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► A bead model of the fibrinogen molecule was developed. ► Presence of flexible arms was considered. ► Calculations of hydrodynamic characteristics of the molecule were performed. ► ...The model proved adequate for interpretation of various experimental data. ► Anisotropic charge distribution over the fibrinogen molecule was predicted.
Hydrodynamic properties of fibrinogen molecules were theoretically calculated. Their shape was approximated by the bead model, considering the presence of flexible side chains of various length and orientation relative to the main body of the molecule. Using the bead model, and the precise many-multipole method of solving the Stokes equations, the mobility coefficients for the fibrinogen molecule were calculated for arbitrary orientations of the arms whose length was varied between 12 and 18nm. Orientation averaged hydrodynamic radii and intrinsic viscosities were also calculated by considering interactions between the side arms and the core of the fibrinogen molecule. Whereas the hydrodynamic radii changed little with the interaction magnitude, the intrinsic viscosity exhibited considerable variation from 30 to 60 for attractive and repulsive interactions, respectively. These theoretical results were used for the interpretation of experimental data derived from sedimentation and diffusion coefficient measurements as well as dynamic viscosity measurements. Optimum dimensions of the fibrinogen molecule derived in this way were the following: the contour length 84.7nm, the side arm length 18nm, and the total volume 470nm3, which gives 16% hydration (by volume). Our calculations enabled one to distinguish various conformational states of the fibrinogen molecule, especially the expanded conformation, prevailing for pH<4 and lower ionic strength, characterized by high intrinsic viscosity of 50 and the hydrodynamic radius of 10.6nm. On the other hand, for the physiological condition, that is, pH=7.4 and the ionic strength of 0.15M NaCl, the semi-collapsed conformation dominates. It is characterized by the average angle equal to <φ>=55°, intrinsic viscosity of 35, and the hydrodynamic radius of 10nm. Additionally, the interaction energy between the arms and the body of the molecule was predicted to be −4kT units, confirming that they are oppositely charged than the central nodule. Results obtained in our work confirm an essential role of the side chains responsible for a highly anisotropic charge distribution in the fibrinogen molecule. These finding can be exploited to explain anomalous adsorption of fibrinogen on various surfaces.
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•The coverage and molecule orientation in the fibrinogen monolayers were determined.•The hybrid random sequential adsorption model was used to theoretical calculations.•The results ...open a spectrum of possibilities for conducting efficient immunoassays.
Deposition kinetics of fibrinogen/polystyrene particle complexes on mica and the silicon/silica substrates was studied using the direct optical and atomic force microscopy. Initially, basic physicochemical characteristics of fibrinogen and the microparticles were acquired using the dynamic light scattering and the electrophoretic mobility methods, whereas the zeta potential of the substrates was determined using the streaming potential measurements. Subsequently an efficient method for the preparation of fibrinogen/polymer microparticle complexes characterized by controlled coverage and molecule orientation was developed. It was demonstrated that for a lower suspension concentration the complexes are stable for pH range 3–9 and for a large concentration for pH below 4.5 and above 5.5. This enabled to carry out thorough pH cycling experiments where their isoelectric point was determined to appear at pH 5. Kinetic measurements showed that the deposition rate of the complexes vanished at pH above 5, whereas the kinetics of the positively charged amidine particles, used as control, remained at maximum for pH up to 9. These results were theoretically interpreted using the hybrid random sequential adsorption model. It was confirmed that the deposition kinetics of the complexes can be adequately analyzed in terms of the mean-field approach, analogously to the ordinary colloid particle behavior. This is in contrast to the fibrinogen molecule behavior, which efficiently adsorb on negatively charged substrates for the entire range pHs up to 9.7. These results have practical significance for conducting efficient immunoassays governed by the specific antigen/antibody interactions.
Background: Exposure of cryptic, functional sites on fibrinogen upon its adsorption to hydrophobic surfaces of biomaterials has been linked to an inflammatory response and fibrosis. Such adsorption ...also induces ordered fibrinogen aggregation which is poorly understood. Objective: To investigate hydrophobic surface‐induced fibrinogen aggregation. Methods: Contact and lateral force scanning probe microscopy, yielding topography, image dimensions and fiber elastic modulus measurements were used along with transmission and scanning electron microscopy. Fibrinogen aggregation was induced under non‐enzymatic conditions by adsorption on a trioctyl‐surface monolayer (trioctylmethylamine) grafted onto silica clay plates. Results: A more than one molecule thick coating was generated by adsorption on the plate from 100 to 200 μg mL−1 fibrinogen solutions, and three‐dimensional networks formed from 4 mg mL−1 fibrinogen incubated with uncoated or fibrinogen‐coated plates. Fibrils appeared laterally assembled into branching and overlapping fibers whose heights from the surface ranged from approximately 3 to 740 nm. The elastic modulus of fibrinogen fibers was 1.55 MPa. No fibrils formed when fibrinogen lacking αC‐domains was used as a coating or was incubated with intact fibrinogen‐coated plates, or when the latter plates were sequentially incubated with anti‐Aα529–539 mAb and intact fibrinogen. When an anti‐Aα241–476 mAb was used instead, fine, long fibers formed. Similarly, sequential incubations of fibrinogen‐coated plates with recombinant αC‐domain (Aα392–610 fragment) or αC‐connector (Aα221–372 fragment) and fibrinogen resulted in distinctly fine fiber networks. Conclusions: Adsorption‐induced fibrinogen self‐assembly is initiated by a more than one molecule‐thick surface layer and eventuates in three‐dimensional networks whose formation requires fibrinogen with intact αC‐domains.
Summary
To date, data regarding the efficacy and safety of administering fibrinogen concentrate in cardiac surgery are limited. Studies are limited by their low sample size and large heterogeneity ...with regard to the patient population, by the timing of fibrinogen concentrate administration, and by the definition of transfusion trigger and target levels. Assessment of fibrinogen activity using viscoelastic point‐of‐care testing shortly before or after weaning from cardiopulmonary bypass in patients and procedures with a high risk of bleeding appears to be a rational strategy. In contrast, the use of Clauss fibrinogen test for determination of plasma fibrinogen level can no longer be recommended without restrictions due to its long turnaround time, high inter‐assay variability and interference with high heparin levels and fibrin degradation products. Administration of fibrinogen concentrate for maintaining physiological fibrinogen activity in the case of microvascular post‐cardiopulmonary bypass bleeding appears to be indicated. The available evidence does not suggest aiming for supranormal levels, however. Use of cryoprecipitate as an alternative to fibrinogen concentrate might be considered to increase plasma fibrinogen levels. Although conclusive evidence is lacking, fibrinogen concentrate does not seem to increase adverse outcomes (i.e., thromboembolic events). Large prospective multi‐centre studies are needed to better define the optimal perioperative monitoring tool, transfusion trigger and target levels for fibrinogen replacement in cardiac surgery.
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