Background Cushing's syndrome (CS) is associated with an hypercoagulable state and an increased risk of venous thromboembolism (VTE). Evidence-based guidelines on thromboprophylaxis strategies in... Show moreBackground Cushing's syndrome (CS) is associated with an hypercoagulable state and an increased risk of venous thromboembolism (VTE). Evidence-based guidelines on thromboprophylaxis strategies in patients with CS are currently lacking. We aimed to map the current clinical practice for thromboprophylaxis management in patients with CS across reference centers (RCs) of the European Reference Network on Rare Endocrine Conditions (Endo-ERN), which are endorsed specifically for the diagnosis and treatment of CS. Using the EU survey tool, a primary screening survey, and subsequently a secondary, more in-depth survey were developed. Results The majority of the RCs provided thromboprophylaxis to patients with CS (n = 23/25), although only one center had a standardized thromboprophylaxis protocol (n = 1/23). RCs most frequently started thromboprophylaxis from CS diagnosis onwards (n = 11/23), and the majority stopped thromboprophylaxis based on individual patient characteristics, rather than standardized treatment duration (n = 15/23). Factors influencing the initiation of thromboprophylaxis were 'medical history of VTE' (n = 15/23) and 'severity of hypercortisolism' (n = 15/23). Low-Molecular-Weight-Heparin was selected as the first-choice anticoagulant drug for thromboprophylaxis by all RCs (n = 23/23). Postoperatively, the majority of RCs reported 'severe immobilization' as an indication to start thromboprophylaxis in patients with CS (n = 15/25). Most RCs (n = 19/25) did not provide standardized testing for variables of hemostasis in the postoperative care of CS. Furthermore, the majority of the RCs provided preoperative medical treatment to patients with CS (n = 23/25). About half of these RCs (n = 12/23) took a previous VTE into account when starting preoperative medical treatment, and about two-thirds (n = 15/23) included 'reduction of VTE risk' as a goal of treatment. Conclusions There is a large practice variation regarding thromboprophylaxis management and perioperative medical treatment in patients with CS, even in Endo-ERN RCs. Randomized controlled trials are needed to establish the optimal prophylactic anticoagulant regimen, carefully balancing the increased risk of (perioperative) bleeding, and the presence of additional risk factors for thrombosis. Show less
Veneuze trombose is een ziekte gekenmerkt door het ontstaan van een ongewenst bloedstolsel. Om inzichten te verkrijgen in de pathofysiologie van dit ziektebeeld zijn voorheen genoomstudies... Show moreVeneuze trombose is een ziekte gekenmerkt door het ontstaan van een ongewenst bloedstolsel. Om inzichten te verkrijgen in de pathofysiologie van dit ziektebeeld zijn voorheen genoomstudies uitgevoerd. Deze studies hebben een nieuwe erfelijke factor voor veneuze trombose geïdentificeerd, namelijk het SLC44A2 gen. Dit was een opmerkelijke bevinding, aangezien SLC44A2 nooit eerder gekoppeld was aan de bloedstolling. Het onderzoek beschreven in dit proefschrift heeft als doel het mechanisme, onderliggend aan deze associatie, te ontrafelen. Er is hiervoor gebruik gemaakt van muizen die dit gen niet meer hebben, zogenaamde SLC44A2 knock-out muizen. Dierstudies maakten het mogelijk om de complexiteit van stromend bloed, de bloedvaatwand en het ontstaan van veneuze trombose nader te onderzoeken. We hebben aangetoond dat de afwezigheid van SLC44A2 de normale bloedstolling ongemoeid laat. De vorming van veneuze trombose in SLC44A2 knock-out muizen is echter afwijkend, met mogelijk betrokkenheid van neutrofielen en von Willebrand factor (VWF), een eiwit met een rol in veneuze trombose. Studies verricht aan SLC44A2 op de neutrofielen van mensen, met aandacht voor de twee verschillende vormen van SLC44A2 die bij mensen voorkomen, geven goede aanwijzingen dat SLC44A2 een rol speelt in de binding van neutrofielen aan VWF. Er werd ook geobserveerd dat de erfelijke variant van SLC44A2 op neutrofielen welke zwak bindt aan VWF, ook degene is die samengaat met een mindere kans op het krijgen van VT. Door deze studies begrijpen we beter hoe veneuze trombose ontstaat, met hopelijk in de nabije toekomst concrete aanknopingspunten voor alternatieve, betere en veiligere behandelingsstrategieën voor veneuze trombose. Show less
Purpose Recombinant human erythropoietin (rHuEPO) is known to increase thrombotic risk in patients and might have similar effects in athletes abusing the drug. rHuEPO is prohibited by anti-doping... Show morePurpose Recombinant human erythropoietin (rHuEPO) is known to increase thrombotic risk in patients and might have similar effects in athletes abusing the drug. rHuEPO is prohibited by anti-doping legislation, but this risk has not been investigated thoroughly. This analysis was designed to evaluate whether rHuEPO impacts hemostatic profile and endothelial and platelet activation markers in trained subjects, and whether the combination with exercise affects exercise induced alterations. Methods This double-blind, randomized, placebo-controlled trial enrolled healthy, trained male cyclists aged 18-50 years. Participants were randomly allocated (1:1) to receive subcutaneous injections of rHuEPO (epoetin-beta; mean dose 6000 IU per week) or placebo (0.9% NaCl) for 8 weeks. Subjects performed five maximal exercise tests and a road race, coagulation and endothelial/platelet markers were measured at rest and directly after each exercise effort. Results rHuEPO increased P-selectin (+ 7.8% (1.5-14.5),p = 0.02) and E-selectin (+ 8.6% (2.0-15.7),p = 0.01) levels at rest. Maximal exercise tests significantly influenced all measured coagulation and endothelial/platelet markers, and in the rHuEPO group maximal exercise tests led to 15.3% ((7.0-24.3%),p = 0.0004) higher E-selectin and 32.1% ((4.6-66.8%),p = 0.0207) higher Platelet factor 4 (PF4) levels compared to the placebo group. Conclusion In conclusion, rHuEPO treatment resulted in elevated E- and P-selectin levels in trained cyclists, indicating enhanced endothelial activation and/or platelet reactivity. Exercise itself induces hypercoagulability, and the combination of rHuEPO and exercise increased E-selectin and PF4 levels more than either intervention alone. Based on this, exercise potentially increases thrombotic risk, a risk that might be enhanced in combination with rHuEPO use. Show less
Von Willebrand disease (VWD) is the most common inherited bleeding disorder. Patients mainly develop mucocutaneous bleeding, like bruises, epistaxis and menorrhagia. The more severely affected... Show moreVon Willebrand disease (VWD) is the most common inherited bleeding disorder. Patients mainly develop mucocutaneous bleeding, like bruises, epistaxis and menorrhagia. The more severely affected patients may also develop joint bleeding, or bleeding from the gastrointestinal tract. Also, trauma, surgery or dental procedures may lead to critical bleeding events. VWD-related bleeding are caused by defects in von Willebrand factor (VWF), a large multimeric protein that is produced by endothelial cells and megakaryocytes. Most VWD patients develop the disease because of dominant-negative mutations in VWF. In this thesis we investigated whether inhibition of production of mutant VWF with limited inhibition of wildtype VWF positively affects the function of VWF and improves VWD phenotypes. We used small interfering RNAs (siRNAs) to selectively inhibit production of mutant VWF. These siRNAs were tested in several models for VWD. We indeed prove that siRNAs can distinguish a mutant and wildtype VWF allele in vitro in heterologous cell systems, ex vivo in patient-derived endothelial cells, and in vivo in a VWD mouse model. We also show in these disease models that we can improve several VWD phenotypes. These results are promising for further development of allele-specific siRNAs as a new treatment strategy for VWD. Show less
The studies presented in this thesis explored several pathogenic mechanisms underlying von Willebrand disease that is characterized by a quantitative or functional deficiency of von Willebrand... Show moreThe studies presented in this thesis explored several pathogenic mechanisms underlying von Willebrand disease that is characterized by a quantitative or functional deficiency of von Willebrand factor, in particular with respect to intracellular storage in Weibel-Palade body and regulated secretion of von Willebrand factor. By using molecular biology, confocal and electron microscopic techniques, storage and secretion of von Willebrand factor were analyzed for von Willebrand disease variants identified in the patients. These studies advanced our understanding of von Willebrand disease at the molecular and cellular levels. HEK293 cells and endothelial cells derived from patients__ peripheral blood were established as two useful model-systems for examining von Willebrand factor structure-function relationships in the context of von Willebrand disease. Using these model-systems we have demonstrated that von Willebrand factor mutations may impair its storage and secretion and thus lead to a quantitative deficiency of this factor in the patients. Furthermore, we demonstrated that alteration in the structure of von Willebrand factor, by natural mutations that occur in von Willebrand disease patients, modulates von Willebrand factor string formation and function. We propose that alteration in von Willebrand factor string formation and function may be another new mechanism that contributes to the bleeding tendency in von Willebrand disease. Show less
According to current guidelines, patients with thrombocytopenia due to myelosuppression are supported with platelet concentrates in order to prevent and treat bleeding complications using... Show moreAccording to current guidelines, patients with thrombocytopenia due to myelosuppression are supported with platelet concentrates in order to prevent and treat bleeding complications using algorithms which include the level of thrombocytopenia as well as varying clinical parameters, e.g. concomitant infection, the use of anticoagulant drugs, specific interventions. In the last three decades, mainly driven by safety issues, several platelet product changes were made with leukoreduction in the eighties of the previous century, plasma reduction and the use of additive solution in the nineties and the use of pathogen reduction in the first decade of this century.This thesis is mainly based on two randomised controlled trials testing the clinical efficacy of the use of additive solutions and pathogen reduction, essentially showing a decreased clinical efficacy as well as a decrease in adverse transfusion events. A bette r understanding of the pathophysiology of bleeding, thrombocytopenia and platelet transfusion refractoriness will lead to improvements in supportive care as well as patient survival, the common goal of all physicians. Show less
The aim of this research was to obtain a better insight into the structure and functioning of clotting factor V (FV), a protein that plays an important role in the regulation of clotting.... Show moreThe aim of this research was to obtain a better insight into the structure and functioning of clotting factor V (FV), a protein that plays an important role in the regulation of clotting. Congenital defects in FV can greatly disturb the coagulation system, and can lead to symptoms ranging from para-haemophilia to thrombosis. One example of a congenital defect in FV I is the R506Q mutation (an aminoacid change at position 506 in the aminoacid chain of FV). This deviating FV molecule (also known as FV Leiden after the town in which the first patient found to have this defect was born) is the most important of all congenital risk factors for thrombosis found up to now (at least in the Western world). This explains the great interest in this clotting factor. In the present study a number of naturally occurring deviations in FV have also been investigated, such as FV Hong Kong and FV Cambridge. On the basis of our data it seems probable that people who are carriers of the gene for these FV variants have a slightly increased risk of deep-vein thrombosis. Another naturally occurring mutation in FV investigated in this study is the D2194G mutation. Our data explain why FV-D2194G combined with FV Leiden gives an increased risk of thrombosis. Het doel van dit onderzoek was om meer inzicht te verkrijgen in de structuur en de werking van stollingsfactor V (FV), een eiwit dat een belangrijke rol speelt in de regulatie van de bloedstolling. Aangeboren afwijkingen in FV kunnen de regulatie van de bloedstolling flink verstoren en kunnen leiden tot verschijnselen die uiteen lopen van bloedingen (parahemofilie) tot overmatige bloedstolling (trombose). Een belangrijk voorbeeld van een erfelijke afwijking in FV is de R506Q mutatie (een aminozuur verandering op positie 506 in de aminozuur keten van FV). Dit afwijkende FV molecuul (ook wel FV Leiden genoemd naar de stad waar de eerste patient bij wie deze afwijking werd aangetroffen werd geboren) is van alle erfelijke risico factoren voor trombose die tot nu toe ontdekt zijn de belangrijkste (in de Westerse wereld althans). Dit verklaart de grote aandacht voor deze stollingsfactor. In deze studie zijn ook een aantal natuurlijk voorkomende afwijkingen in FV onderzocht, zoals FV Hong-Kong en FV Cambridge. Op basis van onze data lijkt het waarschijnlijk dat mensen die drager zijn van het gen voor deze FV varianten een licht verhoogd risico hebben op veneuze trombose. Een andere natuurlijk voorkomende mutatie in FV die onderzocht is in deze studie is de D2194G mutatie in FV. Onze data geven een verklaring waarom FV-D2194G in combinatie met FV Leiden een hoger risico geeft op trombose. Show less
