ALBERT

Description: Introduction Refractory anemia with ring sideroblasts (RARS), as a form of acquired primary sideroblastic anemia, represents about 11% of myelodysplastic syndromes (MDS) and is classified as a low risk MDS. It´s defined by the WHO as a pure dyserythropoietic disorder with presence of 〉15% ringed sideroblasts in the bone marrow. Abnormal expression of several genes of heme synthesis in this MDS subgroup and excessive accumulation of iron especially in mitochondria, the main place of reactive oxygen species (ROS) formation, contributes to the elevated oxidative stress. Oxidative stress is also known as one of the factors involved in the pathogenesis of MDS. High iron concentrations catalyse a Fenton reaction, where a hydroxyl radical is produced from hydrogen peroxide and causes an increase in ROS which may lead to the oxidation of DNA, lipids, and proteins, thereby causing cell damage. The aim of this study was to find a useful method for detection and identification of oxidatively modified proteins in plasma unique for RARS patients. Methods Carbonylated protein levels were determined spectrophotometrically using dinitrophenylhydrazine (DNPH) derivatization. Oxidatively modified proteins of plasma samples were derivatized with biotin hydrazide. The dialyzed biotin hydrazide labeled samples and negative controls were mixed with monomeric avidin resin. Captured carbonylated proteins were digested by trypsin and then identified by MS/MS mass spectrometry coupled to a nano-LC system. Mascot (Matrix Science, London, UK) was used for database searching (Swiss-Prot). Two unique peptides (with a higher Mascot score than the minimum for identification, P

Description: Introduction: Myelodysplastic syndromes (MDS) represent a heterogeneous group of clonal stem cell disorders characterized by ineffective hematopoesis, associated with cytopenias and high risk of leukemic transformations with common morbidity. MDS are hematological malignancies of unclear etiology where oxidative/nitrative stress may contribute to the pathogenesis1. The posttranslational oxidative modifications of proteins and low molecular weight compounds are induced, revealing dysbalance of redox systems in vivo. Nitration of tyrosine either in free form or bound in proteins is important marker of nitric oxide synthase (NOS) activity shift in the presence of oxidative stress in favour of superoxide formation. The aim of this work was to assess whether 3-nitrotyrosine (3-NT) serum concentrations are enhanced also in MDS patients. Methods: Serum samples were obtained using blood of either MDS patients or healthy donors. All tested individuals agreed to the study at the time of blood collection. We proposed HPLC-MS/MS method to estimate 3-NT concentration in serum samples using QTRAP 4000 mass spectrometer (ABSciex, Prague, Czech Republic). Serum proteins were precipitated using ethanol, supernatants were evaporated, reconstituted in 0.1% HCOOH/2% methanol and injected onto HALO C18 microcolumn 100x0.5 mm (ABSciex, Prague, Czech Republic). Oxidative stress in MDS patients and controls was assessed by serum malondialdehyde concentrations measured by HPLC of 2-thiobarbituric acid MDA derivative using UV detection. Results: The sensitivity of method proposed for analysis of 3-NT in sera was sufficient for estimation of differences of 3-NT in patients and control samples. We have found enhanced concentrations of both MDA and 3-nitrotyrosine in serum of MDS patients as compared with healthy donors. Discussion: Enhanced MDA concentrations in MDS patients confirmed the presence of oxidative stress in MDS patients. The reactive oxygen species may oxidize tetrahydrobiopterin, important cofactor of NOS, resulting into nitric oxide synthase uncoupling with enhanced superoxide and consequently peroxynitrite production2. It is known that methylarginines, naturally occurring inhibitors of NOS, can profoundly increase superoxide generation from uncoupled NOS. Recently, we have found significantly enhanced concentration of asymmetric dimethylarginine in a serum of middle age patients with myelodysplastic syndrome3. The observed increased concentrations of 3-NT in MDS patients correspond with assumed enhanced peroxynitrite formation as compared with controls. 3-nitrotyrosine concentrations thus could serve as a new criterion of NOS changed activity in MDS patients. Literature: 1. Farquhar MJ, Bowen DT. Oxidative stress and the myelodysplastic syndromes. Int J Hematol. 2003;77:342-350. 2. Pacher P, Beckman JS, Liaudet L. Nitric oxide and peroxynitrite in health and disease. Physiol Rev. 2007;87:315-424. 3. Štikarová J, Suttnar J, Pimková K, Chrastinová-Mášová L, Čermák J, Dyr JE. Enhanced levels of asymmetric dimethylarginine in a serum of middle age patients with myelodysplastic syndrome. Journal of Hematology & Oncology. 2013;6:58. Disclosures No relevant conflicts of interest to declare.

Description: Introduction Acute myeloid leukemia (AML) represents an aggressive bone marrow malignancy with diverse genetic abnormalities. The tumor cells, to support their own growth and proliferation, may alter metabolism 1) to accelerated glycolysis to provide energy/biosynthetic precursors and 2) to produce intermediates by active TCA cycle for synthesis of essential biomolecules [1]. Mutations of isocitrate dehydrogenase (IDH1/2) as frequent mutations (affecting approximately 20% of AML patients) cause the reduction of α-ketoglutarate to D-2-hydroxyglutarate instead of oxidative decarboxylation of isocitrate to α-ketoglutarate. IDH2 mutations occur almost exclusively in hematopoietic tumors. Whereas IDH2R140 mutation is frequently accompanied by normal cytogenetics and NPM1 mutations, IDH2R172 is frequently the only mutation detected in AML. In addition, IDH2R172 confers a poor prognosis in patients with AML [2, 3]. The aim of this study was to characterize and uncover the differences in metabolism of AML patients with or without IDH2 mutations in diagnosis (the initial stage), in remission (after chemotherapy treatment), and before transplantation (after conditioning). Methods Serum metabolomics profiles were generated with samples obtained at diagnosis, in remission, and before transplantation from patients (n=20) treated in the Institute of Hematology and Blood Transfusion, Prague, Czech Republic. Patients were assigned in IDH2WT (n=7) and IDH2R140/ IDH2R172 (n=7/6) groups. Targeted metabolomic profiling of 19 metabolites related mainly to TCA cycle and glycolysis was performed by LC-MS/MS. Results Using non-parametric randomized block analysis of variance (Friedman test) we found significant differences in levels of 13 metabolites among treatment periods for all AML patients. Moreover, when comparing each treatment periods for all patients, we found significantly decreasing levels of 12 metabolites between the initial stage and the period before transplantation. If we considered the division of patients into groups according to IDH2 mutations, we found significantly different levels of 4 metabolites among treatment periods for samples of patients with IDH2R140,namely 2 metabolites of TCA cycle: isocitrate, succinate; and 3-hydroxybutyrate and urate. We obtained significantly different levels in the same number of other metabolites for IDH2WT. In samples of patients with IDH2R172 we found significantly different levels of 8 metabolites among treatment periods, namely 5 metabolites of TCA cycle: citrate, 2-hydroxyglutarate, succinate, fumarate, malate; 2 metabolites of glycolysis: 3-phosphoglycerate, phosphoenolpyruvate; and pyroglutamate of glutathione metabolism. Furthermore, using Nemenyi post-hoc test we ascertained significantly decreasing levels of named metabolites in IDH2R140 and IDH2R172 samples before transplantation with respect to the initial stages of AML (diagnosis). Conclusion Overall, this study identified significant changes in several metabolites of TCA cycle and glycolysis between initial and final treatment periods and also between remission and period before transplantation in AML patients. With respect to IDH2 mutations we found more significant changes in metabolites specifically in TCA cycle for IDH2R172 patients relative to IDH2R140. The results of our preliminary targeted metabolomic profiling of AML patients with IDH2 mutations are corresponding with the already described differences in morphological and genetic patterns in the patients and, moreover, support the classification of IDH2R172 as separate AML subtype. Metabolomic profiling thus seems to be a new valuable tool providing additional important information. Acknowledgment This work was supported by the European Regional Development Fund and the state budget of the Czech Republic (project AIIHHP: CZ.02.1.01/0.0/0.0/16_025/0007428, OP RDE, Ministry of Education, Youth and Sports), by the project of the Ministry of Health, Czech Republic, 00023736, by Grant from the Academy of Sciences, Czech Republic, P205/12/G118, and by ERDF OPPK CZ.2.16/3.1.00/24001. [1] DeBerardinis RJ, Lum JJ, Hatzivassiliou G, Thompson CB. Cell Metab. 2008;7(1):11-20. [2] Rakheja D, Konoplev S, Medeiros LJ, Chen W. Hum Pathol. 2012;43(10):1541-51. [3] Meggendorfer M, Cappelli LV, Walter W, Haferlach C, Kern W, Falini B, Haferlach T. Leukemia. 2018;32(5):1249-1253. Disclosures No relevant conflicts of interest to declare.

Description: Fibrinogen is a 340 kDA glycoprotein that plays a vital role in the hemostasis. The three pairs of polypeptide chains (Aα, Bβ and γ) form a heterodimer structure of fibrinogen, each chain is encoded by a distinct gene (FGA, FGB and FGG). Congenital dysfibrinogenemia is a rare qualitative disorder characterized by structural alterations in fibrinogen molecule resulting in its defective function. The clinical manifestation of majority cases is asymptomatic (50%); about 30% are associated with bleeding tendencies and only some cases are thrombotic (20%). In this study, we evaluated 25 patients with heterozygous missense mutations in exon 2 of FGA gene from 13 unrelated families, all with low levels of functional fibrinogen and prolonged clotting time. All mutations were located around thrombin cleavage site at N-terminus of a fibrinogen Aα chain. Mutation Aα G13E was found in 6 families (13 patients), Aα R16H in 4 families (6 patients), Aα R16C in 1 family (4 patients), and Aα R19G in 1 family (2 patients). Correlations between the genotype and phenotype were studied by fibrin polymerization, fibrinolysis, kinetics of fibrinopeptides release, and electron and confocal microscopy. The viscoelastic properties of fibrin clots were measured. All mutations caused a delay or absence of fibrinopeptide A release and prolonged fibrin polymerization. Clinical phenotypes of mutations were, unexpectedly and importantly, highly heterogeneous. Out of 25 patients 17 were asymptomatic, 7 had the bleeding tendencies and 1 patient had thrombosis. One woman with Aα G13E had 2 spontaneous abortions and 3 pregnant women with Aα G13E, Aα R16C and Aα R19G mutations suffered for hemorrhages or postpartum bleeding. Eventually, all had successful delivery under provided care with a hematologist. Small surgeries were performed to patients with Aα R16H supplied with fibrinogen concentrates and antifibrinolytics. Our observations show that the patients should be carefully treated based both on the results of the laboratory analyzes and personal and family history. This work was supported by the project of the Ministry of Health, Czech Republic, for conceptual development of research organization 00023736, by Grant from the Academy of Sciences, Czech Republic nr. P205/12/G118, and by ERDF OPPK CZ.2.16/3.1.00/24001. Disclosures No relevant conflicts of interest to declare.

Description: Background Cardiovascular diseases are linked with oxidative stress which is the source of reactive oxidative and nitrative species, contributors of post-translational modification. Fibrinogen due to its high concentration in blood is considered as one of the most sought of targets of oxidative stress substances. Post-translational modifications of fibrinogen might influence its physiological function, thus affect hemostasis in the terms of fibrin nets forming and architecture or interaction with platelets. The aim of this study was to observe influence of in vivo fibrinogen modifications on formation of fibrin net and to identify amino acid residues prone to changes related to oxidative stress. Methods Plasma samples were collected from patients of The Military University Hospital Prague in the agreement with ethical committees of participating institutions and with informed consents from all subjects. Samples were divided into 4 groups: patients with acute coronary syndrome (A), patients with stroke (B), patients with thrombus localized in carotid vein (C) and control group (patients without coronary atherosclerosis; D). Fibrin net architecture was studied by scanning electron microscopy (Mira 3 LMH, Tescan Orsay Holding, a.s., Brno, Czech Republic). For identification of modified amino acids residue mass spectroscopy was used (Triple TOF 6600, Sciex). Molecular dynamics simulations of hydrated protein were performed in Gromacs software with Gromos force fields. Crystal structure 3GHG was used as a reference structure to which post-translational modifications were introduced manually in Yasara View. Results We found extensive both qualitative and quantitative changes in the structure of fibrinogen molecule in all groups of patients. Oxidative stress level differed among patient groups and between the control group. Different oxidative changes caused by in vivo modifications of fibrinogen affected quite distinctly the architecture of fibrin net. Modified amino acids were detected in all three fibrinogen chains. In gamma chain the localisation of modified amino acid residues correlated with the part of fibrinogen important for fibrin polymerisation. The impact of the most pronounced post-translational modifications on the secondary structure of fibrinogen was described by molecular dynamics simulations. Conclusions The results show that the degree of impairment of fibrinogen functions in the cardiovascular diseases is related to the level of oxidative stress. Characterization of oxidative fibrinogen modification and its precise meaning to the function of fibrinogen in hemostasis appears to be extremely helpful to better understanding of thrombotic/bleeding complications linked with various cardiovascular diseases. Acknowledgments This work was supported by the Ministry of Health, Czech Republic, no. 00023736, by the Academy of Sciences, Czech Republic no. P205/12/G118 and NV18-08-00149, by ERDF OPPK CZ.2.16/3.1.00/24001 and by the European Regional Development Fund and the state budget of the Czech Republic (project AIIHHP: CZ.02.1.01/0.0/0.0/16_025/0007428, OP RDE, Ministry of Education, Youth and Sports). Disclosures No relevant conflicts of interest to declare.

Description: Development of tools for direct thrombus imaging represents a key step for diagnosis and treatment of stroke. Nanoliposomal carriers of contrast agents and thrombolytics can be functionalized to target blood thrombi by small protein binders with selectivity for fibrin domains uniquely formed on insoluble fibrin. We employed a highly complex combinatorial library derived from scaffold of 46 amino acid albumin-binding domain (ABD) of streptococcal protein G, and ribosome display, to identify variants recognizing fibrin cloth in human thrombus. We constructed a recombinant target as a stretch of three identical fibrin fragments of 16 amino acid peptide of the Bβ chain fused to TolA protein. Ribosome display selection followed by large-scale Enzyme-Linked ImmunoSorbent Assay (ELISA) screening provided four protein variants preferentially binding to insoluble form of human fibrin. The most specific binder variant D7 was further modified by C-terminal FLAG/His-Tag or double His-tag for the attachment onto the surface of nanoliposomes via metallochelating bond. D7-His-nanoliposomes were tested using in vitro flow model of coronary artery and their binding to fibrin fibers was demonstrated by confocal and electron microscopy. Thus, we present here the concept of fibrin-targeted binders as a platform for functionalization of nanoliposomes in the development of advanced imaging tools and future theranostics.

Description: Introduction Myelodysplastic syndromes are clonal hematopoetic stem cell disorders characterized by refractory cytopenias with displasia as a result of ineffective hematopoiesis. Approximately 30 percent of MDS cases progress to acute myeloid leukemia. Excess blasts are the strongest predictors for poor outcome and are associated with disease progression. Because of its heterogeneity and lack of molecular and protein markers that effectively monitor disease progression, clinical management of MDS patients is challenging. The concentrations of several proteins were found elevated during MDS disease. Their interaction with receptors/ligands is a part of signaling pathways that may play a crucial role in pathogenesis of the disease. Serum levels of vascular cell adhesion protein 1 (VCAM1) and intercellular adhesion molecule 1 (ICAM1) were found higher in MDS patients in comparison with control group and were related to MDS severity. Alpha-2-HS-glycoprotein (FETUA) was analyzed in plasma of MDS patients. Leucine-rich alpha-2-glycoprotein (LRG) was found increased in RAEB-I and RAEB-II patients by proteomic studies. In this work we developed a protein chip for study of molecular interactions in plasma of MDS patients using surface plasmon resonance (SPR) imaging. Interacting proteins were analyzed and identified using LC-MS/MS. Methods Patients with diagnosis of refractory anemia and refractory anemia with ringed sideroblasts (RA/RARS, n=13), refractory cytopenia with multilineage dysplasia (RCMD, n=16), and refractory anemia with excess blasts (RAEB, n=15) as a subgroup of MDS, and MDS patients who progress to acute myeloid leukemia (AML, n=8) were chosen for this study. The high-resolution SPR imaging (SPRi) system with polarization contrast and internal referencing combined with dispersionless microfluidics was used to study protein interactions. Passive mixing structures were employed to further improve the sensing performance of this SPRi biosensor. The respective biomarkers (ICAM1, VCAM1, FETUA and LRG) were covalently attached to the functionalized sensor surface and interaction with their counterparts in MDS plasma samples were monitored. Interacting proteins were removed from the chip surface by diluted NaOH, treated by trypsin, analyzed by nanoLC-MS/MS (TripleTOF 5600) and identified using ProteinPilot database. Results and Conclusion Significant differences were observed between analyzed MDS subtypes for VCAM1, FETUA, and LRG (ANOVA: P = 0,00755, P = 0,0306 and P 〈 0.001 respectively). Using post hoc Tukey contrasts tests we ascertained that sensor responses were significantly higher in group RCMD and AML with respect to the healthy donors for immobilized VCAM1 and in group RA/RARS, RCMD, RAEB and AML with respect to the healthy donors for LRG. Moreover sensor responses were significantly higher in group AML with respect to the RA, RCMD or RAEB for immobilized LRG. Based on our results LRG seems to be a suitable marker of MDS progression. The identified proteins presented in MDS plasma samples unlike in healthy donor plasma are clusterin, protein S100-A8, serum amyloid A-1 protein, annexin A2, and zinc-alpha-2-glycoprotein among others. S100-A8 and clusterin have been connected with MDS or AML previously; it could be tested as a new protein marker of MDS by SPRi. The results show that SPR biosensors combined with nanoLC-MS/MS are a promising tool for improvement of the diagnosis in complex heterogeneous malignancies. Disclosures No relevant conflicts of interest to declare.

Description: Introduction: Myelodysplastic syndromes (MDS) are a heterogenous group of oncohematologic diseases, characterized by bone marrow hypercellularity, dysplasia of myeloid lineage cells, peripheral cytopenias, and an increased risk of evolution to acute myeloid leukemia (AML). Pathophysiology of MDS is not fully understood, however it has been described that oxidative stress plays an important role in initiation and disease progression. Oxidative stress is defined as an imbalance between prooxidative and antioxidative processes that prefers the production of reactive oxygen species (ROS) over an antioxidant defence. The association between MDS and oxidative stress was discussed in several studies, where functional mitochondrial abnormalities in MDS patients have been demonstrated as one of the possible sources of oxidative stress. Another mechanism could be associated with mitochondrial dysfunction via iron overloading, mitochondrial DNA mutation, systemic inflammation, and bone marrow stromal defects. Protein carbonylation is ROS-mediated protein oxidation and it is defined as an irreversible post-translational oxidative modification. The detection of protein carbonyl groups is a specific useful marker of oxidative stress. The aim of this study was to determine the levels of carbonylated proteins in plasma of MDS patients resp. in plasma of individual subtype of MDS patients and evaluate changes of carbonylated plasma proteome in MDS patients compared with healthy controls. Methods: The content of protein carbonyls was measured after derivatization with dinitrophenylhydrazine by monitoring absorbance between 250 and 500nm. Carbonylated proteins of plasma samples were purified after reaction with biotin hydrazide. The negative controls were processed using the exact same procedure, except biotin hydrazide labeling. The dialyzed biotin hydrazide labeled samples and the negative controls were isolated using monomeric avidin resin. All the samples were prepared in doublets. One part of samples was used for the on bead tryptic digestion and the second part of samples was separated by SDS-PAGE after eluation with Laemmli buffer. The obtained carbonylated proteins were identified by mass spectrometry (LC-MS/MS). Results: We have examined 32 patients with different MDS subtype (10 patients RAEB-1,2; 12 RCMD; 10 RARS) and 20 healthy controls. Diagnoses of different subgroups of MDS were established according to the WHO classification criteria. The median age of patients group was 64,5 and presented 17 males (57 %); the median age of healthy controls group was 43 and presented 10 males (50 %). We have found significantly (P

Description: Introduction The use of thromboaspiration in primary percutaneous intervention (PCI) for ST-segment elevation myocardial infarction (STEMI) has offered a unique opportunity to study thrombus composition, its dynamic formation, and architecture in vivo. There has been, however, several limitations, not least the fact that the technique has not yet allowed a precise transversal analysis from one side of the artery to the other, as is done in histological analysis. The dynamic process of intracoronary thrombus formation in STEMI patients is thus still not well understood. Ischemic time was hypothesized to be among the strongest independent correlates of thrombus architecture. In time the platelets are decreasing its proportion and fibrin proportion is increasing (J Silvain, J-P Collet, JW Weisel et al, J Am Coll Cardiol 2011; 57:1359). However, no real report on the internal structures of the in vivo formed thrombi has been shown so far. Therefore, we investigated both the surface and the composition of longitudinally freeze-fractured thrombi. Methods Thrombi were collected by PCI from 119 STEMI patients. Out of the patients there were "early comers " (˃12 h from symptom onset; 23 patients) and "late comers" (more than 720 min; 29 patients). The mean age of all patients was 64 years, 70% of patients were males, 51% were smokers, 50% had arterial hypertension, 20% were diabetics and 23% had chronic renal insufficiency. Scanning electron microscopy; collected thrombi obtained by PCI were thoroughly washed in saline solution and stored in 4% formaldehyde prior dehydration. To reveal the internal structures of the thrombi selected samples were longitudinally freeze fractured in liquid nitrogen and coated with platinum. Samples were examined in SEM Vega Plus TS 5135 (Tescan s.r.o., Brno, Czech Republic). Whole areas of the freeze-fractured thrombi were scanned. Results and discussion The thrombus composition of longitudinally freeze-fractured thrombi was compared between groups of "early-comers" and "late-comers. The distribution of the components in the "early comers" thrombi freeze-fracture seemed to be uniform. Platelets were far the main component (about 75 % in proportion) of the "early comers" thrombus, followed by fibrin and other compounds. The amount of red blood cells was negligible (about 2 - 8 %). We did not observe any significant differences between the thrombi in the group of early comers. Thrombi of the "late-comers" group were composed mainly of red blood cells; platelets and fibrin formed only minority of the thrombi. In contrast to the "early comers" the distribution of the main thrombus components in the "late comers" thrombi was dramatically different between individual parts of the thrombus. The number of platelets and red blood cells varied from 0% to almost 99% and vice versa. It was possible to estimate the initiating place of the thrombus as well as the direction of the growth. Each thrombus could be divided into parts formed mainly either by platelets or by red blood cells. It seems that thrombus develops a regional architecture defined by the extent of platelet activation and packing density. It has been reported that in contracted clots and thrombi, erythrocytes are compressed to close-packed polyhedral structures with platelets and fibrin on the surface demonstrating how contracted clots form an impermeable barrier important for hemostasis and wound healing (D Cines, T Lebedeva, J Weisel et al, Blood 2014; 123:1596). Our investigation of the composition of the in vivo formed thrombi supports these results and helps to explain how fibrinolysis is greatly retarded as clots grow and contract. We have found that on the surfaces of late-comers thrombi fibrin thick fibrils were present. It has been shown that the association of soluble fibrinogen with the fibrin clot results in the reduced adhesiveness of such fibrinogen/fibrin matrices toward leukocytes and platelets (VK Lishko, T Burke, T Ugarova, Blood 2007; 109:1541). Fibrinopeptides A are less accessible for thrombin in surface bound fibrinogen which thus provides additional level of protection of thrombi from premature dissolution (T Riedel, L Medved, JE Dyr, Blood 2011; 117:1700). These findings may have great impact on our knowledge of pathophysiology of the thrombus growth and possible therapeutic consequences related to the time of symptom onset. Disclosures No relevant conflicts of interest to declare.

Description: Introduction Thrombosis is a common pathology underlying ischemic heart disease, stroke, and venous thromboembolism. D-dimer is a global indicator of blood coagulation activation and fibrinolysis and, therefore, an indirect marker of thrombotic activity. D-dimers half-life is 48 hours. D-dimer determination is the standard procedure in the treatment of thrombosis. Serine protease thrombin plays pivotal roles in thrombosis and hemostasis, blood coagulation and platelet activation. Thrombin has a short half-life and naturally occurring inhibitors, such as antithrombin, rapidly bind thrombin, which makes the direct measurements of in vivo active thrombin difficult. Thrombin binds to fibrin where it is quite efficiently protected from inhibition by heparin-antithrombin but susceptible to inactivation by different antithrombin-independent inhibitors. There are two low affinity non-substrate thrombin binding sites, one in each half of the dimeric fibrinogen E region, and one high affinity thrombin non-substrate binding site on fibrinogen gamma' chains inside the D region (Meh DA, Siebenlist KR, Mosesson MW, J Biol Chem. 1996, 23121-5). We have shown that thrombin bound to fibrin promotes further fibrin growth in the presence of fibrinogen and absence of free thrombin in solution (Riedel T, Brynda E, Dyr JE, Houska, M, J. Biomed. Mater. Res. Part A 2009, 437-447). The aim of this project was to look for any thrombin activity on isolated D-dimers using several commercial D-dimer kits in groups of patients with elevated D-dimers. Methods Three D-dimers kits were used (ELISA kits CEA506Hu, USCN and D-Dimer (D2D), BioAssay™; and immunoturbidimetric assay D-Dimer KAI-090, K-ASSAY). To detect thrombin activity on captured D-dimers one chromogenic (S-2238, Chromogenix) and two fluorogenic (SN-59, Haematologic Technologies, Inc.; (p-tosyl-Gly-Pro-Arg)2-R110, Thermo Fisher Scientific, Inc.) specific substrates and specific inhibitors (hirudine and PPACK) were used. Independently, bound proteins were removed from immobilized antibodies in 8 M urea and after treatment with trypsin analyzed by mass spectrometry (TripleTOF 5600, Sciex). 34 patients with high, moderate, and low levels of D-dimers and with different diagnosis were analyzed. Results Out of 18 patients with main diagnosis linked with thrombosis 61 % exhibited active thrombin on D-dimers. In these patients we found active thrombin bound to D-dimers captured by antibodies in all applied D-dimer kits. Using mass spectrometry thrombin bound to isolated D-dimers was detected. Specificity of thrombin activity related to D-dimers was determined by combination of several specific thrombin substrates and inhibitors. The activity of bound thrombin was remarkably stable over the period of more than 24 hours. It showed that precise measurement of even very low activity of thrombin was possible. In the group of 16 non-thrombotic patients with elevated D-dimers only 19 % exhibited thrombin activity. Interestingly, differences in values of thrombin activity were up to five orders of magnitude and differences in the activities related to the value of captured D-dimers were even greater. Conclusion This, to our knowledge, is the first report showing the presence of active thrombin bound to circulating D-dimers. Although the group of patients we were so far able to evaluate is too small to being statistically tested, the results are highly encouraging. The amount of bound active thrombin on fibrin degradation products reflects the way of thrombus formation and its degradation (times, durations and rates of relevant reactions and especially the rate of thrombin generation). The thrombin concentration present at the time of fibrin gelation plays an important role in formation of fibrin clot structure, including its mechanical and fibrinolytic stability. It remains to be seen in further studies with much larger cohorts of patients if the presence of active thrombin has any impact on pathophysiology of thrombosis and if its determination may be of importance for the improvement of diagnosis of thrombotic events. Supported by the project of the Ministry of Health of the Czech Republic for conceptual development of the research organization 00023736, by Grant from the Academy of Sciences, Czech Republic (P205/12/G118), and by ERDF OPPK CZ.2.1.16/3.1.00/28007. Disclosures No relevant conflicts of interest to declare.