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Biomedical subjects

A Bakker

Publications and source records attributed to A Bakker.

At least 109 records · Page 6Linked to original sources
PubMed1995

Peptides which bind to E-selectin and block neutrophil adhesion.

E-selectin is an inducible cell adhesion molecule which mediates rolling of neutrophils on the endothelium, an early event in the development of an inflammatory response. Inhibition of selectin-mediated rolling is a possible means for controlling inflammation-induced diseases, and several classes of compounds have been tested for this use. We describe here the use of recombinant peptide library screening for identification and optimization of novel ligands which bind to E-selectin. Several of these peptides bind with Kd values in the low nanomolar range and block E-selectin-mediated adhesion of neutrophils in static and flow-cell assays. Administration of the peptide to mice undergoing an acute inflammatory response reduced the extent of neutrophil transmigration to the site of inflammation, demonstrating the utility of this compound as a potential therapeutic. The identification of a peptide ligand for E-selectin suggests that the complete natural ligand for this adhesion molecule may include protein as well as carbohydrate moieties.

Amino Acid Sequence↗
PubMed1995

Reduction of EGP-2-positive pulmonary metastases by bispecific-antibody-redirected T cells in an immunocompetent rat model.

Effectiveness of bispecific-monoclonal-antibody (BsMAb)-mediated cellular anti-tumour activity was evaluated in vitro and in vivo in relation to the additional need for T-cell activation in a new immunocompetent rat tumour model. L37 tumour cells, derived from a squamous-cell carcinoma of the lung of Wag/Rij rats, were transfected with the cDNA coding for the human 38-kDa transmembrane pan-carcinoma-associated antigen EGP-2. Intravenous inoculation of EGP-2-positive L37 cells resulted in a rapid outgrowth of EGP-2-positive tumour nodules in the lungs. A BsMAb BIS-19, recognizing EGP-2 on the transfected tumour cells and the T-cell receptor of the rat, was made and allowed specific lysis of EGP-2-transfected L37 tumour cells by activated rat T lymphocytes in vitro. In vivo T-cell activation, assessed by up-regulation of IL-2-receptor expression, could be induced by daily injection of rat rIL-2. Intravenous treatment of tumour-bearing EGP-2-positive L37 tumour with BIS-19 together with rat rIL-2 resulted in almost complete disappearance of established tumour. In contrast, animals treated with BIS-19 alone, IL-2 alone or a combination of anti-EGP-2, anti-TcR and IL-2 showed much less or no tumour reduction. These results show effectiveness of systemic treatment with BsMAbs to induce anti-tumour activity in established tumours. Immune activation prior to or during treatment with BsMAbs, as achieved with IL-2, appears to be a prerequisite for successful treatment.

Animals↗
PubMed1995

A rapid method to estimate the incidence rate and prevalence of insulin-dependent diabetes mellitus in children 0-19 years of age.

OBJECTIVE: To trace new cases of insulin-dependent diabetes mellitus (IDDM) on an ongoing basis and to estimate the incidence rate and prevalence of IDDM in children 0-19 years of age. RESEARCH DESIGN AND METHODS: The estimation of the prevalence and incidence rate of IDDM was based on, respectively, the prevalence and the rate of new users of insulin. The data were obtained from pharmacy, patient-based, drug dispensing histories in a well-defined population encompassing 257,113 individuals in the Netherlands. RESULTS: The IDDM incidence rate was estimated at 11.5 (CI95 6.6-17.8) per 100,000 person years in 1989-1990 in children 0-19 years of age. The prevalence was estimated at 11.0 (CI95 8.6-13.4) per 10,000 children 0-19 years of age. DISCUSSION: The incidence rate is comparable to that found in a large, national survey among all paediatricians and internists in the Netherlands. The method offers ongoing monitoring of the incidence and prevalence of IDDM in children, 0-19 years of age, against low costs. The method is suitable for rapid and cost-efficient recruitment of cohorts of incident IDDM patients, which fosters research to identify and quantify the attribution of different types of aetiologic and prognostic factors of IDDM.

Adolescent↗
PubMed1995

Information on drug use in the elderly: a comparison of pharmacy, general-practitioner and patient data.

Management of pharmacotherapy by the pharmacist and the general practitioner can be a difficult task in elderly patients in whom there is a high concomitant, long-term drug use. Adequate information on drug use is essential in managing pharmacotherapy as well as in an accurate assessment of drug exposure in pharmacoepidemiologic studies. In this study data from computerized pharmacy records, general-practitioner registries and home interviews with 100 elderly patients were compared. Pharmacy records contained 80% of all the prescriptions found at the home interviews, while in general-practitioner data 40% could be traced. Use of drugs dispensed long ago reduced the validity of pharmacy and general-practitioner data. Data on analgesics (70% was found) and respiratory drugs (68%) were less traceable compared to cardiovascular (83%) and psychotropic drugs (81%). Automated pharmacy records are an important source of longitudinal data on drug use and will improve the assessment of drug exposure in pharmacoepidemiologic studies and optimize pharmaceutical care.

Aged↗
PubMed1995

Lidocaine does not prevent the calcium paradox in rat hearts: a laser microprobe mass analysis (LAMMA) study.

The calcium paradox stands for the cell damage that occurs when isolated hearts are perfused with a Ca(2+)-free solution followed by perfusion with a Ca(2+)-containing solution. Although it is generally accepted that a massive Ca2+ influx during the Ca(2+)-repletion phase is responsible for the cell damage, there is no consensus about what makes the heart susceptible to the calcium paradox during the Ca(2+)-depletion phase. It has been suggested that the extent of the calcium paradox is primarily determined by accumulation of Na+ during Ca2+ depletion and a subsequent accumulation of Ca2+ via reverse Na(+)-Ca2+ exchange during Ca2+ repletion. According to another theory, weakening of intercalated disc junctions during Ca2+ depletion and contracture-mediated disruption of the cell membrane during Ca2+ repletion are responsible for the calcium paradox. In the present study we further investigated the possible role of Na+ in the development of the calcium paradox. During Ca2+ depletion, lidocaine was used to inhibit Na+ entry through the Na+ channels. Isolated rat hearts were perfused with Krebs Henseleit buffer (KH) containing 1.4 mM Ca2+ for 15 min, followed by 10 min of Ca(2+)-free perfusion and 10 min of reperfusion with Ca2+. In the treated group 0.1 mM lidocaine was present throughout the experiment. At the end of each experiment, Ca2+ cytochemistry was performed and the intracellular Ca2+ content was analyzed by laser microprobe mass analysis (LAMMA). The results show that during Ca2+ depletion, the intracellular Ca2+ content did not change significantly. Ca2+ repletion, however, gave rise to a full calcium paradox irrespective of the presence of lidocaine: massive cell damage and Ca2+ accumulation in the mitochondria. The results provide further evidence that intracellular Na+ accumulation during Ca2+ depletion is not involved in the occurrence of the calcium paradox.

Animals↗
PubMed1995

Epstein-Barr virus infection abrogates the stimulatory capacity of B cells to a major histocompatibility complex class-II-restricted proliferative T-cell clone.

After BMT, donor T cells are activated which can display GvHD as well as GvL activities. In order to study this GvL-specific T-cell response in vitro, proliferative T-cell clones from post-BMT PBMCs were generated by stimulation with a patient's leukemic cells. One CD4+ T-cell clone (designated M-33) displayed strong proliferative activity against the patient's leukemic cells but not against the patient's EBV-LCLs. The induction of proliferation, however, appeared not to be leukemia specific. Detailed analysis of the reactivity patterns revealed that T-cell clone M-33 recognizes an as yet unknown nonpolymorphic determinant in the context of self HLA-DRw52, presented by all but one type of APC. T-cell clone M-33 proliferated upon stimulation by PB-MCs, freshly isolated B cells, monocytes, dendritic cells, leukemic B cells, and nonleukemic B-cell blasts; solely in vitro EBV-transformed B cells and in vivo EBV-infected B cells failed to induce proliferation of T-cell clone M-33. Neither surface expression of MHC or accessory molecules on the EBV cells nor suppression caused by the EBV-infected cells could explain their failure to stimulate T-cell clone M-33. We therefore hypothesize that the absence of the stimulatory capacity once the B cells are virally infected could be the result of competition for MHC class II binding of the Epstein-Barr viral peptides, thus affecting the postulated DRw52-restricted peptide for recognition by T-cell clone M-33.

Antigen Presentation↗
PubMed1995

Analysis of dendritic-cell-induced primary T-cell responses between HLA genotypically identical individuals.

DCs are known for their superior antigen-processing and antigen-presenting capacities. They are capable of processing intact protein: either endocytosed exogenous proteins or newly synthesized endogenous viral and bacterial proteins. They are potent inducers of primary T-cell immune responses such as in allogeneic MLRs. It is also known that DCs can provide a strong stimulus for autologous T-cell proliferation. So far no information exists on the capacity of DCs to induce primary mH antigen-specific T-cell responses. Therefore, we investigated whether human DCs, isolated from peripheral blood, were able to generate specific T-cell responses between MLR-negative HLA genotypically identical individuals in vitro. To this end, unfractionated cells, monocytes, and B cells were assayed in parallel with DCs to compare their capacity to activate unprimed T cells in a primary MLR. DCs indeed induced significant proliferation between HLA genotypically identical siblings, whereas the other APCs were unable to evoke any T-cell response at all. As expected, besides these allogeneic T-cell responses, autologous T-cell responses were initiated by the DCs as well. Nonetheless, despite further detailed analyses of the responding T cells, neither proliferative nor cytotoxic mH antigen-specific reactivities could yet be detected using the stimulation protocols described herein.

Cell Separation↗
PubMed1995

Angiotensin converting enzyme inhibitor associated cough: a population-based case-control study.

The objectives of this study were to determine the risk for coughing as an adverse reaction to angiotensin converting enzyme (ACE) inhibitors under everyday circumstances in a large population and to study whether this adverse effect is more common in women. A population-based case-control study was used. The study was set in the practices of 161 Dutch general practitioners (GPs), in which all consultations, morbidity, mortality, medical interventions and prescriptions were registered during 4 consecutive 3-month periods in 4 consecutive groups of 40-41 GPs. The subjects were 2436 patients with incident coughing and up to 3 controls per case were obtained (total group: 7348 controls), matched for GP and a contemporary consultation in the same 3 months. All cases and controls were 20 years or older and had no notification of respiratory infections, influenza, tuberculosis, asthma, chronic bronchitis, emphysema, congestive heart failure, sinusitis, laryngitis, haemoptysis or respiratory neoplasms during the 3-month period. The results showed that cases were 3.6 times as likely as controls to have been exposed to ACE inhibitors (95% CI: 2.4-5.5) but after adjustment for potential confounders the odds ratio was 2.5 (95% CI: 1.6-3.9). The crude odds ratio for males was 2.7 (95% CI: 1.4-5.1) and for females 4.2 (95% CI: 2.4-7.5). The adjusted odds ratio for males was 1.8 (95% CI: 0.9-3.5) and for females 2.7 (95% CI: 1.5-4.8).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1995

Polypyrimidine tract-binding protein and heterogeneous nuclear ribonucleoprotein A1 bind to human T-cell leukemia virus type 2 RNA regulatory elements.

Efficient expression of human T-cell leukemia virus (HTLV) and human immunodeficiency virus structural proteins requires Rx and Rev proteins, respectively. Decreased expression of Gag and Env appears to be due, in part, to intragenic RNA sequences, termed cis-acting repressive sequences (CRS), and may be mediated by binding of specific cellular factors. We demonstrated previously that two cellular proteins, p60CRS and p40CRS, interact with HTLV type 2.5' long terminal repeat CRS RNA and that the interaction of both proteins with CRS RNA correlates with function (A. C. Black, C. T. Ruland, J. Luo, A. Bakker, J. K. Fraser, and J. D. Rosenblatt, Virology 200:29-41, 1994). By radioimmunoprecipitation of HeLa nuclear proteins UV cross-linked to CRS RNAs with murine monoclonal antibodies, we now show that p40CRS is heterogeneous nuclear ribonucleoprotein (hnRNP) A1 and p60CRS is polypyrimidine tract-binding protein or hnRNP I. These immunoprecipitation results were confirmed by an immunobinding assay with hnRNP I and hnRNP AI antibodies and by cross-competition electrophoretic mobility shift experiments. In addition, we mapped a putative hnRNP A1 binding site in U5 RNA and demonstrated that p40CRS (hnRNP A1) binding to that site correlates with CRS function. Since both hnRNP I and hnRNP A1 have been shown to influence splicing and potentially other steps in RNA processing, the binding of both hnRNP I and hnRNP A1 to HTLV RNA regulatory elements may alter retrovirus RNA processing and may be involved in regulation by Rex.

Base Sequence↗
PubMed1995

The effect of ischemia and reperfusion on mitochondrial contact sites in isolated rat hearts.

Contact sites may be described as energy channels between the mitochondria and the cytosol, created by fusion of the inner and the outer mitochondrial membranes, and their number depends highly on the energy state of the cell. The aim of the present study was to examine the early changes of ischemia and reperfusion on the number of mitochondrial contact sites. Therefore isolated rat hearts were subjected to short periods of ischemia followed by reperfusion. The left ventricular pressure (LVP), the contractility (dP/dtmax) and the heart rate were measured. The number of contact sites was morphometrically evaluated. As the flow was stopped, LVP, dP/dtmax and HR declined rapidly and became undetectable after 2 min of ischemia. The number of contact sites fell to a minimum after 10 min of ischemia after an initial increase (1 min of ischemia). A 15 min ischemic period resulted in a high number of contact sites which decreased again after 20 min of ischemia. Reperfusion after 2 min of ischemia caused an immediate functional recovery and a high presence of contact sites. After 15 min of reperfusion, all values returned to control values. Reperfusion after 10 min of ischemia resulted in a slow recovery of the number of contact sites and after 15 min of ischemia the number of contact sites remained low upon reperfusion. We may conclude that mitochondria lose the ability to form contact sites after more than 15 min of ischemia and this might be a first indication of irreversible injury.

Animals↗
PubMed1994

The effect of calcium on mitochondrial contact sites: a study on isolated rat hearts.

Mitochondrial contact sites are dynamic structures created by fusion of the inner and outer mitochondrial membranes. Stimulation of the metabolism results in an increase of the number of contact sites. Functionally, it is shown that mitochondrial creatine kinase (Mi-CK) is active in contact sites and therefore, Mi-CK cytochemistry was performed (using a tetrazolium salt) to improve the visibility of the contact sites. As calcium is involved as an intracellular messenger of hormonal stimulation, the effect of increasing extracellular calcium concentrations on the number of contact sites was investigated. Therefore, isolated rat hearts were perfused with Krebs-Henseleit buffers differing in their calcium content. During the perfusions the heart function was evaluated and at the end of each experiment, the hearts were processed for Mi CK cytochemistry and the number of contact sites was expressed as the ratio of surface densities contact sites to mitochondrial membranes (Ss). At 2.2 mM calcium perfusion, the physiological parameters and the Ss reached a maximum. This was in contrast to the 0.6 and the 3.6 mM of calcium perfusions whereby both the physiological values and the Ss were decreased. Treatment with noradrenaline in vivo, as was done in previous studies or perfusion with 2.2 mM of calcium ends up with similar values for Ss. From these results, it could be suggested that there might be a link between calcium, heart function and the formation of Mi CK active contact sites.

Animals↗
PubMed1994

Covalent dimerization of vascular permeability factor/vascular endothelial growth factor is essential for its biological activity. Evidence from Cys to Ser mutations.

Vascular permeability factor, or vascular endothelial growth factor (VPF/VEGF) is an important factor in the regulation of vascular growth and vascular permeability. VPF is a secreted, dimeric protein and has 8 cysteine residues conserved with platelet-derived growth factor (PDGF). To study the role of some of these cysteine residues in maintaining the structure and function of VPF, we replaced the codons for the second, third, fourth, and fifth cysteine by serine codons, and expressed the mutant proteins in a mammalian expression system. Cysteine residues 2 and 4 in VPF were found to be directly involved in anti-parallel interchain disulfide bonds, as in PDGF. VPF mutants lacking one of these cysteins were severely impaired in their S-linked dimerization, while upon coexpression of both mutants the ability to form dimers was restored. The VPF mutants lacking cysteine residue 2 or 4 also competed poorly for receptor binding of labeled VPF and had low biological activity, but these defects were also complemented by coexpressing the two mutants, indicating that for efficient receptor binding and activation VPF needs to be a covalent dimer, unlike PDGF-BB. Furthermore, cysteine residue 5 was found to be essential for VPF dimerization and activity, while the mutant lacking cysteine residue 3 was only mildly affected in its ability to dimerize and had partial biological activity.

Binding, Competitive↗
PubMed1994

Scenario analysis of the future of medicines.

Planning future policy for medicines poses difficult problems. The main players in the drug business have their own views as to how the world around them functions and how the future of medicines should be shaped. In this paper we show how a scenario analysis can provide a powerful teaching device to readjust peoples' preconceptions. Scenarios are plausible, not probable or preferable, portraits of alternative futures. A series of four of alternative scenarios were constructed: "sobriety in sufficiency," "risk avoidance," "technology on demand," and "free market unfettered." Each scenario was drawn as a narrative, documented quantitatively wherever possible, that described the world as it might be if particular trends were to dominate development. The medical community and health policy markers may use scenarios to take a long term view in order to be prepared adequately for the future.

Drug Industry↗
PubMed1994

Characterization of two classes of ribonucleoprotein complexes possibly involved in RNA editing from Leishmania tarentolae mitochondria.

The molecular mechanism of RNA editing in trypanosomatid mitochondria is an unsolved problem. We show that two classes of ribonucleoprotein complexes exist in a mitochondrial extract from Leishmania tarentolae and appear to be involved in RNA editing. The 'G' class of RNP complexes consists of 170-300 A particles which contain guide RNAs and proteins, show little terminal uridylyl transferase (TUTase) activity and exhibit an in vitro RNA editing-like activity. The 'T' class consists of approximately six RNP complexes, the endogenous RNA of which can be self-labeled with [alpha-32P]UTP. The most abundant T complex, T-IV, is visualized by electron microscopy as 80-140 A particles. This complex exhibits TUTase activity in the native gel and contains guide RNAs. Both G and T complexes are possibly involved with RNA editing in vivo. These results are a starting point for the analysis of the biochemistry of RNA editing.

Animals↗
PubMed1994

Ultrastructural localisation of carnitine acetyltransferase activity in mitochondria of rat myocardium.

The acetyl CoA/CoA ratio is an important regulating factor of beta-oxidation in mitochondria and hence of energy production in the myocardium. Carnitine acetyltransferase provides one of the control mechanisms for this ratio during changing energy demand in the heart muscle, possibly by buffering the CoA and carnitine concentration for sustained beta-oxidation. In search for a possible correlation between the activity of this enzyme and ultrastructural changes in heart mitochondria, carnitine acetyltransferase was cytochemically localised in rat myocardium, brought into different metabolic states. In this work we confirm previous observations, namely the formation of contact sites between inner and outer mitochondrial membranes upon catecholaminergic stimulation of the myocardium. It is further shown that this contact site formation might be a prerequisite for carnitine acetyltransferase to demonstrate enzymatic activity and hence control of beta-oxidation in myocardial mitochondria.

Animals↗
PubMed1994

Mitochondrial matrix granules: their behavior during changing metabolic situations and their relationship to contact sites between inner and outer mitochondrial membranes.

Since their discovery in the early fifties mitochondrial granules have been the subject of many researches. Some twenty years ago two hypotheses on their function were introduced. Peachey thought that the granules were a sink of cations and that they would eventually regulate the concentrations of these ions. Alternatively, Barnard thought that the granules were precursors of the mitochondrial inner membrane. There are only a few data on organic constituents of the granules. Phospholipids (e.g., cardiolipin) glycoprotein or lipids, calcium precipitable lipoprotein, cytochrome c oxidase seem to be present in the granules. There has been much debate on whether calcium is present or not. Reports are mostly based on X-ray microanalysis, the result of which depends on preparation techniques. In heart muscle in stimulating situations the NMG (native matrix granules) move towards the inner membrane and are incorporated in it. They appear to create contact sites between inner and outer mitochondrial membranes in which enzymes can function efficiently. It is hypothetized that the system, NMG-contact sites, forms the structural basis of a regulatory mechanism, by which cells can cope with a high and sudden energy demand.

Animals↗