Molecular aspects of albumin functions: indications for its use in plasma substitution

The maintenance of the circulating fluid within the vascular system is a major role of plasma albumin. Besides its role as a protein reservoir the third function of albumin is its ability to bind and transport metabolic products, regulatory mediators, nutrients and proteins and to bind and neutralize endogenous or exogenous toxins. Bilirubin binding was chosen as a method to describe functional quality of albumin preparations. Binding at the high affinity site is well preserved in all commercial albumin-containing plasma substitutes investigated with KA values in the range of 3.2 to 4.8 . 10(7) 1/mol. Presence of absence of conventional stabilizers does not influence binding characteristics since heating of products according to various pharmacopoeia levels out any difference. The importance of ligand binding properties of a plasma substitute is stressed either in intoxications, e.g. hyperbilirubinemia of neonates or in surgical situations were multiple drug applications might disturb a balanced binding situation. Though relatively mild in nature and less frequently observed in comparison with artificial plasma substitutes incidence of adverse reactions in connection with albumin was used to search for causes. Biochemical parameters like residual proteolytic activity in general or specified (prekallikrein activator), content of aggregates, anti-complementary activity and influence on granulocyte activity did not give any clear answer in this task, neither did pharmacological testing designed to detect factors leading to histamine and kinin liberation or to detect pyrogens.