Effects of urea and NaCl on the fibrinogen cryogelation

Fibrinogen is converted to fibrin monomer and forms a three-dimensional gel network in a step wise manner by the enzymatic action of thrombin (thrombin-induced fibrin gelation). On the other hand, when a fibrinogen solution is incubated at low temperatures (e.g. below 4°C), it is converted to a gel without thrombin. The fibrinogen gel induced by lowering temperature is called “cryogel” and is closely related to some diseases. However, the mechanism of fibrinogen cryogelation has not been understood yet. In this study, the effects of urea and NaCl on fibrinogen cryogelation and thrombin-induced fibrin gelation have been studied turbidimetrically. The addition of urea retarded both gelation, and the extent of retardation increased with increasing the concentration of urea. The effects of urea on fibrinogen cryogelation were much larger than those on thrombin-induced fibrin gelation, and fibrinogen cryogelation was completely inhibited by the addition of 150 mM urea. The addition of NaCl retarded fibrinogen cryogelation with increasing the concentration of NaCl. By contrast, the effects of NaCl on thrombin-induced fibrin gelation were only limited. Based on the experimental results, the contributions of hydrogen and ionic bonds to each gelation are discussed.