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Cross-linking through thrombin

Fibrin ( Latin fibra 'fiber', factor Ia of the blood coagulation cascade) is the activated, cross-linked “glue” of plasmatic blood coagulation . It is a protein that is formed by the action of the enzyme thrombin (factor IIa of the coagulation cascade) from the thread-like soluble precursor, fibrinogen (factor I of the coagulation cascade). The fibrin then polymerizes and forms a network, the blood clot ("white thrombus"), which closes the wound. Only later does the soft thrombus become a hard crust through cross-linking with the help of factor XIIIa . Fibrin can accelerate wound healing in the presence of pure oxygen or special oxidative wound irrigation solutions. In many chronic wounds , however, fibrin often develops in excess due to a constant inflammatory reaction and forms large-scale coverings that hinder healing and must be removed by means of debridement .

Details of fibrin formation

During the formation of the white thrombus, the 16 amino acid long fibrinopeptide A and the 14 amino acid long fibrinopeptide B from the β chain are first split off by thrombin from the α chain of the fibrinogen . As a result, the N-terminal position on the peptides is exposed and these bind to the γ chain of the fibrinogen, where they form what are known as protofibrils . In the next step, protofibrils come together to form more or less thick fibrin fibers in a process known as lateral association. This also leads to branches, so that a three-dimensional structure is created.

Pathology of fibrin formation

The genes FGA, FGB and FGG, which encode the sub-chains of fibrinogen , can have various mutations which can impair the formation of fibrinogen and thus the fibrinopeptides. Thus afibrinogenemias (no fibrinogen), hypofibrinogenemias (reduced fibrinogen content of the blood) and dysfibrinogenemia (abnormal fibrinogen) known.

Structural changes in the fibrinogen can result in various defects in clot formation:

  • Disruption of the release of fibrinopeptides;
  • changed aggregation of the monomers;
  • altered lateral association of the protofibrils;
  • Disturbance of the later networking.

About 60 percent of the defects are asymptomatic. Bleeding tendencies dominate the symptoms , in 15 percent there is a tendency to thrombosis . It is worth mentioning a group of defects with the accumulation of protein aggregates in the kidneys and spleen (renal amyloidosis ), where renal dysfunction dominates the picture.

Web links

Wiktionary: Fibrin  - explanations of meanings, word origins, synonyms, translations

Individual evidence

  1. A. Piaggesi, C. Goretti et al. a .: A randomized controlled trial to examine the efficacy and safety of a new super-oxidized solution for the management of wide postsurgical lesions of the diabetic foot. In: The International Journal of Lower Extremity Wounds . Volume 9, Number 1, March 2010, pp. 10-15, ISSN  1552-6941 . doi : 10.1177 / 1534734610361945 . PMID 20207618 .
  2. Kerstin Protz: Modern wound care , 8th edition, Elsevier Verlag Urban & Fischer, Munich 2016, ISBN (Print) 978-3-437-27885-3, (e-Book) 978-3-437-17302-8, page 30th
  3. UniProt entry FGA .
  4. a b M. Meyer: Molecular Biology of Coagulation: Fibrinogen, Factor VIII Haemostaseology 24 / - / 2004 pp. 108–115 Article as PDF .