fibrinopeptide-a and Renal-Insufficiency

Carbamylation is a non-enzymatic post-translational modification induced upon exposure of free amino groups to urea-derived cyanate leading to irreversible changes of protein charge, structure and function. Levels of carbamylated proteins increase significantly in chronic kidney disease and carbamylated albumin is considered as an important biomarker indicating mortality risk. High plasma concentrations and long half-life make fibrinogen a prime target for carbamylation. As aggregation and cross-linking of fibrin monomers rely on lysine residues, it is likely that carbamylation impacts fibrinogen processing. In this study we investigated carbamylation levels of fibrinogen from kidney disease patients as well as the impact of carbamylation on fibrinogen cleavage by thrombin, fibrin polymerisation and cross-linking in vitro. In conjunction, all these factors determine clot structure and stability and thus control biochemical and mechanical properties. LC-MS/MS analyses revealed significantly higher homocitrulline levels in patient fibrinogen than in fibrinogen isolated from control plasma. In our in vitro studies we found that although carbamylation does not affect thrombin cleavage per se, it alters fibrin polymerisation kinetics and impairs cross-linking and clot degradation. In addition, carbamylated fibrin clots had reduced fiber size and porosity associated with decreased mechanical stability. Using mass spectroscopy, we discovered that N-terminally carbamylated fibrinopeptide A was generated in this process and acted as a strong neutrophil chemoattractant potentially mediating recruitment of inflammatory cells to sites of fibrin(ogen) turnover. Taken together, carbamylation of fibrinogen seems to play a role in aberrant fibrin clot formation and might be involved in haemostatic disorders associated with chronic inflammatory diseases.

Topics: Blood Coagulation; Chemotaxis, Leukocyte; Citrulline; Cyanates; Factor XIIIa; Fibrin; Fibrinogen; Fibrinolysis; Fibrinopeptide A; Humans; Kinetics; Neutrophils; Polymerization; Protein Conformation; Protein Processing, Post-Translational; Protein Stability; Renal Dialysis; Renal Insufficiency; Structure-Activity Relationship; Thrombin; Urea

The level of urinary FPA was assayed by high performance liquid chromatography (HPLC) in 42 normal controls, 57 cases of chronic glomerulonephritis, including 24 with normal renal function, 12 with renal insufficiency and 21 with uremia. Their levels were 24.40 +/- 10.30 micrograms/L, 26.99 +/- 5.77 micrograms/L, 38.81 +/- 6.28 micrograms/L, 79.74 +/- 18.76 micrograms/L, respectively. The level of urinary FPA in renal insufficiency function group was significantly higher than those of the control group and normal renal function group (P < 0.01). The patients with uremia presented dramatically higher level of urinary FPA than those in the renal insufficiency group (P < 0.01). A positive correlation was found between the level of urinary FPA and the blood creatine (r = 0.9120, P < 0.01). It was suggested that a hypercoagulable state existed in the patients with chronic nephritis with renal failure, in which the severity was closely related with the occurrence and development of the disease. The urinary FPA could serve as a good indicator for renal function.

Topics: Biomarkers; Case-Control Studies; Chronic Disease; Fibrinopeptide A; Humans; Kidney; Nephritis; Renal Insufficiency