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Circulation Research. 1996;78:643-649

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(Circulation Research. 1996;78:643-649.)
© 1996 American Heart Association, Inc.

Articles

Inhibitory Effects of TA-993, a New 1,5-Benzothiazepine Derivative, on Platelet Aggregation

Akio Odawara, Kohei Kikkawa, Makoto Katoh, Hiromi Toryu, Tamotu Shimazaki, Yasuhiko Sasaki

From the Pharmacological Research Laboratory, Tanabe Seiyaku Co, Ltd, Toda, Japan.

Correspondence to Dr Akio Odawara, Pharmacological Research Laboratory, Tanabe Seiyaku Co, Ltd, 2-2-50 Kawagishi, Toda, Saitama 335, Japan.


*    Abstract
up arrowTop
 *Abstract
down arrowIntroduction
 down arrowMaterials and Methods
down arrowResults
down arrowDiscussion
down arrowReferences
 
Abstract TA-993, an l-cis 4',8-dimethyl derivative of the Ca2+ antagonist diltiazem, and some of its metabolites inhibited platelet aggregation induced by collagen, ADP, epinephrine, platelet activating factor, arachidonic acid, and U-46619 in human platelets in vitro. Among the metabolites, MB3 was the most potent (IC50, <1 µmol/L; several hundred times more potent than the parent compound). The d isomer of MB3 was >100 times less potent than the l isomer. Unlike acetylsalicylic acid (ASA), TA-993 inhibited both primary and secondary phases of ADP-induced platelet aggregation and also exhibited a disaggregating effect on human platelet aggregates. The inhibitory effect of TA-993 was enhanced when used in combination with ASA. In ex vivo studies involving rats, TA-993 ({approx}0.3 to 100 mg/kg PO) dose-dependently inhibited collagen-induced platelet aggregation (ED50, 3 mg/kg PO). In the whole-blood platelet aggregation system in rats, orally administered TA-993 was also inhibitory in single (3 to 30 mg/kg) or repeated daily (10 mg/kg per day for 10 days) dosage. Orally administered TA-993 dose-dependently inhibited ADP-induced platelet aggregation ex vivo in dogs (0.3 to 10 mg/kg), significantly protected mice against collagen+epinephrine–induced thromboembolic death (10 mg/kg), and inhibited thrombus formation in an arteriovenous shunt in rats (30 mg/kg). The Ca2+-antagonistic action of TA-993 was very weak in depolarized canine basilar arteries: the potency was {approx}1/10 that of diltiazem (d-cis) and d-TA-993. These results suggest that antiplatelet action is more characteristic of the l-cis than the d-cis 1,5-benzothiazepine structure and that TA-993 may become a clinically useful antiplatelet agent of this structure series.


Key Words: TA-993 • antiplatelet effect • ticlopidine • acetylsalicylic acid • diltiazem


*    Introduction
up arrowTop
 up arrowAbstract
 *Introduction
down arrowMaterials and Methods
down arrowResults
down arrowDiscussion
down arrowReferences
 
It is generally accepted that platelets play a pivotal role in the progress and development of thrombotic disorders,1 2 3 4 especially cerebral vascular diseases such as transient ischemic attack,5 ischemic heart diseases such as myocardial infarction,6 7 8 and peripheral vascular diseases.9 Recently, the inhibition of platelet functions by drugs is thought to be a useful therapeutic means for the prophylaxis and treatment of these diseases. For this purpose, many inhibitors of platelet aggregation such as ASA, sulfinpyrazone, dipyridamole, and ticlopidine have been used clinically.10 11 12 13 14 15 16 17 18 19

Meanwhile, diltiazem, a Ca2+ antagonist of the 1,5-benzothiazepine structure, has been developed, and its efficacy on angina pectoris, hypertension, and myocardial infarction has been well established.20 It has already been reported that diltiazem shows antiplatelet action,21 22 23 24 25 and we have also reported that diltiazem,26 27 its derivative clentiazem, and their basic metabolites28 have inhibitory effects on platelet aggregation.

Among numerous 1,5-benzothiazepine derivatives tested, TA-993 (Fig 1Down) was found to possess a highly potent antiplatelet activity, whereas it shows only very weak Ca2+-antagonistic cardiovascular effects. In the present study, we describe its in vitro, ex vivo, and in vivo antiaggregatory effects on human, dog, and rodent platelets in comparison with those of ASA and ticlopidine.



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  		Figure 1. Chemical structures of TA-993 and its metabolites.


*    Materials and Methods
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 up arrowAbstract
 up arrowIntroduction
 *Materials and Methods
down arrowResults
down arrowDiscussion
down arrowReferences
 
Preparation of PRP
PRP was prepared from blood withdrawn with a plastic syringe from the forearm vein of healthy male volunteers or beagle dogs or from the abdominal aorta of rats under ether anesthesia. Blood samples from humans and dogs were instantly mixed with 1/10 vol of 3.8% trisodium citrate and centrifuged at 150g for 6 minutes, and those from rats were mixed with 1/10 vol of 2.2% trisodium citrate29 and centrifuged at 250g for 6 minutes to give PRP. The remaining blood was further centrifuged at 1000g for 10 minutes to give PPP. The platelet counts of human, dog, and rat PRP were adjusted to {approx}4x105, 2x105, and 8x105 cells per microliter plasma, respectively, by dilution with PPP.

Platelet Aggregation
In Vitro Studies
Platelet aggregation was measured by the method of Born30 as the optical density at 600 nm of PRP during aggregation and expressed as the percentage of the difference in optical density between PRP at maximum aggregation and untreated PRP. PRP (200 µL) was preincubated with a 25-µL test compound solution at 37°C for 2 minutes in the cell of an aggregometer (Hema tracer 1 [model pat-4A], Hema tracer 601, Niko Bio Science), and then with a 25-µL solution or suspension of various aggregating agents, such as collagen (Hormon-Chemie), ADP (Sigma Chemical Co), epinephrine (Bosmin Inj, Daiichi Seiyaku Co), platelet activating factor (synthesized at organic Chemistry Research Laboratory of Tanabe Seiyaku Co), arachidonic acid (Sigma), and U-46619 (Cayman Chemical), was added to activate the platelets. The concentrations of the inducers were adjusted so as to give a concentration that would cause an aggregation of {approx}70% upon addition to PRP. Test compounds were dissolved in physiological saline with ultrasonic treatment. The disaggregating effect was investigated by adding test drugs to PRP 1 minute after platelet aggregation was induced by ADP.

Ex Vivo Studies
Test compounds were dissolved or suspended in pure water in a volume of 10 mL/kg and then orally administered to rats (male, 6 weeks old) fasted overnight. Three hours after the administration, blood (4.5 mL) was withdrawn from the abdominal aorta under ether anesthesia with a plastic syringe containing 0.5 mL of 2.2% trisodium citrate solution and quickly centrifuged at 250g for 6 minutes to afford PRP. The remaining blood was further centrifuged at 1000g for 10 minutes to yield PPP. Platelet counts were adjusted to 8x105 cells per microliter plasma by dilution with PPP. After the PRP (225 µL) was preincubated at 37°C for 2 minutes in the cell of an aggregometer, platelet aggregation was measured by adding 25 µL of collagen suspension (final concentration, 3.6 to 5 µg/mL).

In the whole-blood platelet aggregation test, compounds were orally administered to rats (male, 5 to 6 weeks old) in a single dose (3 to 30 mg/kg) or in repeated daily dosage at 10 mg/kg per day for 10 consecutive days. Thirty minutes or 3 hours after the single dose or 3 hours after the last drug administration, blood (4.5 mL) was taken with a plastic syringe from the abdominal aorta of rats under ether anesthesia. Blood samples were instantly mixed with 1/10 vol of 3.13% trisodium citrate.31 Whole-blood platelet aggregation was measured by the impedance method of Cardinal and Flower.32 Whole blood (1 mL) was preincubated at 37°C for 3 minutes in the cell of a whole-blood platelet aggregometer (model C 560, Chrono-Log), and then 4 µL of a suspension of collagen (1 mg/mL, Chrono-Log) was added to activate the platelets.

Beagle dogs weighing 9 to 13 kg were used after overnight fasting. The animals were orally administered drugs in a capsule. Blood (4.5 mL) was taken from the forearm vein with a plastic syringe containing 0.5 mL of 3.8% trisodium citrate solution just before drug administration and 1, 3, 5, and 7 hours after. Platelet aggregation in PRP was measured by adding ADP (final concentration, 2 to 25 µmol/L) in the above in vitro studies.

In Vivo Antithrombotic Activity
Collagen+Epinephrine–Induced Pulmonary Thrombosis in Mice
The experiment was performed according to the method of Ortega.33 TA-993, ASA, and ticlopidine were dissolved in 0.25% carboxymethylcellulose and then orally administered to overnight-fasted male mice weighing 21 to 28 g. Three hours after the drug administration, pulmonary thrombosis was induced by injection of a mixture of collagen suspension (900 µg/kg) and epinephrine solution (70 µg/kg) into the tail vein, and mortality from thromboembolic death 1 hour after the inducer injection was observed.

Arteriovenous Shunt Model in Rats
The experiment was performed according to the method of Paris et al.34 TA-993, ASA, and ticlopidine were dissolved in 0.25% carboxymethylcellulose and then orally administered to overnight-fasted male rats weighing 220 to 268 g. Three hours after the administration, the rats were anesthetized by intraperitoneal administration of sodium pentobarbital (50 mg/kg). Two 12.5-cm pieces of polyethylene tubing, one with an inner diameter of 0.5 mm and an external diameter of 1.0 mm and the other with an inner diameter of 1.0 mm and an external diameter of 2.0 mm (Hibiki Tube Nos. 3 and 6, Hibiki Co), were filled with heparin and connected to each other with a small piece of silk thread inserted between them. The thinner end was inserted into the right carotid artery, and the thicker end was inserted into the left jugular vein to make an extracorporeal loop shunt between the carotid artery and the jugular vein. Thirty minutes after the start of blood circulation, a thrombus produced on the thread was excised, and its dry weight was measured.

Ca2+-Antagonistic Activity in Depolarized Canine Basilar Arteries
Suppression of Ca2+-Induced Contraction
The experiment was performed according to the method of Kikkawa et al.35 Mongrel dogs of either sex weighing 7.2 to 14.0 kg were anesthetized by intravenous injection of sodium pentobarbital (30 mg/kg) and were sacrificed by exsanguination. The basilar arteries (external diameter, 1.0 to 1.2 mm) were removed immediately, cleaned of surrounding connective tissue, and cut into ring segments 5 mm in length.

The ring segment was suspended in a buffer (see below for composition), which was maintained at 37°C and aerated with 95% O2/5% CO2. The resting tension was adjusted according to the size of the artery. The composition of the buffer was as follows (mmol/L): NaCl 72.6, KCl 80.0, MgCl2 1.0, NaHCO3 14.5, and glucose 5.4 (pH 7.3 to 7.4).

Isometric tension of the artery was measured by a strain-gauge transducer (UL-10, Minebea). Contraction was induced by the addition of Ca2+ (1 mmol/L) to the Ca2+-free K+-depolarizing medium, and the relaxing effect of drugs on the contraction was evaluated as Ca2+-antagonistic activity.

Animals and Drugs
Male rats (Sprague-Dawley strain) and male mice (ddy strain) were purchased from Japan SLC, Inc. Beagle dogs were purchased from Yoshiki Farm. TA-993, its metabolites, and diltiazem were synthesized at Organic Chemistry Research Laboratory of Tanabe Seiyaku Co, Ltd. Ticlopidine was extracted from Panaldine (Daiichi Seiyaku Co, Ltd) and purified at the above laboratory. ASA was obtained from Nacalai Tesque, Inc.

Statistical Analysis
Data were expressed as the mean±SEM and statistically analyzed by one-way ANOVA or the Kruskal-Wallis test. When any significant differences were found, Tukey's method was applied.


*    Results
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 up arrowAbstract
 up arrowIntroduction
 up arrowMaterials and Methods
*Results
down arrowDiscussion
down arrowReferences
 
Inhibition of Platelet Aggregation
In Vitro Studies
The TableDown lists the antiaggregating activities of TA-993 as IC50 or IC30 determined in in vitro studies. TA-993 strongly inhibited platelet aggregation of human, dog, and rat PRP preparations induced by various agonists. The potencies of TA-993 were equivalent to those of ASA and greater than those of ticlopidine. The metabolites of TA-993 (MB1, MB2, and MB3; Fig 1Up) also showed inhibitory effects, and their activities were greater than those of TA-993. In particular, MB3 was the most potent and 20 to 800 times more potent than TA-993. The d isomer of TA-993 was nearly equipotent to TA-993 in collagen-induced platelet aggregation with human platelets (data not shown). However, the d isomer of MB3 was 150 and 580 times less potent than the l isomer in collagen- and ADP-induced platelet aggregation, respectively (TableDown). TA-993 (300 µmol/L) and MB3 (1 µmol/L) inhibited both ADP-induced primary and secondary aggregation of human platelets and further caused disaggregation to human platelet aggregates, whereas ASA did not show the latter effect even at 1000 µmol/L (Fig 2Down). Although TA-993 alone at a concentration of 30 µg/mL did not show any inhibitory effect on collagen-induced human platelet aggregation, the inhibitory effect of TA-993 was enhanced in the presence of ASA (10 µg/mL). A combination of ASA (10 µg/mL) and ticlopidine (100 µg/mL), on the other hand, produced only a weak effect (Fig 3Down).


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  		Table 1. Inhibitory Effects of TA-993, Its Metabolites, and Reference Antiplatelet Drugs on Platelet Aggregation In Vitro



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  		Figure 2. Effects of TA-993, MB3, and ASA on ADP-induced primary platelet aggregation and aggregated human platelets. See the text for the experimental conditions. Drugs were added 2 minutes before (a) or 1 minute after (b, c, and d) the addition of ADP (final concentration, 5 µmol/L).



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  		Figure 3. In vitro effects of TA-993 alone and in combination with ASA on collagen-induced platelet aggregation in human PRP. Platelet aggregation was induced by collagen (final concentration, 0.5 to 1 µg/mL) in the presence of drugs at the concentrations (in micrograms per milliliter) shown in parentheses. Each column shows the mean±SEM of four volunteers. Ticlo. indicates ticlopidine. **P<.01 vs control (Cont.); {dagger}P<.05 and {dagger}{dagger}P<.01 vs drug alone (Tukey's method).

Ex Vivo Studies
When administered orally to rats, TA-993 exhibited dose-dependent inhibitory activity ex vivo on collagen-induced platelet aggregation, with the ED50 being {approx}3 mg/kg, and its potency was greater than that of ASA (ED50, 12 mg/kg), ticlopidine (ED50, 119 mg/kg), and diltiazem (ED50, >100 mg/kg) (Fig 4Down). In the whole-blood platelet aggregation system, orally administered TA-993 (3, 10, and 30 mg/kg) also inhibited collagen-induced whole-blood platelet aggregation in rats in a dose-dependent manner 30 minutes after drug administration (Fig 5aDown). Three hours after single oral administration of 30 mg/kg, only ASA exhibited depression of the whole-blood platelet aggregation, whereas TA-993 and ticlopidine did not (Fig 5bDown). However, when these drugs were administered orally for 10 consecutive days at 10 mg/kg per day, all the drugs showed inhibitory activity on the collagen-induced whole-blood platelet aggregation 3 hours after the last drug administration (Fig 5cDown).



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  		Figure 4. Ex vivo effects of oral administration of TA-993, ticlopidine, ASA, and diltiazem on collagen-induced platelet aggregation in rats. Blood was taken 3 hours after the drug administration. Platelet aggregation in PRP was induced by adding collagen (final concentration, 3.6 to 5 µg/mL). Each plot shows the mean±SEM of aggregation, and the numbers in parentheses represent the number of animals.



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  		Figure 5. Ex vivo effects of TA-993, ticlopidine, and ASA on collagen-induced whole-blood platelet aggregation in rats. Blood was taken 30 minutes after administration (a), 3 hours after administration (30 mg/kg) (b), and 3 hours after the last administration of repeated medication (10 mg/kg/day) for 10 days (c). The whole-blood platelet aggregation (see the text) was induced by adding collagen (final concentrations: a, 3 µg/mL; b and c, 4 µg/mL). Each column shows the mean±SEM. Numbers on the columns represent the number of animals. **P<.01 vs control (Tukey's method).

In beagle dogs, orally administered TA-993 (0.3, 1, and 10 mg/kg) exhibited dose-dependent inhibition of ADP-induced platelet aggregation, which showed a peak effect 1 or 3 hours after administration, and this effect persisted even at 7 hours, when the dose was 10 mg/kg (Fig 6Down). Although a similar dose-dependent effect was observed with ASA (1 and 10 mg/kg), this activity was weaker than that of TA-993, and ticlopidine (10 mg/kg) was ineffective under these experimental conditions.



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  		Figure 6. Ex vivo effects of oral administration of TA-993, ticlopidine, and ASA on ADP-induced platelet aggregation in beagle dogs. Platelet aggregation was induced by adding 2 to 25 µmol/L ADP. Each plot shows the mean±SEM of inhibition (percentage) with respect to the pretreatment values.

Antithrombotic Activity
Intravenous injection of a mixture of collagen and epinephrine into the tail vein of mice caused pulmonary embolism resulting in death, giving a survival rate of 30% in the control group. Previous oral administration of TA-993 (10, 30, and 100 mg/kg) exhibited a significant dose-dependent preventive effect (Fig 7Down). Similarly, ASA and ticlopidine, given orally at doses of 30 and 100 mg/kg, respectively, exhibited significant preventive effects on pulmonary thromboembolic death.



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  		Figure 7. Protective effects of TA-993, ticlopidine, and ASA on pulmonary thromboembolic death in mice. Test compounds were orally administered 3 hours before injection with a mixture of collagen (900 µg/kg) and epinephrine (70 µg/kg) into the tail vein of mice (20 animals per group). *P<.05 and **P<.01 vs control (Kruskal-Wallis method).

In the atrioventricular shunt model in rats, TA-993 administered orally at 30 mg/kg significantly inhibited thrombus formation, and so did oral administration of ticlopidine and ASA at the same dose. However, statistical significance was not observed among these three compounds (Fig 8Down).



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  		Figure 8. Effects of TA-993, ticlopidine, and ASA on thrombus formation in an arteriovenous shunt of rats (eight animals per group). Test compounds were orally administered (30 mg/kg) 3 hours before the installation of the vascular shunt. Thirty minutes after the start of blood circulation, the thrombus produced on the thread was obtained, and the dry weight was measured. *P<.05 and **P<.01 vs control (Tukey's method).

Inhibition of Ca2+-Induced Contraction in Depolarized Canine Basilar Arteries
Typical tracings of the relaxing effects of TA-993, d-TA-993, and diltiazem on the sustained tonic contraction induced by 1 mmol/L Ca2+ in depolarized canine basilar arteries are shown in Fig 9ADown. TA-993 (3 µmol/L), diltiazem (0.3 µmol/L), and d-TA-993 (0.3 µmol/L) relaxed Ca2+-induced contraction in the artery, and the relaxing actions were antagonized by further addition of CaCl2 solution (3 or 10 mmol/L). The Ca2+-antagonistic potency of TA-993 was {approx}1/10 that of diltiazem, although d-TA-993 was almost as active as diltiazem as a Ca2+-antagonist (Fig 9BDown).



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  		Figure 9. Ca2+-antagonistic action of TA-993, d-TA-993, and diltiazem in isolated canine basilar arteries. Preparations were depolarized with 80 mmol/L K+/Ca2+-free buffer. A, Typical tracings showing the effects of TA-993, d-TA-993, and diltiazem on Ca2+-induced contraction. B, Concentration-response curves for the inhibitory actions of TA-993, d-TA-993, and diltiazem.


*    Discussion
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 up arrowAbstract
 up arrowIntroduction
 up arrowMaterials and Methods
up arrowResults
*Discussion
down arrowReferences
 
Among the numerous 1,5-benzothiazepine derivatives so far synthesized, TA-993 is one of the most potent antiplatelet agents when administered to experimental animals. In the ex vivo study, TA-993 was shown to be more potent than ASA and ticlopidine in dogs, and its oral administration at doses below 1 mg/kg was effective in inhibiting aggregation of the platelets from the blood withdrawn 3 hours after drug administration. There were also qualitative differences in the antiplatelet action of TA-993 compared with ASA. Unlike ASA, TA-993 inhibited ADP-induced primary aggregation and U-46619–induced aggregation of human platelets (TableUp), and it showed a disaggregating effect on the human platelets aggregated by ADP (Fig 2Up). Thus, the mechanism of antiplatelet action of TA-993 must be different from that of ASA. This conclusion is supported by the synergism observed between TA-993 and ASA (Fig 3Up).

ASA is known to exert its antiplatelet effect through prevention of thromboxane A2 production by inhibiting cyclooxygenase activity in platelets.36 37 However, ASA at higher concentrations also inhibits the cyclooxygenase of vascular endothelial cells involved in prostaglandin I2 production.38 39 This inhibition may conversely enhance the progression of thrombosis or atherosclerosis.40 Therefore, if clinical doses of ASA could be lowered by combination with TA-993, the combination therapy would be advantageous over a therapy with each drug alone in terms of diminishing side effects as well as potentiating the efficacy. It has already been reported that dipyridamole or diltiazem in combination with ASA clinically augments their platelet aggregation–depressing activities.41 42 43 We have also reported that diltiazem and clentiazem, a derivative of diltiazem, shows synergistic inhibitory effects on platelet aggregation in combination with ASA or ticlopidine.28 However, any possible benefit of the combination therapy of TA-993 and ASA that has been suggested in the animal studies will need to be clarified in clinical studies. The reason for the presence of a synergistic effect by TA-993 and ASA is possibly derived from the difference in the mechanism of their antiplatelet actions.

Meanwhile, the antiplatelet action of ticlopidine has been reported to be mediated by elevation of cAMP levels in the platelets through activation of adenylate cyclase activity.44 However, the exact mechanism of the action of ticlopidine is still unknown. Chap et al45 have reported that ticlopidine only at high concentrations inhibited the intake of arachidonic acid into platelets. This agrees with our present finding that the IC50 or IC30 values were high with any of the inducers used.

In the case of oral administration, TA-993 is converted to MB3 via MB1 or MB2 (authors' unpublished data, 1995) and may exert its action through its metabolites. In fact, the metabolites of TA-993, especially MB3, showed much higher activities than the parent compound in vitro (TableUp). Kiyomoto et al27 also found that some metabolites of diltiazem were stronger inhibitors of platelet aggregation than diltiazem itself. There is an additional report that much of the clinical antiplatelet effect of diltiazem depended on the contribution of its metabolites.41 Such a contribution of the metabolites to the antiplatelet effect of orally administered TA-993 is also likely. The ex vivo potency of TA-993, which was greater than expected from its in vitro activity, supports this possibility (Figs 4Up and 6Up). In the whole-blood platelet aggregation system, TA-993 was more effective by consecutive administration than by single administration (Fig 5Up). This augmented efficacy of consecutive administration may be attributable to the elevated plasma levels of its active metabolites (data not shown).

TA-993 also demonstrated remarkable inhibitory effects on thrombus formation in vivo. In the mouse pulmonary embolization model, death is considered to occur as a result of the embolization caused by platelet aggregates that have been generated intravascularly in the pulmonary microcirculation system after intravenous injection of platelet aggregation inducers.46 The induction of pulmonary embolism by collagen+epinephrine is considered to occur by a synergistic effect of these inducers.47 TA-993 and ASA appeared to be equally effective in this system (Fig 7Up).

In the atrioventricular shunt model, the thrombi formed within the atrioventricular shunt in rats histologically consist of platelets.34 Since ticlopidine and ASA were effective in these in vivo models,48 49 50 51 the antithrombotic effects of TA-993 (Fig 8Up) are also likely to be based on its antiplatelet activity.

Diltiazem is widely used in the treatment of cardiovascular diseases, and its efficacy is based on Ca2+-antagonist action.20 The potency of TA-993 as a Ca2+ antagonist proved to be {approx}1/10 that of diltiazem (Fig 9Up). Doyle and Ruegg52 have reported that the platelet lacks voltage-dependent Ca2+ channels. Therefore, the antiplatelet action of TA-993 must be based on mechanisms other than Ca2+-antagonist action. Besides, notwithstanding its 1,5-benzothiazepine skeleton, TA-993 is an l isomer, and the d isomer of the most potent metabolite MB3 was >100 times less potent than the l isomer (TableUp), whereas the relationship is reversed in their Ca2+-antagonist activities (Fig 9Up). In other words, the optical resolution of 1,5-benzothiazepine derivatives could result in partial dissociation between the Ca2+-antagonistic and antiplatelet actions. The mechanism of the antiplatelet action of TA-993 has not been fully elucidated and is currently under investigation.

In conclusion, the above results indicate that TA-993 is the first selective antiplatelet agent of the 1,5-benzothiazepine structure, and it possesses not only a potent antiplatelet activity but also a unique mode of action. This compound may be useful in the prevention and/or treatment of thrombotic disorders.


*    Selected Abbreviations and Acronyms
 
ASA = acetylsalicylic acid
PPP = platelet-poor plasma
PRP = platelet-rich plasma
TA-993 = cis-(-)-2-(4-methylphenyl)-3-acetoxy-2,3-dihydro-5-(2-dimethylaminoethyl)-8-methyl-1,5-benzothiazepine-4(5H)-one maleate


*    Acknowledgments
 
We would like to thank Dr S. Murata and Dr T. Ikeo for their helpful discussions throughout this study, Dr I. Yamaguchi for his constant encouragement, Dr S. Takeyama for his valuable suggestions regarding the manuscript, and H. Okonogi for his excellent technical assistance.

Received February 27, 1995; accepted January 2, 1996.


*    References
up arrowTop
 up arrowAbstract
 up arrowIntroduction
 up arrowMaterials and Methods
up arrowResults
up arrowDiscussion
*References
 

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