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Biomedical subjects

A Siegbahn

Publications and source records attributed to A Siegbahn.

At least 73 records · Page 4Linked to original sources
PubMed1995

Thrombin generation during cardiopulmonary bypass using heparin-coated or standard circuits.

For quantitative comparison of thrombin generation during cardiopulmonary bypass (CPB) with heparin-coated vs conventional CPB circuits, thrombin-antithrombin III complex (TAT) and prothrombin fragment 1 + 2 (F1 + 2) were analyzed in 20 patients undergoing combined heart valve surgery and coronary artery bypass grafting (CABG), in ten cases with heparin-coated circuits (COMB-HC) and in ten with standard circuits (COMB-C). Extensive thrombin generation was found in both groups, with maximal TAT and F1 + 2 levels at the end of CPB. Of 15 operations with only CABG, seven were performed with heparin-coated circuits and heparin dose 40% of normal (CABG-HC), and eight with standard circuits and normal heparin doses (CABG-C). TAT was maximal at the end of CPB and F1 + 2 peaked 3 hours after protamine injection. At the end of CPB both levels were significantly higher in the CABG-HC than in the CABG-C group, though thrombin generation was less than in the COMB groups. The abundant thrombin generation during CPB thus was much more pronounced during complex operations. Use of heparin-coated circuits did not reduce thrombin generation, which was increased by 60% reduction of the systemic heparin dose. The clinical implications are still unknown, as no complications were observed.

Anticoagulants↗
PubMed1994

Different signal transduction properties of KDR and Flt1, two receptors for vascular endothelial growth factor.

Vascular endothelial growth factor (VEGF) is a homodimeric peptide growth factor which binds to two structurally related tyrosine kinase receptors denoted Flt1 and KDR. In order to compare the signal transduction via these two receptors, the human Flt1 and KDR proteins were stably expressed in porcine aortic endothelial cells. Binding analyses using 125I-VEGF revealed Kd values of 16 pM for Flt1 and 760 pM for KDR. Cultured human umbilical vein endothelial (HUVE) cells were found to express two distinct populations of binding sites with affinities similar to those for Flt1 and KDR, respectively. The KDR expressing cells showed striking changes in cell morphology, actin reorganization and membrane ruffling, chemotaxis and mitogenicity upon VEGF stimulation, whereas Flt1 expressing cells lacked such responses. KDR was found to undergo ligand-induced autophosphorylation in intact cells, and both Flt1 and KDR were phosphorylated in vitro in response to VEGF, however, KDR much more efficiently than Flt1. Neither the receptor-associated activity of phosphatidylinositol 3'-kinase nor tyrosine phosphorylation of phospholipase C-gamma were affected by stimulation of Flt1 or KDR expressing cells, and phosphorylation of GTPase activating protein was only slightly increased. Members of the Src family such as Fyn and Yes showed an increased level of phosphorylation upon VEGF stimulation of cells expressing Flt1 but not in cells expressing KDR. The maximal responses in KDR expressing porcine aortic endothelial cells were obtained at higher VEGF concentrations as compared to HUVE cells, i.e. in the presence of Flt1. This difference could possibly be explained by the formation of heterodimeric complexes between KDR and Flt1, or other molecules, in HUVE cells.

Actins↗
PubMed1994

Stem cell factor is a chemotactic factor for human mast cells.

The mast cell is one of the major effector cells in inflammatory reactions and can be found in most tissues throughout the body. During inflammation, an increase in the number of mast cells can be seen, e.g., in the intraepithelial cell layer after a provoked allergic reaction. Such accumulation probably requires directed migration of mature mast cells or their precursors. To study the migration of human mast cells we used as a model the human mast cell line, HMC-1, and stem cell factor-dependent (also referred to as mast cell growth factor or Kit ligand) cord blood-derived mast cells. The results show that stem cell factor is a potent chemotactic factor for human mast cells in vitro. The chemotactic response to SCF was found to be dose dependent, reaching a maximum at 50 ng/ml. The activity of SCF could be blocked by anti-SCF Abs. We also tested the effect of different intercrines, i.e., IL-8, MIP-1 alpha, MIP-1 beta, RANTES, and MCAF (also referred to as monocyte chemotactic protein 1), on human mast cell migration. Only RANTES was chemotactic for in vitro-developed mast cells. None of the tested intercrines induced migration of HMC-1 cells. For migration, the mast cells were dependent on binding to an extracellular matrix protein. Thus, coating of the filters with fibronectin was required, whereas collagen or laminin did not promote migration. Adhesion of HMC-1 cells to fibronectin could also be shown in an adhesion assay. In addition, expression of receptors for fibronectin could be detected on the surface of the mast cells. These results show that SCF is not only a growth and differentiation factor for human mast cells in vitro but also a potent chemoattractant for such cells.

Cell Adhesion Molecules↗
PubMed1994

A unique autophosphorylation site in the platelet-derived growth factor alpha receptor from a heterodimeric receptor complex.

The platelet-derived growth factor (PDGF) alpha and beta receptors undergo dimerization as a consequence of ligand binding. Depending on the PDGF isoform (PDGF-AA, -AB or -BB), homodimers or heterodimers of receptors are formed. In this study, we have used transfected porcine aortic endothelial cells, coexpressing cDNAs for the alpha receptor and the beta receptor at comparable levels, to investigate the properties of the alpha beta-heterodimeric receptor complex. PDGF-AB, which mainly induced alpha beta-heterodimeric complexes, was the most efficient isoform for stimulating mitogenicity. Actin reorganization, in the form of circular membrane ruffling and chemotaxis, was induced by PDGF-AB and PDGF-BB, but not by PDGF-AA, thus indicating that the beta receptor in the homodimeric or heterodimeric configuration was required for induction of motility responses. The molecular basis for the apparent receptor dimer-specific properties was examined by analyzing receptor autophosphorylation and phosphorylation of substrates. The alpha receptor was found to be phosphorylated at an additional tyrosine residue, Tyr754, in the heterodimeric complex as compared to the alpha alpha receptor homodimer. Phosphorylation of this tyrosine residue could permit the binding of a specific signal-tranducing protein. A candidate is a 134,000-M(r) protein, which was shown to associate preferentially with the alpha receptor in the heterodimeric receptor complex. It is possible that phosphorylated Tyr754 in the alpha receptor mediates activation of specific signal-tranducing molecules like the 134,000-M(r) substrate, and thereby initiates signal-tranduction pathways from the alpha beta receptor heterodimer, which are distinct from those initiated via homodimeric receptor complexes.

Amino Acid Sequence↗
PubMed1994

Hemostasis profile and lipid metabolism with long-interval use of a desogestrel-containing oral contraceptive.

Thirty healthy women, aged 18 to 37, were randomly allocated to treatment with a desogestrel-containing oral contraceptive, with 20 women using a nine-week on, one-week off regimen, and 10 women using the traditional regimen. At 0, 3 and 12 months, blood samples were drawn for liver proteins, lipoproteins and hemostatic variables. No significant changes were observed between the two regimens. Sex hormone binding globulin (SHBG) and corticosteroid binding globulin (CBG, transcortin) were increased two- to four-fold, as a measure of estrogenicity. Minimal changes occurred within the lipoprotein cholesterol fractions, whereas there were some increases within the lipoprotein triglyceride fractions. Among the hemostatic variables, there were significant increases of fibrinogen, factor VII and thrombin/antithrombin III (TAT) complex. The coagulation inhibitors, antithrombin III, protein C and protein S, were essentially unchanged. A decrease of both tissue plasminogen activator antigen (t-PA) and tissue plasminogen activator inhibitor activity (PAI activity) of the fibrinolytic system was observed. A nine-week regimen does not seem to alter lipid metabolism and coagulation more than a three-week regimen.

Adolescent↗
PubMed1994

Malondialdehyde concentration in plasma is inversely correlated to the proportion of linoleic acid in serum lipoprotein lipids.

It has been suggested that the susceptibility of low density lipoprotein (LDL) to oxidative stress depends on the balance between its contents of polyunsaturated fatty acids and antioxidants. In a healthy reference population (n = 103), the plasma concentration of malondialdehyde (MDA) (mean 0.86, range 0.50-1.27 mumol/l) was positively correlated to the serum concentrations of LDL cholesterol (r = 0.31, P = 0.001), very low density lipoprotein triglycerides (r = 0.25, P = 0.009) and apolipoprotein B (r = 0.23, P = 0.03), and negatively correlated to lipid corrected alpha tocopherol in serum (r = -0.22, P = 0.02) and lipoprotein(a) (Lp(a)) (r = -0.26, P = 0.01). Plasma MDA was negatively correlated to the content of linoleic acid in the serum lipoprotein phospholipids (r = -0.35, P = 0.0008). In a stepwise regression analysis 12% of the variation in plasma MDA was explained by variations in the content of linoleic acid and 27% after addition of Lp(a) and abdominal sagittal diameter. The significant negative relation between plasma MDA and the amount of linoleic acid in the lipoprotein lipids indicates that other factors, e.g. the availability of anti-oxidants and the lipoprotein metabolism, may be of greater importance for intravascular lipid peroxidation than the proportion of polyunsaturated fatty acids in the lipoprotein lipids.

Adult↗
PubMed1994

Epstein-Barr virus (EBV) can immortalize B-cll cells activated by cytokines.

B-type of chronic lymphocytic leukemia (B-CLL) cells are inert to the potent transforming action of Epstein-Barr virus (EBV). The mitogenic action of Staphylococcus aureus Cowan I (SAC), MP6-thioredoxin, and interleukin 2 (IL-2), agents previously shown to induce proliferation in normal as well as in B-CLL cells, lifted this block, and EBV-positive cell lines could be established. It was not possible to establish cell lines of leukemic origin from cultures that were incubated with EBV alone or cytokine mix alone. CLL-cells infected with EBV only, expressed the viral nuclear antigen complex (EBNA), but not the viral latent membrane protein (LMP). They were not activated as measured by cell size and 3H-thymidine incorporation. In contrast, cells incubated with EBV and cytokine mix expressed both EBNA and LMP in parallel with enlargement and increased 3H-thymidine incorporation. These results emphasize that LMP expression is a prerequisite for growth transformation and immortalization and that cytokine activation signals are required for its expression in B-CLLs. Cells incubated with SAC/MP6-thioredoxin/IL-2 did not express any of the viral antigens, but were activated with regard to the mentioned parameters. Nine cell lines were established from six patients. From each of the three patients, we obtained 'twin'-pair lines: one corresponding to the malignant cell and the other to a normal B-lymphoblastoid cell. Thus, malignant and normal B-cell counterparts, from the very same donor, are at hand for comparative studies. The cell lines have been carried out for more than 12 months in culture. We conclude that B-CLL that are refractory to EBV-transformation can be rendered susceptible through in vitro cytokine activation.

Antigens, CD↗
PubMed1994

Membrane ruffling and chemotaxis transduced by the PDGF beta-receptor require the binding site for phosphatidylinositol 3' kinase.

Activation of the platelet-derived growth factor (PDGF) beta-receptor results in motility responses in the forms of membrane ruffling and chemotaxis. Porcine aortic endothelial cells expressing the PDGF beta-receptor or a chimeric fibroblast growth factor (FGF) receptor, in which the endogenous kinase insert was replaced with the corresponding region from the PDGF beta-receptor, migrated efficiently towards a concentration gradient of PDGF-BB and bFGF, respectively, and exhibited both pronounced edge ruffling and circular membrane ruffling in response to ligand-stimulation. The wildtype FGF receptor-1 showed weak or no response in these assays. Further analyses were conducted on mutant receptors, in which tyrosine residues that can serve as autophosphorylation sites and thereby mediate interactions with specific signal transduction molecules, were changed to phenylalanine residues. Each one of the analysed mutants were mitogenically active, however, a mutant in which Tyr740 and Tyr751 were replaced failed to mediate ruffling and chemotaxis. These two residues are implicated in the binding of phosphatidylinositol 3' kinase. The notion that this enzyme is involved in PDGF beta-receptor-induced cell motility is furthermore supported by the finding that another mutant, in which Met743 and Met754 were replaced, and which failed to interact with phosphatidylinositol 3' kinase, was also unable to mediate motility responses.

Animals↗
PubMed1993

Increased Kit/SCF receptor induced mitogenicity but abolished cell motility after inhibition of protein kinase C.

The product of the c-kit proto-oncogene, denoted Kit/SCF-R, encodes a tyrosine kinase receptor for stem cell factor (SCF). Kit/SCF-R induces proliferation, differentiation or migration of cells within the hematopoietic, gametogenic and melanogenic lineages at different developmental stages. We report here that protein kinase C (PKC) mediates phosphorylation of Kit/SCF-R on serine residues in response to SCF or PMA in intact cells. The phosphorylation inhibits SCF-induced tyrosine autophosphorylation of Kit/SCF-R. In vitro studies showed that PKC phosphorylated the Kit/SCF-R directly on serine residues and inhibited autophosphorylation of Kit/SCF-R, as well as its kinase activity towards an exogenous substrate. The PKC-induced phosphorylation did not affect Kit/SCF-R ligand binding affinity. Inhibition of PKC led to increased SCF-induced tyrosine autophosphorylation, as well as increased SCF-induced mitogenicity. In contrast, PKC was necessary for SCF-induced motility responses, including actin reorganization and chemotaxis. Our data suggest that PKC is involved in a negative feedback loop which regulates the Kit/SCF-R and that the activity of PKC determines whether the effect of SCF will be preferentially mitogenic or motogenic.

Animals↗
PubMed1993

The influence of pretransplant lipoprotein abnormalities on the early results of renal transplantation.

Lipoprotein patterns were investigated before and after renal transplantation in a prospective study including 151 patients. Kidney graft losses during the first 6 months were associated with higher total cholesterol (P = 0.03), LDL cholesterol (P = 0.003) and LDL triglyceride levels (P = 0.01) before transplantation. Patients with serum cholesterol > or = 6.9 mmol l-1 before transplantation had more acute rejections (1.7 vs. 0.9), a worse graft function and more vascular intimal hyperplasia and glomerular mesangial changes in transplant biopsies at 6 months. Patients with serum creatinine levels exceeding 160 mumol l-1 at 6 months had more severe lipid disorders already before transplantation. Serum creatinine at 6 months was influenced by the number of acute rejection episodes (P = 0.0001) and the age of the donor (P = 0.009) while the number of acute rejections was found to be related to pretransplant total cholesterol levels (P = 0.0086) and the age of the recipient (P = 0.025). In conclusion, pretransplant lipoprotein disturbances have an impact on the early outcome of renal transplantation. Since there is a progression of hyperlipidaemia following transplantation, this may have an influence also on the cardiovascular morbidity and late graft dysfunction.

Adolescent↗
PubMed1992

Neomycin is a platelet-derived growth factor (PDGF) antagonist that allows discrimination of PDGF alpha- and beta-receptor signals in cells expressing both receptor types.

The aminoglycoside neomycin has recently been found to affect certain platelet-derived growth factor (PDGF) responses in C3H/10T1/2 C18 fibroblasts. Using porcine aortic endothelial cells transfected with PDGF alpha- or beta-receptors, we explored the possibility that neomycin interferes with the interaction between the different PDGF isoforms and their receptors. We found that neomycin (5 mM) inhibited the binding of 125I-PDGF-BB to the alpha-receptor with only partial effect on the binding of 125I-PDGF-AA; in contrast, the binding of 125I-PDGF-BB to the beta-receptor was not affected by the aminoglycoside. Scatchard analyses showed that neomycin (5 mM) decreased the number of binding sites for PDGF-BB on alpha-receptor-expressing cells by 87%. Together with cross-competition studies with 125I-labeled PDGF homodimers, the effect of neomycin indicates that PDGF-AA and PDGF-BB bind to both common and unique structures on the PDGF alpha-receptor. Neomycin specifically inhibited the autophosphorylation of the alpha-receptor by PDGF-BB, with less effect on the phosphorylation induced by PDGF-AA and no effect on the phosphorylation of the beta-receptor by PDGF-BB. Thus, neomycin is a PDGF isoform- and receptor-specific antagonist that provides a possibility to compare the signal transduction pathways of alpha- and beta-receptors in cells expressing both receptor types. This approach was used to show that activation of PDGF beta-receptors by PDGF-BB mediated a chemotactic response in human fibroblasts, whereas activation of alpha-receptors by the same ligand inhibited chemotaxis.

Aminoglycosides↗
PubMed1992

PDGF alpha- and beta-receptors activate unique and common signal transduction pathways.

We have examined the signal transduction pathways of the PDGF alpha- and beta-receptors, in order to characterize the specificity of each receptor type in the signaling. Porcine aortic endothelial cell lines expressing equal levels of either PDGF alpha- or beta-receptors were established. The alpha- and beta-receptor cells responded mitogenically to stimulation with the proper PDGF isoforms. Three aspects of actin reorganization were examined after ligand stimulation: loss of stress fibres, appearance of edge ruffles and formation of circular membrane ruffles. The beta-receptor cells showed a response to ligand stimulation which included all three features. The alpha-receptor cells exhibited edge ruffles and loss of stress fibres, but circular ruffles could not be found in several independent alpha-receptor cell lines. The beta-receptor cells, but not the alpha-receptor cells, were able to migrate chemotactically towards a concentration gradient of ligand. The molecular basis for the differences in signalling were explored by comparing the pattern of increased phosphorylation of potential substrates for the alpha- and beta-receptors in [32P]orthophosphate labelled intact cells and using an in vitro kinase assay. Certain of the observed substrates were common for the two receptors, whereas others were specific for either one. We conclude that certain of the known PDGF induced cellular effects are transduced only by the beta-receptor; the presence of alpha-receptor-specific substrates suggests that there are also alpha-receptor-specific signals, which have yet to be identified.

Actins↗
PubMed1992

Supplementation with n-3 fatty acids reduces triglycerides but increases PAI-1 in non-insulin-dependent diabetes mellitus.

The effects of dietary supplementation with n-3 fatty acids on lipid and glucose metabolism and on fibrinolysis were evaluated in 14 non-insulin-dependent diabetic patients who were given 10 g of MaxEPA (3 g n-3 fatty acids) or placebo (olive oil) per day in a randomized double-blind cross-over study during two consecutive 8-week periods. The serum triglyceride (TG) concentrations decreased by 27% (P < 0.01) after addition of MaxEPA with a reduction of VLDL TG by 36% (P < 0.05) while LDL cholesterol increased by 6% (P = 0.05). The fasting blood sugar and HbA1c concentrations increased significantly after addition of MaxEPA but the changes were not significantly different from those during the placebo period. The highest glucose concentrations at fasting and after an i.v. glucose injection were seen after MaxEPA while the serum insulin concentrations were unchanged. The peripheral insulin sensitivity, as measured by a euglycaemic, hyperinsulinaemic clamp technique, did not change during the study. The mean plasminogen inhibitor-1 (PAI-1) activity of the patients was elevated compared with healthy controls. In spite of the reduction of the triglyceride concentrations and unchanged insulin levels, there was a significant increase of the activity of PAI-1 (+21%, P < 0.01) after MaxEPA suggesting a possible impairment of the fibrinolytic capacity. In many situations there seems to be a reduction of PAI-1 when the triglycerides are lowered. In the diabetic patients given n-3 fatty acids this was not the case.

Aged↗
PubMed1992

Platelet-derived growth factor is angiogenic in vivo.

PDGF receptors have recently been found to be expressed in microvascular endothelium in vivo under circumstances of endothelial cell activation and angiogenesis suggesting that PDGF may have a direct effect on endothelial cells. We have tested the angiogenic activity of PDGF-AA and -BB homodimers in the chick chorioallantoic membrane in vivo. PDGF-BB was found to consistently induce an angiogenic response whereas PDGF-AA was less active. Morphological analyses revealed that there was little inflammation associated with this response but an increase in vessel density suggested a direct effect of PDGF on embryonic chorioallantoic endothelial cells. In vitro, PDGF-BB was found to be more potent than PDGF-AA in stimulating the chemotaxis of rat brain capillary endothelial cells. This is consistent with a direct effect of PDGF on endothelial cells. Thus, this novel angiogenic activity of PDGF has implications for several developmental and pathological events in which PDGF, particularly the B-chain, is expressed.

Allantois↗
PubMed1991

Activation of the human c-kit product by ligand-induced dimerization mediates circular actin reorganization and chemotaxis.

The proto-oncogene c-kit is allelic with the murine white spotting (W) locus and encodes a transmembrane protein tyrosine kinase that is structurally related to the receptors for platelet-derived growth factor (PDGF) and colony-stimulating factor-1 (CSF-1). Recently the ligand for the c-kit product, stem cell factor (SCF), was identified in both transmembrane and soluble forms. In order to examine the mechanism for receptor activation by SCF and biological properties of the activated c-kit product, we transfected the wild-type human c-kit cDNA into porcine aortic endothelial cells. We found that the receptor was down-regulated and transmitted a mitogenic signal in response to stimulation with soluble SCF. We also demonstrate that SCF induces dimerization of the c-kit product in intact cells, and that dimerization of the receptor is correlated with activation of its kinase. Activation of the c-kit product by SCF was found to induce circular actin reorganization indistinguishable from that mediated by the PDGF beta-receptor in response to PDGF-BB. Furthermore, soluble SCF was a potent chemotactic agent for cells expressing the c-kit product, a property which might be of importance during embryonic development.

Actins↗
PubMed1991

Effects of dietary supplementation with vitamin E on human neutrophil chemotaxis and generation of LTB4.

Three weeks' dietary supplementation with a moderate dose of vitamin E (45 IU DL-alpha-tocopherol acetate daily), in eight healthy volunteers significantly increased the serum vitamin E level from 12.3 +/- 3.3 to 16.2 +/- 3.7 mg/L (means +/- SD) and significantly decreased neutrophil chemotaxis from 15 +/- 3 to 4 +/- 1 micron/h (means +/- standard error of the means). Generation of leukotriene B4 was not influenced by vitamin E, suggesting that the decrease in neutrophil chemotaxis was not due to blockage of the lipoxygenase pathway. Neither was the plasma malondialdehyde concentration influenced by vitamin E, contradicting the possibility of an antioxidant effect of vitamin E. As one early event in neutrophil chemotaxis is an increase in intracellular calcium concentration resulting from increased membrane permeability, it is possible that vitamin E influenced chemotaxis by a stabilizing effect on the neutrophil membrane, rather than by its antioxidant effect. Vitamin E supplementation could thus be beneficial in pathological conditions with activated neutrophils, such as ischaemic heart disease.

Adult↗
PubMed1990

Primary haemostasis, plasmatic coagulation and fibrinolysis in renal transplantation.

The disturbed coagulation state seen in patients with uremia has been suggested to contribute to thrombotic events in kidney grafts following transplantation. Primary haemostasis, plasmatic coagulation and fibrinolysis were investigated in eight patients before and during four weeks after kidney transplantation. In spite of an improved renal function there was postoperatively still a depressed platelet aggregation and the prostacyclin concentrations in plasma were low. The plasma coagulation seemed to be activated according to short activated partial thromboplastin time, high levels of FVIII:C and prothrombin complex. The fibrinolysis was increased and the PAI-1 levels were decreased. It is concluded that the overall haemostatic balance is characterized by a high degree of activation in uremic patients and that this activation persisted four weeks after transplantation.

Blood Coagulation↗