Anti-platelet actions of salicylates: in vivo, ex vivo and in vitro effects of choline salicylate

Effects of choline salicylate, sodium salicylate, choline chloride and acetylsalicylic acid on platelet aggregation in vivo, ex vivo and in vitro in mice were studied. These drugs all inhibited adenosine diphosphate (ADP)-induced respiratory depression, which is closely related to platelet aggregation in vivo, with choline salicylate showing the strongest inhibitory effect. Choline salicylate had a tendency to reduce the mortality of animals injected intravenously with endotoxin, but the other drugs had no such effect. The inhibitory effects of these drugs on ADP-induced platelet aggregation ex vivo were in the order of choline salicylate greater than acetylsalicylic acid congruent to sodium salicylate greater than choline chloride congruent to no effect, and plasma concentrations of protein-unbound salicylic acid at 1 hr after oral administration of drugs were in the order of choline salicylate greater than acetylsalicylic acid congruent to sodium salicylate. The in vitro effects of these drugs were in the order of choline salicylate congruent to sodium salicylate greater than choline chloride congruent to acetylsalicylic acid congruent to no effect. Therefore, it was considered that salicylic acid played an important role on the in vivo, ex vivo and in vitro effects of choline salicylate and that choline increased plasma concentrations of salicylic acid and consequently enhanced the in vivo and ex vivo effects of salicylic acid. Furthermore, the ex vivo effects of choline salicylate were found when ADP-induced platelet aggregation was measured with platelet-rich plasma prepared from blood collected with heparin as anti-coagulant, but not when blood was collected with citrate.(ABSTRACT TRUNCATED AT 250 WORDS)     

Inhibitory effect of various traditional Chinese medicines on rabbit platelet phospholipase A2 in vitro and suppressive effect of t?ki-syakuyaku-san on increased aggregability in hypercholesterolemic rabbit ex vivo

The inhibitory mechanism of 6 traditional Chinese medicines on rabbit platelet aggregation in vitro, and the suppressive effect of oral administration of T?ki-syakuyakusan on hyper-aggregability of the platelet from rabbit fed high cholesterol diet for 2 months, were investigated. Collagen-induced aggregation was inhibited by Keisi-bukury?gan, Kami-sy?y?-san, Dai-saiko-t?, T?ki-syakuyaku-san, Hatimi-zi?-gan and Sy?-saiko-t? in their lower concentrations than those inhibiting arachidonic acid- and thrombin-induced aggregation. These traditional Chinese medicines inhibited the release of [3H]arachidonic acid from membrane phospholipids by phospholipase A2, in [3H]arachidonic acid-labelled platelets under stimulation with collagen and thrombin in the concentration ranges that inhibited each aggregation. In their higher concentrations to inhibit arachidonic acid-induced aggregation, they suppressed the conversion of arachidonic acid to thromboxane A2 by about 50%. However, they had no effect on diacylglycerol formation induced by thrombin. The oral administration of T?ki-syakuyaku-san depressed the increased aggregability of platelets from rabbit fed high cholesterol diet by 20-40% at the period of 1-2 months of feeding, without affecting plasma and platelet cholesterol level. These results indicate that the traditional Chinese medicines used here have an inhibitory effect on platelet phospholipase A2 activation, rather than on cyclooxygenase, and therefore inhibit platelet activation in vitro and ex vivo.     

Antiplatelet and antithrombotic effects of the diterpene spiramine Q from Spiraea japonica var. incisa

Spiramine Q, a diterpene, was isolated from a Chinese herbal plant Spiraea japonica var. incisa Yu. Born's and Wan HY's methods were used to investigate effects of spiramine Q on rabbit platelet aggregation and serotonin release, respectively. Its antithrombotic effect in mice was also evaluated by Myers' method. Spiramine Q selectively inhibited arachidonic acid-induced platelet aggregation in vitro or ex vivo, and decreased serotonin secretion from rabbit platelets. Spiramine Q (5 mg/kg) decreased the mouse mortality caused by injection of 80 mg/kg arachidonic acid in the tail vein. The results suggested that spiramine Q showed potent antiplatelet and antithrombotic activites.     

Inhaled budesonide regimen enhances serotonin- and arachidonic acid-induced platelet aggregation.

The influence of inhaled budesonide regimen (400 micrograms x 2 for 7 days), on agonist-induced platelet aggregation and secretion, was investigated in 18 volunteers. Platelet activation induced by serotonin and arachidonic acid was significantly enhanced after budesonide, as demonstrated by an increase in aggregation velocity (Vmax) and amplitude (Amax), and in arachidonic acid-induced ATP-secretion. We found no change in platelet aggregation induced by ADP, epinephrine, and A23187. With the exception of epinephrine-induced platelet aggregation, which was inhibited by 10(-5)-10(-4) M budesonide, in vitro studies revealed no influence of 10 min budesonide preincubation (10(-9)-10(-4) M) on agonist-induced platelet activation, suggesting that the ex vivo enhancement of platelet function was mediated by secondary corticosteroid mechanisms. A tentative explanation of the increased arachidonic acid-induced platelet activation, may be a budesonide-induced stimulation of cyclooxygenase. The enhanced serotonin-induced platelet aggregation may be a reflection of exogenous corticosteroid stimulation of the 5-HT2-receptor.     

Biochemical and pharmacological effects of dipyrone and its metabolites in model systems related to arachidonic acid cascade

The metabolites of dipyrone (metamizol, Novalgin) were compared with appropriate standard drugs for their influences on the pathways of the arachidonic acid metabolism. The drugs in this study had no significant effects on the lipoxygenase pathway in human neutrophils in vitro. The dipyrone metabolites 4-methylaminoantipyrine (MAAP) and 4-aminoantipyrine (AAP) inhibited prostaglandin synthesis in the 10(-3) to 10(-4) mol/l range thus being comparable to acetylsalicylic acid (ASA), whereas the two additional metabolites 4-acetylaminoantipyrine (AAAP) and 4-formylaminoantipyrine (FAAP) were practically inactive. This result is in accordance with the effects of the metabolites on the formation of oedema in the arthritis rat model, and supports published data showing that MAAP and AAP are the metabolites responsible for the clinical effects of dipyrone. Further systems in our study depending at least partially on the prostaglandin pathway were the release of antiaggregatory activity from rat aortae in vitro and the aggregation of human platelets induced by arachidonic acid in vitro. MAAP exhibits antiaggregatory activity (IC50 5 x 10(-6) mol/l), whereas the inhibitory effect on the vascular antiaggregatory release is much weaker. Compared to normals platelet aggregability ex vivo is enhanced in arthritic rats, but could significantly be lowered again by treatment of the rats with MAAP. A further system studied was the release of 6-keto-PGF1 alpha from rat mucosa in vitro and ex vivo. In vitro there is inhibition to be found with MAAP as well as with ASA. Ex vivo, however, dipyrone or MAAP slightly stimulates mucosal 6-keto-PGF1 alpha rather than inhibiting it, whereas ASA exerts inhibition, as expected.(ABSTRACT TRUNCATED AT 250 WORDS)     

Pharmacology: Effects of Copper-aspirin Complex on Platelet Aggregation and Thrombosis in Rabbits and Mice

The effects of intragastric and intraduodenal copper-aspirin complex on rabbit platelet aggregation were observed by Born's method. Myers's method was used to evaluate the antithrombotic effect of copper-aspirin complex in mice. In-vitro copper-aspirin complex selectively inhibited arachidonic acid-induced platelet aggregation with an IC50 value (concentration resulting in 50% inhibition) of 13.2 μM (95% confidence limits 9.1–16.8 μM). Copper-aspirin complex (10 mg kg^?1 given intragastrically or intraduodenally) was more potent than aspirin in inhibiting arachidonic acid-induced platelet aggregation. Copper-aspirin complex (10 mg kg^?1) had a stronger inhibitory effect and a longer duration of action when given intragastrically than when given intraduodenally. It was shown by radioimmunoassay that copper-aspirin complex significantly reduced the level of thromboxane B₂ in plasma while markedly increasing that of 6-ketoprostaglandin F_1α (6keto-PGF_1α). Copper-aspirin complex (10 mg kg^?1 given intragastrically for 7 days) significantly reduced mouse mortality caused by intravenous injection of arachidonic acid. The results suggest that both in-vitro and in-vivo copper-aspirin complex is more potent in selectively inhibiting arachidonic acid-induced platelet aggregation than aspirin. When given intragastrically the complex has a more potent antiplatelet effect and a longer duration of action than when given intraduodenally. The antithrombotic effect of the complex was more potent than that of aspirin.     

Pharmacological properties of the novel anti-platelet aggregating agent 4-cyano-5,5-bis(4-methoxyphenyl)-4-pentenoic acid

Various pharmacological properties of a new antiplatelet aggregating agent, 4-cyano-5,5-bis(4-methoxyphenyl)-4-pentenoic acid (E-5510), were examined in order to elucidate its mode of action, Firstly, the inhibitory effect on in vitro aggregation of platelets from humans and various experimental animals was studied. E-5510 inhibited human platelet aggregation induced by collagen, arachidonic acid, adenosine diphosphate (ADP), platelet activating factor (PAF) and epinephrine. Thrombin-induced platelet aggregation, which was not inhibited by acetylsalicylic acid (ASA) or the thiazole drug, 4,5-bis(4-methoxyphenyl)-2-(trifluoromethyl) thiazole, was inhibited by E-5510. E-5510 inhibited collagen-induced platelet aggregation in platelet-rich plasma (PRP) from guinea pigs, beagle dogs and monkey to the same degree as in human PRP, but its effect was weaker in rat PRP. Human platelet adhesion to a collagen-coated plastic disk and thrombin-induced adenosine triphosphate (ATP) release from human platelets were also inhibited by this compound. Next, the ex vivo anti-platelet effect of E-5510 was examined in guinea pigs and beagle dogs. E-5510 was the most potent among the tested drugs (ticlopidine, ASA, cilostazol and the thiazole drug. The anti-platelet effect of this compound appeared within 1 h and lasted more than 8 h after oral administration. The above results suggest that E-5510 may antagonize platelet activation by inhibiting phospholipase C and/or A2, which results in suppression of both phosphatidylinositol breakdown and arachidonic acid release from phospholipids, as well as by inhibiting cyclooxygenase. E-5510 exerted its anti-platelet action without affecting prostaglandin I2 production in the blood vessels. It is considered that E-5510 has a highly potent anti-platelet aggregating effect and a unique multi-site mode of action. This compound is a promising candidate as an antithrombotic drug for clinical use.     

Effects of propranolol in vitro and in vivo on platelet function and thromboxane formation in normal volunteers

In vitro and ex vivo effects of propranolol on platelet aggregation, formation of thromboxane B2 (TXB2) and platelet sensitivity to prostacyclin were studied in healthy men. Propranolol, added in vitro to platelet rich plasma (PRP) inhibited platelet aggregation and TXB2 formation induced by ADP, 1-epinephrine, collagen and arachidonic acid. Concentrations of 20-100 microM propranolol were effective when ADP, 1-epinephrine and collagen were used as stimuli. Higher concentrations (250-500 microM) were needed to inhibit aggregation induced by arachidonic acid. Oral administration of propranolol either as a single dose (120 mg) or for one week (3 x 40 mg/day) did, however, not affect platelet aggregation, thromboxane formation and platelet sensitivity to prostacyclin. In addition, withdrawal of propranolol was without effect on these parameters. Although propranolol has potent effects on platelet function in vitro, it seems that the blood levels achievable by oral administration of propranolol are too low to affect platelet aggregation and TXB2 formation.     

Effects of salicylic and acetylsalicylic acid alone and in combination on platelet aggregation and prostanoid synthesis in man.

The present study was designed to investigate the effects of salicylate on the antiplatelet action of acetylsalicylic acid as well as on in vivo prostanoid formation and platelet function in healthy volunteers. In the first study six female volunteers received 350 mg acetylsalicylic acid intravenously, with and without previous oral administration of sodium salicylate (1200 mg daily for 3 days). Urinary prostanoid excretion as well as platelet aggregation and thromboxane formation were measured before and during salicylate and after acetylsalicylic acid. In the second study seven female volunteers received sodium salicylate (52.6 mg kg-1) or acetylsalicylic acid (60.7 mg kg-1) for 8 days in a randomized cross-over protocol. Urinary prostanoid excretion, platelet aggregation and thromboxane formation as well as salicylate plasma concentrations were determined before, during and after administration of each drug. Sodium salicylate did not impair the complete suppression of arachidonic acid-induced platelet thromboxane formation and aggregation obtained by the single intravenous dose of acetylsalicylic acid in the first study. Sodium salicylate in the second study did not affect urinary excretion of prostaglandin E2, its major urinary metabolite (7 alpha-hydroxy-5,11-diketo-tetranor-prostane-1,16-dioic acid), and 2,3-dinor-6-keto-prostaglandin F1 alpha, the main urinary metabolite of epoprostenol (prostacyclin, PGI2). In contrast, acetylsalicylic acid significantly decreased excretion rates of these prostanoids by 64, 59 and 61%, respectively. In both studies platelet aggregation and thromboxane formation induced by collagen, thrombin or arachidonic acid were not significantly affected by salicylate administration, whereas acetylsalicylic acid inhibited platelet aggregation induced by all three agents as well as thrombin- and arachidonic acid induced thromboxane formation.(ABSTRACT TRUNCATED AT 250 WORDS)     

Can we use adenosine diphosphate (ADP) to study "aspirin resistance"? The Janus faces of ADP-triggered platelet aggregation

There is a growing number of contradictory reports indicating that adenosine diphosphate (ADP) can be a useful agonist in monitoring of the antiplatelet action of acetylsalicylic acid (ASA) in humans and animals. In the current study, we aimed to determine the conditions for using ADP to trigger platelet aggregation in order to detect ASA-mediated inhibition of rat platelet reactivity. Initially, we examined the usefulness of different ADP concentrations (0.25, 0.5, 1, 5 and 10 muM) in detecting the in vitro ASA mediated platelet inhibition using whole blood aggregometry, as well as we monitored the role of ADP in generation of thromboxane A(2) (TXA(2)). To study ex vivo ASA inhibitory potential on platelet aggregation induced by a range of ADP concentrations, animals were subjected to one or 10-day ASA administration at the dose of 50 mg/kg. Our experiment shows that ADP in a concentration-dependent manner induces TXA(2) generation in the whole blood with hirudin as an anticoagulant. However, in vitro and ex vivo examination of ASA inhibitory potential on platelet aggregation revealed that irrespectively of administration regimen, ASA failed to block platelet aggregation induced byADPat the concentrations higher than 0.5 muM. Our findings suggest that the mechanism of ADP-induced platelet aggregation depends on agonist concentration. It appears that only low ADP concentrations (up to 0.5 muM) induce TXA(2)-dependent rat platelet aggregation. Therefore, ADP could be considered a useful platelet agonist for monitoring of ASA-mediated platelet inhibition only if used at much lower concentrations than those commonly employed.     

Antiplatelet effects of 2-methyl-3-(1,4,5,6-tetrahydronicotinoyl)pyrazolo[1,5-a]pyridine in relation to its disposition in rats, rabbits and dogs.

KC-764 (2-methyl-3-(1,4,5,6-tetrahydronicotinoyl)pyrazolo[1,5-a]pyridine, CAS 94457-09-7) was evaluated for the inhibition of platelet aggregation and prostanoid production in rats, rabbits and dogs, comparing with acetylsalicylic acid (ASA). Correlations between the inhibitory action and plasma concentration of KC-764 were examined in rabbits. KC-764 was 200 times more potent than ASA in inhibiting collagen-induced rabbit platelet aggregation and TXA2 production in vitro. KC-764 exhibited more selective inhibition of TXA2 production over PGI2 production than ASA. The ratio of IC50's of PGI2 production to TXA2 production of KC-764 was 175 in rats, 72 in rabbits and 65 in dogs, respectively. Such a selectivity was also confirmed ex vivo. The depression of plasma TXB2 levels was well correlated with the ex vivo antiaggregatory activity in rabbits at oral doses of KC-764 ranging from 0.02-1.5 mg/kg. The concentrations/in vitro inhibitory activity relationship was expressed by a sigmoid Imax model equation. The ex vivo antiplatelet activity and prostanoid production were reconstructed with Imax model equation using the simulated plasma drug concentrations and in vitro Imax model parameters in all animals. The relationship could be applied for the prediction of the inhibitory activity of KC-764 in humans. These results indicate that KC-764 is a potent, selective and reversible antiplatelet drug, being different from ASA.     

Relationship of arachidonic acid concentration to cyclooxygenase-dependent human platelet aggregation

Inhibition of ex vivo arachidonic acid (AA)-induced aggregation is a biomarker for the isotype selectivity of cyclooxygenase (COX) inhibitors since platelets express COX-1 but not COX-2. At low concentrations, there is broad inter- and intrasubject variability in AA-induced aggregation of platelets ex vivo. This study defined a concentration that reliably induces aggregation without overcoming inhibition by therapeutic aspirin therapy (ASA, 81-mg) treatment. Logistic regression analysis of ex vivo aggregation, induced with increasing concentrations of AA in platelet-rich plasma (PRP), estimated that platelets from > or = 90% of subjects would aggregate at > or = 1.5 mM AA (95% confidence interval [CI], 1.1, 2.1). A concentration of 1.6 mM AA failed to aggregate platelets from 26 healthy volunteers, who had previously aggregated at this concentration, following six daily oral doses of 81 mg of ASA. These data demonstrate that 1.6 mM AA reproducibly induces platelet aggregation in PRP from healthy volunteers without overcoming the antiplatelet effect of daily low-dose aspirin therapy.     

Differential Inhibitory Effects of Isosorbide Dinitrate and its Mononitrate Metabolites on Platelet Aggregation and Thromboxane Formation

The effects of isosorbide dinitrate (ISDN) and its 2- and 5-mononitrate metabolites (2-ISMN and 5-ISMN) against platelet aggregation and thromboxane release were investigated by analysis of platelet aggregation curves. ISDN, 2-ISMN and 5-ISMN (isosorbide nitrates, ISN) inhibited both ADP- and epinephrine (EPI)-induced platelet aggregation. ISN affected specifically the extent of ADP-induced aggregation and the velocity of EPI-induced effects. 2-ISMN was more potent against platelet aggregation compared to ISDN and 5-ISMN. The isosorbide nitrates were poor inhibitors of both arachidonic acid-induced aggregation and platelet TxB2 release. The differential inhibition by the three isosorbide nitrates of endogenous TxB2 release during ADP-induced aggregation further indicates that 2-ISMN is a significantly more potent platelet inhibitor than either ISDN or 5-ISMN. These studies suggest a role of the metabolites in modulating the pharmacological effects of ISDN on platelet activity.     

Platelet anti-aggregating activities of bupleurumin from the aerial parts of<Emphasis Type="Italic">Bupleurum falcatum</Emphasis>

An aryltetralin lactone, (-)-(1S,2R,3R)-1-(3',4'-methylenedioxyphenyl)-3-(hydroxymethyl)-6,7-dimethoxy-1,2,3,4-tetrahydronaphthalene-2-carboxylic acid lactone, was isolated from the methanol extract of the aerial parts of Bupleurum falcatum and named bupleurumin. The structure of the compound was determined on the basis of chemical and spectroscopic methods, including two-dimensional NMR spectrometry (e.g., 1H- and 13C-NMR, homo- and heteronuclear COSY, HMBC). Bupleurumin showed an 8-fold potent inhibitory effect (IC50: 47.5 uM) compared to that of acetylsalicylic acid (ASA, IC50 : 420 uM) on collagen induced platelet aggregation and comparable effects as ASA on arachidonic acid-induced platelet aggregation.     

Inhibition of platelet aggregation by 2-(p-chlorophenyl)-4-thiazoleacrylic acid (Wy-23,049)--comparison with acetylsalicylic acid

2-(p-Chlorophenyl)-4-thiazoleacrylic acid (Wy-23,049) inhibited the first phase of adenosine diphosphate (ADP) and epinephrine-induced platelet aggregation, while acetylsalicylic acid (ASA) had little effect on the first but effectively inhibited the second phase. ASA was more effective than Wy-23,049 in inhibiting collagen-induced platelet aggregation. An ex vivo guinea-pig experiment demonstrated that Wy-23,049 inhibited the first phase and prevented the appearance of the second phase of ADP-induced platelet aggregation, while ASA inhibited the second phase. Oral administration of Wy-23,049 to rats was much more effective than ASA in protecting the animal against ADP-induced platelet loss. At an oral dose of 40mg/kg, Wy-23,049 prolonged the Lee-White clotting time in rats; ASA did not prolong it.     

Effect of curcumin on platelet aggregation and vascular prostacyclin synthesis

In vitro and ex vivo effects of 1,7-bis(4-hydroxy-3-methoxyphenyl)-1,6-heptadiene-3,5-dione (diferuloylmethane, curcumin) and acetylsalicylic acid (ASA) on the synthesis of prostacyclin (PGI2) and on platelet aggregation has been studied in rat. Both drugs inhibited adenosine diphosphate (ADP)-, epinephrine (adrenaline)- and collagen-induced platelet aggregation in monkey plasma. Pretreatment with ASA (25-100 mg/kg), but not curcumin (100-300 mg/kg), inhibited PGI2 synthesis in rat aorta. In the in vitro system, too, curcumin caused a slight increase in the synthesis of PGI2, while ASA inhibited it. Curcumin may, therefore, be preferable in patients prone to vascular thrombosis and requiring antiarthritic therapy.     

Hydroxychavicol, a novel betel leaf component, inhibits platelet aggregation by suppression of cyclooxygenase, thromboxane production and calcium mobilization

BACKGROUND AND PURPOSE: Platelet hyperactivity is important in the pathogenesis of cardiovascular diseases. Betel leaf (PBL) is consumed by 200-600 million betel quid chewers in the world. Hydroxychavicol (HC), a betel leaf component, was tested for its antiplatelet effect. EXPERIMENTAL APPROACH: We tested the effect of HC on platelet aggregation, thromboxane B(2) (TXB(2)) and reactive oxygen species (ROS) production, cyclooxygenase (COX) activity, ex vivo platelet aggregation and mouse bleeding time and platelet plug formation in vivo. The pharmacokinetics of HC in rats was also assessed. KEY RESULTS: HC inhibited arachidonic acid (AA) and collagen-induced platelet aggregation and TXB(2) production. HC inhibited the thrombin-induced TXB(2) production, but not platelet aggregation. SQ29548, suppressed collagen- and thrombin-induced TXB(2) production, but not thrombin-induced platelet aggregation. HC also suppressed COX-1/COX-2 enzyme activity and the AA-induced ROS production and Ca(2+) mobilization. HC further inhibited the ex vivo platelet aggregation of platelet-rich plasma (>100 nmole/mouse) and prolonged platelet plug formation (>300 nmole/mouse) in mesenteric microvessels, but showed little effect on bleeding time in mouse tail. Moreover, pharmacokinetics analysis found that more than 99% of HC was metabolized within 3 min of administration in Sprague-Dawley rats in vivo. CONCLUSIONS AND IMPLICATIONS: HC is a potent COX-1/COX-2 inhibitor, ROS scavenger and inhibits platelet calcium signaling, TXB(2) production and aggregation. HC could be a potential therapeutic agent for prevention and treatment of atherosclerosis and other cardiovascular diseases through its anti-inflammatory and antiplatelet effects, without effects on haemostatic functions.     

Actions and interactions of acetylsalicylic acid,salicylic acid and diflunisal on platelet aggregation

Summary Acetylsalicylic acid (ASA) is increasingly employed in the secondary prophylaxis of thromboembolic diseases, due to its capacity to inhibit platelet aggregation. The anti-aggregatory effect of ASA on platelets can be inhibited in vitro by a high concentration of salicylic acid (SA). SA is generated in vivo upon ASA administration, and the SA thus formed might impair the antiplatelet effect of ASA. To assess this possibility, the platelet response to ASA was tested in healthy volunteers before and after medication for 1 week with ASA 1 g t.i.d., with SA 1 g t.i.d., and with the SA derivative diflunisal 0.5 g b.i.d. Pre-medication test doses of 1 g ASA always inhibited platelet aggregation in vivo. Neither treatment with SA nor diflunisal, producing plasma steady-state concentrations of about 1.0 and 0.35 mmol/l, respectively, inhibited platelet aggregation. Nor did administration of SA, diflunisal or ASA itself impair the anti-aggregatory effect of a fresh test dose of ASA. ASA inhibited platelet aggregation in vitro at 0.03 mmol/l, whereas SA and diflunisal failed to impair platelet aggregation until concentrations exceeding 2.0 and 0.5 mmol/l, respectively, were reached. These findings make it unlikely that SA formed upon administration of ASA would impair the anti-aggregating capacity of ASA.     

Comparison of in vitro and ex vivo antiplatelet effects of 1,2-benzisothiazolin-3-one and its 2-amino derivative

The in vitro and ex vivo antiplatelet effects of 2-amino-1,2-benzisothiazolin-3-one (1) are compared with those of its parent compound 1,2-benzisothiazolin-3-one (2) and with acetylsalicylic acid (ASA) against different agonists. 2-Amino-1,2-benzisothiazolin-3-one inhibits adenosine diphosphate (ADP)-, arachidonic acid (AA)- and collagen-induced human platelet aggregation in vitro, with IC50 values of 8.90 x 10(-5), 1.50 x 10(-6) and 5.11 x 10(-8) mol/l, respectively. The strong inhibitory activity is significant not only for collagen but also for AA-induced aggregation. The same compound inhibits ex vivo collagen- and particularly AA-induced rabbit platelet aggregation at the tested dose of 10 mg/kg i.m. In view of the potential use of 2-amino-1,2-benzisothiazolin-3-one as antithrombotic agent, the log P values for both 1,2-benzisothiazolin-3-one derivatives 1 and 2 are determined, to gain an understanding of the significance of the 2-amino group in the 1,2-benzisothiazolin-3-one moiety with respect to the biological activity under study.     

Effects on platelet functions and pharmacokinetics of azapropazone and ketorolac tromethamine given as single parenteral doses.

The biosynthesis of thromboxane (TX) B2 and immunoreactive prostaglandin (PG) F2 alpha in clotting whole blood ex vivo as well as collagen-induced platelet aggregation were determined before and up to 72 h after intravenous injection of 600 mg azapropazone 2H2O and intramuscular injection of 30 mg ketorolac tromethamine in six healthy subjects. The drug doses were selected on the basis of comparable analgesic activity (maximal recommended analgesic dose). Both platelet aggregation and prostanoid biosynthesis were inhibited by racketorolac to a significantly greater extent and for a longer period of time than by azapropazone. Correlations between serum concentrations and the inhibitory effects on TXB2 biosynthesis were observed for both drugs. Using the sigmoidal Emax model the mean serum concentration of azapropazone inhibiting platelet TXB2 generation by 50% (EC50) was found to be 98.1 +/- 41.9 (s.d.) micrograms ml-1, a value 1000 times higher than that for rac-ketorolac. The moderate inhibition of platelet function by azapropazone as compared with rac-ketorolac might be an advantage with regard to its use as a post-operative analgesic.