Role of Sialic Acid in the Dysfibrinogenemia Associated with Liver Disease

Abstract

We have described an abnormal fibrinogen in 6 patients with liver disease who had prolonged plasma thrombin times due to impaired fibrin monomer aggregation. To investigate the role of sialic acid in this functional abnormality, fibrinogen was purified from normal and patient plasmas by the glycine precipitation method. Sialic acid content of the fibrinogens was measured by the thriobarbituric acid assay after acid hydrolysis. Normal fibrinogen had 6.1 ± 0.5 residues per molecule of fibrinogen, whereas patient fibrinogen sialic acid content ranged between 7.5 and 10 residues per molecule. The reduced fibrinogen demonstrated normal mobility of Aα, B3 and γ chains on SDS Polyacrylamide gel electrophoresis when stained for protein and, similar to normal fibrinogen, only the Bβ and γ chains stained with PAS. The degree of prolongation of the thrombin times of the purified patient fibrinogens appeared to correlate with the increase in the fibrinogen sialic acid. The effect on fibrin monomer aggregation of decreasing patient fibrinogen sialic acid content was studied. Partially desialated patient fibrinogen was prepared by treating the protein with Vibrio cholerae neuraminidase for varying periods of time. Partial removal of sialic acid from patient fibrinogen resulted in normalization of the thrombin time and improvement in fibrin monomer aggregation. Thrombin times ranged from 31.5 to 49.5 seconds prior to removal of excess sialic acid compared to 20.5 to 25.5 seconds post removal. These findings indicate that the dysfibrinogenemia associated with liver disease is biochemically characterized by increased sialic acid content and removal of this sialic acid results in a functional normalization of the protein.

Fibrinogen and Fibrin in Hemostasis and Thrombosis

“…119,121 Compared to controls, both plasma clots and clots made from purified fibrinogen from cirrhotic patients demonstrate abnormal clotting characteristics, including decreased clot permeability and shorter clot lysis times. 119 Somewhat paradoxically, patients included in this study 119 reported bleeding, mostly variceal, rather than thrombosis.…”

Evidence for age-related differences in human fibrinogen

“…In addition, specific thrombin clotting times were prolonged in newborns suggesting differences in polymerization of fibrin from 'fetal' fibrinogen [8], an observation that has led to a claim that fibrinogen in infants is 'dysfunctional' [9]. Observations that an increase in sialic acid content of fibrinogen is associated with a decreased rate of fibrin polymerization and the removal of sialic acid residues leads to increase in polymerization [10] provide a possible explanation for the differences in thrombin clotting times. Definite evidence of the importance of differences in sialic acid content of fibrinogen is provided by observations that sialic residues of fibrinogen directly bind Ca 2þ [11].…”

Relevance of clotting tests in liver disease

“…Dysfibrinogenaemia, where the function of the fibrinogen is impaired, is also one of the earliest clotting abnormalities seen in chronic liver disease 35. These defective forms of fibrinogen may be synthesised because of abnormal post-translational modification or excessive sialic acid content 36 37…”