Naohiro Yamada

Inhibition of restenosis by beraprost sodium (a prostaglandin I2 analogue) in the atherosclerotic rabbit artery after angioplasty

We examined the effect of beraprost sodium (EPS), a stable prostaglandin I2 (PGI2) analogue, on re-stenosis after balloon angioplasty in the atherosclerotic artery in rabbits. Regional atherosclerosis was induced in the femoral artery of New Zealand white rabbits by balloon deendothelialization and 2% cholesterol diet. After establishment of atheroma in the femoral artery, angioplasty was performed. In all, 65 rabbits were assigned to the following six subcutaneous drug treatment groups: control group (n = 13, saline 0.25 ml/kg); BPS low-dose group (n = 11, BPS 50 μg/kg twice daily); BPS high-dose group (n = 12, BPS 100 μg/kg twice daily); 2-day BPS high-dose group (n = 11, BPS 100 μg/kg twice daily for 2 days after angioplasty); aspirin (ASA) group (n = 10, ASA 30 mg once daily); and BPS + ASA group (n = 8, BPS 50 μg/kg twice daily plus ASA 30 mg once daily). Administration of each drug was started 30 min before balloon angioplasty and was continued until 4 weeks thereafter, except in the 2-day BPS high-dose group. Re-examination 4 weeks after the angioplasty showed significant (p < 0.05) preservation of the luminal diameter in the BPS high-dose and 2-day BPS high-dose groups (1.30 ± 0.15 and 1.25 ± 0.09 mm, respectively) as compared with that in the control group (0.83 ± 0.10 mm); however, the luminal diameter in the BPS low-dose, ASA, and BPS + ASA groups (0.94 ±0.18, 1.06 ± 0.11, and 1.05 ±0.15 mm, respectively) was not significantly different from that in the control group.

TRA-418, a novel compound having both thromboxane A2 receptor antagonistic and prostaglandin I2 receptor agonistic activities: its antiplatelet effects in human and animal platelets

Summary.  TRA‐418 is a novel compound that has been found in our screening for compounds having both thromboxane A2 (TP) receptor antagonistic and prostaglandin I2 (IP) receptor agonistic activities. In the binding assays, TRA‐418 showed a 10‐fold higher affinity to TP‐receptors than IP‐receptors. TRA‐418 inhibited platelet aggregation induced by the TP‐receptor agonist, U‐46619 and by arachidonic acid at concentrations lower than those required for inhibition of ADP‐induced aggregations. Furthermore, TRA‐418 inhibited not only platelet aggregation induced by ADP alone, but also that induced by ADP in the presence of the TP‐receptor antagonist, SQ‐29548. When the IC50 values of TRA‐418 for platelet aggregation were estimated in platelet preparations from monkeys, dogs, cats, and rats using ADP and arachidonic acid as the platelet stimulating agents, it was found that the values estimated in monkey platelets were quite similar to those estimated in human platelets. In ex vivo platelet aggregation in monkeys, TRA‐418 exhibited significant inhibitory effects on arachidonic acid‐induced aggregation in platelet preparations from monkeys treated at 3 µg kg min−1 or higher doses, where neither a significant decrease in blood pressure nor a significant increase in heart rate was observed. These results are consistent with the fact that TRA‐418 has a relatively potent TP‐receptor antagonistic activity together with a relatively weak IP‐receptor agonistic activity.

Effects of TRA-418, a novel TP-receptor antagonist, and IP-receptor agonist, on human platelet activation and aggregation.

{4‐[2‐(1,1‐Diphenylethylsulfanyl)‐ethyl]‐3,4‐dihydro‐2H‐benzo[1,4]oxazin‐8‐yloxy}‐acetic acid N‐Methyl‐D‐glucamine salt (TRA‐418) has both thromboxane A2 (TP)‐receptor antagonist and prostacyclin (IP)‐receptor agonist properties. The present study examined the advantageous effects of TRA‐418 based on the dual activities, over an agent having either activity alone and also the difference in the effects of TRA‐418 and a glycoprotein αIIb/β3 integrin (GPIIb/IIIa) inhibitor. TRA‐418 inhibited platelet GPIIb/IIIa activation as well as P‐selectin expression induced by adenosine 5′‐diphosphate, thrombin receptor agonist peptide 1–6 (Ser‐Phe‐Leu‐Leu‐Arg‐Asn‐NH2), and U‐46619 in the presence of epinephrine (U‐46619+ epinephrine). TRA‐418 also inhibited platelet aggregation induced by those platelet‐stimulants in Ca2+ chelating anticoagulant, citrate and in nonchelating anticoagulant, D‐phenylalanyl‐L‐prolyl‐L‐arginyl‐chloromethyl ketone (PPACK). The TP‐receptor antagonist SQ‐29548 inhibited only U‐46619+epinephrine‐induced GPIIb/IIIa activation, P‐selectin expression, and platelet aggregation. The IP‐receptor agonist beraprost sodium inhibited platelet activation. Beraprost also inhibited platelet aggregation induced by platelet stimulants we tested in citrate and in PPACK. The GPIIb/IIIa inhibitor abciximab blocked GPIIb/IIIa activation and platelet aggregation. However, abciximab showed slight inhibitory effects on P‐selectin expression. TRA‐418 is more advantageous as an antiplatelet agent than TP‐receptor antagonists or IP‐receptor agonists separately used. TRA‐418 showed a different inhibitory profile from abciximab in the effects on P‐selectin expression.

TRA-418, a thromboxane A2 receptor antagonist and prostacyclin receptor agonist, inhibits platelet-leukocyte interaction in human whole blood

TRA-418, a compound with both thromboxane A2 receptor (TP receptor) antagonistic and prostacyclin receptor (IP receptor) agonistic activities, was synthesised in our laboratory as a new antithrombotic agent. In this study, we examined the effects of TRA-418 on platelet-leukocyte interactions in human whole blood. Platelet-leukocyte interactions were induced by U-46619 in the presence of epinephrine (U-46619 + epinephrine) or with thrombin receptor agonist peptide 1-6 (TRAP). Platelet-leukocyte interactions were assessed by flow cytometry, with examination of both platelet-neutrophil and platelet-monocyte complexes. In a control experiment, the TP receptor antagonist SQ-29548 significantly inhibited the induction of platelet-leukocyte complexes by the combination of U-46619 and epinephrine, but not TRAP-induced formation of platelet-leukocyte complexes. Conversely, the IP receptor agonist beraprost sodium inhibited platelet-leukocyte complex formation induced by both methods, although the IC50 values of beraprost sodium for U-46619 + epinephrine were at least 10-fold greater than for TRAP. Under such conditions, TRA-418 inhibited both U-46619 + epinephrine-induced and TRAP-induced platelet-leukocyte complex formation in a concentration-dependent manner, in a similar range. These results suggest that TRA-418 exerts its inhibitory effects on platelet-leukocyte interactions by acting as a TP receptor antagonist as well as an IP receptor agonist in an additive or synergistic manner. These inhibitory effects of TRA-418 on formation of platelet-leukocyte complexes suggest the compound is beneficial effects as an antithrombotic agent.

Effects of beraprost sodium and prostaglandin E1 on skin blood flow in diabetic rats and normal dogs

1. The present study was undertaken to compare the effects of beraprost sodium (BPS), a stable prostaglandin I2 analog, with prostaglandin E1 (PGE1) on the skin blood flow in anesthesized diabetic rats and anesthetized dogs. 2. In anesthetized diabetic rats, BPS, but not PGE1, caused a dose-dependent and significant increase in femoral skin blood flow. 3. In anesthetized dogs, PGE1 significantly increased femoral arterial blood flow than BPS. However, BPS significantly increased in-step skin blood flow than PGE1. 4. The above data suggest that BPS may be clinically useful for the treatment of circulatory insufficiency of lower extremities in diabetic patients.