Albumin-fibrinogen adsorption, effect

The enhancement of albumin binding, and its potential effectiveness in improving thromboresistance, is further demonstrated in the results of simultaneous fibrinogen-albumin exposure, shown in Figure 12. Reduction of fibrinogen adsorption is proportional to add-on of albumin, presumed to be bound to octadecyl residues. Varying yield may depend on the manufacturer s polymer process variables, the derivatization process variables, and the protein solution exposure technique. 

Figure 12. Effect of enhanced binding of defatted albumin to octadecyl residues on reduction of fibrinogen adsorption.

Figure 5. Effect of albumin preadsorption on fibrinogen adsorption. Air drying and partial gold decoration TEM were used for all samples. Key F, 30 mg/dl fibrinogen (Cohn I) and A F,...

Adsorption of the three most abimdant plasma proteins (albumin, fibrinogen, IgG) onto hydiophiUc surfaces has no apparent effect on monoc3rte activation, whereas the adsorption of the same plasma proteins onto an otherwise inert but strongly hydrophobic (e.g., silicone) surface, strongly activates these phagocytic cells (Naim et al., 1998). 

The most widely studied synthetic polymers for blood contact applications are polyether urethane ureas ( Biomer (Ethicon)). These materials have been used in artificial hearts, as coatings for lead wires in pacemakers, have been used and are being considered for blood vessel prostheses. The success of these materials is believed to be due to preferential adsorption of albumin rather than globulin or fibrinogen which promote a clotting response. However, these materials are hydrophobic and questions of long-term effectiveness are unresolved. Particularly, these materials may shed emboli or may be susceptible to surface calcification. Thus, it may be desirable to have synthetic polymers which are hydrophilic and better resemble blood vessels [475]. 

Recently Horbettl02) and Brash and ten Hove 103) have quantitatively demonstrated the Vroman effect in a series of experiments studying competitive adsorption of fibrinogen, albumin, IgG, and hemoglobin from diluted plasma. 

The effects of conditioning layers of two important blood serum proteins, albumin and fibrinogen were investigated. Protein adsorption was studied using bovine serum albumin (BSA) and fibrinogen (F) from Sigma. The samples were incubated for 3 h at 37°C in solutions of albumin (1 mg/mL) and fibrinogen (0.2 mg/mL) prepared in phosphate buffered saline (PBS, 0.01 M phosphate buffer, 0.0027 M KC1, 0.137 MNaCl, pH 7.4). After the incubation period, the samples were rinsed 3 times with PBS and analyzed by the various surface characterization techniques. 

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... 

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%). 

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