A turbidimetric assay for quantitating functional fibrin(ogen) using polystyrene-divinylbenzene microparticles

Label-free detection of fibrinogen based on the fibrinogen-enhanced peroxidase activity of a fibrinogen-hemin composite

A simple, label-free colorimetric method for the determination of fibrinogen (Fib) in plasma is presented. In this work, it was observed that Fib interacted with hemin to form a hemin-Fib composite. Because Fib prevented hemin from the formation of m-oxo-dimers, the hemin-Fib composite possesses excellent peroxidase-like activity. Importantly, the peroxidase-like activity of Fib-hemin increased with the increase in the Fib. This allows us to utilize the H₂O₂-ABTS colorimetric system for the quantitative analysis of Fib. This optimized method provided a linear determination range of 2.0-100 pM with a correlation of 0.9975. The limit of detection for Fib was experimentally determined to be 0.7 pM based on a signal-to-noise ratio (S/N) of 3. This novel approach provides a rapid, sensitive, cost efficient and robust bioassay for detection of Fib in pathology and clinical applications.

Fibrinogen in rat gastrointestinal lymph before, during and after intraduodenal administration of emulsified triglyceride: fibrinogen bound to chylomicrons in gastrointestinal lymph is functional

Samples of gastrointestinal lymph were collected from fasted, male, Sprague-Dawley rats before, during and after intraduodenal administration of either a phospholipid-stabilized, triglyceride-rich emulsion or the dextrose-saline diluent of the emulsion. In lipid-treated rats, the triglyceride, total protein, and functional fibrinogen contents of lymph increased significantly during the 4 h of continuous lipid infusion, with all analytes returning to near baseline values by 20 h later. Levels of the same analytes changed little, if at all, in control animals. As assessed using immunoblotting, chylomicrons in gastrointestinal lymph are coated with fibrinogen. Fibrinogen-coated chylomicrons readily incorporate into solution phase clots and, in the presence of thrombin, adhere in heparin-preventable fashion to each other and to other fibrinogen-coated surfaces. Taken together, these data indicate that lipid feeding creates in gastrointestinal lymph a condition that is conducive temporally to the physical association of fibrinogen with newly ingested lipids before they reach the circulatory system.

Reactivity of human platelets with immobilized fibrinogen is dictated by the chemical character of the surface

Quiescent platelets readily adhere to surface-immobilized fibrinogen. In contrast, platelets exposed to soluble fibrinogen do not demonstrate such activity. As part of an effort to characterize this phenomenon, a solid-phase reagent was prepared by adsorbing human fibrinogen to polystyrene-divinylbenzene microparticles. Using a suspension of human platelets, phase-contrast microscopy was used to quantitate directly platelets bound to fibrinogen-coated beads. This method is fast, straightforward, and requires minimal amounts of reagents and sample. An existing turbidimetric assay was modified to monitor optically the rate and extent of platelet-fibrinogen binding. When platelet-rich plasma was added to a stirred suspension of fibrinogen-coated beads, the rate of aggregation was related directly to the concentration of fibrinogen on the bead surface. This response could not be mitigated by the thrombin inhibitor, hirudin, indicating that any thrombin generated in the reaction has no role in bead aggregation. Conversely, the alpha(IIb)beta(3) antagonist, abciximab (ReoPro), completely prevented aggregation, implicating specific fibrinogen-alpha(IIb)beta(3) interactions as responsible for the observed effect. Beads coated with either albumin or a densely packed, pure film of the neutral phospholipid, phosphatidylcholine (lecithin), do not aggregate under identical conditions, nor do fibrinogen-coated beads aggregate when platelet-depleted plasma is added. When fibrinogen was coated to beads as a mixed film with lecithin, a striking increase in reactivity toward platelets was demonstrated, compared to unmodified beads. These studies indicate that the observed adhesion of platelets to beads is a direct result of platelet-fibrinogen interactions and platelets respond differently to fibrinogen when presented as a mixed film with lipid, compared to the protein alone at an interface.