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Biomedical subjects

A Thomas

Publications and source records attributed to A Thomas.

At least 199 records · Page 11Linked to original sources
PubMed1999

The structural and functional organization of H-NS-like proteins is evolutionarily conserved in gram-negative bacteria.

The structural gene of the H-NS protein, a global regulator of bacterial metabolism, has been identified in the group of enterobacteria as well as in closely related bacteria, such as Erwinia chrysanthemi and Haemophilus influenzae. Isolated outside these groups, the BpH3 protein of Bordetella pertussis exhibits a low amino acid conservation with H-NS, particularly in the N-terminal domain. To obtain information on the structure, function and/or evolution of H-NS, we searched for other H-NS-related proteins in the latest databases. We found that HvrA, a trans-activator protein in Rhodobacter capsulatus, has a low but significant similarity with H-NS and H-NS-like proteins. This Gram-negative bacterium is phylogenetically distant from Escherichia coli. Using theoretical analysis (e.g. secondary structure prediction and DNA binding domain modelling) of the amino acid sequence of H-NS, StpA (an H-NS-like protein in E. coli), BpH3 and HvrA and by in vivo and in vitro experiments (e.g. complementation of various H-NS-related phenotypes and competitive gel shift assay), we present evidence that these proteins belong to the same class of DNA binding proteins. In silico analysis suggests that this family also includes SPB in R. sphaeroides, XrvA in Xanthomonas oryzae and VicH in Vibrio cholerae. These results demonstrate that proteins structurally and functionally related to H-NS are widespread in Gram-negative bacteria.

Amino Acid Sequence↗
PubMed1999

Embryo transfer: ultrasound-guided versus clinical touch.

In this prospective control study, the pregnancy and implantation rates were compared between ultrasound-guided and clinical touch uterine embryo transfers. In addition, a subset of patients was sought that would particularly benefit from embryo transfer under ultrasound guidance. A total of 187 patients (93 ultrasound and 94 clinical touch) was enrolled. Allocation was random and depended on whether their embryo transfers were done during the 1 h each day in which the ultrasound was available. Pregnancy and implantation rates of 37.8 and 20.4% respectively were achieved when ultrasound was used, compared with 28.9 and 16.2% respectively with clinical touch. This difference was not statistically significant. There was no significant difference in the pregnancy rate when the number of embryos transferred was controlled. Older women (>/=37 years old) had an apparently higher pregnancy rate (38.1 versus 20.4%; not significant) with ultrasound guidance during embryo transfer. In the subgroup where the clinician rated the transfer procedure as difficult, there appeared to be a substantial improvement in the pregnancy rate in the group that used ultrasound (54.5 versus 10.0%; not significant). Although our results were not statistically significant, we believe that ultrasound-guided embryo transfers should be used in clinically difficult embryo transfers and in older women, as it appears to improve the pregnancy rate over clinical touch transfers.

Adult↗
PubMed1999

Memory CD44(int) CD8 T cells show increased proliferative responses and IFN-gamma production following antigenic challenge in vitro.

F5 TCR transgenic mice challenged in vivo with peptide generate long-lived primed CD8 T cells that hyper-proliferate in response to peptide in vitro. These primed CD8 T cells can be subdivided into three distinct populations on the basis of CD44 cell surface expression. In this report, we show that among primed CD8 T cells, those expressing intermediate levels of CD44 appear to be true memory T cells by the measurement of a variety of characteristics. Indeed, these cells hyper-proliferate in response to peptide re-stimulation in vitro, and produce IFN-gamma with faster kinetics and at higher levels than naive populations in vitro. We also show that CD8 T cells expressing high levels of CD44 express several activation markers and cycle in vivo in the absence of antigen. However, this population is unable to respond to peptide stimulation in vitro as measured by both proliferation and IFN-gamma secretion. The origin and specificity of these cells is unknown. These results provide evidence that memory CD8 T cells are functionally different from naive CD8 T cells both in terms of proliferation and cytokine secretion. They identify the CD8/CD44(int) T cells as the population responsible for hyper-reactivity in vitro.

Animals↗
PubMed1999

Microvascular "supercharged" cervical colon: minimizing ischemia in esophageal reconstruction.

Traditional colonic reconstruction of the esophagus is performed by cervical transposition of an isolated segment of colon with the vascular supply derived from one of the mesenteric colic vessels. The transposed cervical portion of the colon is farthest from the vascular supply and is at risk of ischemic injury. Despite notable risk of ischemic complications to the colonic neoesophagus, reports advocating a "supercharged" microvascular augmentation of the vascular supply to the cervical portion of the colon remain few in number. Herein, the ischemic complications associated with traditional transposition of the colon for esophageal reconstruction are reviewed, and avoidance by microvascular "supercharging" of the cervical colon is advocated under particular circumstances. The authors present a case of colonic interposition for esophageal replacement requiring a cervical microvascular anastomosis for survival of the transferred colon.

Adult↗
PubMed1999

Timing and effectiveness of requirements for a second dose of measles vaccine.

OBJECTIVE: Previous measles elimination goals have failed in the United States despite high coverage of schoolchildren with a single dose of measles vaccine. Since 1989 advisory groups have recommended that schoolchildren receive a second dose of measles vaccine as part of a revised strategy to eliminate measles from the US. States have responded by phasing in requirements for a second dose of measles vaccine at school entry for various age groups at primary school entrance, secondary school entrance or both. The purpose of this analysis was to evaluate the effectiveness of the requirements for a second dose of measles vaccine and to determine whether a primary or secondary school entrance requirement was more effective in lowering measles incidence. METHODS: Using national surveillance data we examined the influence of state requirements for the second dose of measles vaccine on measles incidence from 1993 through 1995. RESULTS: Overall measles incidence was lower in states that had a requirement for a second dose of measles vaccine at either primary school entrance [relative risk (RR) = 0.35; 95% confidence interval, 0.25 to 0.49] or secondary school entrance (RR = 0.38; 95% confidence interval 0.29 to 0.50), compared with states without a second dose requirement. Incidence was lowest in states that required a second dose of measles vaccine at both primary and secondary school entrance (RR = 0.22; 95% confidence interval, 0.13 to 0.37). CONCLUSIONS: Our findings demonstrate that a requirement for a second dose of measles vaccine at either primary or secondary school entrance is effective in lowering measles incidence, with a greater reduction occurring in states where the second dose is required for both age groups.

Adolescent↗
PubMed1999

Possible interactions between the NS-1 protein and tumor necrosis factor alpha pathways in erythroid cell apoptosis induced by human parvovirus B19.

Human erythroid progenitor cells are the main target cells of the human parvovirus B19 (B19), and B19 infection induces a transient erythroid aplastic crisis. Several authors have reported that the nonstructural protein 1 (NS-1) encoded by this virus has a cytotoxic effect, but the underlying mechanism of NS-1-induced primary erythroid cell death is still not clear. In human erythroid progenitor cells, we investigated the molecular mechanisms leading to apoptosis after natural infection of these cells by the B19 virus. The cytotoxicity of NS-1 was concomitantly evaluated in transfected erythroid cells. B19 infection and NS-1 expression induced DNA fragmentation characteristic of apoptosis, and the commitment of erythroid cells to undergo apoptosis was combined with their accumulation in the G(2) phase of the cell cycle. Since B19- and NS-1-induced apoptosis was inhibited by caspase 3, 6, and 8 inhibitors, and substantial caspase 3, 6, and 8 activities were induced by NS-1 expression, there may have been interactions between NS-1 and the apoptotic pathways of the death receptors tumor necrosis factor receptor 1 and Fas. Our results suggest that Fas-FasL interaction was not involved in NS-1- or B19-induced apoptosis in erythroid cells. In contrast, these cells were sensitized to tumor necrosis factor alpha (TNF-alpha)-induced apoptosis. Moreover, the ceramide level was enhanced by B19 infection and NS-1 expression. Therefore, our results suggest that there may be a connection between the respective apoptotic pathways activated by TNF-alpha and NS-1 in human erythroid cells.

Apoptosis↗
PubMed1999

BRCA1/BRCA2 germline mutations in locally recurrent breast cancer patients after lumpectomy and radiation therapy: implications for breast-conserving management in patients with BRCA1/BRCA2 mutations.

PURPOSE: Breast cancer patients treated conservatively with lumpectomy and radiation therapy (LRT) have an estimated lifetime risk of local relapse (ipsilateral breast tumor recurrence [IBTR]) of 10% to 15%. For breast cancer patients carrying BRCA1 or BRCA2 (BRCA1/2) mutations, the outcome of treatment with LRT with respect to IBTR has not been determined. In this study, we estimate the frequency of BRCA1/2 mutations in a study of breast cancer patients with IBTR treated with LRT. PATIENTS AND METHODS: Between 1973 and 1994, there were 52 breast cancer patients treated with LRT who developed an IBTR within the prior irradiated breast and who were willing to participate in the current study. From our database, we also identified 52 control breast cancer patients treated with LRT without IBTR. The control patients were individually matched to the index cases with respect to multiple clinical and pathologic parameters. Lymphocyte DNA specimens from all 52 locally recurrent patients and 15 of the matched control patients under age 40 were used as templates for polymerase chain reaction amplification and dye-primer sequencing of exons 2 to 24 of BRCA1, exons 2 to 27 of BRCA2, and flanking intron sequences. RESULTS: After LRT, eight (15%) of 52 breast cancer patients had IBTR with deleterious BRCA1/2 mutations. By age, there were six (40%) of 15 patients with IBTR under age 40 with BRCA1/2 mutations, one (9.0%) of 11 between ages 40 and 49, and one (3.8%) of 26 older than age 49. In comparison to the six (40%) of 15 of patients under age 40 with IBTR found to have BRCA1/2 mutations, only one (6.6%) of 15 matched control patients without IBTR and had a BRCA1/2 mutation (P =.03). The median time to IBTR for patients with BRCA1/2 mutations was 7.8 years compared with 4.7 years for patients without BRCA1/2 mutations (P =.03). By clinical and histologic criteria, these relapses represented second primary tumors developing in the conservatively treated breast. All patients with BRCA1/2 mutations and IBTR underwent successful surgical salvage mastectomy at the time of IBTR and remain alive without evidence of local or systemic progression of disease. CONCLUSION: In this study, we found an elevated frequency of deleterious BRCA1/2 mutations in breast cancer patients treated with LRT who developed late IBTR. The relatively long time to IBTR, as well as the histologic and clinical criteria, suggests that these recurrent cancers actually represent new primary breast cancers. Early onset breast cancer patients experiencing IBTR have a disproportionately high frequency of deleterious BRCA1/2 mutations. This information may be helpful in guiding management in BRCA1 or BRCA2 patients considering breast-conserving therapy.

Adult↗
PubMed1999

An assessment of the value of midfinger smears in multibacillary leprosy patients.

In view of the different opinions on fingers as sites for persisting bacilli in multibacillary leprosy patients, it was decided to examine the midfingers for the presence of acid-fast bacilli (AFB) and establish its usefulness. Sixty-nine multibacillary leprosy patients, [lepromatous (LL) and borderline lepromatous (BL)] treated with multidrug therapy for fixed duration (2 years) were analysed. The bacillary load in the midfinger sites was lower when compared to that in the 'compulsory' (both earlobes) and 'optional' (four active lesions) sites. The midfinger bacterial index (BI) was higher among LL patients when compared to BL patients (p < 0.001). However, the difference in mean BI in 'optional' and 'compulsory sites' was not significant. The overall fall in BI was gradual and on expected lines for all sites, including midfingers, during treatment and follow-up period. Except in one case, at no time were the smears from midfinger sites positive when all other sites were negative, and their inclusion did not contribute to the early detection of relapse. Furthermore, the collection of blood-free smears from this site is technically difficult and often painful for the patient. The inclusion of midfinger smears in this study in patients in South India did not contribute useful information to that which is routinely available from smears of earlobes and other active sites.

Bacteriological Techniques↗
PubMed1999

Factor V Leiden, prothrombin 20210G-->A and the MTHFR C677T mutations in childhood stroke.

Ischaemic stroke is a rare occurrence in children and in a proportion of cases the aetiology remains unknown. We have investigated the role of thrombophilia in the aetiology of this condition. Of 50 cases identified at two centres, 37 were available for detailed haematological analysis. No cases were identified with deficiencies of antithrombin, protein C or protein S. One case had elevated IgG anticardiolipin antibodies at low titre. The prevalence of the prothrombin 20210 G-->A mutation, factor V Leiden (FVL) mutation and the C677T mutation in the MTHFR gene was compared in cases to that observed in random unselected cord blood controls. The odds ratio for stroke was not significantly increased in carriers of the prothrombin mutation (OR 1.2; 95% CI 0.1-10.7), FVL (OR 2.5; 95% CI 0.5-13.5), or the C677T mutation (OR 1.7; 95% CI 0.6-4.5). Our findings suggest that thrombophilia may not play a significant role in the aetiology of stroke in children, although a large prospective study is required to investigate this area further.

Age Factors↗
PubMed1999

[Obstructive malformation of the verumontanum].

The authors report the case of a 23-year-old man presenting with obstructive polypoid hyperplasia of the verumontanum, 4 cm long, inducing dysuria with residual urine, demonstrated on urethroscopy and requiring endoscopic resection. The symptoms resolved completely after treatment.

Adult↗
PubMed1998

Quantitative analysis of gene expression in organotypic slice-explant cultures by particle-mediated gene transfer.

Biolistics, also known as particle-mediated gene transfer, has been used as an effective, method to transfect primary neurons in cultured slices when all other methods have proven unsuccessful. Most of these uses have provided qualitative or semi-quantitative data based on visual assays such as immunohistochemistry. In this paper, we describe a quantitative method of biolistics to analyze gene expression in organotypic cultures of hippocampus and hypothalamus. The method involves co-transfection of the experimental promoters and standard (cytomegalovirus or Rous sarcoma virus) promoters coupled to different reporters (luciferase or beta-galactosidase), with the standard promoter-reporter construct used to 'normalize' the experimental data. Examples and validations of this technique with various cell specific promoters are given: for example, astrocyte-specific and neuron-specific (alpha-tubulin and N-type calcium channel alpha-1B gene) promoters and various tissues (Neuro 2A cells and hippocampal and hypothalamic organotypic slice-explants). An analysis of deletion constructs of the alpha 1B calcium channel subunit gene is described. This method should provide a new opportunity for the analysis of gene expression in diverse neuronal phenotypes.

Animals↗
PubMed1998

Bax cleavage is mediated by calpain during drug-induced apoptosis.

The anti-apoptotic molecule Bcl-2 is located in the mitochondrial and endoplasmic reticulum membranes as well as the nuclear envelope. Although its location has not been as rigorously defined, the pro-apoptotic molecule Bax appears to be mainly a cytosolic protein which translocates to the mitochondria upon induction of apoptosis. Here we identify a protease activity in mitochondria-enriched membrane fractions from HL-60 cells capable of cleaving Bax which is absent from the cytosolic fraction. Bax protease activity is blocked in vitro by cysteine protease inhibitors including E-64 which distinguishes it from all known caspases and granzyme B, both of which are involved in apoptosis. Protease activity is also blocked by inhibitors against the calcium-activated neutral cysteine endopeptidase calpain. Partial purification of the Bax protease activity from HL-60 cell membrane fractions by column chromatography revealed that a calpain-like activity was the protease responsible for Bax cleavage. In addition, purified calpain enzymes cleaved Bax in a calcium-dependent manner. Pretreatment of HL-60 cells with the specific calpain inhibitor calpeptin effectively blocked both drug-induced Bax cleavage and calpain activation, but not PARP cleavage or cell death. These results suggest that calpains and caspases are activated during drug-induced apoptosis and that calpains, along with caspases, may be involved in modulating cell death by acting selectively on cellular substrates.

Alanine↗
PubMed1998

Cell cycle phase-specific surface expression of nerve growth factor receptors TrkA and p75(NTR).

Expression of the nerve growth factor (NGF) receptors TrkA and p75(NTR) was found to vary at the surface of PC12 cells in a cell cycle phase-specific manner. This was evidenced by using flow cytometric and microscopic analysis of cell populations labeled with antibodies to the extracellular domains of both receptors. Differential expression of these receptors also was evidenced by biotinylation of surface proteins and Western analysis, using antibodies specific for the extracellular domains of TrkA and p75(NTR). TrkA is expressed most strongly at the cell surface in M and early G1 phases, whereas p75(NTR) is expressed mainly in late G1, S, and G2 phases. This expression reflects the molecular and cellular responses to NGF in specific phases of the cell cycle; in the G1 phase NGF elicits both the anti-mitogenic effect, i.e., inhibition of the G1 to S transition, and the differentiation response whereas a survival effect is provoked elsewhere in the cell cycle. A model is proposed relating these responses to the surface expression of the two receptors. These observations open the way for novel approaches to the investigation of the mechanism of NGF signal transduction.

Animals↗