The Synergy of Dipyridamole, Adenosine and Nitric Oxide in the Presence of P2Y12 Inhibitors

Background: Dual anti-platelet therapy (DAPT), consisting of aspirin and a P2Y12 receptor blocker, such as prasugrel, is used to maximise the prevention of platelet activation though the blockade of cyclooxygenase-derived thromboxane (Tx) A2 generation and ADP receptor activation. P2Y12 receptor blockers synergise with endogenous mediators, such as nitric oxide (NO), to potentiate their anti-platelet actions. Furthermore, a synergy exists between P2Y12 inhibitors and adenosine, which can be derived from ADP. Dipyridamole is a phosphodiesterase inhibitor, which prevents the breakdown of cyclic nucleotides responsible for this synergy.

Objectives: To investigate the inhibitory interactions of dipyridamole, prasugrel, adenosine and nitric oxide (NO) on platelet function.

Methods: Blood was taken from healthy volunteers by venepuncture and platelet rich plasma (PRP) prepared by centrifugation. PRP was incubated with dipyridamole (10-300 µM) and/or prasugrel active metabolite (PAM; 0.1-100 nM) or vehicle, followed by NO donor, diethylamine NONOate (DEA/NONOate), adenosine analogue, 5’-N-ethylcarboxamidoadenosine (NECA) or vehicle. Platelets were stimulated using the thromboxane A2 mimetic, U46619, and aggregation was measured using 96-well light transmission aggregometry. Data was analysed by two-way ANOVA and P<0.05 taken as significant.

Results: Dipyridamole did not produce platelet inhibition either alone or when in combination with PAM or DEA/NONOate. In the presence of higher concentrations of dipyridamole (100 µM), however, DEA/NONOate enhanced the inhibition of aggregation in combination with NECA (P<0.05; logIC50: -6.8±0.3 M to -7.1±0.2 M, Figure 1). NECA, dipyridamole and DEA/NONOate were also shown to synergise by isobolographic analyses, though in the presence of PAM did not cause any further inhibition of aggregation.

Conclusions: Here we show that dipyridamole adds little to the platelet inhibition produced by PAM. Nevertheless, our experiments confirmed previous findings that dipyridamole potentiates the anti-platelet actions of both NECA and NO. Though dipyridamole did not significantly effect the inhibition of platelet aggregation in PRP, it may have a greater role to play in vivo. Dipyridamole inhibits the reuptake of adenosine by red blood cells and the increased presence of adenosine will enhance the synergy between itself and P2Y12 inhibitors. Therefore, dipyridamole may still provide benefit as an adjuvant to DAPT for the secondary prevention of arterial thrombotic events.