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Inhibition by simendan (OR-1259) of collagen-and Ca2+-ionophore induced aggregation of human platelets
1 58
Pharmacological Research, Vol. 25, Supplement 2, 1992
INHIBITION BY SIMENDAN (OR-1259) OF COLLAGEN-and Cat+IONOPHORE , INDUCED AGGREGATION OF HUMAN PLATELETS JANOS PATARICZA and JULIUS GY . PAPP .Department of Pharmacology, Albert Szent-Gyorgyi University Medical School, Szeged, Hungary Keywords : Simendan, Platelet aggregation, Collagen, A 23187 A newly synthetized propanedinitrile derivative, Simendan (Fig .1) has been shown to posses calcium senzitizing and some inhibitory effect on cAMP PDE (PDE III) of the heart with positive inotropic, vasodilating and antiarrhythmic properties (1,2) . Platelet inhibition was also demonstrated by Simendan against arachidonic acid and ADP induced aggregation of human platelets without affecting thromboxane production (personal communication) . The antiaggregatory effects of PDE III inhibitors are theoretically more promising than other antiplatelet agents which modify arachidonate metabolism, because platelets incubated with these drugs may not respond to most of the physiological agonists (3) . Collagen and Ca 2 +-ionophore, A 23187 induced aggregation of human
platelets were used to study the effects of Simendan in comparison to a known PDE III inhibitor, Milrinone . Washed platelets for collagen aggregation were obtained by the method of Radomski and Moncada (4) and for A 23187 induced aggregation according to Siess and Lapetina (5) . Platelet counts of platelet suspensions were adjusted to 250-300 .000/ Ml and aggregation was measured by the absorbance method using a platelet aggregometer .
Fig . 1 Chemical structure of Simendan (OR- 1259) The 50% inhibitory concentrations (IC50) of Simendan and Milrinone calculated from the dose-response curves against two inducers of platelet aggregation are summarized in Table I . Simendan inhibited the receptor mediated aggregation (3 .4 ,ug/ml collagen) with similar potency as the non-receptormediated platelet aggregation (0 .5 ,umol/I A 23187) . The drug was found to be more potent than the reference compound, Milrinone on both types of aggregation .
1043-6618/92/25110158-02/$03 .00/0
© 1992 The Italian Pharmacological Society
1 59
Pharmacological Research, Vol . 25, Supplement 2, 1992
Table I . Comparison of the effects of Simendan and Milrinone on human platelet aggregation
IC50 (limol/l )
washed human platelets I /agonist : collagen 2/agonist : A 23187
Simendan
Milrinone
0 .17
0 .76
0 .20
0 .85
In conclusion, Simendan is a potent inhibitor of human platelet aggregation in vitro. The inhibition of collagen induced aggregation by Simendan may have a therapeutic value especially when the subendothelial collagen has a direct contact with platelets in certain pathological conditions (e .g .endothelial damage in atherosclerosis) . The inhibitory action of Simendan on A 23187 aggregation suggests the participation of Cat+-dependent protein kinase C pathway in the antiaggregatory mechanism of the drug, an effect that is characteristic for the elevation of intraplatelet CAMP (5) . Although this novel cAMP PDE inhibitor is specifically developed as an inotropic drug, its wide spectrum on platelet inhibition may attract interest in the therapy of thrombotic diseases . References 1 .Raasmaja A, Talo A, Nissinen E, Linden I-B, Pohto P. Biochemical mechanisms of the novel cardiotonic agent OR-1259.J Mol Cell Cardiol 1991 ; 23(Suppl V) :S129 . 2 .Haikala H, Levijoki J, Leino T, Linden I-B, Pohto P. Antiarrhythmic effect and altered calcium sequestration by a cardiotonic agent OR-1259 .J Mol Cell Cardiol 1991 ; 23(Suppl V) :S130 . 3 .Hidaka H, Hayashi H, Kohri H,Kimura Y, Hosokawa T, Igawa T, Saitoh Y . Selective inhibitor of platelet cyclic adenosine monophosphate phosphodiesterase,cilostamide, inhibit platelet aggregation . J Pharmacol Exp Ther 1979 ; 211 :26-30 . 4 .Radomski MW, Moncada S . An improved method for washing human platelets with prostacyclin . Thromb Res 1983 ; 30 :383-89 . 5 .Siess W, Lapetina EG . Prostacyclin inhibits platelet aggregation induced by phorbol ester or Cat+ionophore at steps distal to activation of protein kinase C and Cat+-dependent protein kinases . Biochem J 1989 ;258 :57-65
Pharmacological Research, Vol. 25, Supplement 2, 1992
INHIBITION BY SIMENDAN (OR-1259) OF COLLAGEN-and Cat+IONOPHORE , INDUCED AGGREGATION OF HUMAN PLATELETS JANOS PATARICZA and JULIUS GY . PAPP .Department of Pharmacology, Albert Szent-Gyorgyi University Medical School, Szeged, Hungary Keywords : Simendan, Platelet aggregation, Collagen, A 23187 A newly synthetized propanedinitrile derivative, Simendan (Fig .1) has been shown to posses calcium senzitizing and some inhibitory effect on cAMP PDE (PDE III) of the heart with positive inotropic, vasodilating and antiarrhythmic properties (1,2) . Platelet inhibition was also demonstrated by Simendan against arachidonic acid and ADP induced aggregation of human platelets without affecting thromboxane production (personal communication) . The antiaggregatory effects of PDE III inhibitors are theoretically more promising than other antiplatelet agents which modify arachidonate metabolism, because platelets incubated with these drugs may not respond to most of the physiological agonists (3) . Collagen and Ca 2 +-ionophore, A 23187 induced aggregation of human
platelets were used to study the effects of Simendan in comparison to a known PDE III inhibitor, Milrinone . Washed platelets for collagen aggregation were obtained by the method of Radomski and Moncada (4) and for A 23187 induced aggregation according to Siess and Lapetina (5) . Platelet counts of platelet suspensions were adjusted to 250-300 .000/ Ml and aggregation was measured by the absorbance method using a platelet aggregometer .
Fig . 1 Chemical structure of Simendan (OR- 1259) The 50% inhibitory concentrations (IC50) of Simendan and Milrinone calculated from the dose-response curves against two inducers of platelet aggregation are summarized in Table I . Simendan inhibited the receptor mediated aggregation (3 .4 ,ug/ml collagen) with similar potency as the non-receptormediated platelet aggregation (0 .5 ,umol/I A 23187) . The drug was found to be more potent than the reference compound, Milrinone on both types of aggregation .
1043-6618/92/25110158-02/$03 .00/0
© 1992 The Italian Pharmacological Society
1 59
Pharmacological Research, Vol . 25, Supplement 2, 1992
Table I . Comparison of the effects of Simendan and Milrinone on human platelet aggregation
IC50 (limol/l )
washed human platelets I /agonist : collagen 2/agonist : A 23187
Simendan
Milrinone
0 .17
0 .76
0 .20
0 .85
In conclusion, Simendan is a potent inhibitor of human platelet aggregation in vitro. The inhibition of collagen induced aggregation by Simendan may have a therapeutic value especially when the subendothelial collagen has a direct contact with platelets in certain pathological conditions (e .g .endothelial damage in atherosclerosis) . The inhibitory action of Simendan on A 23187 aggregation suggests the participation of Cat+-dependent protein kinase C pathway in the antiaggregatory mechanism of the drug, an effect that is characteristic for the elevation of intraplatelet CAMP (5) . Although this novel cAMP PDE inhibitor is specifically developed as an inotropic drug, its wide spectrum on platelet inhibition may attract interest in the therapy of thrombotic diseases . References 1 .Raasmaja A, Talo A, Nissinen E, Linden I-B, Pohto P. Biochemical mechanisms of the novel cardiotonic agent OR-1259.J Mol Cell Cardiol 1991 ; 23(Suppl V) :S129 . 2 .Haikala H, Levijoki J, Leino T, Linden I-B, Pohto P. Antiarrhythmic effect and altered calcium sequestration by a cardiotonic agent OR-1259 .J Mol Cell Cardiol 1991 ; 23(Suppl V) :S130 . 3 .Hidaka H, Hayashi H, Kohri H,Kimura Y, Hosokawa T, Igawa T, Saitoh Y . Selective inhibitor of platelet cyclic adenosine monophosphate phosphodiesterase,cilostamide, inhibit platelet aggregation . J Pharmacol Exp Ther 1979 ; 211 :26-30 . 4 .Radomski MW, Moncada S . An improved method for washing human platelets with prostacyclin . Thromb Res 1983 ; 30 :383-89 . 5 .Siess W, Lapetina EG . Prostacyclin inhibits platelet aggregation induced by phorbol ester or Cat+ionophore at steps distal to activation of protein kinase C and Cat+-dependent protein kinases . Biochem J 1989 ;258 :57-65