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Biomedical subjects

D Walker

Publications and source records attributed to D Walker.

At least 163 records · Page 9Linked to original sources
PubMed1996

Comparison of HT29-18-C1 and Caco-2 cell lines as models for studying intestinal paracellular drug absorption.

PURPOSE: To compare the permeability characteristics of HT29-18-C1 colonic epithelial cell line with Caco-2, an established model of intestinal drug transport. METHODS: Cell lines were grown as epithelial monolayers. Permeability was measured over a range of transepithelial electrical resistance (Rt) using a group of drug compounds. RESULTS: HT29-18-C1 develop Rt slowly when grown in culture, allowing permeability to be measured over a wide range (80-600 Omega x cm2). In contrast, Caco-2 monolayers rapidly develop Rt of approximately equal 300 Omega x cm2 and require Ca2+ -chelation to generate Rt equivalent to human intestine (60-120 Omega x cm2). Permeability of atenolol, ranitidine, cimetidine, hydrochlorothiazide and mannitol across HT29-18-C1 decreased 4-5 fold as Rt developed from 100-300 Omega x cm2 indicating they permeate via the paracellular route. In contrast, ondansetron showed no difference in permeability with changing Rt consistent with transcellular permeation. Permeability profiles across low Rt HT29-18C1 and pulse EGTA-treated Caco-2 monolayers were the same for all 5 paracellular drugs suggesting that transient Ca2+ removal does not alter selectivity of the tight junctions. Permeabilities of cimetidine, hydrochlorothiazide and atenolol across 100 Omega x cm2 HT29-18-C1 monolayers reflect more closely those reported for the human ileum in vivo than did mature Caco-2 monolayers. CONCLUSIONS: HT29-18-C1 monolayers can be used to study drug permeability at Rt values similar to human intestine without the need for Ca2+ chelation. As such, they offer a useful alternative to Caco-2 for modelling intestinal drug absorption.

Atenolol↗
PubMed1996

Lack of a temporal gradient of retrograde amnesia following NMDA-induced lesions of the basolateral amygdala assessed with the fear-potentiated startle paradigm.

M. Kim and M. Davis (1993b) previously reported that electrolytic lesions of the central nucleus of the amygdala, made 6 or 30 days after training, completely blocked the expression of fear-potentiated startle in rats. The present study shows that excitotoxic lesions of the basolateral amygdala also block fear-potentiated startle and do so whether the lesions are made soon (i.e., 6 days) or long (i.e., 30 days) after training. The relevance of these findings to various theories of amygdala function is discussed.

Amygdala↗
PubMed1996

Structure and function of the Bacillus SpoIIE protein and its localization to sites of sporulation septum assembly.

Functioning of the spoIIE locus of Bacillus subtilis is required for formation of a normal polar septum during sporulation and for activation of the transcription factor sigma F, which directs early forespore-specific gene expression. We have determined the DNA sequence of the wild type and several mutant alleles of the spoIIE gene of B. subtilis and sequenced a substantial portion of its presumptive homologue in Bacillus megaterium. We show that the spoIIE locus encodes a single large protein with a predicted molecular mass of 92 kDa. Each of five point-mutation alleles, which have traditionally defined the locus, and two transposon-generated mutations were shown to fall within the coding sequence for the 92 kDa gene product or within sequences expected to be required for its expression. The amino-terminal portion of the predicted SpoIIE gene product, comprising approximately 40% of the protein, is extremely hydrophobic and is expected to contain up to 12 membrane-spanning segments. The remainder of the protein contains no hydrophobic segments long enough to span a lipid bilayer and is therefore presumed to comprise one or more globular, aqueous-phase exposed domains. An in-frame fusion joining the 3' end of the B. megaterium spoIIE coding sequence to the 5' end of gfp, a gene encoding the green fluorescent protein (GFP) of Aquorea victoria, resulted in a strong, sporulation-specific fluorescent signal localized to the sites of sporulation septum assembly. We speculate that SpoIIE plays a role in assembling the sporulation septum, perhaps determining the special properties of the structure that permit intercompartment signalling during development.

Alleles↗
PubMed1996

Choice and accountability in health promotion: the role of health economics.

Choices need to be made between competing uses of health care resources. There is debate about how these choices should be made, who should make them and the criteria upon which they should be made. Evaluation of health care is an important part of this debate. It has been suggested that the contribution of health economics to the evaluation of health promotion is limited, both because the methods and principles underlying economic evaluation are unsuited to health promotion, and because the political and cultural processes governing the health care system are more appropriate mechanisms for allocating health care resources than systematic economic analysis of the costs and benefits of different health care choices. This view misrepresents and misunderstands the contribution of health economics to the evaluation of health promotion. It overstates the undoubted methodological difficulties of evaluating health promotion. It also argues, mistakenly, that economists see economic evaluation as a substitute for the political and cultural processes governing health care, rather than an input to them. This paper argues for an economics input on grounds of efficiency, accountability and ethics, and challenges the critics of the economic approach to judge alternative mechanisms for allocating resources by the same criteria.

Choice Behavior↗
PubMed1996

Intrauterine insemination: evaluation of the results according to the woman's age, sperm quality, total sperm count per insemination and life table analysis.

We report on 332 infertile couples who underwent 1115 cycles of intrauterine insemination (IUI) with washed husband's semen. The indication for IUI was an abnormal post-coital test due to either a male or cervical infertility factor. The mean number of IUI cycles per patients was 3.4, the overall pregnancy rate 18.7%, and the pregnancy rate per cycle 5.6%. The cumulative pregnancy rate calculated by life table analysis showed that 16.0% of pregnancies occurred in the first three treatment cycles, while the cumulative pregnancy rate was 26.9% by the sixth cycle. The outcome of the therapy was adversely affected if the woman's age was > 39 years and/or total motile sperm count per insemination was < 1 x 10(6). No pregnancy occurred in women older than 44 years or in cases with a total motile sperm count before semen preparation of < 1 x 10(6).

Adult↗
PubMed1996

Nuclei number in human embryos co-cultured with human ampullary cells.

A study was undertaken to evaluate the effect on nuclei number in human embryos cultured in vitro with primary cell lines of human Fallopian tube epithelium. The development of 203 surplus human embryos, cultured in standard culture medium (Earle's balanced salt solution + 15% A5) with or without ampullary cells, was observed from day 2 to day 5.5 post-insemination. The expanded blastocysts in both culture conditions were analysed for nuclei numbers per blastocyst. Embryos transferred to co-culture at the 2-cell stage had an average of 120.7 nuclei per blastocyst, which was significantly higher than the average of 62.9 nuclei per blastocyst (P = 0.023) for the embryos transferred to co-culture at the 4-cell stage. The embryos cultured in the control medium had an average of 42.1 nuclei per blastocyst, which was significantly less than co-cultured embryos (P = 0.04). Severely fragmented embryos (grades 3 and 4) did not show recovery in co-culture. Our results show that when human embryos are transferred to co-cultures before the 4-cell stage, the blastulation rate and the cell number per embryo increase significantly compared to the embryos cultured in standard culture medium. The possible effect of co-culture on embryonic gene expression is discussed.

Adult↗
PubMed1996

An intensive multiagent chemotherapy regimen for brain tumours occurring in very young children.

Standard treatment for the majority of malignant brain tumours consists of surgery and radiotherapy. This treatment has late morbidity which is accentuated in the very young child. As part of a strategy to improve quality of life and overall survival of young children with brain tumours, members of the United Kingdom Children's Cancer Study Group (UKCCSG) have piloted an intensive chemotherapy regimen which aims to avoid or delay radiotherapy following surgery. Twenty eight children with a variety of malignant brain tumours have received the regimen, which contains carboplatin, vincristine, cyclophosphamide, methotrexate, and cisplatin. The treatment is toxic, resulting in one death from infection. The bulk of the toxicity was associated with the administration of carboplatin. All but three children eventually required adjuvant radiotherapy and this was given between 1.5 and 27 months from diagnosis (median delay to radiotherapy, 12 months). Using this treatment regimen, overall survival at four years is 35% (confidence intervals 10% to 60%). While there is no evidence from this study that radiotherapy can be abandoned in the management of malignant brain tumours, its introduction may be delayed using suitable chemotherapy, thus allowing time for further CNS development. This treatment strategy has been taken forward as an international clinical trial run through the International Society for Paediatric Oncology, but using a smaller dose of carboplatin to reduce toxicity.

Age Distribution↗
PubMed1996

Analysis of 21 Stargardt's disease families confirms a major locus on chromosome 1p with evidence for non-allelic heterogeneity in a minority of cases.

BACKGROUND: Autosomal recessive Stargardt's disease is a macular degeneration characterised by a juvenile onset and a rapidly progressive course resulting in an atrophic macular area typically surrounded by yellowish retinal flecks. METHOD: The disease locus has previously been assigned to markers from chromosome 1p21-p13 by genetic linkage analysis in eight multiplex Stargardt's disease families. RESULTS: In an extended analysis, the assignment to chromosome 1p was confirmed in the majority of the 21 families with Stargardt's disease who were studied. In addition, a series of recombinant chromosomes further narrowed the Stargardt's disease region to an approximately 3 cM interval between markers at D1S424 and D1S497. CONCLUSION: Multipoint linkage analysis most probably excludes this locus in three of these families suggesting non-allelic heterogeneity with at least one additional minor Stargardt's disease locus.

Chromosomes, Human, Pair 1↗
PubMed1996

Cross-linking the TCR complex induces apoptosis in CD4+8+ thymocytes in the presence of cyclosporin A.

Although it is generally agreed that TCR ligation is a minimal requirement for negative selection in the CD4+8+ double-positive (DP) thymocyte subset, the costimulatory requirements and specific signaling events necessary to induce apoptosis are not well defined. We have explored the consequences of cross-linking CD3/TCR complexes on thymocytes from H-Y TCR transgenic (Tg) mice. In agreement with previous reports, we demonstrate that culturing DP thymocytes with plate-bound anti-TCR antibody induces downregulation of CD4 and CD8 and upregulation of CD69 expression. Nevertheless, the activated cells did not undergo apoptosis, as determined by viable cell recoveries and by quantitation of DNA fragmentation using the TUNEL assay. However, specific depletion of the DP subset occurred within 24 hr when thymocytes were incubated in the presence of both anti-TCR and the immunosuppressant cyclosporin A (CsA). CsA also induced depletion of anti-CD3 stimulated normal DP thymocytes. Using mice homozygous for the lpr or gld mutation, we also have shown that Fas/Fas ligand interactions are not involved in the CsA-induced death of TCR-stimulated DP thymocytes. These data verify that TCR cross-linking alone is insufficient to induce apoptosis of DP thymocytes and further suggest that TCR stimulation activates a CsA-sensitive protective pathway that interferes with signaling events leading to apoptosis in DP thymocytes.

Animals↗
PubMed1996

A "bottom-line" approach to nurse staffing.

A method is described for facilitating staffing decisions by determining productivity standards for each defined nursing unit. Results include improved patient care, reduced staffing costs and team building among hospital departments.

Efficiency, Organizational↗
PubMed1996

Collaborative study on assays of activated FIX (FIXa). On behalf of the factor VIII and factor IX subcommittee of the ISTH. International Society on Thrombosis and Haemostasis.

A collaborative study has been organised by NIBSC to examine the performance of FIXa assays between laboratories, and to investigate the need for a standard. Ampoules of 3 materials, one monocomponent concentrate (coded C) and 2 different preparations of purified human FIXa (one proposed reference preparation, coded A and a test material coded B), have been assayed in 11 laboratories for FIXa using either the NIBSC method or a local method, with local standards (if available, coded D) to determine their potencies. The data showed high between assay variability; with the exception of one laboratory, most of the between assay variation expressed as %geometric coefficients of variation (gcv) were over 15%. The interlaboratory gcv when preparation B was assayed against the local standard was over 1700%, suggesting that most of the local standards are poorly calibrated. The %gcv was improved to 80% when reference A was used as the standard. These data clearly show that an international reference standard for FIXa would help to standardise FIXa preparations and would also improve in house assays for FIXa. However, an accelerated degradation study has shown that reference A is not suitable as a long term standard and another material with suitable stabilizers has to be established as an international standard for FIXa.

Factor IX↗
PubMed1995

Evolutionary duplication of a hepatic control region in the human apolipoprotein E gene locus. Identification of a second region that confers high level and liver-specific expression of the human apolipoprotein E gene in transgenic mice.

We have identified a second hepatic control region (HCR-2) in the human apolipoprotein (apo) E gene locus that confers liver expression of the human apoE gene in transgenic mice. This HCR-2 sequence is located 27 kilobases downstream of the apoE gene and 10 kilobases downstream of the previously described liver-specific enhancer (HCR-1). Nucleotide sequence analysis of the HCR-2 region revealed a sequence that shares 85% identity to the functional 319-base pair domain of HCR-1. To test its activity, transgenic mice were prepared with a fusion construct containing a human apoE gene fragment, which is not normally expressed in the liver, ligated to a 632-base pair region containing the HCR-2 sequence. This construct resulted in high levels of liver-specific apoE transgene expression, indicating that HCR-2 can function as a hepatic enhancer and has an activity similar to that of HCR-1. Hence, these findings suggest that there are at least two hepatic control regions, HCR-1 and HCR-2, capable of controlling the liver expression of this human apolipoprotein gene locus.

Animals↗
PubMed1995

Structure of the hepatic control region of the human apolipoprotein E/C-I gene locus.

The specificity of expression in the liver of the human apolipoprotein (apo) E/C-I gene locus is determined by a hepatic control region (HCR) that is located 15 kilobases downstream of the apoE gene. DNase I footprint studies of this sequence using nuclear extracts identified a region of the HCR that is enriched in nuclear protein-binding sites. Nuclease analysis of chromatin revealed liver-specific DNase I-hypersensitive sites that were associated with this region, and additional liver-specific nuclease-sensitive sites associated with the apoE gene were identified. The HCR domain has a limited binding affinity for the nuclear scaffold. The specific domain required for liver expression was tested by ligating subfragments of the HCR to the apoE gene and examining their activity in transgenic mice. A segment of 319 nucleotides that contained several potential regulatory sequences was required for full activity of liver-specific transcription with shorter segments yielding much lower levels of expression in the liver. All constructs that contained a fully active HCR were expressed in approximately a copy-dependent manner, suggesting that transgene expression was independent of integration position. Taken together, the properties of the HCR are consistent with its function as a locus control region for the liver-specific expression of the apoE gene.

Animals↗
PubMed1995

Quality of life.

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Child↗