The combined effect of fibrin formation and factor XIII A subunit Val34Leu polymorphism on the activation of factor XIII in whole plasma

The first step in the activation of blood coagulation factor XIII (FXIII) is the proteolytic cleavage of the potentially active A subunit (FXIII-A) by thrombin at Arg37-Gly38. Both fibrin formation and FXIII-A Val34Leu polymorphism influence the rate of proteolytic activation of purified factor XIII, however their relative importance and interaction in determining the time of onset and the rate of FXIII activation in whole plasma have not yet been explored. In the present study it was shown that in plasma, fibrin formation preceded the truncation of FXIII-A by thrombin, the activation process took place exclusively on the surface of newly formed fibrin and activated FXIII remained associated with the fibrin clot. The time of fibrin formation closely correlated with the time of FXIII activation, while there was no significant relationship between the time of FXIII activation and FXIII-A Val34Leu genotype. However, in the case of Leu34 variant the lag phase between fibrin formation and FXIII-A truncation was significantly shorter than in the case of Val34 variant. The results suggest that in whole plasma the onset of FXIII activation is determined by fibrin formation, while the rate of activation is modulated by Val34Leu polymorphism.

Coagulation factor XIII-A. A flow cytometric intracellular marker in the classification of acute myeloid leukemias

The association of coagulation factors with leukocytes have been demonstrated in several previous studies. This study was designed to study the sensitivity and specificity of factor XIII subunit A (FXIII-A) labelling in cultured myeloblastic and monoblastic cell lines and to investigate the intracytoplasmic expression of FXIII-A in de novo acute myeloid leukemia (AML) samples. Myeloblastic and a monoblastic cell lines were cultured and investigated for lineage specific maturation markers and FXIII-A expression. Furthermore, FXIII-A expression was investigated in 12 normal samples (7 bone marrow and 5 peripheral blood), 86 de novo AML samples and 6 chronic myelomonocytic leukemia (CMML) samples. In the monoblastic MonoMac6 cell line the appearance of FXIII-A preceded that of CD14 while it remained negative in the myeloblastic PLB-985 cell line throughout its maturation period. Among the AML samples the average frequency of FXIII-A positive cells in myeloblastic leukemia samples was below 10%, while in M4 and M5AML samples it was above 50% and was significantly higher than the generally used CD14 marker (p < 0.0001). In the AML M4 and M5 cases, FXIII-A proved sensitive for the identification of monoblasts. FXIII-A can be considered as a reliable intracytoplasmic marker for the monocytic and megakaryocytic series and its presence is highly predictive for mono- and megakaryocytic AML and for CMML.

High-throughput scintillation proximity assay for transglutaminase activity measurement

Members of the transglutaminase enzyme family are involved in a broad range of biological phenomena, including haemostasis, apoptosis, semen coagulation, skin formation, and wound healing. A new and rapid method for measurement of transglutaminase activity is described in this article. The enzyme links tritium-labeled putrescine to biotinylated oligoglutamine, and the tritiated peptide is bound to a streptavidin-coated microtiter plate permanently covered by a thin layer of scintillant. Only the radioisotope incorporated into the peptide substrate is close enough to the scintillant molecules for photons to be produced. The signal generation depends on the transglutaminase activity, and it can be detected by appropriate light-measuring instrumentation without separation steps. The assay is sensitive, specific, linear at concentrations of tissue transglutaminase between 0.05 and 1.6m U/ml, and suitable for high-throughput measurements.

Factor XIII in bronchoalveolar lavage fluid from children with chronic bronchoalveolar inflammation

BACKGROUND

Extravascular activation of the coagulation system and consequent fibrin deposition is involved in the pathomechanism of chronic bronchoalveolar inflammatory diseases. The turnover of extravascular fibrin is attenuated by its cross-linking with activated factor XIII (FXIII).

OBJECTIVES

Determination of cellular and plasmatic forms of FXIII and their correlation with D-dimer level in the bronchoalveolar lavage fluid (BALF) from healthy children and from children with bronchoalveolar inflammation.

PATIENTS AND METHODS

Highly sensitive immunoassays were used for the quantitation of cellular and plasma FXIII and D-dimer in the BALF of children with recurrent wheezy bronchitis and fibrosing alveolitis. BALF was investigated for FXIII-containing cells by flow cytometry.

RESULTS AND CONCLUSIONS

In the BALF of controls a low amount of the cellular form of FXIII (FXIII A2) and D-dimer were measured, while plasma FXIII (FXIII A2B2) was absent. Alveolar macrophages represented the single cell population in BALF that contained FXIII. In the BALF of both patients' groups the concentration and the total amount of FXIII A2 was significantly elevated, and plasma FXIII also appeared in the BALF of most patients. The D-dimer concentration was also elevated in the patients' groups and it correlated both with plasma FXIII and neutrophil count. These findings suggest that FXIII A2 is released from activated or injured alveolar macrophages into the bronchoalveolar lining fluid and in bronchoalveolar inflammatory diseases, FXIII A2B2 also leaks out from the capillaries. By cross-linking fibrin and inhibitors of fibrinolysis to fibrin, FXIII might be a key regulator of fibrin turnover in the extravascular compartment.

Fibrin stabilization (factor XIII), fibrin structure and thrombosis

Factor XIII (FXIII) is a zymogen that is converted into an active transglutaminase (FXIIIa) by the concerted action of thrombin and Ca2+. Its main task is to crosslink alpha-, and gamma-chains of fibrin and alpha2-plasmin inhibitor to fibrin. By this way FXIIIa strengthens fibrin and protects it from the prompt elimination by fibrinolytic system.The changes of FXIII level in thrombotic diseases are hardly explored and there are contradictory results concerning the protective effect of Val34Leu polymorphism against arterial or venous thrombosis. The results suggest that the thrombo-protective effect of Leu34 allele prevails only in certain genetic and/or environmental constellations.

Rapid detection of the factor XIII Val34Leu (163 G-->T) polymorphism by real-time PCR using fluorescence resonance energy transfer detection and melting curve analysis

The Val34Leu polymorphism in the A subunit of blood coagulation factor XIII (FXIII-A) is located in the activation peptide, just three amino acids upstream of the thrombin cleavage site. The Val-->Leu replacement accelerates the rate of the proteolytic activation of FXIII and it seems to provide protection against myocardial infarction. Methods available for the assessment of the FXIII-A Val34Leu polymorphism are rather time-consuming, laborious and not easily applicable for large-scale studies. In this study a new method based on real-time PCR with fluorescence resonance energy transfer (FRET) detection and melting curve analysis was developed. The rapid, simple method was adapted to the widely used real-time PCR instrument, LightCycler (Roche Diagnostics). The results showed 100% coincidence with those obtained by the traditional PCR-restriction fragment length polymorphism (RFLP) assay and fluorescent DNA sequencing. Using this method, an allele frequency of 24.2% was obtained (n=113), which well agrees with the allele frequency obtained by PCR-RFLP on a different group of the same ethnic Hungarian population (25.9%).

GJB2mutations in patients with non-syndromic hearing loss from Northeastern Hungary

Mutations in the GJB2 gene encoding the gap-junction protein connexin 26 have been identified in many patients with childhood hearing impairment (HI). One single mutation, c.35delG, accounts for the majority of mutations in Caucasian patients with HI. In the present study we screened 500 healthy control individuals and a group of patients with HI from Northeastern Hungary for GJB2 mutations. The patients' group consisted of 102 familial from 28 families and 92 non-familial cases. The most common mutation in the Hungarian population is the c.35delG, followed by the c.71G>A (p.W24X) mutation. 34.3% of the patients in the familial group were homozygous, and 17.6% heterozygous for 35delG. In the non-familial group the respective values were 37% and 18% (allele frequency: 46.2%). In the general population an allele frequency of 2.4% was determined. Several patients were identified with additional, already described or new GJB2 mutations, mostly in heterozygous state. The mutation c.380G>A (p.R127H) was formerly found only in heterozygous state and its disease relation was controversial. We demonstrated the presence of this mutation in a family with three homozygous patients and 4 heterozygous unaffected family members, a clear indication of recessively inherited HI. Furthermore, we provided evidence for the pathogenic role of two new mutations, c.51C>A (p.S17Y) and c.177G>T (p.G59V), detected in the present study. In the latter case the pattern of inheritance might be dominant. Our results confirm the importance of GJB2 mutations in the Hungarian population displaying mutation frequencies that are comparable with those in the Mediterranean area.

Platelets but not monocytes contribute to the plasma levels of factor XIII subunit A in patients undergoing autologous peripheral blood stem cell transplantation

Factor XIII subunit A (FXIII A) is synthesized by megakaryocytes, and monocytes/macrophages. In addition, the liver has been reported as an extrahaematopoietic source of FXIII A. At present, the extent of contribution of either haematopoietic or extrahaematopoietic sources to the plasma FXIII A level is unknown. We studied the effect of bone marrow aplasia due to high-dose chemotherapy followed by autologous peripheral blood stem cell transplantation (ASCT) on plasma FXIII A activity and concentration in 20 patients with haematological or solid tumour malignancies. A multiple linear regression model was used to assess the effect of gender, age, malignancy and treatment types, platelet and monocyte counts, abnormal liver function tests, prothrombin time, and number of platelet transfusions on FXIII activity measured in plasma before and following ASCT. Significant correlation between platelet counts and FXIII A activity in plasma was observed (r = 0.51, P = 0.0001), which remained after the adjustment for the aforementioned parameters (multiple R = 0.52, P = 0.0001). In contrast, no significant correlation between FXIII A levels and monocyte counts was observed (r = 0.19), and this lack of correlation persisted after the adjustment. These results suggest that in the ASCT model, following myeloablation, platelets but not monocytes are the haematopoietic cells that contribute significantly to plasma FXIII A levels. In addition, extra-haematopoietic sources of FXIII synthesis may also contribute to FXIII levels in plasma.

Possible role of factor XIII subunit A in Fcγ and complement receptor-mediated phagocytosis

Besides its traditional role in hemostasis, factor XIII subunit A (FXIII-A) is supposed to function as a cellular transglutaminase and to be involved in certain intracellular processes, including cytoskeletal remodeling. To investigate its intracellular role, the aim of the present study was to follow changes in FXIII-A production in combination with the receptor-mediated phagocytic activities of monocytes/macrophages and to examine the phagocytic functions of monocytes in patients with FXIII-A deficiency. Human blood monocytes were isolated from the buffy coats of healthy volunteers and cultured for 4 days. The FcgammaR-mediated phagocytosis of sensitized erythrocytes (EA) and the complement receptor (CR)-mediated phagocytosis of complement-coated yeast particles were studied during monocyte/macrophage differentiation. Changes in the gene expression of FXIII-A were detected by real-time quantitative RT-PCR. FXIII-A protein production was investigated with fluorescent image analysis at single cell level and Western immunoblot analysis. Both the FcgammaR and CR-mediated phagocytosis increased during culturing, which peaked on day 3. The phagocytic activity of the cells could be markedly inhibited with monodansylcadaverine, an inhibitor of the transglutaminase-induced crosslinking of proteins. The phagocytosis of EA, complement-coated and uncoated yeast particles was found to be strongly diminished in monocytes of FXIII-A deficient patients. The phagocytic functions of cultured cells showed a change in parallel with the alterations in FXIII-A mRNA expression, as well as with that in FXIII-A in protein synthesis detected by image and Western immunoblot analyses in concert. Our results suggest that FXIII-A plays a role in the Fcgamma and complement receptor-mediated phagocytic activities of monocytes/macrophages.

[Lipid profile in patients with systemic lupus erythematosus, with special focus on lipoprotein(a) in lupus nephritis]

Systemic lupus erythematosus (SLE) is a multifactorial polysystemic autoimmune disorder. Although life expectance in SLE has been improved by adequate immune suppressive therapy, the importance of chronic renal failure has not been reduced. Among late complications of the disease accelerated atherosclerosis attempts increasing attention. Dyslipoproteinemia and increased concentration of lipoproteins are important risk factors of atherosclerotic cardiovascular complication in SLE. Serum lipid parameters of 50 patients with lupus were examined in the present work. Thirty patients had histologically proven lupus nephritis (LN+), while the other group did not have renal involvement (LN-). Serum triglyceride, total cholesterol, LDL-C and apolipoprotein B (apoB) concentrations were significantly higher in the lupus nephritis (LN+) group. On the other hand, HDL-C and apoAI levels were also elevated in patients with LN. As a consequence of that, LDL-C/HDL-C and the apoB/apoAI ratios did not differ between patients with or without kidney involvement. This concluded the authors to measure the concentration of lipoprotein (a) in SLE patients, as Lp(a) is known to be an independent risk factor of atherosclerosis. Results indicated a significantly increased Lp(a) concentration in patients with lupus nephritis as compared to the LN- group. All but 2 patients without kidney involvement had lower than 100 mg/L Lp(a) concentration, while 27% of patients with lupus nephritis has an Lp(a) level between 100-300 mg/L. Further more, Lp(a) concentration was higher than 300 mg/L in 13% of the LN+ group. In a good correlation of these observations patients with nephritis suffered more frequently from deep venous thrombosis and ischaemic heart disease. The frequencies of hypertension and non-insulin dependent diabetes mellitus were slightly elevated in patients with nephritis. Present results suggest the importance of elevated lipoprotein (a) concentration in patients with lupus nephritis, further increasing the risk of athero-thrombotic cardiovascular complications.

Evaluation of clinical and laboratory features of antiphospholipid syndrome: a retrospective study of 637 patients

We retrospectively analysed the data of 1519 antiphospholipid antibody (APLA) positive patients between 1986 and 1999. Among them 637 were considered to have antiphospholipid syndrome (APS) based on the 1999 preliminary classification criteria, while 704 patients had no clinical signs of the syndrome. Our aim was to compare the autoantibody profile and clinical characteristics of primary and secondary APS, moreover to evaluate the associations between different APLA and specific symptoms attributable to APS. In our results, the APLA profiles for primary and SLE-associated secondary APS were similar. Among the evaluated clinical symptoms, cerebrovascular thrombosis was found to be more frequent in the SLE-associated, than in the primary APS group (P = 0.04). We identified important differences in the clinical profile of patient populations with various types of APLA. Venous thrombosis occurred more frequently in subjects withlupus anticoagulant (LA), than in those with IgG or IgM type ACLA (P < 0.0001), while coronary, carotid and peripheral artery thrombosis occurred more often in subjects with IgG or IgM ACLA (P < 0.0001). These findings may support the role of antibodies to cardiolipin or its cofactor, beta2glycoprotein I (beta2-GPI) in the initiation and progression of atherosclerosis. Cerebrovascular thrombosis was detected in larger proportion of LA or IgG ACLA-positive patients compared with to IgM ACLA-positive subjects, while the occurrence of foetal loss was similar in all three groups.

Anti-factor V auto-antibody in the plasma and platelets of a patient with repeated gastrointestinal bleeding

Development of autoantibody against coagulation factor V (FV) is a rare clinical condition with hemorrhagic complications of varying severity. The aim of this study was to establish the pathomechanism of an acquired FV deficiency and characterize the FV inhibitor responsible for the clinical symptoms. A 78-year-old female was admitted to hospital with severe gastrointestinal bleeding. General clotting tests and determination of clotting factors were performed by standard methods. FV antigen and FV containing immune complexes were measured by ELISA. The FV molecule was investigated by Western blotting and by sequencing the f5 gene. The binding of patient's IgG to FV and activated FV (FVa) was demonstrated in an ELISA system and its effect on the procoagulant activity of FVa was tested in clotting tests and in a chromogenic prothrombinase assay. Localization of the epitope for the antibody was performed by blocking ELISA. FV activity was severely suppressed both in plasma and platelets. FV antigen levels were normal by ELISA using polyclonal anti-FV antibody or monoclonal antibody against the connecting region of FV, but depressed when HV1 monoclonal antibody against the C2 domain in the FV light-chain was used as capture antibody. The FV molecule was found intact. An IgG reacting with both FV and FVa was present in the patient's plasma and its binding to FV was inhibited by HV1 antibody. FV-containing immune complexes were detected in the patient's plasma and platelet lysate. The patient's IgG inhibited the procoagulant function of FVa. An anti-FV IgG was present in the patient's plasma and platelets. The autoantibody reacted with an epitope in the C2 domain of FV light chain and neutralized the procoagulant function of FVa.

[Frequency of hyperhomocysteinemia in hemodialysis patients with folic acid supplementation]

BACKGROUND

It is known that hyperhomocystinemia is an independent risk factor for development of atherosclerosis. In end stage renal disease the frequency of hyperhomocystinemia is much greater than in normal populations.

AIM

In this study homocystein (Hcy), folic acid and vitamin B12 concentrations were determined in 125 chronic renal failure patients being on folic acid supplementation (3 mg/day). In 107 patients the frequency of C667T polymorphism of methylene tetrahyrofolate reductase (MTHFR) was also determined. The relationships between these parameters were also studied.

RESULTS

It was found that in these patients who are under continuous folic acid supplementation the mean level of homocysteine was 16.8 +/- 7.2 mumol/L, a value considerably lower than the homocysteine concentration reported for non-supplemented patients. The elevation of homocysteine concentrations was independent of gender, time spent in renal replacement therapy, and the type of renal replacement therapy (hemodialysis: 17.6 +/- 12.6; hemodiafiltration: 16.6 +/- 12.9 mumol/L). Data showed an inverse relation between plasma homocysteine concentrations and the concentrations of folic acid and vitamin B12. Moderately severe hyperhomocystinemia (Hcy > 20 mumol/L) was found in about 30% of patients. In those the frequency of patients for homozygous T677 allele of MTHFR was about 25-30%. However, in all ESRD patients the frequency of the homozygotes was the same then in the normal population. Homocysteine plasma levels correlated with MTHFR polymorphism: in the wild type group Hcy was 14 +/- 7 mumol/L, in the heterozygous group was 17.2 +/- 6.2 mumol/L, and in the homozygous group was 21 +/- 19 mumol/L.

CONCLUSIONS

Long-term folic acid supplementation decreased the homocysteine level in end stage renal disease patients. However, in folic acid resistant group, who were in 30% homozygotes for C667T of MTHFR (suggesting that homocysteine-methionine remethylation cycle is disturbed), instead of the administration of folic acid, methylene tetrahydrofolate supplementation might be considered.

Severe coagulation factor V deficiency caused by 2 novel frameshift mutations: 2952delT in exon 13 and 5493insG in exon 16 of factor 5 gene

A male infant with severe bleeding tendency had undetectable factor V activity. Sequence analysis of the proband's DNA revealed one base deletion in exon 13 (2952delT) and one base insertion in exon 16 (5493insG) in heterozygous form. Both mutations introduced a frameshift and a premature stop at codons 930 and 1776, respectively. The proband's father and mother were heterozygous for 2952delT and for 5493insG, respectively. Both mutations would result in the synthesis of truncated proteins lacking complete light chain or its C-terminal part. In the patient's plasma, no factor V light chain was detected by enzyme-linked immunosorbent assay. The N-terminal portion of factor V containing the heavy chain, and the connecting B domain was severely reduced but detectable (1.7%). A small amount of truncated factor V-specific protein with a molecular weight ratio of 236 kd could be immunoprecipitated from the plasma and detected by Western blotting. This protein, factor V(Debrecen), corresponds to the translated product of exon 16 mutant allele.

Enzyme-linked immunosorbent assay for the determination of blood coagulation factor XIII A-subunit in plasma and in cell lysates

A new one-step ELISA was developed for the determination of the concentration of blood coagulation factor XIII subunit A (FXIII-A) in plasma and in cell lysates. Monoclonal antibodies directed against different epitopes on FXIII-A were used for the assay. The capture antibody was biotinylated on its carbohydrate moiety and the detection antibody was labelled with horseradish peroxidase. The antigen-antibody reaction was carried out in the well of a streptavidin-coated microplate. Complex formation with FXIII subunit B (FXIII-B) and association to fibrinogen did not influence the accessibility of the antibodies to FXIII-A. The method could be performed within 2 h and demonstrated good reproducibility, recovery and sensitivity. Plasma samples could be assayed after storage at -20 degrees C for at least 6 months. However, in the case of platelet lysates freezing and rethawing resulted in a significant loss of FXIII-A. FXIII-A concentrations measured in the plasma samples of healthy individuals and patients correlated well with the concentrations of complexed plasma FXIII (A2B2) and with the results of FXIII activity measurements. A reference range of 46-82 fg/platelet was established for platelet FXIII-A.

Organization of the glycoprotein (GP) IIb/IIIa heterodimer on resting human platelets studied by flow cytometric energy transfer

Glycoprotein IIb/IIIa is a heterodimer of glycoproteins IIb and IIIa which serves as the inducible receptor for fibrinogen and other adhesive proteins at the surface of platelets. Although a model of the quaternary structure of the GPIIb/IIIa molecule has been constructed in solution by Calvete et al. [Biochem. J. 282 (1992) 523], a corresponding model at the surface of intact platelets is still missing. In the present work conformation and lateral distribution of the GPIIb/IIIa heterodimer were studied at a nanometer resolution on the surface of resting human platelets under physiological conditions. The experiments were based on dual wavelength flow cytometric detection of fluorescence resonance energy transfer and application of a panel of monoclonal antibodies raised against well described binding sites. Monodisperse distribution of the GPIIb/IIIa heterodimer has been observed and a detailed three-dimensional proximity map of antibody binding sites was constructed on the platelet membrane, under physiological conditions, for the first time. Our data support the view that the GPIIb subunit is in a bent conformation. A detailed analysis of the K(d)-values and the number of binding sites for a set of monoclonal antibodies was also carried out giving supplementary data for the topology of the binding sites. Our results provide a refinement of the membrane-topology of the GPIIb/IIIa heterodimer.

Calcium binding of transglutaminases: a 43Ca NMR study combined with surface polarity analysis

Transglutaminases (TGases) form cross-links between glutamine and lysine side-chains of polypeptides in a Ca2+-dependent reaction. The structural basis of the Ca2+-effect is poorly defined. 43Ca NMR, surface polarity analysis combined with multiple sequence alignment and the construction of a new homology model of human tissue transglutaminase (tTGase) were used to obtain structural information about Ca2+ binding properties of factor XIII-A2, tTGase and TGase 3 (each of human origin). 43Ca NMR provided higher average dissociation constants titrating on a wide Ca2+-concentration scale than previous studies with equilibrium dialysis performed in shorter ranges. These results suggest the existence of low affinity Ca2+ binding sites on both FXIII-A and tTGase in addition to high affinity ones in accordance with our surface polarity analysis identifying high numbers of negatively charged clusters. Upon increasing the salt concentration or activating with thrombin, FXIII-A2 partially lost its original Ca2+ affinity; the NMR data suggested different mechanisms for the two activation processes. The NMR provided structural evidence of GTP-induced conformational changes on the tTGase molecule diminishing all of its Ca2+ binding sites. NMR data on the Ca2+ binding properties of the TGase 3 are presented here; it binds Ca2+ the most tightly, which is weakened after its proteolytic activation. The investigated TGases seem to have very symmetric Ca2+ binding sites and no EF-hand motifs.

[Comparative analysis of clinical and laboratory charactiristics of antiphospholipid syndrome]

The authors detected lupus anticoagulant and/or anticardiolipin antibodies in 1519 patients' blood samples between 1986-1999 in 3rd Department of Internal Medicine of Medical School of Debrecen. Examining only the proved thrombotic events and fetal losses as symptoms of antiphospholipid syndrome 218 patients had suffered from this syndrome. Secunder antiphospholipid syndrome was the diagnosis in case of 420 patients, the most common in Systemic Lupus Erythematosus (288 patients). In 704 antiphospholipid antibody positivity cases the diagnosis of antiphospholipid syndrome was not fulfilled. Analysing the antibodies profile of primary and secondary antiphospholipid syndrome in SLE, IgG type anticardiolipin antibody positivity was significantly higher in blood samples of SLE patients (82 patients, p < 0.01). Among thrombotic manifestations of antiphospholipid syndrome cerebrovascular thrombosis were significantly higher in patients suffering from SLE (128 patients, p < 0.04), while the occurrence of venous thrombosis, thrombosis of coronary, carotic, aorta and peripheral arteries and recurrent abortions was not significantly different in case of primary and secondary antiphospholipid syndrome. Lupus anticoagulant positivity means higher risk for venous thrombosis (94 patients, p < 0.0001), but anticardiolipin antibody positivity associated with a higher risk for thrombosis of coronary, carotic, aorta and peripheral arteries (59 patients, p < 0.00006). Comparing IgG- and IgM-type anticardiolipin antibody positivity the authors found significantly higher cerebrovascular thrombosis events in IgG-anticardiolipin group (p < 0.004). Sneddon syndrome were detected in 17 patients in the primary antiphospholipid syndrome group and in 16 cases in secundary, SLE-associated antiphospholipid syndrome group. One of the patients had died because of the Catastrophic Antiphospholipid Syndrome.