Thomas Siegemund

Thrombin generation in severe haemophilia A and B: the endogenous thrombin potential in platelet-rich plasma

Thrombin generation was investigated in platelet-rich plasma (PRP) from 11 healthy controls, 17 patients with severe haemophilia A and 7 patients with severe haemophilia B. Mean endogenous thrombin potential (ETP) in arbitrary fluorescence units (FU) was 226.9 +/- 44.6, 186.4 +/- 22.5, 154.2 +/- 41.3 in controls, haemophilia A and B, respectively, all at a platelet count of 200 x 10(9)/l (p = 0.004 for controls vs. haemophilia A, p = 0.003 for controls vs. haemophilia B, no significant difference between haemophilia A and B). The contribution of FVIII to thrombin generation in haemophilia A was 1.31 +/- 0.16 FU/% of FVIII:C activity, while for FIX in haemophilia B this was 0.80 +/- 0.21 FU/% of FIX activity. There was an almost linear relationship between increasing platelet count and thrombin generation up to a mean platelet count of 100 x 10(9)/l. Further increase in platelet count has only a marginal influence on thrombin generation. Platelets increase ETP in haemophilia A by 0.184 +/- 0.022 FU/10(9) platelets/l and in haemophilia B by 0.319 +/- 0.085 FU/10(9) platelets/l, and this was significantly different between the two groups (p = 0.0002). This influence of plate-lets diminishes with increasing concentration of either FVIII or FIX. In conclusion, there is a difference in thrombin generation between haemophilia A and B, and this may be attributed to the role of platelets in the assembly of the tenase complex on their surface.

The endogenous thrombin potential and high levels of coagulation factor VIII, factor IX and factor XI

High plasma concentrations of factor VIII, factor IX and factor XI have been reported as thrombosis risk factors. Using the thrombin generation test in platelet-poor plasma, it was aimed to describe the mechanism for this increased thrombosis risk. Endogenous thrombin potential was measured in platelet-poor plasma in 180 patients with a history of thromboembolism, and results were compared with those of 180 age-matched and sex-matched controls. Subjects with major hereditary and acquired thrombophilia were excluded. Plasma concentrations of the clotting factor VIII, factor IX and factor XI were significantly elevated in patients compared with controls. The mean endogenous thrombin potential was significantly higher in patients than in controls: 191.3 ± 3.1 (95% confidence interval, 185.3–197.4) arbitrary units versus 180.8 ± 2.6 (95% confidence interval, 175.7–185.9) arbitrary units (P = 0.009). The endogenous thrombin potential was significantly higher in patients with elevated factor IX and factor XI, but elevated factor VIII was not associated with a significant increase in endogenous thrombin potential. In conclusion, the increased thrombosis risk associated with high plasma concentrations of factor IX and factor XI may be explained by the increase in endogenous thrombin potential. However, this did not help explain the association between elevated factor VIII and thrombosis risk.

Immunohistochemical characterization and quantitative analysis of neurons in the myenteric plexus of the equine intestine

The present study was performed on whole-mount preparations to investigate the chemical neuroanatomy of the equine myenteric plexus throughout its distribution in the intestinal wall. The objective was to quantify neurons of the myenteric plexus, especially the predominant cholinergic and nitrergic subpopulations. Furthermore, we investigated the distribution of vasoactive intestinal polypeptide and the calcium-binding protein calretinin. Samples from different defined areas of the small intestine and the flexura pelvina were taken from 15 adult horses. After fixation and preparation of the tissue, immunofluorescence labeling was performed on free floating whole-mounts. Additionally, samples used for neuropeptide staining were incubated with colchicine to reveal the neuropeptide distribution within the neuronal soma. The evaluation was routinely accomplished using confocal laser-scanning microscopy. For quantitative and qualitative analysis, the pan-neuronal marker anti-HuC/D was applied in combination with the detection of the marker enzymes for cholinergic neurons and nitrergic nerve cells. Quantitative data revealed that the cholinergic subpopulation is larger than the nitrergic one in several different locations of the small intestine. On the contrary, the nitrergic neurons outnumber the cholinergic neurons in the flexura pelvina of the large colon. Furthermore, ganglia are more numerous in the small intestine compared with the large colon, but ganglion sizes are bigger in the large colon. However, comparison of the entire population of neurons in the different locations of the gut showed no difference. The present study adds further data on the chemoarchitecture of the myenteric plexus which might facilitate the understanding of several gastrointestinal disorders in the horse.

The effect of different anticoagulants on thrombin generation.

Decrease in thrombin generation is the key effect in anticoagulation. The aim of the present study was to investigate the effect of anticoagulants on thrombin generation and the relation to platelet count. Plasma samples from 10 healthy volunteers (mean age 43.0 ± 9 years) were incubated at preset platelet counts with different doses of the anticoagulants lepirudin, fondaparinux and low molecular weight heparins. Thrombin generation was measured in a tissue factor-mediated assay using a fluorometer and a slow-reacting fluorogenic substrate. The endogenous thrombin potential, the lag phase, the maximum reaction velocity (Vmax) and the concentration of a given anticoagulant required for 50% inhibition of thrombin generation (IC50) are presented. All three anticoagulants decreased endogenous thrombin potential and prolonged the lag phase in a dose-dependent manner. Fondaparinux and low molecular weight heparins, but not hirudin, decreased Vmax in a concentration-dependent manner. With increasing platelet count, the IC50 increased but the extent of this increase was not uniform for the three anticoagulants and the three variables investigated. The influence of anticoagulants on thrombin generation is variable, depending on their basic mechanism of action. In defining and comparing their effects, the endogenous thrombin potential, the lag phase and the maximum reaction velocity should be considered together. Platelets have a considerable influence on the magnitude of thrombin generation.

Redistribution of CB1 cannabinoid receptors during evolution of cholinergic basal forebrain territories and their cortical projection areas: A comparison between the gray mouse lemur (Microcebus murinus, primates) and rat

Endocannabinoid signaling, mediated by presynaptic CB1 cannabinoid receptors on neurons, is fundamental for the maintenance of synaptic plasticity by modulating neurotransmitter release from axon terminals. In the rodent basal forebrain, CB1 cannabinoid receptor-like immunoreactivity is only harbored by a subpopulation of cholinergic projection neurons. However, endocannabinoid control of cholinergic output from the substantia innominata, coincident target innervation of cholinergic and CB1 cannabinoid receptor-containing afferents, and cholinergic regulation of endocannabinoid synthesis in the hippocampus suggest a significant cholinergic-endocannabinergic interplay. Given the functional importance of the cholinergic modulation of endocannabinoid signaling, here we studied CB1 cannabinoid receptor distribution in cholinergic basal forebrain territories and their cortical projection areas in a prosimian primate, the gray mouse lemur. Perisomatic CB1 cannabinoid receptor immunoreactivity was unequivocally present in non-cholinergic neurons of the olfactory tubercule, and in cholecystokinin-containing interneurons in layers 2/3 of the neocortex. Significantly, CB1 cannabinoid receptor-like immunoreactivity was localized to cholinergic perikarya in the magnocellular basal nucleus. However, cortical cholinergic terminals lacked detectable CB1 cannabinoid receptor levels. A dichotomy of CB1 cannabinoid receptor distribution in frontal (suprasylvian) and parietotemporal (subsylvian) cortices was apparent. In the frontal cortex, CB1 cannabinoid receptor-containing axons concentrated in layers 2/3 and layer 6, while layer 4 and layer 5 were essentially devoid of CB1 cannabinoid receptor immunoreactivity. In contrast, CB1 cannabinoid receptors decorated axons in all layers of the parietotemporal cortex with peak densities in layer 2 and layer 4. In the hippocampus, CB1 cannabinoid receptor-containing terminals concentrated around pyramidal cell somata and proximal dendrites in the CA1-CA3 areas, and granule cell dendrites in the molecular layer of the dentate gyrus. CB1 cannabinoid receptors frequently localized to inhibitory GABAergic terminals while leaving glutamatergic boutons unlabeled. Aging did not affect either the density or layer-specific distribution of CB1 cannabinoid receptor-immunoreactive processes. We concluded that organizing principles of CB1 cannabinoid receptor-containing neurons and their terminal fields within the basal forebrain are evolutionarily conserved between rodents and prosimian primates. In contrast, the areal expansion and cytoarchitectonic differentiation of neocortical subfields in primates is associated with differential cortical patterning of CB1 cannabinoid receptor-containing subcortical and intracortical afferents.

Influence of Factor V HR2 on Thrombin Generation and Clinical Manifestation in Rare Bleeding Disorders

In this study we investigated the influence of the presence of the factor V HR2 haplotype, defined by the factor V gene mutation H1299R (FVHR2), on thrombin generation. Measurements were performed in platelet-poor plasma of individuals with factor VHR2 or factor VLeiden in comparison to a control group carrying none of these mutations. Coagulation was triggered by low concentrations of recombinant tissue factor in the presence of activated protein C. Thrombin generation was monitored by a fluorogenic substrate. The endogenous thrombin potential was calculated from the obtained curves. As a result we observed an increased thrombin generation both for individuals heterozygous and homozygous for FVHR2. The level of endogenous thrombin potential is in the same range as in samples of patients heterozygous or homozygous for FVLeiden. The results indicate that FVHR2 plays a role as a risk factor for venous thrombosis in homozygous patients through an increased thrombin generation. The association between different clinical manifestations in individuals with FVII deficiency and endogenous thrombin potential and the presence of FVHR2 was studied.

Thrombin Generation — Comparison of ROTEM and Technothrombin TGA

Measurement of thrombin generation (TG) with fluorimetric methods demands a high technical support. On the other hand ROTEM analyzer is used in many laboratories. Both methods allow the measurement of TG in platelet rich plasma. Using identical reagents and calculation procedures for both methods the results of both techniques are comparable. The basic ideas for this were published by Ingerslev et al. [1].