Zsuzsanna Bereczky

Factor XIII: A Coagulation Factor With Multiple Plasmatic and Cellular Functions

Factor XIII (FXIII) is unique among clotting factors for a number of reasons: 1) it is a protransglutaminase, which becomes activated in the last stage of coagulation; 2) it works on an insoluble substrate; 3) its potentially active subunit is also present in the cytoplasm of platelets, monocytes, monocyte-derived macrophages, dendritic cells, chondrocytes, osteoblasts, and osteocytes; and 4) in addition to its contribution to hemostasis, it has multiple extra- and intracellular functions. This review gives a general overview on the structure and activation of FXIII as well as on the biochemical function and downregulation of activated FXIII with emphasis on new developments in the last decade. New aspects of the traditional functions of FXIII, stabilization of fibrin clot, and protection of fibrin against fibrinolysis are summarized. The role of FXIII in maintaining pregnancy, its contribution to the wound healing process, and its proangiogenic function are reviewed in details. Special attention is given to new, less explored, but promising fields of FXIII research that include inhibition of vascular permeability, cardioprotection, and its role in cartilage and bone development. FXIII is also considered as an intracellular enzyme; a separate section is devoted to its intracellular activation, intracellular action, and involvement in platelet, monocyte/macrophage, and dendritic cell functions.

Factor XIII Deficiency.

Factor XIII (FXIII) is a tetrameric zymogen (FXIII-A (2)B (2)) that is converted into an active transglutaminase (FXIIIa) by thrombin and Ca (2+) in the terminal phase of the clotting cascade. By cross-linking fibrin chains and alpha (2) plasmin inhibitor to fibrin, FXIIIa mechanically stabilizes fibrin and protects it from fibrinolysis. Severe deficiency of the potentially active A subunit (FXIII-A) is a rare but severe hemorrhagic diathesis. Delayed umbilical stump bleeding is characteristic, and subcutaneous, intramuscular, and intracranial bleeding occurs with a relatively high frequency in nonsupplemented patients. In addition, impaired wound healing and spontaneous abortion in women are also features of FXIII deficiency. The extremely rare B subunit deficiency results in milder bleeding symptoms. FXIII concentrate is now available for on-demand treatment and primary prophylaxis. A quantitative FXIII activity assay is recommended as a screening test for the diagnosis of FXIII deficiency. For classification purposes, FXIII-A (2)B (2) antigen in the plasma is first determined, and if decreased, further measurement of the individual subunits is recommended in the plasma and FXIII-A in platelet lysate. Analytical aspects of FXIII activity and antigen assays are discussed in this article. There are no hot-spot mutations in the F13A1 and F13B genes, and the majority of causative mutations are missense/nonsense point mutations.

The involvement of blood coagulation factor XIII in fibrinolysis and thrombosis.

It has been known for a long time that blood coagulation factor XIII (FXIII) is essential for maintaining haemostasis, its deficiency leads to severe bleeding complication. Biochemical studies have revealed that FXIII is a key regulator of fibrinolysis and, in addition to its role in haemostasis, it has also been implicated in the pathology of arterial and venous thrombosis. Most recently, the polymorphisms in the FXIII subunit genes and their influence on the risk of thrombotic diseases have stirred a lot of interest. This review, besides including the basic biochemistry of FXIII, mainly concentrates on the biochemical and clinical aspects of the involvement of FXIII in fibrinolysis and thrombosis. Biochemical aspects: Basics on the structure and activation of plasma and cellular FXIII. The enzymological features of activated FXIII and its main substrates. The interaction of FXIIIa with fibrinogen/fibrin and with components of the fibrinolytic system. The impact of cross-linked fibrin clot formation on the fibrinolytic processes. The down-regulation of FXIIIa within the fibrin clot. FXIII polymorphisms and their biochemical consequences. Clinical Aspects: FXIII level and the risk of arterial thrombosis (coronary artery disease, peripheral artery disease, ischemic stroke). The effect of FXIII subunit polymorphisms on the risk of arterial thrombotic diseases. The interplay between FXIII polymorphisms and other factors influencing the risk of arterial thrombosis. FXIII and venous thromboembolism.

Severe bleeding complications caused by an autoantibody against the B subunit of plasma factor XIII: a novel form of acquired factor XIII deficiency

Acquired factor XIII (FXIII) deficiency due to autoantibody against FXIII is a very rare severe hemorrhagic diathesis. Antibodies directed against the A subunit of FXIII, which interfere with different functions of FXIII, have been described. Here, for the first time, we report an autoantibody against the B subunit of FXIII (FXIII-B) that caused life-threatening bleeding in a patient with systemic lupus erythematosus. FXIII activity, FXIII-A(2)B(2) complex, and individual FXIII subunits were undetectable in the plasma, whereas platelet FXIII activity and antigen were normal. Neither FXIII activation nor its activity was inhibited by the antibody, which bound to structural epitope(s) on both free and complexed FXIII-B. The autoantibody highly accelerated the elimination of FXIII from the circulation. FXIII supplementation combined with immunosuppressive therapy, plasmapheresis, immunoglobulin, and anti-CD20 treatment resulted in the patients recovery. FXIII levels returned to around 20% at discharge and after gradual increase the levels stabilized above 50%.

Factor XIII Val34Leu variant protects against coronary artery disease - A meta-analysis

Several studies suggested that Val34Leu variant of factor XIII (FXIII) might have a protective effect against coronary artery disease (CAD), but studies not supporting these findings have also been published. The authors performed a meta-analysis of 16 studies on 5,346 cases and 7,053 controls that investigated the association between Val34Leu polymorphism and CAD defined as history of myocardial infarction or significant stenosis on a coronary artery assessed by coronary angiography. Because of the heterogeneity of the study-specific results, the pooled effect estimates were calculated by a random-effects empirical Bayes model. The combined odds ratios for CAD were 0.82 (95% confidence interval [95% CI] 0.73, 0.94) for the heterozygotes of the FXIIIVal34Leu variant, 0.89 (95% CI 0.69, 1.13) for the homozygotes, and 0.81 (95% CI 0.70, 0.92) for the heterozygotes and homozygotes combined. The results were essentially the same when only myocardial infarction was considered as outcome. The beneficial effect of the polymorphism might be smaller than the effect estimates obtained in this meta-analysis, because the analysis raised the possibility of publication bias. Data published in the literature suggest that gene-gene and gene-environmental interactions might significantly influence the protective effect of FXIII-A Val34Leu polymorphism.

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.

Factor XIII and Atherothrombotic Diseases

Factor XIII (FXIII) is a protransglutaminase that, after activation, cross-links fibrin chains and several plasma proteins, most importantly alpha (2) plasmin inhibitor, to fibrin. FXIII strengthens the fibrin clot by covalent bonds and protects fibrin from the prompt elimination by the fibrinolytic system. In the last two decades, FXIII has emerged as a key regulator of fibrinolysis. FXIII is also present in platelets, monocytes, and macrophages, but this cellular form does not contribute significantly to maintaining hemostasis. FXIII deficiency is a life-threatening bleeding diathesis whose clinical consequences are well studied. In contrast, the involvement of FXIII in thrombotic disorders and its association with the risk of such diseases are less clear. This review gives an account of the data accumulated mainly in the last decade on the association of FXIII with atherothrombotic diseases and presents conclusions and hypotheses drawn from these data as well as exposing the limitations of the published studies and our knowledge on this topic. The involvement of FXIII in atherogenesis, its role in coronary artery disease, atherothrombotic ischemic stroke, and peripheral artery disease are discussed, with particular reference to the association of FXIII levels and polymorphisms with the risk of these diseases.

Protein C and protein S deficiencies: similarities and differences between two brothers playing in the same game

Abstract Protein C (PC) and protein S (PS) are vitamin K-dependent glycoproteins that play an important role in the regulation of blood coagulation as natural anticoagulants. PC is activated by thrombin and the resulting activated PC (APC) inactivates membrane-bound activated factor VIII and factor V. The free form of PS is an important cofactor of APC. Deficiencies in these proteins lead to an increased risk of venous thromboembolism; a few reports have also associated these deficiencies with arterial diseases. The degree of risk and the prevalence of PC and PS deficiency among patients with thrombosis and in those in the general population have been examined by several population studies with conflicting results, primarily due to methodological variability. The molecular genetic background of PC and PS deficiencies is heterogeneous. Most of the mutations cause type I deficiency (quantitative disorder). Type II deficiency (dysfunctional molecule) is diagnosed in approximately 5%–15% of cases. The diagnosis of PC and PS deficiencies is challenging; functional tests are influenced by several pre-analytical and analytical factors, and the diagnosis using molecular genetics also has special difficulties. Large gene segment deletions often remain undetected by DNA sequencing methods. The presence of the PS pseudogene makes genetic diagnosis even more complicated. Clin Chem Lab Med 2010;48:S53–66.

Trombophilic screening for nonarteritic anterior ischemic optic neuropathy

BackgroundNonarteritic anterior ischemic optic neuropathy (NAION) is an ischemic infarction of the optic nerve head, frequently leading to sudden, mostly irreversible loss of vision. In this study blood thrombophilic factors, as well as cardiovascular risk factors were investigated for their relevance to this pathology. Trombophilic risk factors so far not evaluated were included in the study.Patients and methods37 NAION patients (4 with sequential second eye involvement) and 81 matched control subjects were examined. From blood, protein C, protein S, antithrombin, von Willebrand antigen levels (vWFAg), and factor V (Leiden) mutation, factor VIIIC level, plasminogen activity, lipoprotein (a) and fibrinogen levels, and presence of anticardiolipin antibodies were investigated. Possibly relevant pathologies [e.g. diabetes mellitus (DM), hypertension, and ischemic heart disease] were also registered.ResultsElevated Lp(a) and vWFAg levels, DM, F V (Leiden), hypercholesterolemia, and hyperfibinogenemia proved to be significant risk factors associated with NAION. Forward stepwise logistic regression analysis revealed that high Lp(a), DM, and FV (Leiden) were the main predictive components, with odds ratios 16.88 (p=0.012), 5.78 (p=0.022) and 4.44 (p=0.033), respectively.ConclusionsBased on our results it appears that thrombophilia is likely to contribute to the development of NAION besides vascular damage due to the presence of cardiovascular risk factors. Further data are needed, however, to justify the suggested use of secondary prophylaxis using anticoagulant/antiplatelet therapy.

Antithrombin deficiency and its laboratory diagnosis

Abstract Antithrombin (AT) belongs to the serpin family and is a key regulator of the coagulation system. AT inhibits active clotting factors, particularly thrombin and factor Xa; its absence is incompatible with life. This review gives an overview of the protein and gene structure of AT, and attempts to explain how glucosaminoglycans, such as heparin and heparan sulfate accelerate the inhibitory reaction that is accompanied by drastic conformational change. Hypotheses on the regulation of blood coagulation by AT in physiological conditions are discussed. Epidemiology of inherited thrombophilia caused by AT deficiency and its molecular genetic background with genotype-phenotype correlations are summarized. The importance of the classification of AT deficiencies and the phenotypic differences of various subtypes are emphasized. The causes of acquired AT deficiency are also included in the review. Particular attention is devoted to the laboratory diagnosis of AT deficiency. The assay principles of functional first line laboratory tests and tests required for classification are discussed critically, and test results expected in various AT deficiency subtypes are summarized. The reader is provided with a clinically oriented algorithm for the correct diagnosis and classification of AT deficiency, which could be useful in the practice of routine diagnosis of thrombophilia. Clin Chem Lab Med 2010;48:S67–78.