Turid M. Pedersen

Dickkopf-1 Enhances Inflammatory Interaction Between Platelets and Endothelial Cells and Shows Increased Expression in Atherosclerosis

Objective—Based on the emerging importance of the wingless (Wnt) pathways in inflammation and vascular biology, we hypothesized a role for Dickkopf-1 (DKK-1), a major modulator of Wnt signaling, in atherogenesis and plaque destabilization. Methods and Results—We report increased levels of DKK-1 in experimental (ApoE−/− mice) and clinical (patients with coronary artery disease [n=80] and patients with carotid plaque [n=47]) atherosclerosis, both systemically (serum) and within the lesion, with particularly high levels in advanced and unstable disease. We identified platelets as an important cellular source of DKK-1 as shown by in vitro experiments and by immunostaining of thrombus material obtained at the site of plaque rupture in patients with acute ST-elevation myocardial infarction, with strong immunoreactivity in platelet aggregates. Our in vitro experiments identified a role for platelet- and endothelial-derived DKK-1 in platelet-dependent endothelial activation, promoting enhanced release of inflammatory cytokines. These inflammatory effects of DKK-1 involved inhibition of the Wnt/&bgr;-catenin pathway and activation of nuclear factor &kgr;B. Conclusion—Our findings identify DKK-1 as a novel mediator in platelet-mediated endothelial cell activation. The demonstration of enhanced DKK-1 expression within advanced carotid plaques may suggest that this DKK-1-driven inflammatory loop could be operating within the atherosclerotic lesion.

Activation of platelets by Aspergillus fumigatus and potential role of platelets in the immunopathogenesis of Aspergillosis.

ABSTRACT Aspergillus fumigatus is the most frequent cause of invasive mold infections worldwide. Platelets contribute to inflammation and promote thrombosis, characteristically seen in aspergillosis, and might be involved both in antifungal defense and in the histopathological process. In the experiments reported here, in vitro activation of platelets by conidia, swollen conidia, and hyphae from A. fumigatus was assessed by flow cytometry and enzyme immunoassays. THP-1 monocytes and human monocytes with and without platelets were cultured with hyphae from A. fumigatus, and the release of interleukin-8 (IL-8) was measured by enzyme immunoassays. A. fumigatus potently induced the expression of CD62-p and CD63 and the release of CD40 ligand, RANTES, and Dickkopf homolog 1 in platelets, with particularly enhancing effects of hyphae compared with conidia. The hypha-mediated activation of platelets further enhanced the release of IL-8 both in THP-1 monocytes and in human adherent monocytes. In conclusion, we have found that A. fumigatus is a potent inducer of platelet-mediated inflammation, potentially promoting protective as well as harmful responses during aspergillosis.

Elevated levels of activin A in clinical and experimental pulmonary hypertension.

Activin A, a member of the transforming growth factor (TGF)-beta superfamily, is involved in regulation of tissue remodeling and inflammation. Herein, we wanted to explore a role for activin A in pulmonary hypertension (PH). Circulating levels of activin A and its binding protein follistatin were measured in patients with PH (n = 47) and control subjects (n = 14). To investigate synthesis and localization of pulmonary activin A, we utilized an experimental model of hypoxia-induced PH. In mouse lungs, we also explored signaling pathways that can be activated by activin A, such as phosphorylation of Smads, which are mediators of TGF-beta signaling. Possible pathophysiological mechanisms initiated by activin A were explored by exposing pulmonary arterial smooth muscle cells in culture to this cytokine. Elevated levels of activin A and follistatin were found in patients with PH, and activin A levels were significantly related to mortality. Immunohistochemistry of lung autopsies from PH patients and lungs with experimental PH localized activin A primarily to alveolar macrophages and bronchial epithelial cells. Mice with PH exhibited increased pulmonary levels of mRNA for activin A and follistatin in the lungs, and also elevated pulmonary levels of phosphorylated Smad2. Finally, we found that activin A increased proliferation and induced gene expression of endothelin-1 and plasminogen activator inhibitor-1 in pulmonary artery smooth muscle cells, mediators that could contribute to vascular remodeling. Our findings in both clinical and experimental studies suggest a role for activin A in the development of various types of PH.

Clopidogrel increases expression of chemokines in peripheral blood mononuclear cells in patients with coronary artery disease: results of a double-blind placebo-controlled study

Summary.  Background: Chemokines and platelet activation are both important in atherogenesis. Platelet inhibitors are widely used in coronary artery disease (CAD), and we hypothesized that the platelet inhibitor clopidogrel could modify chemokines in CAD patients. Objectives: We sought to investigate the effect of clopidogrel on the expression of chemokines and chemokine receptors in peripheral blood mononuclear cells (PBMC) in CAD patients. Patients/methods: Thirty‐seven patients with stable angina were randomized to clopidogrel (n = 18) or placebo (n = 19). PBMC, blood platelets and plasma were collected at baseline and after 7–10 days in the patients, and in 10 healthy controls. mRNA levels of chemokines and chemokine receptors in PBMC were analyzed by ribonuclease protection assays and real‐time reverse transcriptase polymerase chain reaction. Platelet activation was studied by flow cytometry. Results: (i) At baseline, the gene expression of the regulated on activation normally T‐cell expressed and secreted (RANTES) chemokines and macrophage inflammatory peptide (MIP)‐1β in PBMC, the expression of CD62P and CD63 on platelets and the levels of platelet‐derived microparticles (PMP) were elevated in angina patients comparing healthy controls; (ii) markers of platelet activation were either reduced (CD63) or unchanged (CD62P, PMP, β‐thromboglobulin) during clopidogrel therapy; (iii) in contrast, clopidogrel significantly up‐regulated the gene expression of RANTES and MIP‐1β in PBMC, while no changes were found in the placebo group; (iv) a stable adenosine 5′‐diphosphate metabolite attenuated the release of MIP‐1β, but not of RANTES, from activated PBMC in vitro. Conclusions: Even if we do not argue against a beneficial role for clopidogrel in CAD, our findings may suggest potential inflammatory effects of clopidogrel in CAD.

Effect of activated platelets on expression of cytokines in peripheral blood mononuclear cells - potential role of prostaglandin E2

Platelets may act as inflammatory cells. To study the effects of soluble and cell-bound platelet factors on the expression of several cytokines and related mediators in leukocytes, peripheral blood mononuclear cells (PBMC) were incubated with platelet-free supernatants from SFLLRN-activated platelet-rich plasma (PRP) or SFLLRN-activated PRP in itself. Our main findings were: (i) the gene expression of several chemokines and some cytokines were markedly increased by both activated PRP and supernatants, as also confirmed at the protein level for IL-6, IL-8 and MIP-1alpha; (ii) the selective protein kinase A type I (PKAI) antagonist Rp-8-Br-cAMP reduced this platelet-induced expression of IL-6, IL-8 and MIP-1alpha in PBMC, suggesting a role of cAMP/PKAI mediated mechanisms in this interaction; (iii) PGE(2) dose-dependently increased the release of IL-6, IL-8 and MIP-1alpha from PBMC mimicking the effect of activated platelets. Furthermore, activated platelets released comparable amounts of PGE(2), suggesting that platelet-derived PGE2 could interact with PBMC in co-cultures; (iv) IL-10 inhibited the platelet-inducing effect on IL-6, IL-8 and MIP-1alpha in PBMC, and notably, the addition PGE2 totally abolished this IL-10 effect suggesting that the suppressive effect of IL-10 on the plateletinduced activation of PBMC might at least partly involve PGE(2) related mechanisms. The present study supports a view of platelets as inflammatory cells, and suggests a potential role of platelet-derived PGE(2) in platelet-induced inflammatory responses.

Complement-mediated permeabilization of platelets by monoclonal antibodies to CD9: Inhibition by leupeptin, and effects on the GP Ib-actin-binding protein system

Two monoclonal antibodies to CD9 of the IgM and IgG2a categories (FN 52 and FN 99), reproducibly induced platelet alterations in platelet-rich plasma by activation of the complement system with membrane incorporation of the pore-forming C5b-9 complex. The permeabilization could be monitored by measurements of extracellular ATP and observed as a shape change followed by an increase in light transmission in the aggregometer, and was associated with formation of tiny platelet aggregates. This could be accomplished by only minor lysis observed as extracellular lactate dehydrogenase (LDH). When leupeptin was added prior to, or immediately after the antibody, a total inhibition of the platelet alterations could be obtained. When added soon after the shape change, leupeptin had little effect on the liberation of ATP. However, whereas the ability of the platelets to become agglutinated by ristocetin was lost during the complement-mediated platelet alterations, addition of leupeptin immediately after the shape change, prevented this loss. The lost ability of the permeabilized platelets to undergo ristocetin-induced agglutination is not ascribed to degradation of GP Ib as this was relatively little affected in these studies as compared to the actin-binding protein (ABP) which was profoundly degraded. This protein represents a link between GP Ib and the submembraneous cytoskeleton, and the inhibition of its degradation by leupeptin, was clearly demonstrated. Experiments with digitonin-induced permeabilization showed that leupeptin did not inhibit permeabilization as such, but it did prevent the loss of ristocetin-induced agglutination even with this inducer.

The charge-heterogeneity of human fibrinogen as investigated by 2D electrophoresis

The charge-heterogeneity of human plasma fibrinogen subunit chains was characterized by two-dimensional electrophoresis (2DE). Western blotting with antibodies specific for the gamma-chain demonstrated that the gamma-chains focus at varying isoelectric points (pI). This microheterogeneity was also observed in fibrinogen secreted from hepatocytic cells and in recombinant fibrinogen expressed in Chinese hamster ovary (CHO) cells. Further, covalent gammagamma-dimerization by FXIIIa was not influenced by the charge-heterogeneity, and removal of the carbohydrate did not reduce the number of gamma-chain pI variants. These observations suggest that the microheterogeneity of the gamma-chain is a multifactorial phenomenon that is not due to physiologic modification of the glycoprotein in circulation.

Statins affect the presentation of endothelial chemokines by targeting to multivesicular bodies.

Background In addition to lowering cholesterol, statins are thought to beneficially modulate inflammation. Several chemokines including CXCL1/growth-related oncogene (GRO)-α, CXCL8/interleukin (IL)-8 and CCL2/monocyte chemoattractant protein (MCP)-1 are important in the pathogenesis of atherosclerosis and can be influenced by statin-treatment. Recently, we observed that atorvastatintreatment alters the intracellular content and subcellular distribution of GRO-α in cultured human umbilical vein endothelial cells (HUVECs). The objective of this study was to investigate the mechanisms involved in this phenomenon. Methodology/ Principal Findings The effect of atorvastatin on secretion levels and subcellular distribution of GRO-α, IL-8 and MCP-1 in HUVECs activated by interleukin (IL)-1β were evaluated by ELISA, confocal microscopy and immunoelectron microscopy. Atorvastatin increased the intracellular contents of GRO-α, IL-8, and MCP-1 and induced colocalization with E-selectin in multivesicular bodies. This effect was prevented by adding the isoprenylation substrate GGPP, but not the cholesterol precursor squalene, indicating that atorvastatin exerts these effects by inhibiting isoprenylation rather than depleting the cells of cholesterol. Conclusions/ Significance Atorvastatin targets inflammatory chemokines to the endocytic pathway and multivesicular bodies and may contribute to explain the anti-inflammatory effect of statins at the level of endothelial cell function.

Variability in aggregometry response before and after initiation of clopidogrel therapy.

Abstract Background: Evaluation of clopidogrel therapy by in vitro methods has limitations which may be of clinical importance. We wanted to explore the variability in aggregometry response in aspirin sensitive patients before and after initiation of clopidogrel therapy. Methods: ADP 9.37 μM, AA 1.2mM and TRAP 25mM stimulated light transmissions aggregometry (LTA) were performed twice before (Exams 1 and 2; 3 weeks apart)-and within one year after-initiation of clopidogrel therapy (Exam 3) in 79 patients treated with PCI. Repeated ADP aggregometry was also performed in 16 healthy volunteers in order to estimate LTA measurement error. Result:. Inter-individual differences in ADP aggregation e.g. at Exam 1 were substantial (range 17–77%, SD 15.8%). Intra-individual changes between Exams 1 and 2 were significant (−27 to +36%, SD 14.6%, p<0.05). Inter-individual differences at Exam 3 (on clopidogrel treatment) were larger than expected from Exams 1 and 2 (p<0.01). AA aggregation was the same before and during clopidogrel treatment. In controls, inter-individual differences were smaller at ADP 10 than at ADP 5μM. Conclusions. Inter-individual differences in ADP aggregation were significant both before and during clopidogrel therapy, and there were significant intra-individual variations over time. Therefore, prediction of aggregometry response before or during clopidogrel therapy based on single tests may be unreliable. Inter-individual differences in healthy controls are smaller at high concentrations of ADP, and comparisons of aggregometry response should be performed with caution unless ADP concentrations are standardized.

Thrombin generation and platelet activation related to subintimal percutaneous transluminal angioplasty

Abstract Objective: The purpose of this study was to measure the in vivo platelet activation and thrombin generation in arterial blood after passing a subintimal conduit. Methods: Subintimal percutaneous transluminal angioplasty (SPTA) is a technique where a subintimal channel is created, allowing recanalization of long peripheral arterial occlusion. From 10 patients with intermittent claudication, undergoing successful SPTA for femoropopliteal occlusive disease, we collected antecubital venous blood samples immediately before treatment, preprocedural arterial blood samples taken at the entry level proximal to the vessel occlusion, and subsequently at the reentry level after successful recanalization. Venous follow-up blood samples were taken after 24 hours. Plasma concentrations of β-thromboglobulin (β-TG), RANTES, and Prothrombin fragment (F1 + 2), were determined by immunoassay. Fibrinogen binding to platelets, leukocyte-platelet adhesion, and P-selectin were determined by flow cytometry. Results: We found a statistically significant transluminal increase in the plasma concentrations of RANTES, β-TG and F1 + 2 (p = 0.002, 0.001 and 0.001 respectively), which all normalized within 24 hours. Platelet-leukocyte aggregates significantly decreased after 24 hours compared with preprocedural and preentry levels (3.26% versus 5.26 %, p = 0.017). P-selectin expression on circulating platelets was statistically significantly increased in the blood sample taken at the re-entry level compared with the pre-procedural and pre-entry level (p = 0.007). After 24 hours there was no statistically significant difference to pre-procedural levels. There was no significant change in platelet fibrinogen binding at any levels. Conclusion: When passing a subintimal conduit, in vivo sampled blood demonstrated an extremely rapid and substantial uniform platelet activation and thrombin generation.