Binding of adenosine derivatives to carrier proteins may reduce their antiplatelet activity

Adenosine analogues have high affinity and selectivity for adenosine receptors (AR), and exhibit anti-platelet activity. Plasma proteins play an important role in the regulation of platelet function and may influence the action of anti-platelet compounds. Little is known about the interactions of AR agonists with plasma proteins. This study investigates the interplay between AR agonists and plasma proteins and the consequences of those interactions. Surface plasmon resonance was employed together with molecular docking study to determine the binding kinetics of four selected AR agonists (PSB 0777, Cl-Ado, MRE 0094, UK 432097) to several carrier proteins and to clarify the nature of these interactions. The influence of a whole plasma and of some plasma components on the effectiveness of AR agonists in the inhibition of platelet function was assessed by flow cytometry (platelet activation) and ELISA (platelet adhesion). Plasma proteins remarkably diminished the effectiveness of AR agonists in inhibiting platelet activation and adhesion in vitro. AR agonists were found to strongly bind to human serum albumin (HSA) and the protein components of lipoproteins - apolipoproteins; HSA was essential for the binding of water-soluble PSB 0777, whereas apolipoproteins were needed for interactions with poorly-water soluble compounds such as UK 432097 and MRE 0094. In addition, HSA was shown to significantly reduce the effectiveness of PSB 0777 in inhibiting ADP-induced platelet activation. In conclusion, HSA and lipoproteins are important carriers for AR agonists, which can affect pharmacodynamics of AR agonists used as platelet inhibitors.