The established antiplatelet and
anticoagulant agents show beneficial effects in the treatment of thromboembolic diseases; however, these drugs still have considerable limitations. The effects of
NP-184, a synthetic compound, on platelet functions, plasma
coagulant activity, and mesenteric venule
thrombosis in mice were investigated.
NP-184 concentration-dependently inhibited the human platelet aggregation induced by
collagen,
arachidonic acid (AA), and
U46619, a
thromboxane (TX)A(2) mimic, with IC(50) values of 4.5 +/- 0.2, 3.9 +/- 0.1, and 9.3 +/- 0.5 microM, respectively. Moreover,
NP-184 concentration-dependently suppressed TXA(2) formations caused by
collagen and AA. In exploring effects of
NP-184 on
enzymes involved in TXA(2) synthesis, we found that
NP-184 selectively inhibited TXA(2) synthase activity with an IC(50) value of 4.3 +/- 0.2 microM. Furthermore,
NP-184 produced a right shift of the concentration-response curve of
U46619, indicating a competitive antagonism on TXA(2)/
prostaglandin H(2) receptor. Intriguingly,
NP-184 also caused a concentration-dependent prolongation of the activated partial thromboplastin time (aPTT) with no changes in the
prothrombin and thrombin time, indicating that it selectively impairs the intrinsic coagulation pathway.
Oral administration of
NP-184 significantly inhibited
thrombus formation of the irradiated mesenteric venules in
fluorescein sodium-treated mice without affecting the bleeding time induced by tail transection. However, after
oral administration,
NP-184 inhibited the ex vivo mouse platelet aggregation triggered by
collagen and
U46619 and also prolonged aPTT. Taken together, the dual antiplatelet and
anticoagulant activities of
NP-184 may have therapeutic potential as an oral
antithrombotic agent in the treatment of thromboembolic disorders.