Fibrinogen adsorption concentration, plasma

Fibrinogen adsorption from plasma was found to be maximal at intermediate plasma concentrations, and was considerably lower from 70-100% plasma or from 0.01% plasma than from 0.1 or 1% plasma, an observation called the Vroman effect. 

The adsorption experiments were carried out by quantifying each of proteins adsorbed on the material from mono-component protein solutions, from four-component protein solutions, and from plasma and diluted plasma. Adsorption profiles of protein were largely different, depending on the aforementioned experimental conditions. For instance, the behavior of any particular protein from diluted plasma varied in response to the extent of plasma dilution. Cooper s results are illustrated in Fig. 3, on fibrinogen adsorption onto five polymer surfaces. It is seen that the adsorption profiles are different one another, being influenced by the different nature of the polymer surfaces. The surface concentrations of adsorbed protein are mostly time-dependent, and maxima in the adsorption profiles were observed. This is interpreted in terms of replacement of adsorbed fibrinogen molecules by other proteins later in time (Vroman effect). Corresponding profiles were also presented for FN and VN. 

Figure 3 Adsorption of albumin, IgG, and fibrinogen from plasma to glass as a function of plasma concentration. Plasma was diluted with isotonic Tris, pH 7.35 and adsorptions were for J min. Reproduced with permission from Ref. 44. Copyright 1984, F.K. Schattauer-Verlag.

Fig. 23. Brash and ten Hove s results on the adsorption of three plasma proteins from diluted plasma as a function of total plasma concentration. Up adsorption on glass showing a maximum adsorption of fibrinogen at about 1% plasma Down adsorption on polyethylene plasma was diluted with isotonic Tris, pH 7.35. Adsorption time was 5 minutes (reprinted from Ref.1031)...

Table V shows that the amount of adsorption onto Silastic from plasma is significantly depressed below its saturation value measured in buflFer presumably because of competition from other components of the plasma. The diflFerence in adsorption from the two plasma pools may result from the increased fibrinogen concentration in one pool which would allow more eflFective competition for adsorption onto Silastic and result in enhanced adsorption. Since the adsorption of fibrinogen onto poly (HEMA)/Silastic from plasma is not so greatly depressed relative to adsorption from buflFer (see Table V), an increase in plasma fibrinogen concentration might not have so large an eflFect on adsorption onto poly-(HEMA)/Silastic as it apparently does on adsorption onto Silastic itself.

The reduced adsorption of fibrinogen from plasma onto Silastic and poly (HEMA)/Silastic compared with that from pure buffered saline solutions could be caused by competition from other proteins for the adsorption sites. Albumin and y-globulin are both present in plasma in relatively high concentrations (about 45 and 10 mg/ml, respectively, compared with ca. 3 mg/ml for fibrinogen), so either might compete effectively with fibrinogen for adsorption. To test this, mixtures of I-fibrinogen... 

A concerted effort is presently needed to study the mechanisms influencing adsorption behavior in protein mixtures. Does adsorption from mixtures behave as the sum of independent adsorption events determined by specific affinity constants charactertistic of each species Can such a simple explanation suffice to explain the peak in adsorption isotherms seen for fibrinogen from plasma ("the Vroman effect") and also from binary mixtures (56,57) If the differences in adsorption behavior of mixtures compared to single adsorbates are better understood than at present, a greater degree of control of the adsorption process to achieve a desired end (e.g., selection of a desired protein) may be possible. For example, if the Vroman effect is a general feature of all protein mixtures, then clearly there is an optimum concentration for adsorption to achieve the greatest selectivity. 

The rate constants in Equation 2 include the solution concentration of the protein which is assumed to be constant in the initial stages of adsorption. Since the concentrations of plasma proteins albumin y-globulin fibrinogen are in the ratio 42.0 22.4 5.6, the rate constants from Equation 2 were weighted accordingly to give the values shown in Table II. Thus, the apparent rate constant,, ... 

As we and others continue this line of investigation it is becoming evident that the whole area of competitiveness of protein adsorption in the blood context, which at the moment seems hopelessly mired and anecdotal, may eventually reveal a rational, orderly nature. Vroman has postulated (50) that a rapid sequence of adsorption and displacement events occurs by which, over time, more abundant proteins are displaced by less abundant. The time frame of these events is such that albumin is adsorbed and replaced in a fraction of a second, thus accounting for the fact that it is not often observed on the surface after plasma contact. Clearly the time frame may be expected to vary with the surface so that in some cases the sequence will be relatively fast and in others relatively slow. Thus the apparent absence of a Vroman Effect for hydrophilic polyurethanes may reflect a very rapid sequence, such that a fibrinogen peak would be observed only at very short times or at low plasma concentrations (less than 0.05%). 

The adsorption method of fibrinogen is as follows each of the different PU beads was first contacted with bovine plasma containing C-labeled human fibrinogen as a function of adsorption time or plasma concentration. Sample was then rinsed with phosphate buffered saline (PBS, pH 7.4, 0.15M) twice and placed in 2% sodium dodecyl sulfate (SDS) solution for 2 days, and the surface concentration of fibrinogen was determined by counting the radioactivity. 

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