| 1. |
- Chaireti, Roza, 1979-
(författare)
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Thrombin generation in different cohorts : Evaluation of the haemostatic potential
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The aim of this thesis is to evaluate thrombin generation in patients with thrombophilia (Paper I), in patients with venous thromboembolism (Paper II), in healthy women during the menstrual cycle (Paper III), in patients with liver disease (Paper IV) and in patients with mild deficiency of factor VII (Paper V).For this purpose, thrombin generation was measured in platelet poor plasma by the calibrated automated thrombogram (CAT®) assay. Thrombin generation expresses the overall haemostatic potential, in contrast to the more traditional coagulation tests, which concentrate on individual factors or coagulation pathways. The thrombin generation markers that were measured and studied were: lagtime (clotting time), endogenous thrombin potential (ETP, total thrombin concentration), peak (maximum thrombin concentration) and time to peak (ttpeak).The cohorts for Papers I and II are part of a larger cohort (The LInköping Study on Thrombosis, LIST), which included 516 consecutive patients who presented at the Emergency Department of Linköping University Hospital, Sweden with the clinical suspicion of venous thrombosis. In Paper I thrombin generation was measured in the absence of thrombomodulin in patients with thrombophilia (factor V Leiden, n=98 and prothrombin G20210A mutation, n=15) and in an equal number of age- and gendermatched controls. The results were associated with the presence of thrombosis, as well as gender and age. It was shown that thrombin generation did not differ significantly among patients and controls. Patients with and patients without thrombophilia who had suffered a thrombosis upon inclusion had longer lagtime compared with their counterparts without thrombosis. Neither age nor gender had any effect on the results.In Paper II, thrombin generation at the time of an acute thromboembolic episode was studied as a potential early marker for recurrence during a 7-year follow-up in 115 patients with venous thrombosis upon inclusion. It was shown that patients with recurrences during follow-up had longer lagtime and ttpeak at the time of the acute thrombosis, whereas those without recurrences had higher ETP and peak. Those results were particularly evident in the group of patients with an unprovoked thrombosis upon inclusion.In Paper III, thrombin generation was measured in the follicular and luteal phase of a normal menstrual cycle in 102 healthy women not taking oral contraceptives. The results were associated with haemostatic parameters (fibrinogen, antithrombin, D-dimer, plasminogen activator inhibitor-1, factors VII, VIII, X and von Willebrand) as well as the physiological concentrations of oestradiol, progesterone, antimüllerian hormone and sex hormone-binding globulin and the number of pregnancies and deliveries for these women. ETP was significantly higher during the luteal phase. However, this could not be explained by the elevation of other procoagulant factors during the same phase. Progesterone was found to exert a more significant effect on haemostasis than oestradiol during both phases (multiple regression analysis).In Paper IV, thrombin generation was measured in the presence and absence of thrombomodulin in 47 patients with portal vein thrombosis, PVT (11 with cirrhotic PVT and 36 with non-cirrhotic PVT), 15 patients with Budd-Chiari syndrome and 24 patients with cirrhosis, as well as 21 healthy controls. Since 15 patients with PVT (2 with cirrhotic PVT and 13 with non-cirrhotic PVT) and 10 patients with Budd-Chiari syndrome were treated with warfarin at the time of the blood sampling, an equal number of patients matched for age, gender and prothrombin time-international normalized ratio with atrial fibrillation and no hepatic diseases were used as controls. It was shown that hypercoagulability, expressed as total and maximum concentration of generated thrombin as well as thrombomodulin resistance [thrombin generation markers measured in the presence]/[thrombin generation markers measured in the absence of thrombomodulin] was pronounced in the groups of patients with cirrhosis, regardless of the presence of splanchnic thrombosis.In Paper V, thrombin generation in the presence of human and different concentrations of rabbit thromboplastin was measured in 10 patients with mild deficiency of factor VII and in 12 controls. In these patients, the levels of factor VII varied slightly depending on the origin of the thromboplastin used in the reagent. Nine out of 10 patients had a mutation in common (Arg353Gln), which was, however, not associated with the diversity in the factor VII measurements due to the origin of thromboplastin. ETP in patients with mild factor VII deficiency was about 86% of the ETP in the control group. The expected thrombin generation patterns with increasing concentrations of thromboplastin did not differ depending on the origin of thromboplastin in the patient group.
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| 2. |
- Milovanovic, Micha, 1966-
(författare)
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Platelets : with special reference to platelet density subpopulations, stable coronary heart disease and atrial fibrillation
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The current thesis was divided into two parts. Basic platelet research is the topic of the first section. The subsequent clinical part examines platelet reactivity in stable angina pectoris (AP) and in atrial fibrillation.Platelet heterogeneity was investigated in the first section (papers 1 and 2). The cells were separated according to density using linear Percoll™ (a density medium) gradients. The latter contained EDTA, prostaglandin E1 and theophylline to prevent platelet in vitro activity. The platelet population was then divided into density subpopulations (n = 16 - 20). Membrane attached fibrinogen was determined with a flow cytometer technique and used as a marker reflecting platelet in vivo activity. Platelet P-Selectin content was employed to estimate the quantity of platelet α-granules. Paper I examined healthy blood donors (n = 3). The second report (paper II) compared healthy volunteers (n = 2) and subjects with essential thrombocythemia (ET) (n = 2). The latter is a clonal disease being characterized by an excessive platelet production. Platelet counts were determined in all fractions. In manuscripts I and II determination of surface bound fibrinogen and intracellular P-Selectin was carried out in 12 and 16 platelet density fractions, respectively.High density platelets displayed more surface bound fibrinogen indicating in vivo activity. They also contained less P-Selectin. The latter finding implies platelet in vivo release reactions. Low density platelets circulated with more surface bound fibrinogen as well. Compared with peak density platelets, lighter cells contained more P-Selectin. ET was characterized by a similar platelet density pattern in that high and low density platelets displayed more surface bound fibrinogen. The similarity may explain why severe bleedings do not occur more frequently in ET. It is also obvious from the current thesis that the significance of platelet heterogeneity remains unclear and stimulates to further research. In particular, future work must involve more patients.The second part (papers III-VI) of the thesis was devoted to stable AP and atrial fibrillation. Determination of platelet reactivity i.e. platelet bound fibrinogen after stimulation was carried out in whole blood. A flow cytometer technique was employed (papers III-VI). Adenosine diphosphate (ADP) (1.7 and 8.5 μmol/L) and a thrombin-receptor activating peptide (TRAP-6) (57 and 74 μmol/L) were used as stimulating agents. Determination of peak platelet density (kg/L) was utilized as a further measure reflecting platelet reactivity (paper V). Surface bound and soluble P-Selectin were employed as platelet activity markers (paper VI).Gender differences with respect to platelet reactivity were investigated in paper III. Paper IV examined platelets in stable AP without significant coronary flow obstruction(s) as determined by coronary angiography. In a following study platelet reactivity was analysed in diabetes type II complicated by stable AP (paper V). Finally, long-term (more than 2 years) outcome of atrial fibrillation was related to platelet reactivity and activity (paper VI). In this study the subjects were investigated at the initial electrical cardioversion and the analysis were repeated after more than 2 years.Postmenopausal women with stable AP demonstrated more reactive platelets when stimulating with TRAP-6. They had higher platelet counts (paper III) as well. Stable AP without significant coronary flow obstruction(s) was associated with elevated platelet reactivity (paper IV). Diabetes type II was linked to higher peak platelet density and elevated platelet reactivity (paper V). Augmented platelet reactivity proved to be a feature of subjects remaining in atrial fibrillation more than 2 years after the electrical cardioversion (paper VI). In contrast, the irregular heart rhythm did not affect platelet activity.It is to assume that platelets at least partly are responsible for the sometimes atypical symptoms of females with stable AP. It is also conceivable to speculate that platelets contribute to chest pain in AP free from significant coronary flow obstruction(s). Theoretically, enhanced platelet reactivity could at least partly explain why diabetes type II affects the prognosis of coronary heart disease. The thesis further shows a possible theoretical link between atrial fibrillation, increased platelet reactivity and clot formation.
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| 3. |
- Nylander, Martina
(författare)
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The role of platelet thrombin receptors PAR1 and PAR4 in health and disease
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Blood cells are continuously flowing in our systems maintaining haemostasis in the arteries and veins. If a vessel is damaged, the smallest cell fragments in the blood (platelets) are directed to cover the wound and plug the leakage to prevent blood loss. Most of the time platelets stop the blood leak without any difficulties. During other, pathological, circumstances, platelets continue to form a thrombus, preventing the blood flow and may cause myocardial infarction or stroke.Thrombin is the most potent platelet agonist and is a product created in the coagulation cascade. This thesis is focused on the interactions between the two platelet thrombin receptors; protease activated receptors 1 (PAR1) and PAR4 in vitro. We have investigated potential differences between these receptors in several situations associated with cardiovascular disease.First we studied interactions between PAR1 and PAR4 and the oral pathogen Porphyromonas gingivalis (which secretes enzymes, gingipains, with properties similar to thrombin). Here we showed that P. gingivalis is signaling mainly, but not exclusively, via PAR4. Our second study showed that the cross-talk between the stress hormone epinephrine and thrombin occur exclusively through PAR4 if the key-substance ATP is present and cyclooxygenase-1 inhibited by aspirin. The third study investigated platelet secretion, with focus on the protein plasminogen activator inhibitor 1(PAI-1), an inhibitor of the fibrinolytic process responsible for dissolving a formed clot. Here we showed that PAI-1 secretion and synthesis was more sensitive to stimulation through PAR1 than PAR4. Finally this thesis describes differences between PAR1 and PAR4 in cell-signaling pathways regulating the stability of a platelet aggregate, where PAR4 seems to be of importance to create stable platelet aggregates and that this stability is dependent on ADP activation via P2Y12 and cell signaling via PI3-kinase.Until now, PAR1 has been considered to be the most important thrombin receptor, due to its high affinity for thrombin. However, there must be a reason why platelets express two different thrombin receptors. This thesis highlights several situations where PAR4 plays a complementary and important role in platelet signaling and haemostasis.In conclusion, this thesis suggests that PAR4 plays a major role in calcium signaling and the induction of sustained aggregation, while PAR1 shows a more prominent role in platelet secretion and synthesis. This thesis also reveals new interactions between platelet thrombin receptors and the ADP-, ATP- and epinephrine receptors. The results described in this thesis contribute to an increased knowledge of the platelet thrombin receptors and their interplay in situations such as infection, stress, fibrinolysis, and platelet aggregation.
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| 4. |
- Rajani, Rupesh, 1973-
(författare)
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Hepatic and Portal Vein Thrombosis : studies on epidemiology and risk factors
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Budd-Chiari syndrome (BCS) i.e. thrombosis in the hepatic veins and/or inferior vena cava, and portal vein thrombosis (PVT) are rare disorders. Epidemiological data are scarce and previous reports have been from highly specialised referral centres.The aims of the thesis were: (i) to investigate the epidemiology, clinical features and survival of Swedish patients with BCS or PVT, and to (ii) determine common underlying risk factors i.e. thrombophilic factors and genetic markers of myeloproliferative disorders (MPD).In the first two papers we retrospectively reviewed the medical records of all BCS (1986-2003) and PVT (1995-2004) patients identified by searching the computerized patient registers of 11 hospitals including all university hospitals and liver transplantation units. In the following two papers we excluded patients with malignancy and included new cases diagnosed during the years 2004-2009; blood samples were collected and compared with controls and other patient groups.A total of 43 patients with BCS were identified (median age 40 years, 24 women). The mean agestandardised incidence and prevalence rates were 0.8 per million per year and 1.4 per million inhabitants respectively. Two or more risk factors were present in 44%. The overall transplantationfree survival at 1, 5 and 10 years was 47%, 28% and 17% respectively.173 patients (median age 57 years, 93 men) with portal vein thrombosis were identified. The incidence and prevalence rates were 0.7 per 100 000 per year and 3.7 per 100 000 inhabitants, respectively. In the absence of cirrhosis and malignancy, being the most common risk factors, the survival at 1 year and 5 years was 92% and 76%, respectively.We observed an increased plasma level of the procoagulant factor VIII in BCS (mean 1.63 kIE/L), PVT without cirrhosis (1.87 kIE/L), PVT with cirrhosis (1.97 kIE/L), deep vein thrombosis (1.41 kIE/L) and cirrhosis patients alone (2.22 kIE/L), all p <0.001 compared to healthy controls (1.04 kIE/L). Elevated factor VIII levels were found in 50% of BCS and in 85% of PVT patients without previously identified prothrombotic risk factors.The somatic JAK2 V617F-mutation, a marker of MPD, was present in 63% of BCS and 14% of PVT patients. The frequency of the germline JAK2 46/1 haplotype was significantly higher in BCS (53%) and PVT (36%) patients compared to controls (27%) (p=0.02). However, the enrichment was only observed in JAK2 V617F positive patients.Conclusions: The incidence and prevalence rates of BCS in Sweden were calculated to be 0.8/million inhabitants per year and 1.4/million inhabitants, respectively. The rates of PVT were higher; 0.7/100 000 inhabitants per year and 3.7/100 000 inhabitants, respectively. In BCS the transplantation-free survival was poor, whereas in PVT the survival was variable and highly dependent on the presence of underlying disease. Concurrent prothrombotic risk factors are common in both disorders. High plasma levels of procoagulant factor VIII was observed in a majority of idiopathic BCS and PVT. The prevalence of the somatic JAK2 V617F mutation was high in our cohort and associated with the presence of a germline JAK2 46/1 haplotype.
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