Adenosine-mediated inhibition of platelet aggregation by acadesine. A novel antithrombotic mechanism in vitro and in vivo.

Abstract

Inhibition of platelet aggregation by acadesine was evaluated both in vitro and ex vivo in human whole blood using impedance aggregometry, as well as in vivo in a canine model of platelet-dependent cyclic coronary flow reductions. In vitro, incubation of acadesine in whole blood inhibited ADP-induced platelet aggregation by 50% at 240±60 ,IM.Inhibition of platelet aggregation was time dependent and was prevented by the adenosine kinase inhibitor, 5 '-deoxy 5-iodotubercidin, which blocked conversion of acadesine to its 5 '-monophosphate, ZMP, and by adenosine deaminase. Acadesine elevated platelet cAMP in whole blood, which was also prevented by adenosine deaminase. In contrast, acadesine had no effect on ADP-induced platelet aggregation or platelet cAMP levels in platelet-rich plasma, but inhibition of aggregation was restored when isolated erythrocytes were incubated with acadesine before reconstitution with platelet-rich plasma. Acadesine (100 mg/kg i.v.) administered to human subjects also inhibited platelet aggregation ex vivo in whole blood. In the canine Folts model of platelet thrombosis, acadesine (0.5 mg/kg per mm i.v.) abolished coronary flow reductions, and this activity was prevented by pretreatment with the adenosine receptor antagonist, 8-sulphophenyltheophylline. These results demonstrate that acadesine exhibits antiplatelet activity in vitro, ex vivo, and in vivo through an adenosine-dependent mechanism. Moreover, the in vitro studies indicate that inhibition of platelet aggregation requires the presence of erythrocytes and metabolism of acadesine to acadesine monophosphate (ZMP). (J. Clin. Invest. 1994. 94:1524-1532

Effect of adenosine A2 receptor stimulation on platelet activation–aggregation: Differences between canine and human models

“…In contrast, impedance in matched aliquots pretreated with CGS was significantly reduced to a mean of 12 ohms ( Figure 3B), a finding consistent with previous in vitro data obtained with adenosine A 2 agonists [4,11,12,22] and consistent with the concept that CGS attenuates thrombosis.…”

“…Although recurrent thrombosis was seen in all dogs, pre-treatment with CGS was, as anticipated from previous studies [1][2][3][4], associated with better maintenance of patency in the damaged and stenotic vessel. Specifically: flow-time area averaged 76±13% and the duration of total thrombotic occlusion was 10±6 min, significant improvements versus the values of 23±5% and 59±14 min observed in the concurrent controls ( Figure 1).…”

“…Previous studies conducted in anesthetized dogs have shown that adenosine and adenosine agonists attenuate recurrent thrombosis in damaged and stenotic coronary arteries [1][2][3][4], and inhibit the formation of microemboli in the setting of stable coronary hypoperfusion [5,6]. Moreover, although the mechanisms by which these agents improve coronary patency are poorly understood, stimulation of platelet adenosine A 2 receptors and subsequent sustained suppression of platelet activation-aggregation has been proposed to play a role [1][2][3][4][5][6].…”

“…adenosine; platelets; thrombosis; P-selectin; heterotypic aggregates; fibrinogen Adenosine and adenosine receptor agonists have been shown to improve arterial patency in experimental models of recurrent thrombosis mimicking unstable angina and augment blood flow in models of coronary hypoperfusion [1][2][3][4][5][6]. Moreover, release of adenosine from ischemic-reperfused cardiomyocytes has been hypothesized to contribute to the favorable attenuation of recurrent thrombosis evoked by brief antecedent preconditioning ischemia [1][2][3]7,8].…”

“…Moreover, release of adenosine from ischemic-reperfused cardiomyocytes has been hypothesized to contribute to the favorable attenuation of recurrent thrombosis evoked by brief antecedent preconditioning ischemia [1][2][3]7,8]. These improvements in patency have been proposed to be a consequence of the welldocumented, platelet inhibitory effects of adenosine, initiated via stimulation of adenosine A 2 receptors on the platelets' surface [1][2][3][4][5][6][8][9][10][11][12]. However, there is at present no direct evidence to substantiate this premise, and the specific site of action of adenosine/adenosine agonists (i.e., stimulation of A 2 receptors on platelets versus other blood-borne elements and/or vascular smooth muscle) has not been established.…”