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Biomedical subjects

T Thomas

Publications and source records attributed to T Thomas.

At least 19 recordsLinked to original sources
PubMed1997

Effects of chain length modification and bis(ethyl) substitution of spermine analogs on purine-purine-pyrimidine triplex DNA stabilization, aggregation, and conformational transitions.

The natural polyamines--putrescine, spermidine, and spermine--are known to stabilize pyrimidine-purine-pyrimidine and purine-purine-pyrimidine triplex DNA formation. We studied the ability of two tetramine and two pentamine analogs of spermine and their bis(ethyl) derivatives to stabilize triplex DNA formation between 5'-TG3TG4TG4TG3T-3' and its target duplex probe, consisting of the oligonucleotides 5'-TCGAAG3AG4AG4AG3A-3' and 5'-TCGATC3TC4TC4TC3T-3'. We used electrophoretic mobility shift assay (EMSA), melting temperature (Tm) measurements, and circular dichroism (CD) spectroscopy to evaluate the effects of these novel polyamine analogs on triplex DNA stability, dissociation constants, aggregation, and conformation. In general, pentamines were more efficacious than tetramines in stabilizing triplex DNA, although most of the polyamines with pendant free amino groups caused DNA aggregation below 50% conversion to triplex DNA. Ethyl substitution of these pendant amino groups lowered their efficacy approximately 2-fold in stabilizing triplex DNA; however, this effect was more than compensated for by the lack of DNA aggregation in the presence of bis(ethyl)polyamines. A concentration-dependent increase in the Tm of triplex DNA was observed in the presence of polyamines. CD spectral measurements showed distinct differences in the conformation of triplex DNA stabilized in the presence of polyamines compared to the CD spectra of the oligonucleotides alone. Temperature-dependent CD spectra of triplex DNA showed monophasic melting in the absence and presence of polyamines, suggesting duplex/triplex --> single-stranded DNA transition. These results indicate that structural modifications of polyamines is an effective strategy to develop triplex DNA-stabilizing ligands, with potential applications in antigene therapeutics.

Circular Dichroism↗
PubMed1997

beta-amyloid-induced endothelial necrosis and inhibition of nitric oxide production.

Deposits of amyloid beta-peptide (A beta) in senile plaques and cerebral blood vessels is the prominent feature of Alzheimer's disease (AD), regardless of genetic predisposition. The cellular origin of cerebral deposits of A beta or its precise role in the neurodegenerative process has not been established. Recently we demonstrated a novel action of beta-amyloid on blood vessels--vasoactivity and endothelial damage through superoxide radicals. Since endothelial dysfunction is associated with vascular degenerative diseases, we examined the direct action of A beta on endothelial cells in culture. Cells treated with A beta displayed characteristics of necrotic cell death which was prevented by the free radical scavenging enzyme superoxide dismutase. Stimulation of endothelial nitric oxide (NO) production by the calcium ionophore, A23187, or bradykinin was inhibited by beta-amyloid. We conclude that an imbalance of NO and oxygen radicals may mediate the A beta-induced endothelial damage on endothelial cells in culture and may also contribute to a variety of pathophysiological conditions associated with aging: hypertension, cerebral ischemia, vasospasm, or stroke.

Amyloid beta-Peptides↗
PubMed1997

Germ line chimeras from female ES cells.

Murine embryonic stem cells (ES cells) are pluripotent cells that can contribute to all tissues of developing mice including the germ line when aggregated with 8-cell-stage embryos or injected into the blastocoel cavity of murine blastocysts. As well as for in vitro studies, they are used to introduce mutations into the murine genome, thereby producing new mutant mouse lines. All ES cell lines so far described that contribute to the germ line have been male. However, for many studies female ES cell lines may be essential. Female ES cells may be particularly useful for mutating genes located on the X chromosome which would otherwise be hemizygously lethal in males. We show here that female ES cells are able to form germ line chimeras and to sex convert a male host embryo.

Animals↗
PubMed1997

A new 'two step' procedure for 4.5 log depletion of T and B cells in allogeneic transplantation and of neoplastic cells in autologous transplantation.

To evaluate a new 'two step' method for purging T, B and neoplastic cells from hematopoietic progenitor cells (PC), PCs were collected by apheresis and some suspensions were deliberately contaminated with 2-5% breast cancer cells. PCs were first processed through CellPro columns for positive selection of cells that express CD34. After this first step, the mean CD34+ cell recovery was 68 +/- 12%, and CD34+ cell purity was 61 +/- 11%; CD3+ and neoplastic cell depletion were 2.1 +/- 0.4 and 1.9 +/0 0.4 logs, respectively. Cells were further processed through the StemSep device for direct depletion of T and B cells or of breast cancer cells. After the first and the second step, overall CD34+ cell recovery was 50 +/- 7%, T and B cell removal was 4.7 +/- 0.4 log and neoplastic cell purging was 4.4 +/- 0.3 log, ie significantly superior to methods described in the past.

Antigens, CD34↗
PubMed1997

A source of adenosine involved in cardiovascular responses to defense area stimulation.

We have investigated the source of central adenosine important in modulating the cardiovascular response to hypothalamic defense area (HDA) stimulation in alpha-chloralose-anesthetized rats. Microinjections of an ecto-5'-nucleotidase inhibitor, alpha,beta-methylene ADP (alpha,beta-meADP), were made into caudal nucleus of the solitary tract (cNTS) and rostral ventrolateral medulla (RVLM), and its effects on HDA-evoked responses were observed. Stimulation of HDA evoked an increase in arterial pressure and a secondary rise in arterial pressure after stimulation ceased. There was also an increase in heart rate and hindlimb blood flow. alpha,beta-meADP had no effect on resting levels of arterial pressure, heart rate, and hindlimb blood flow when injected into the cNTS or RVLM. alpha,beta-meADP also had no effect on the HDA-evoked tachycardia and increase in muscle blood flow. However, alpha,beta-meADP reduced the primary increase in arterial pressure evoked by HDA stimulation when microinjected into the cNTS. In contrast, alpha,beta-meADP reduced the secondary increase in arterial pressure when microinjected into the RVLM. From these results, we suggest that at least part of the adenosine released centrally during HDA stimulation is derived extracellularly from ATP metabolism.

5'-Nucleotidase↗
PubMed1996

Structural specificity effects of trivalent polyamine analogues on the stabilization and conformational plasticity of triplex DNA.

Natural polyamines, i.e. putrescine, spermidine and spermine, are excellent promoters of triplex DNA. Using melting temperature (Tm) measurements and CD spectroscopy, we found that structural alterations on spermidine backbone, including methylation, or acetylation at the N1-, N4- and/or N8-positions had a profound influence on the stability and conformation of poly(dA).2poly(dT) triplex. The conformation of the polynucleotide complex underwent sequential changes from B-DNA to triplex DNA as the concentration of spermidine increased from 0 to 50 microM in a buffer containing 10 mM sodium cacodylate and 1 mM EDTA (pH 7.2). At 60 microM spermidine, the CD spectrum of triplex DNA was comparable with that of psi-DNA, with a strong positive band centred around 260 nm. A negative band was also found at 295 nm. At higher concentrations of spermidine, however, the intensity of the positive band progressively decreased and the peak intensity was found at a 1:0.3 molar ratio of DNA phosphate:spermidine. Temperature-dependent CD analysis showed that the psi-DNA structure melted to single-stranded DNA at temperatures above the Tm determined from the absorbance versus temperature profile. Comparable effects were exerted on the conformation of triplex DNA by Co(NH3)6(3+), an inorganic trivalent cation. Substitution of the N4-hydrogen of spermidine by a cyclohexyl ring or the fusion of the N4-nitrogen in a cyclic ring system, as in piperidine, enhanced the ability of spermidine analogues to stabilize triplex and psi-DNA forms over a wider concentration range compared with spermidine. These data demonstrate a differential effect of trivalent cations in stabilizing triplex DNA and provoking unusual conformations such as psi-DNA. Synthetic homologues of spermidine that stabilize triplex DNA over a wider range of concentrations than that stabilized by spermidine itself might have potential therapeutic applications in the development of an anti-gene strategy against several diseases, including cancer and AIDS.

DNA↗
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↗
PubMed1996

Rapid and efficient selection of human hematopoietic cells expressing murine heat-stable antigen as an indicator of retroviral-mediated gene transfer.

Recombinant retroviruses offer many advantages for the genetic modification of human hematopoietic cells, although their use in clinical protocols has thus far given disappointing results. There is therefore an important need to develop new strategies that will allow effectively transduced primitive hematopoietic target populations to be both rapidly characterized and isolated free of residual nontransduced but biologically equivalent cells. To address this need, we constructed a murine stem cell virus (MSCV)-based retroviral vector containing the 228-bp coding sequence of the murine heat-stable antigen (HSA) and generated helper virus-free amphotropic MSCV-HSA producer cells by transfection of GP-env AM12 packaging cells. Light density and, in some cases, lineage marker-negative (lin-) normal human marrow or mobilized peripheral blood cells preactivated by exposure to interleukin-3 (IL-3), IL-6, and Steel factor in vitro for 48 hours were then infected by cocultivation with these MSCV-HSA producer cells for a further 48 hours in the presence of the same cytokines. Fluorescence-activated cell sorting (FACS) analysis of the cells 24 hours later showed 21% to 41% (mean, 27%) of those that were still CD34+ to have acquired the ability to express HSA. The extent of gene transfer to erythroid and granulopoietic progenitors (burst-forming unit-erythroid and colony-forming unit-granulocyte-macrophage), as assessed by the ability of these cells to form colonies of mature progeny in the presence of normally toxic concentrations of G418, averaged 11% and 12%, respectively, in 6 experiments. These values could be increased to 100% and 77%, respectively, by prior isolation of the CD34+HSA+ cell fraction and were correspondingly decreased to an average of 2% and 5%, respectively, in the CD34+HSA- cells. In addition, the extent of gene transfer to long-term culture-initiating cells (LTC-IC) was assessed by G418 resistance. The average gene transfer to LTC-IC-derived colony-forming cells in the unsorted population was < or = 7% in 4 experiments. FACS selection of the initially CD34+HSA+ cells increased this value to 86% and decreased it to 3% for the LTC-IC plated from the CD34+HSA- cells. Transfer of HSA gene expression to a phenotypically defined more primitive subpopulation of CD34+ cells, ie, those expressing little or no CD38, could also be shown by FACS analysis of infected populations 24 hours after infection. These findings underscore the potential use of retroviral vectors encoding HSA for the specific identification and non-toxic selection immediately after infection of retrovirally transduced populations of primitive human hematopoietic cells. In addition, such vectors should facilitate the subsequent tracking of their marked progeny using multiparameter flow cytometry.

Animals↗
PubMed1996

Structure-activity relations of S-adenosylmethionine decarboxylase inhibitors on the growth of MCF-7 breast cancer cells.

SAMDC is a key enzyme in the biosynthesis of spermidine and spermine, 2 polyamines that are essential for cell proliferation. Inhibition of polyamine biosynthesis is often targeted as a therapeutic strategy to suppress cancer cell growth as these cells contain elevated levels of polyamines. We examined the effect of a new group of SAMDC inhibitors, CGP33829, CGP35753, CGP36958, CGP39937, and CGP48664, (obtained from Ciba-Geigy, Basel, Switzerland), and their parent compound, MGBG, on the proliferation of MCF-7 breast cancer cells. MGBG had minimal effects on the proliferation of MCF-7 cells up to 6 microM concentration. In contrast, CGP48664 and CGP39937, containing 2 aromatic rings that delocalize the pi electron system of the backbone of MGBG, were potent inhibitors with 50% growth inhibition at 0.5 microM concentration. Other CGP compounds were less effective in inhibiting cell growth. The ability of CGP48664 to inhibit MCF-7 cell proliferation was related to its ability to inhibit SAMDC and to consequently deplete spermidine and spermine levels in the cell. Exogenous spermidine and spermine could reverse the growth inhibitory effects of this compound. CGP compounds also increased the activity of ODC, another enzyme involved in polyamine biosynthesis. Northern blot analysis of mRNA from MCF-7 cells progressing in cell cycle after G1 synchronization did not show an increase in ODC mRNA level by CGP48664. These data demonstrate structure-activity relationships of a series of MGBG derivatives on cell growth, enzyme activities, and polyamine biosynthesis in a hormone-responsive breast cancer cell line and suggest potential application of SAMDC inhibitors as therapeutic agents.

Acetyltransferases↗
PubMed1996

Localization of type II phospholipase A2 messenger RNA and immunoactivity in human placenta and fetal membranes.

Although Type II phospholipase A2 (PLA2) immunoactivity has been identified in homogenates of human placenta and fetal membranes, there is a paucity of information concerning the sites of synthesis of this secreted PLA2 isozyme. The aim of this study, therefore, was to establish the cellular localization of Type II PLA2 messenger RNA (mRNA) in human term placental and fetal membranes by in situ hybridization. In addition, the co-localization of immunoreactive Type II PLA2 in gestational tissues was determined, and the effect of labour status and pre-eclampsia on immunolabelling intensity were established. Type II PLA2 mRNA was identified in all tissue sections examined and was localized principally in placental villous vasculature and mesenchymal elements of placenta, chorion and amnion. Within the vasculature, Type II PLA2 mRNA was associated with smooth muscle cells. Immunoreactive Type II PLA2 was identified in the fibroblast and spongy layers of the amnion, the fibroblast and reticular layer of the chorion, and in the mesenchymal core and trophoblasts of placental villi. Immunolabelling staining intensity was greater in placenta and chorion than that observed in amnion, however, staining intensity was unaffected by labour status. Pre-eclampsia was associated with increased immunolabelling for Type II PLA2 in placenta but not fetal membranes. The data obtained clearly established that Type II PLA2 is synthesized by multiple cell types within human gestational tissues and co-localization of Type II PLA2 mRNA and immunoreactive protein has been established. The role of Type II PLA2 in gestational tissue phospholipid metabolism and, in particular, in vascular and mesenchymal elements, has yet to be established. Possible roles for this isozyme may include, the provision of substrate for eicosanoid synthesis, maintaining cell membrane phospholipid asymmetry and prevention of clot formation within the placental vascular bed.

Amnion↗
PubMed1996

Evaluation of 1-(9-anthracenylmethyl) piperazine for the analysis of isocyanates in spray-painting operations.

A new reagent, 1-(9-anthracenylmethyl)piperzine (MAP), was used for the derivatization of airborne 1,6-hexamethylene diisocyanate (HDI) and polyisocyanates generated during spray-painting operations. The new reagent, which offers enhanced sensitivity and uniformity of response to both the monomeric and oligomeric forms of HDI, was compared directly with 1-(2-methoxyphenyl)piperazine (MOP), the currently employed derivatizing reagent used in the National Institute for Occupational Safety and Health Method 5521. Both the validity of the side-by-side sampling protocol and the efficacy of two derivatizing reagents were evaluated in field studies. The analytical results indicate that there is no significant difference at the 95% confidence level in the concentration of polyisocyanate in the aerosol as determined by two impingers containing MAP and a third containing MOP when these are positioned in a side-by-side-by-side arrangement.

Air Pollutants, Occupational↗
PubMed1996

Health promotion across the continuum: challenges for the future of cardiovascular nursing.

Issues surrounding health care spending, reform, and future directions have generated much concern and debate among health care providers. Increasingly, cardiovascular nurses are challenged to respond to the health care needs of clients in the 21st century. This article discusses trends in the health care system, including the current emphasis on illness and emerging efforts supporting health promotion. The discussion includes an overview of health care restructuring and the use of care management as a comprehensive strategy for cardiovascular nursing practice to support health promotion across a trajectory of illness and wellness.

Cardiovascular Diseases↗
PubMed1996

Outpatient management of lipid disorders.

Outpatient cardiac centers, diabetic treatment clinics, multispecialty medical groups, and primary care medicine currently have a unique opportunity to establish cost-effective lipid management clinics. Such programs have been shown to reduce progression of coronary vascular disease, reduce mortality and clinical events, and ultimately reduce health care costs. Successful lipid clinic operation requires thorough clinical assessment, comprehensive and aggressive nonpharmacologic and pharmacologic therapy, productive compliance strategies, and meaningful outcomes measures. Also required are sound billing procedures, an effective marketing plan, a continual relationship with lipid training organizations, and full integration in the disease management process throughout the continuum of care. This systematic and aggressive approach to lipid management affords a significant opportunity for qualified nurses and allied health professionals to help reduce the unnecessary burden of premature cardiovascular disease.

Adult↗
PubMed1996

The role of adenosine receptors in the rostral ventrolateral medulla in the cardiovascular response to defence area stimulation in the rat.

The effects of microinjections of adenosine and an adenosine receptor antagonist into the rostral ventrolateral medulla (RVLM) on the cardiovascular changes associated with the defence reaction were investigated in anaesthetized rats. Responses to electrical and chemical stimulation in RVLM were determined in alpha-chloralose-anaesthetized, paralysed and artificially ventilated rats. Microinjections of adenosine (10 nM) and the adenosine receptor antagonist 8-sulphophenyl-theophylline (8-SPT; 0.12 microM) were made into the RVLM and their effects on arterial pressure (ABP), heart rate (HR) and skeletal muscle blood flow determined. Microinjections of adenosine into the RVLM evoked either an increase or a decrease in ABP, with variable effects on HR. These actions of adenosine were blocked by prior injection of 8-SPT at the same site. Histological analysis showed that adenosine evoked an increase in arterial pressure when injected into rostral areas of the RVLM, and a depressor response when injected into caudal regions. Furthermore, microinjections of adenosine into the RVLM augmented the increase in ABP evoked by electrical stimulation of the hypothalamic defence area (HDA). Whilst microinjection of 8-SPT into RVLM had no effect on the baseline levels of the variables measured, it reduced the HDA-evoked increase in ABP. From these results we propose that adenosine modulates the cardiovascular changes evoked upon stimulation of the HDA via an action on sympatho-excitatory neurones within the rostral ventrolateral medulla.

Adenosine↗
PubMed1996

Covert video surveillance--an assessment of the Staffordshire protocol.

An assessment of a protocol devised to guide practitioners thinking of using covert video surveillance. Such surveillance is particularly used to help identify cases of Munchausen's syndrome by proxy. The protocol in question has been written by staff at the Academic Department of Paediatrics, North Staffordshire Hospital, Stoke-on-Trent in association with their local Area Child Protection Committee and has been commended by the Department of Health to others wishing to implement covert video surveillance.

Behavioral Research↗
PubMed1996

Covert video surveillance: the Staffordshire Protocol--a response to Dr Shinebourne.

This paper is a response to Dr Shinebourne's response to my recent paper assessing the relative merits of the Staffordshire Protocol on covert video surveillance. Dr Shinebourne does not take the opportunity to rebut the criticisms made of the text of the protocol. It is further suggested that judicial oversight of the use of CVS might accord the process a degree of proportionality.

Child↗
PubMed1996

Identifying cervical infection among pregnant women in Nairobi, Kenya: limitations of risk assessment and symptom-based approaches.

OBJECTIVES: To examine characteristics of pregnant women associated with cervical infection, and to evaluate the accuracy of symptom-based and risk assessment systems which have been developed for identifying cervical infection in antenatal women. METHODS: Interviews were conducted and physical examinations performed on 291 consecutive antenatal clinic attenders in nairobi, Kenya. Vaginal, cervical, urine and blood specimens were also obtained for analysis. RESULTS: The following disease prevalences were observed: candidiasis 26.2%; trichomoniasis 19.9%; bacterial vaginosis 20.6%; any vaginal infection 53.8%; chlamydial cervicitis (CT) 8.8%; gonococcal cervicitis (GC) 2.4%; any cervical infection 10.8%. The only statistically significant association with GC and/or CT cervical infection was the presence of cervical friability (OR = 2.1, P = 0.05). There were trends towards associations with the presence of endocervical mucopus (OR = 2.6, P = 0.06), reporting a new sex partner in the past 3 months (OR = 2.2, P = 0.16) and reporting that a sex partner had an STD-related symptom (OR = 4.4, P = 0.13). There were no associations with other demographic, behavioural or medical characteristics. Risk scores previously developed for detecting GC/CT cervicitis in developing country antenatal populations generally performed poorly. CONCLUSIONS: The prevalences of vaginal and cervical infection observed were extremely high among these "low risk" women. Owing probably to high levels of vaginal infection and to behavioural characteristics of this urban population, factors which elsewhere have been associated with cervical infection were not found to be so in this setting. Further work on symptom-based approaches and risk assessment for STD case detection in pregnant women is required before STD management recommendations can be generalised.

Adult↗