The Nature of the Inhibitory Action of Anionic Polyamidoamine Dendrimers of Generation 1.5-3.5 on the Activity of the Fibrinolytic System

摘要

Polyamidoamine (PAMAM) dendrimers are used in medicine for systemic drug delivery. The safety assessment of biomaterials, which come into contact with blood components and tissues is especially important. For example, PAMAM-NH2 dendrimers G4-G7 cause platelet and fibrinogen aggregation. We have studied the effect of the PAMAM-COOH dendrimers G1.5-G3.5 on key components of the fibrinolysis system. The dendrimers have not affected the plasmin activity. However, the amidolytic activities of tissue activators of plasminogen (tPA) and urokinase (uPA) have decreased markedly with increasing the dendrimer concentration and generation. The peak intensity at 340 nm of Glu-plasminogen fluorescence in the absence and presence of 0.15 M NaCl has decreased with increasing the dendrimer concentration, thus indicating the change in the microenvironment of the Trp residues and molecular conformation of the open and closed Glu-plasminogen forms. A comparison of the fluorescence quenching constants suggests that the anionic dendrimer and chloride ion simultaneously bind to Glu-plasminogen and each of these ligands exerts its independent effects through the separate binding sites. With increasing the dendrimer concentration, the rate of the tPA- and uPA-induced activation of Glu-plasminogen has dramatically decreased due probably to the formation of dendrimer*plasminogen complexes with the increasing dendrimer content, which makes the plasminogen bond increasingly unavailable for the cleavage by the activators. The rate of tPA- and uPA-induced lysis of the plasma clot in plasma has moderately decreased with increasing the dendrimer concentration due probably to the reduced effect of the dendrimer on the fibrin-bound plasminogen. Thus, the nature of the inhibitory action of the anionic PAMAM dendrimers on the Glu-plasminogen activation and tPA- and uPA-induced thrombolysis consists of a noticeable inactivation of the activators and a significant change in plasminogen conformation. The PAMAM-COOH dendrimers in circulation can affect other physiological and pathological processes, which are associated with an important role of the plasminogen/plasmin system.