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Biomedical subjects

K Stewart

Publications and source records attributed to K Stewart.

At least 55 records · Page 3Linked to original sources
PubMed1999

Scrapie replication in lymphoid tissues depends on prion protein-expressing follicular dendritic cells.

The immune system is central in the pathogenesis of scrapie and other transmissible spongiform encephalopathies (TSEs) or 'prion' diseases. After infecting by peripheral (intraperitoneal or oral) routes, most TSE agents replicate in spleen and lymph nodes before neuroinvasion. Characterization of the cells supporting replication in these tissues is essential to understanding early pathogenesis and may indicate potential targets for therapy, for example, in 'new variant' Creutzfeldt-Jakob disease. The host 'prion' protein (PrP) is required for TSE agent replication and accumulates in modified forms in infected tissues. Abnormal PrP is detected readily on follicular dendritic cells (FDCs) in lymphoid tissues of patients with 'new variant' Creutzfeldt-Jakob disease, sheep with natural scrapie and mice experimentally infected with scrapie. The normal protein is present on FDCs in uninfected mice and, at lower levels, on lymphocytes. Studies using severe combined immunodeficiency (SCID) mice, with and without bone marrow (BM) grafts, have indicated involvement of FDCs and/or lymphocytes in scrapie pathogenesis. To clarify the separate roles of FDCs and lymphocytes, we produced chimeric mice with a mismatch in PrP status between FDCs and other cells of the immune system, by grafting bone marrow from PrP-deficient knockout mice into PrP-expressing mice and vice versa. Using these chimeric models, we obtained strong evidence that FDCs themselves produce PrP and that replication of a mouse-passaged scrapie strain in spleen depends on PrP-expressing FDCs rather than on lymphocytes or other bone marrow-derived cells.

Animals↗
PubMed1999

Collection of peripheral blood progenitor cells (PBPC) based on a rising WBC and platelet count significantly increases the number of CD34+ cells.

The kinetics of mobilization and optimal timing of peripheral blood progenitor cell (PBPC) collection were evaluated in 190 patients with multiple myeloma undergoing stem cell harvest after mobilization with cyclophosphamide, prednisone and G-CSF. There was a strong correlation between the WBC count and the number of CD34+ cells circulating in peripheral blood (r = 0.875). Initiating leukapheresis based on rising WBC and platelet counts rather than on a fixed day increased the mean number of CD34+ cells 115% (9.7 to 20.9 x 10(6) CD34+ cells/kg; P = 0.010) for the total of all leukaphereses and 59% for the total of all CD34-selected products (5.1 to 8.1 x 10(6) CD34+ cells/kg; P = 0.011). Although the yield and purity of the CD34-selected product were not significantly affected (P > or = 0.071), the percentage of patients with concentrations of CD34+ cells in the initial leukapheresis of > 1% increased from 47% to 70% (P = 0.004). The mean purity of the selected product was related to the starting percentage: 48.9% if < 1% and 81.5% if > or = 1% (P < 0.001). Collection of stem cells based on rising WBC and platelet counts significantly increased the number of CD34+ cells in leukaphereses and CD34-selected products in comparison with collection on a fixed day.

Adult↗
PubMed1999

Phase I trial of sequential topotecan followed by etoposide in adults with myeloid leukemia: a National Cancer Institute of Canada Clinical Trials Group Study.

Prolonged exposure to a topoisomerase I inhibitor may increase expression of topoisomerase II, making cells more susceptible inhibitors of that enzyme. This study was undertaken to establish the maximum tolerated dose (MTD) of a topotecan/topoisomerase II inhibitor sequential combination that may be active in acute leukemia, and to evaluate the effects of in vivo exposure to topotecan on topoisomerase II levels in leukemic blast cells as measured by image cytometry. Patients who were eligible for this phase I study had relapsed or refractory acute myeloid leukemia (< or = 2 prior regimens) or CML blast crisis (0 or 1 prior regimen). Topotecan was given as a 5 day continuous i.v. infusion and was to be escalated through three levels (1.5, 1.75 and 2.0 mg/m2 day), followed by etoposide at two dose levels (100 and 150 mg/m2) i.v. bolus days 6, 7 and 8. Topoisomerase IIalpha levels in leukemic blasts from bone marrow were measured by image cytometry prior to starting treatment, on day 5 of topotecan infusion and on day 28; and daily during topotecan in peripheral blood blasts. Dose-limiting toxicity was seen in two of six patients at the first dose level (topotecan 1.5 mg/m2/day, etoposide 100 mg/m2/day; > or = grade 3 mucositis in both cases). This cohort was expanded to 10 patients; no further non-hematologic dose-limiting toxicity was observed, but given the extent of toxicity seen, further dose escalation was judged not to be feasible. Topo IIalpha levels increased in peripheral blood blasts during the first 72 h of topotecan infusion and returned to near baseline by day 5, whereas levels appeared to decrease in bone marrow blasts by day 5 compared to pretreatment. One complete hematologic and cytogenetic remission in a patient with CML blast crisis was observed in the 10 patients evaluable for response. The sequential administration of topotecan 1.5 mg/m2/day continuous infusion for 5 days followed by etoposide 100 mg/m2/day x 3 is the recommended phase II dose for this schedule. Topotecan increases topo IIalpha expression in vivo in leukemia cells, but levels of the enzyme are cell cycle dependent. Pharmacodynamic evaluation of the sequential or combination administration of novel antileukemic agents may help improve treatment strategies in acute leukemia.

Acute Disease↗
PubMed1999

The role of audit in making do not resuscitate decisions.

Audit has been proposed as a useful means of implementing and evaluating 'Do Not Resuscitate (DNR)' policies. This paper explores the background to the introduction of DNR policies and reviews published reports of their use in clinical practice. Problems with auditing and implementing DNR policies are highlighted.

Aged↗
PubMed1999

Evaluation of a diagnostic protocol using screening diagnostic peritoneal lavage with selective use of abdominal computed tomography in blunt abdominal trauma.

BACKGROUND: The optimal method of evaluating blunt abdominal trauma remains controversial. A combination of a sensitive screening test, diagnostic peritoneal lavage (DPL), and a specific test, abdominal computed tomography (CT), may be a safe, efficient approach to adult blunt abdominal trauma. METHODS: A prospective cohort study compared a protocol using screening DPL followed by selective use of abdominal CT (DPL/abdominal CT) and the use of abdominal CT alone in the evaluation of hemodynamically stable, adult blunt trauma patients. RESULTS: One hundred sixty-seven adult blunt trauma patients were initially evaluated by DPL (n = 71) or abdominal CT (n = 96). Emergency department evaluation required less time in the DPL/abdominal CT group than in the abdominal CT alone group (41 minutes vs. 2.5 hours; p < 0.001). There were no missed injuries in the DPL/abdominal CT group versus seven missed injuries in the abdominal CT group (p = 0.02). There were no nontherapeutic celiotomies in either study group. CONCLUSION: Screening DPL, followed by abdominal CT if positive, is a safe, efficient method of evaluating adult blunt abdominal trauma that reduces the time required to evaluate the abdomen, does not result in increased nontherapeutic celiotomies, results in fewer missed injuries, and reduces the overall use of abdominal CT.

Abdominal Injuries↗
PubMed1999

Further characterization of cells expressing STRO-1 in cultures of adult human bone marrow stromal cells.

Primitive cells of the osteoblast lineage are not well characterized but are known to be present within the STRO-1+ fraction of adult human bone and marrow. A survey of human osteosarcoma cell lines revealed that STRO-1 is expressed by MG-63 but not SaOS-2. Among murine cell lines tested, expression of STRO-1 was detected in the bipotential (adipocyte/osteoblast) line BMS-2 but not the committed osteoblast precursor MC3T3-E1. A proportion of cultured adult human bone marrow stromal cells (BMSCs) consistently expressed the STRO-1 antigen. The expression of a range of cell surface antigens was studied in relation to STRO-1 by flow cytometry and several, including the bone/liver/kidney isoform of alkaline phosphatase (ALP), were found to subtype the STRO-1+ population of BMSCs. Further, BMSCs dual-labeled with antibodies recognizing STRO-1 and ALP could be assigned to one of four fractions: STRO-1-/ALP-, STRO-1+/ALP-, STRO-1+/ALP+, and STRO-1-/ALP+. Cells from each fraction could be isolated in high purity and, when recultured, remained viable and exhibited a limited degree of phenotypic stability. Using reverse transcriptase-polymerase chain reaction, cells in the four fractions were found to express different levels of transcripts for the parathyroid hormone receptor (PTHr) and bone sialoprotein (BSP). The expression of transcripts for the nuclear transcription factor core-binding factor alpha 1/osteoblast-specific factor-2 (CBFA1/OSF2) was restricted to those fractions expressing STRO-1 and/or ALP. Treatment with 10 nM dexamethasone consistently increased the proportion of cells present in those fractions which expressed the highest levels of transcripts for PTHr and BSP (STRO-1+/ALP+ and STRO-1-/ALP+) while simultaneously decreasing the proportion present in the STRO-1+/ALP- fraction. In conclusion, the expression of STRO-1 in vitro remains a characteristic of less well differentiated cells of the osteoblast lineage; in cultures of BMSCs and in established human osteosarcoma cell lines, there is an inverse association between the expression of STRO-1 and ALP; dual labeling of BMSCs with monoclonal antibodies recognizing STRO-1 and ALP permits the identification and isolation of cells of the osteoblast lineage at different stages of differentiation.

Adult↗
PubMed1999

The effects of low-intensity warfarin on coagulation activation in patients with antiphospholipid antibodies and systemic lupus erythematosus.

The optimal intensity of oral anticoagulant therapy for the prevention of thromboembolism in patients with antiphospholipid antibodies (APLA) and systemic lupus erythematosus is controversial. Retrospective studies have suggested that patients with APLA are resistant to oral anticoagulant therapy, with a targeted International Normalization Ratio (INR) of 2.0 to 3.0, and that a higher intensity of anticoagulation (INR: 2.6 to 4.5) is required to prevent recurrent thromboembolism. To investigate if patients with APLA are resistant to the anticoagulant effect of low intensities of warfarin therapy, we performed a randomized trial in which 21 patients with APLA and systemic lupus erythematosus were allocated to receive one of three intensities of warfarin (INR: 1.1 to 1.4, 1.5 to 1.9 or 2.0 to 2.5) or placebo for four months. The main outcome was the effect of each intensity of warfarin therapy on prothrombin fragment 1+2 level (F1+2), that was used as a marker of coagulation activation. When F1+2 levels in patients allocated to the three warfarin intensities were compared to F1+2 levels in the placebo group, there was a statistically significant decrease (p<0.05) in the patient group receiving warfarin with a targeted INR of 2.0 to 2.5 at two, three and four months, and in the patient group with a targeted of INR 1.5 to 1.9 at three months. We conclude that in patients with APLA and systemic lupus erythematosus, warfarin therapy, with a targeted INR of 2.0 to 2.5, is effective in suppressing coagulation activation, and therefore, might be effective in preventing thromboembolism.

Adolescent↗
PubMed1998

Structure of secreted aspartic proteinases from Candida. Implications for the design of antifungal agents.

Pathogens of the genus Candida can cause life threatening infections in immuno-compromised patients. The three-dimensional structures of two closely related secreted aspartic proteinases from C. albicans complexed with a potent (Ki = 0.17 nM) inhibitor, and an analogous enzyme from C. tropicalis reveal variations on the classical aspartic proteinase theme that dramatically alter the specificity of this class of enzymes. The novel fungal proteases present: i) an 8 residue insertion near the first disulfide (Cys45-Cys50, pepsin numbering) that results in a broad flap extending towards the active site; ii) a seven residue deletion replacing helix hN2 (Ser110-Tyr114), which enlarges the S3 pocket; iii) a short polar connection between the two rigid body domains that alters their relative orientation and provides certain specificity; and i.v.) an ordered 12 residue addition at the carboxy terminus. The same inhibitor (A-70450) binds in an extended conformation in the two variants of C. albicans protease, and presents a branched structure at the P3 position. However, the conformation of the terminal methylpiperazine ring is different in the two crystals structures. The implications of these findings for the design of potent antifungal agents are discussed.

Antifungal Agents↗
PubMed1998

Diet design for a multicenter controlled feeding trial: the DELTA program. Delta Research Group.

OBJECTIVE: To describe the process and results of diet standardization, diet validation, and monitoring of diet composition, which were key components of protocol 1 of Dietary Effects on Lipoproteins and Thrombogenic Activity (DELTA-1), the initial protocol in a program of multicenter human feeding studies designed to evaluate the effects of amount and type of fat on lipoproteins and hemostasis parameters in various demographic groups. DESIGN: DELTA-1 was based on a randomized, blinded, crossover experimental design. Three diets were fed for 8 weeks to 103 healthy men and women aged 22 to 67 years at 4 field centers. Diet A, an average American diet, was designed to provide 37% of energy from fat, 16% of energy from saturated fatty acids (SFAs); diet B (step 1 diet) was designed to provide 30% of energy from fat, 9% of energy from SFA; and diet C (low SFA diet) was designed to provide 26% of energy from fat, 5% of energy from SFA. Key features of diet standardization included central procurement of fat-containing foods, inclusion of standard ingredients, precision weighing of foods--especially sources of fat and cholesterol--and use of standardized written procedures. SETTING: For menu validation, a set of 12 menus for each diet was prepared in duplicate and chemically assayed. For monitoring of diet composition during the study, an 8-day diet cycle (6 weekday and 2 weekend menus) was sampled by every field center twice during each of 3 feeding periods. STATISTICAL ANALYSES: Means (+/- standard error) were calculated and compared with target nutrient specifications. RESULTS: DELTA-1 was able to provide a standardized diet that met nutrient specifications across 4 field centers over 24 weeks of participant feeding spanning a total of 8 months. APPLICATIONS: Prestudy chemical validation of menus and continuous sampling and assay of diets throughout the study are essential to standardize experimental diets and to ensure that nutrient target goals are met and maintained throughout a controlled multicenter feeding study.

Adult↗
PubMed1998

ABT-378, a highly potent inhibitor of the human immunodeficiency virus protease.

The valine at position 82 (Val 82) in the active site of the human immunodeficiency virus (HIV) protease mutates in response to therapy with the protease inhibitor ritonavir. By using the X-ray crystal structure of the complex of HIV protease and ritonavir, the potent protease inhibitor ABT-378, which has a diminished interaction with Val 82, was designed. ABT-378 potently inhibited wild-type and mutant HIV protease (Ki = 1.3 to 3.6 pM), blocked the replication of laboratory and clinical strains of HIV type 1 (50% effective concentration [EC50], 0.006 to 0.017 microM), and maintained high potency against mutant HIV selected by ritonavir in vivo (EC50, </=0. 06 microM). The metabolism of ABT-378 was strongly inhibited by ritonavir in vitro. Consequently, following concomitant oral administration of ABT-378 and ritonavir, the concentrations of ABT-378 in rat, dog, and monkey plasma exceeded the in vitro antiviral EC50 in the presence of human serum by >50-fold after 8 h. In healthy human volunteers, coadministration of a single 400-mg dose of ABT-378 with 50 mg of ritonavir enhanced the area under the concentration curve of ABT-378 in plasma by 77-fold over that observed after dosing with ABT-378 alone, and mean concentrations of ABT-378 exceeded the EC50 for >24 h. These results demonstrate the potential utility of ABT-378 as a therapeutic intervention against AIDS.

Animals↗
PubMed1998

Advance directives and living wills.

Under certain circumstances, living wills or advance directives may carry legal force in the UK. This paper traces the development of advance directives, clarifies their current legal position and discusses potential problems with their use. Case histories are used to illustrate some of the common dilemmas which doctors may face.

Adolescent↗
PubMed1998

Effects of reducing dietary saturated fatty acids on plasma lipids and lipoproteins in healthy subjects: the DELTA Study, protocol 1.

Few well-controlled diet studies have investigated the effects of reducing dietary saturated fatty acid (SFA) intake in premenopausal and postmenopausal women or in blacks. We conducted a multicenter, randomized, crossover-design trial of the effects of reducing dietary SFA on plasma lipids and lipoproteins in 103 healthy adults 22 to 67 years old. There were 46 men and 57 women, of whom 26 were black, 18 were postmenopausal women, and 16 were men > or =40 years old. All meals and snacks, except Saturday dinner, were prepared and served by the research centers. The study was designed to compare three diets: an average American diet (AAD), a Step 1 diet, and a low-SFA (Low-Sat) diet. Dietary cholesterol was constant. Diet composition was validated and monitored by a central laboratory. Each diet was consumed for 8 weeks, and blood samples were obtained during weeks 5 through 8. The compositions of the three diets were as follows: AAD, 34.3% kcal fat and 15.0% kcal SFA; Step 1, 28.6% kcal fat and 9.0% kcal SFA; and Low-Sat, 25.3% kcal fat and 6.1% kcal SFA. Each diet provided approximately 275 mg cholesterol/d. Compared with AAD, plasma total cholesterol in the whole group fell 5% on Step 1 and 9% on Low-Sat. LDL cholesterol was 7% lower on Step 1 and 11% lower on Low-Sat than on the AAD (both P<.01). Similar responses were seen in each subgroup. HDL cholesterol fell 7% on Step 1 and 11% on Low-Sat (both P<.01). Reductions in HDL cholesterol were seen in all subgroups except blacks and older men. Plasma triglyceride levels increased approximately 9% between AAD and Step 1 but did not increase further from Step 1 to Low-Sat. Changes in triglyceride levels were not significant in most subgroups. Surprisingly, plasma Lp(a) concentrations increased in a stepwise fashion as SFA was reduced. In a well-controlled feeding study, stepwise reductions in SFA resulted in parallel reductions in plasma total and LDL cholesterol levels. Diet effects were remarkably similar in several subgroups of men and women and in blacks. The reductions in total and LDL cholesterol achieved in these different subgroups indicate that diet can have a significant impact on risk for atherosclerotic cardiovascular disease in the total population.

Adult↗
PubMed1998

Emerging models of care management for older people and those with mental health problems in the United Kingdom.

Care management has emerged as a central component in the development of community-based care in many countries. It has been government policy for providers of social services to develop care management systems in the United Kingdom since 1993. This paper examines the extent to which it is possible to begin to discern models of care from the different care management arrangements which are now emerging. First, the background to changes in policy and the role of care management in the UK social care system are discussed; second, evidence from the early phases of care management development in the UK is also examined; and third, based upon the pilot phase of a major national study of care management, the key dimensions of variation in care management through which models may be constituted are identified.

Aged↗
PubMed1997

Uptake of alpha-(L)-iduronidase produced by retrovirally transduced fibroblasts into neuronal and glial cells in vitro.

The uptake of recombinant alpha-(L)-iduronidase into glial and neuronal cells, produced by retrovirally transduced NIH3T3 fibroblasts, was studied. We demonstrate that: (1) neuronal and glial cells take up alpha-(L)-iduronidase released into the medium by retrovirally transduced fibroblasts expressing high levels of alpha-(L)-iduronidase; (2) both glial and neuronal cells express the cation independent mannose-6-phosphate receptor responsible for lysosomal enzyme uptake; and (3) uptake of the lysosomal enzyme can be blocked by excess free mannose-6-phosphate, but not glucose-6-phosphate. Thus, various brain cells take up alpha-(L)-iduronidase, possibly through a cation independent mannose-6-phosphate receptor mediated pathway, and this uptake is higher in actively dividing or immature brain cells. Consequently, (1) neuronal metabolism ought to be capable of cross correction by enzyme provided by genetically engineered and transplanted cells provided by bone marrow transplantation (BMT); (2) that BMT could have a more beneficial effect on neurological function if performed as early as possible; and (3) given that the uptake mechanism of glial cells has a higher capacity, it might be easier to target diseases like the leukodystrophies in which lysosomal enzymes are needed in glial cells, compared to diseases where lysosomal enzymes ought to be delivered into neurons.

3T3 Cells↗