Evaluation of fibrinogen self-assembly: role of its αC region

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 mu g 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 alpha C-domains was used as a coating or was incubated with intact fibrinogen-coated plates, or when the latter plates were sequentially incubated with anti-A alpha 529-539 mAb and intact fibrinogen. When an anti-A alpha 241-476 mAb was used instead, fine, long fibers formed. Similarly, sequential incubations of fibrinogen-coated plates with recombinant alpha C-domain (A alpha 392-610 fragment) or alpha C-connector (A alpha 221-372 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 alpha C-domains.