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Biomedical subjects

M Contreras

Publications and source records attributed to M Contreras.

At least 37 records · Page 2Linked to original sources
PubMed2000

Prospective investigation of transfusion transmitted infection in recipients of over 20 000 units of blood. TTI Study Group.

OBJECTIVES: To follow up recipients of 20 000 units of blood to identify any transmissions of infections through blood transfusion. DESIGN: Follow up study of recipients of transfusion. SETTING: 22 hospitals in north London. PARTICIPANT: Adult patients who had recently been transfused. MAIN OUTCOME MEASURES: Patients had further blood samples taken at 9 months that were tested for markers of hepatitis B and C and HIV and human T cell leukaemia/lymphoma virus type I or II (HTLV) infections. Recent infections were distinguished from pre-existing infections by comparison with blood samples taken before transfusion. RESULTS: 9220 patients were recruited, and 5579 recipients of 21 923 units of blood were followed up. No transfusion transmitted infections were identified. The incidence of transfusion transmitted infections was 0 in 21 043 units (95% confidence interval for risk 0 to 1 in 5706 recipients) for hepatitis B; 0 in 21 800 units (0 to 1 in 5911 recipients) for hepatitis C; 0 in 21 923 units (0 to 1 in 5944 recipients) for HIV; and 0 in 21 902 units (0 to 1 in 5939 recipients) for human T cell leukaemia/lymphoma virus. Three patients acquired hepatitis B during or after hospital admission but not through transfusion; 176 (3%) had pre-existing hepatitis B infection. Sixteen (0.29%) patients had hepatitis C, and five (0.09%) had human T cell leukaemia/lymphoma virus. CONCLUSIONS: The current risk of transfusion transmitted infections in the United Kingdom is very small, though hospital acquired infections may arise from sources other than transfusion. A considerable proportion of patients have pre-existing infections.

Adolescent↗
PubMed2000

Cytokine accumulation in stored red cell concentrates: effect of buffy-coat removal and leucoreduction.

The accumulation of cytokines in stored red blood cell concentrates (RCCs) has been implicated as a potential cause of transfusion reactions associated with the use of such products. At present, it is unclear whether there is any link between residual leukocyte and/or platelet content with cytokine levels in various RCCs. In this study, we have therefore assessed cytokine levels of leukocyte (e.g., IL8) and platelet (e.g., RANTES, TGF-beta1) origin in supernatants of RCCs prepared by the plasma reduced method or by depletion of the buffy coat. We have also assessed whether the Duffy antigen receptor (DARC, a promiscuous receptor for some chemokines) has any role in the diminution of cytokine levels in stored blood components by comparing cytokine levels in stored plasma reduced RCCs derived from both DARC +ve and DARC -ve individuals. In addition, comparison of filtered and non-filtered products of the same origin has also been conducted. Results showed that supernatants from DARC -ve concentrates contained higher levels of IL-8 up to days 14/15 of storage compared with DARC +ve RCCs. However, at later time points, similar levels of IL-8 were observed in RCCs regardless of their Duffy receptor status. For TGF-beta1 and RANTES, no significant difference in the levels of these cytokines was detected between DARC +ve and DARC -ve concentrates. Removal of leukocytes and platelets by conventional leukocyte filtration significantly reduced the accumulation of cytokines. Buffy coat reduced RCCs contained minimal amounts of IL-8 and TGF-beta1 but no RANTES. We conclude therefore, that the levels of cytokines in the supernatants of RCCs stored at 4 degrees C are related mainly to their leucocyte and platelet content.

Blood Preservation↗
PubMed2000

HLA-A, -B and -DR antigen frequencies of the London Cord Blood Bank units differ from those found in established bone marrow donor registries.

Patients requiring allogeneic stem cell transplantation who do not have an HLA-matched related donor can sometimes obtain an unrelated donor by searching volunteer registries. The majority of donors in the registries are Caucasoid, which results in a lower probability of a non-Caucasoid patient finding a suitable donor. Cord blood is increasingly used as a source of haematopoietic stem cells for allogeneic bone marrow reconstitution and so far the London Cord Blood Bank has banked almost 3000 cord blood units. An analysis of the first 1500 units banked showed that more than 30% of the London Cord Blood Bank units are derived from UK ethnic minorities compared with only 2% of individuals recruited locally for the British Bone Marrow Registry (BBMR). The HLA types found in these cord blood units reflect their ethnic diversity and include: HLA-A34, A36, A80, B75, B61, B53, B78, B81 and B82. The units stored by the London Cord Blood Bank show an HLA profile which differs considerably from that of locally typed adult volunteers for the BBMR panel and this should help to increase the chances of obtaining acceptably HLA-matched donors for patients from ethnic minorities. Bone Marrow Transplantation (2000) 25, 475-481.

Adult↗
PubMed2000

Splitless large-volume GC-MS injection for the analysis of organophosphorus and organochlorine pesticides in vegetables using a miniaturised ethyl acetate extraction.

A simple, rapid and sensitive multiresidue method has been developed for the determination of ten organophosphorus and organochlorine pesticides, commonly used in crop protection. The analysis uses a miniaturised extraction with ethyl acetate followed by large volume injection (10 microL) GC-EI-MS analysis in SIM (selective ion monitoring) mode. Sensitivity and selectivity of the method were acceptable with limits of detection (LODs) lower than 0.01 mg kg-1, except for endosulfan alpha and beta (0.05 mg kg-1). Average recoveries of between 63-99% were obtained and good linearity was observed in the range from 0.01 to 1.00 mg kg-1. Repeatability and reproducibility studies yielded relative standard deviations lower than 20% in all the cases. The method was applied to the analysis of 110 tomato, pepper and cucumber samples, as part of the monitoring programme of the Association of Producers and Exporters of Fruits and Vegetables of Almería.

Acetates↗
PubMed2000

Cytokines in WBC-reduced apheresis PCs during storage: a comparison of two WBC-reduction methods.

BACKGROUND: Several studies have suggested that cytokine accumulation during storage of platelet concentrates (PCs) may mediate nonhemolytic febrile transfusion reactions and that a reduction in WBC numbers prevents the generation of cytokines. Despite efforts to minimize WBC contamination in apheresis PCs, high numbers of WBCs and increased cytokine levels may still occur, depending on the quality of the apheresis device employed. STUDY DESIGN AND METHODS: This study was undertaken to investigate whether PCs collected with WBC-reduction devices (Spectra LRS, COBE;or MCS+ LDP, Haemonetics) were sufficiently depleted of WBCs to limit cytokine accumulation during storage. The study evaluated 1) the levels of cytokines of WBC and platelet origin in two types of apheresis PCs during storage and 2) the effects of prestorage filtration on cytokine levels in the Spectra LRS PCs. RESULTS: In the Spectra LRS PCs, low levels of IL-6, IL-8, and monotype chemoattractant protein 1 (MCP-1) were detected in Day 1 PCs, and they remained consistent during the shelf life. RANTES, platelet factor 4 (PF4), beta-thromboglobulin (beta-TG), and transforming growth factor (TGF)-beta1 were also detected in these PCs, and their levels increased significantly on storage. Prestorage filtration of Spectra LRS PCs did not further reduce the levels of IL-6, IL-8, MCP-1, PF4, beta-TG, and TGF-beta1 in the filtered component. In the MCS+ LDP PCs, IL-6 was detected on Day 1, and its level increased significantly on storage, whereas the levels in the Spectra PCs remained steady. IL-8 levels were lower in MCS+ LDP PCs than in Spectra LRS PCs of the same age. MCP-1 levels were similar in both products on Day 1 and marginally increased in stored MCS+ LDP PCs. Substantial amounts of RANTES, PF4, beta-TG, and TGF-beta1 occurred in Day 1 MCS+ LDP PCs, and, on storage, these levels rose significantly. CONCLUSION: Despite a significant reduction in levels of WBC-derived cytokines, platelet-derived cytokines were present in different amounts in the two products.

Blood Platelets↗
PubMed2000

Fitting nonlinear and constrained generalized estimating equations with optimization software.

In this article, we present an estimation approach for solving nonlinear constrained generalized estimating equations that can be implemented using object-oriented software for nonlinear programming, such as nlminb in Splus or fmincon and lsqnonlin in Matlab. We show how standard estimating equation theory includes this method as a special case so that our estimates, when unconstrained, will remain consistent and asymptotically normal. To illustrate this method, we fit a nonlinear dose-response model with nonnegative mixed bound constraints to clustered binary data from a developmental toxicity study. Satisfactory confidence intervals are found using a nonparametric bootstrap method when a common correlation coefficient is assumed for all the dose groups and for some of the dose-specific groups.

Animals↗
PubMed2000

Retrospective study on red cell usage in primary total knee replacement surgery.

BACKGROUND AND OBJECTIVES: There is wide variation in the use of red cell transfusions for the same clinical indication. The purpose of the study was to comment on preoperative and discharge haemoglobin (Hb) levels and perioperative blood loss, and to project the Hb level if transfusions were not administered. MATERIALS AND METHODS: The case notes of 187 patients who underwent primary total knee replacement were reviewed retrospectively. RESULTS: More than 90% of the transfusions were given in the immediate postoperative period as a matter of routine and a significant number of transfusions appeared to be unnecessary. CONCLUSION: For surgical procedures involving moderate blood loss, transfusions should not be given as a routine and the decision to transfuse should take into consideration the clinical state of the patient, blood loss and pre- and postoperative Hb levels.

Aged↗
PubMed2000

Endotoxin-induced alterations of lipid and fatty acid compositions in rat liver peroxisomes.

The structure/function of peroxisomal lipids in rat liver treated with a sublethal dose of endotoxin, a lipopolysaccharide (LPS), was investigated. Peroxisomes isolated from LPS-treated rat liver had remarkable alterations in lipid content compared with saline treated control liver peroxisomes. Cholesterol and phospholipids (PL) decreased significantly by 28.7% and 50.8%, respectively, leading to the change in the ratio of cholesterol/phospholipids (control 0.081 versus LPS 0.118, P < 0.001). A quantitative analysis from LPS-treated rat liver peroxisomes showed a general decrease in all classes of PL. No such alterations were observed in lipid content of other subcellular organelles. The peroxisomal fatty acid composition in LPS-treated animals was also altered. An analysis of fatty acid composition in PL and phosphatidylcholine from LPS-treated peroxisomes showed an increase in arachidonic acid (C20:4) and docosahexaenoic acid (C22:6). Very long chain (VLC) fatty acids (> C22:0) were also found increased in all classes of lipids in LPS-treated peroxisomes. Gadolinium chloride (GAD) mediated inactivation of Kupffer cells (KC) normalized cholesterol/PL ratio in LPS-treated peroxisomes. Collectively, the results indicate that the peroxisome metabolism of lipids and fatty acids is specifically altered in endotoxin-treated rat liver and at least part of the alterations may be mediated by factors released by KC.

Animals↗
PubMed1999

Photostimulable storage phosphor image acquisition: evaluation of three commercially available state-of-the-art systems.

Photostimulable storage phosphor (PSP) image acquisition systems have been available for several years. The technology has had the opportunity to mature; however, there has not been an independent comparison of recently marketed commercial systems. For this study, three computed radiography (CR) systems using PSP technology (Kodak CR System 400 with autoloader [Eastman Kodak, Rochester, NY], Fuji FCR AC-3CS [Fuji Medical Systems, Stamford, CT], and Agfa ADC Compact [Bayer Corp, Ridgefield Park, NJ]) were connected to an IBM RadWorks diagnostic radiology workstation (IBM Corp, White Plains, NY) and evaluated for conformance to their performance specifications using guidance provided in the most recent draft acceptance testing protocol from Task Group No. 10, American Association of Physicists in Medicine. In addition, the physical requirements (e.g., space and power) and connectivity to another manufacturer's diagnostic workstation were examined. X-ray technologist comfort with each PSP imaging system and an assessment by our supporting biomedical equipment maintenance activity of their ability to service each PSP imaging system were also considered.

Artifacts↗
PubMed1999

Cord blood banking: volume reduction of cord blood units using a semi-automated closed system.

Clinical evidence indicates that placental/umbilical cord blood (CB) is an alternative source of haematopoietic stem cells for bone marrow reconstitution. To establish a CB bank large panels of frozen, HLA-typed CB units need to be stored. Cryopreserved, unprocessed CB units require vast storage space. This study describes a method, using the Optipress II Automated Blood Component Extractor (Opti II) from Baxter Healthcare Corporation, to reduce the volume of the CB collection, preserving the quantity and quality of the progenitor cells, in a closed system. The CB collection was transferred to a triple bag system, centrifuged to produce a buffy coat layer and processed using a standard Opti II protocol to separate the whole blood into three components: plasma, buffy coat and buffy coat-depleted red cell concentrate. The buffy coat volume was standardised to 25 ml; mean reduced volume of 24.5 ml (s.d. 1.5 ml) with 53% red cell depletion. Good recovery of cells was observed: 92%, 98%, 96% and 106% recovery of nucleated, mononuclear, CD34+ and total colony-forming cells, respectively. Using this method for processing CB units reduces storage requirement by two-thirds but preserves the quantity and quality of the progenitor cells.

Blood Banks↗
PubMed1999

Cord blood banking in London: the first 1000 collections.

The London Cord Blood Bank was established with the aim of collecting, processing and storing 10000 unrelated stem cell donations for the significant number of children in the UK requiring transplantation, for whom a matched unrelated bone marrow donor cannot be found. Collection is performed at two hospitals by dedicated cord blood bank staff after delivery of the placenta. Mothers are interviewed regarding medical, ethnic and behavioural history by nurse counsellors and sign a detailed consent form. Donations are returned to the bank for processing. Volume reduction is undertaken by a simple, closed, semi-automated blood processing system, with excellent recovery of progenitor cells. Units are cryopreserved and stored in the vapour phase of liquid nitrogen. Blood samples from mothers and cord blood donations are tested for the UK mandatory red cell and microbiology markers for blood donors. Donations are typed for HLA-A, B and DR at medium resolution (antigen split) level using sequence-specific oligonucleotide probing and sequence-specific priming techniques. The selection of collection hospitals on the basis of ethnic mix has proven effective, with 41.5% of donations derived from non-European caucasoid donors. Bacterial contamination of collections has been dramatically reduced by implementation of improved umbilical cord decontamination protocols.

Blood Banks↗
PubMed1998

Comparison of various sample handling and analytical procedures for the monitoring of pesticides and metabolites in ground waters.

Various sample handling techniques such as liquid-liquid extraction off-line and on-line, solid-phase extraction followed by either gas chromatography (GC) with electron-capture, flame photometric or mass spectrometric detection, or liquid chromatography (LC) with diode array detection were applied in the determination of a selected group of insecticides and fungicides in ground water samples at sub-micrograms/l levels. An evaluation of the advantages and drawbacks in the application of the proposed methodologies for water monitoring studies is discussed. For the selected group of pesticides studied, off-line C18 or polymeric cartridges followed by GC-MS using an ion trap analyzer have been revealed as the more powerful technique. But very polar compounds such as methamidophos or acephate have not been recovered with this procedure. On the contrary, on-line C18 LC-DAD offered a few drawbacks for the trace determination of a large group of pesticides as a consequence of many important interferences in the chromatographic traces. Other techniques evaluated were LC-MS and GC-MS using a quadrupole analyzer, which offered complementary information and were useful for a limited range of analytes. An interlaboratory study was performed using all the methodologies evaluated in this work and the results obtained showed a good agreement between all the applied techniques. The various methodologies were for a ground water pilot survey study in Almeria (Spain). Endosulfan was the most ubiquitous pesticide detected in this area.

Chromatography, Gas↗
PubMed1998

Intracellular cytokine profile of cord and adult blood lymphocytes.

Umbilical cord blood (CB) transplantation is thought to be associated with a reduced risk of severe graft-versus-host-disease (GVHD) compared with bone marrow transplantation (BMT). The cytokine cascade is known to be important in the pathogenesis of GVHD; however, previous studies investigating the cytokine secretion pattern of CB cells have been contradictory because of variations in experimental techniques. In this study, the cytokine profile of cord and adult blood lymphocytes and lymphocyte subsets has been assessed at the single-cell level by flow cytometry, using CD4/CD8 and CD45RA/CD45RO markers. Cord and adult blood mononuclear cells were stimulated with phorbol 12-myristate 13-acetate (PMA) and ionomycin in the presence of monensin. After 4 to 24 hours of incubation, interleukin-2 (IL-2), IL-4, interferon-gamma (IFN-gamma), and tumor necrosis factor-alpha (TNF-alpha) production was measured by three-color flow cytometry. The results show that cord blood lymphocytes (CBL) produce less IL-2, IL-4, IFN-gamma, and TNF-alpha than adult peripheral blood lymphocytes (ABL). Further subset analysis showed that in CBL the majority of cytokine producing cells were CD4(+)CD45RA+, whereas in ABL the cytokine-producing cells were both CD4(+)CD45RO+ and CD8(+)CD45RO+. These results suggest that the reduced incidence of GVHD in CB transplantation may partly due to the altered cytokine profile seen in CBL.

Adult↗