The mechanisms of antiplatelet action of
adenosine and
inosine in vitro and in vivo, and their differential biological effects by molecular modeling were investigated.
RESULTS:
Adenosine (0.5, 1 and 2 mmol/L) inhibited
phosphatidylserine exposure from 52±4% in the control group to 44±4 (p<0.05), 29±2 (p<0.01) and 20±3% (p<0.001).
P-selectin expression in the presence of
adenosine 0.5, 1 and 2 mmol/L was inhibited from 32±4 to 27±2 (p<0.05), 14±3 (p<0.01) and 9±3% (p<0.001), respectively. At the concentrations tested, only
inosine to 4 mmol/L had effect on platelet
P-selectin expression (p<0.05).
Adenosine and
inosine inhibited platelet aggregation and
ATP release stimulated by
ADP and
collagen.
Adenosine and
inosine reduced
collagen-induced platelet adhesion and aggregate formation under flow. At the same concentrations
adenosine inhibited platelet aggregation, decreased the levels of sCD40L and increased intraplatelet cAMP. In addition, SQ22536 (an
adenylate cyclase inhibitor) and
ZM241385 (a potent
adenosine receptor A2A antagonist) attenuated the effect of
adenosine on platelet aggregation induced by
ADP and intraplatelet level of cAMP.
Adenosine and
inosine significantly inhibited
thrombosis formation in vivo (62±2% occlusion at 60 min [n = 6, p<0.01] and 72±1.9% occlusion at 60 min, [n = 6, p<0.05], respectively) compared with the control (98±2% occlusion at 60 min, n = 6). A2A is the
adenosine receptor present in platelets; it is known that
inosine is not an A2A
ligand. Docking of
adenosine and
inosine inside A2A showed that the main difference is the formation by
adenosine of an additional hydrogen bond between the NH2 of the
adenine group and the residues Asn253 in H6 and Glu169 in EL2 of the A2A receptor.
CONCLUSION: