-389 site is mutated to an acidic residue in the double-truncation background, the activation of the resulting mutant is insensitive to the wortmannin and SQ20006 block, but interestingly, the mutant is activated to a significantly greater level than a control in the presence of rapamycin. These data are consistent with the hypothesis that T-389 is the principal regulatory phosphorylation site, which, in combination with hyperphosphorylation of the autoinhibitory domain S/TP sites, is acutely regulated by external effectors, whereas T-229 phosphorylation is regulated primarily by internal mechanisms.

Amino Acid Sequence↗
PubMed1996

Quantitative risk assessment and the limitations of the linearized multistage model.

1. Quantifying carcinogenic risk is an important objective for assisting in the assessment and management of risks from chemical exposure. The most widely used of the many mathematical models proposed for extrapolation of carcinogenicity data from animal studies to low dose human exposures is the linearized multistage (LMS) model. This has, in effect, become the default approach for much of Quantitative Risk Assessment (QRA). The practical properties of this model have been investigated. 2. Analysis of stimulated data using the LMS model showed (i) that the Maximum Likelihood Estimate (MLE) of the low dose slope, q1, was unstable and extremely sensitive to small changes in the data; (ii) the 95% Upper Confidence Limit (UCL) estimate, q1*, preferred by the US Environmental Protection Agency (EPA) was insensitive with only small changes in values being obtained for large changes in the data; (iii) data sets where there was no statistical significance could give risk estimates similar to those obtained from data sets with clear dose-related effects; (iv) the size of the values of the Virtually Safe Dose (VSD) obtained did not necessarily relate to the biological interpretation of the data sets; (v) the value of q1* obtained was closely related to the top dose used in the study. 3. Limitations of the LMS model were illustrated by examples of its use in assessing the carcinogenicity of 2, 3, 7, 8-TCDD leading to the conclusion that the existing models are not suitable for routine use in the estimation of the risk from chemical carcinogens. The use of the LMS model has been justified in part by its original derivation from a mathematical model based upon a multistage model of carcinogenesis. However, estimates of the parameters of the model used to provide estimates of low dose risk to humans have no direct relationship to specific biological event in carcinogenesis. Further developments in mathematical models and increased understanding of the biological events underlying the carcinogenesis will lead to more biologically plausible QRA methods which would then justify serious consideration of QRA by regulatory authorities throughout the world.

Animals↗