Efficacy of different doses of aspirin in decreasing blood levels of inflammatory markers in patients with cardiovascular metabolic syndrome

Objectives Inflammation and platelet aggregation and activation are key processes in the initiation of a cardiovascular event. Patients with metabolic syndrome have a high risk of cardiovascular events. This study determined whether small and medium doses of aspirin have anti‐inflammation and antiplatelet aggregation effects in patients with metabolic syndrome. Methods One hundred and twenty‐one consecutive patients with metabolic syndrome were randomized into three groups, receiving 100 mg/day of aspirin, 300 mg/day of aspirin or a placebo, respectively, for 2 weeks. The blood levels of thromboxane B2 (TXB2), a stable product of the platelet aggregation mediator TXA2, 6‐keto‐prostaglandin F1‐α (6‐keto‐PGF1‐α), a stable product of the endogenous cyclooxygenase metabolite prostaglandin I2, and inflammatory mediators including high‐sensitivity C‐reactive protein (hs‐CRP), tumour necrosis factor‐α (TNF‐α) and interleukin‐6 (IL‐6), were determined by ELISA and radioimmunoassay. Key findings The blood levels of hs‐CRP, TNF‐α, IL‐6 and TXB2 were significantly decreased after 2 weeks of treatment with 300 mg/day of aspirin. Patients who received 100 mg/day of aspirin had decreased blood levels of hs‐CRP and TXB2. The blood level of IL‐6 in the 300 mg/day aspirin group was significantly lower than that in the other two groups after 2 weeks of therapy. Aspirin at either dose did not affect the blood level of 6‐keto‐PGF1‐α. Conclusions Aspirin at all doses suppresses the blood levels of inflammatory markers and the platelet aggregation mediator TXA2 in Chinese patients with metabolic syndrome. Since the suppression induced by 300 mg/day of aspirin was greater than that induced by 100 mg/day of aspirin, these data suggest that 300 mg/day of aspirin may be beneficial in decreasing the risk of cardiovascular events in Chinese patients with metabolic syndrome.     

Acute hypotension due to carrageenan, arachidonic acid and slow reacting substance C in the rabbit: role of platelets and nature of pharmacological antagonism.

Carrageenan injected i.v. to rabbits induced thrombocytopenia, hypotension and death. The latter two phenomena, but not the former, were prevented by aspirin and by indomethacin. Immune platelet depletion protected against the effects of carrageenan, but failed to interfere with hypotension by arachidonic acid (AA) and by slow reacting substance C. Inhibition by aspirin of hypotension due to AA was short lasting (< 1 h for 5 mg/kg), whereas inhibition of AA-induced platelet aggregation lasted more than 7 h. It thus appears that neither hypotension due to AA nor its inhibition by aspirin, depend upon a platelet effect. In contrast, hypotension by carrageenan is platelet-dependent. Generation of prostaglandin (PG)-like activity and of rabbit aorta contracting activity in blood incubated with AA or with carrageenan was suppressed after i.v. injection of aspirin. Aggregation by AA was also inhibited, wheras aggregation by carrageenan was only partly delayed. Prostaglandin synthetase was not inhibited by salicylic acid, although this compound delayed aggregation by carrageenan as potently as did aspirin. Salicylic acid failed to interfere with in vivo effects of AA or of carrageenan, and prevented aspirin-indcued inhibition of in vivo and in vitro effects of AA. Salicylic acid inhibits transport and/or binding of aspirin to PG synthetase-related sites, but does not interfere with the mechanisms through which aspirin inhibits platelet aggregation by carrageenan. Release of platelet mediators by carrageenan requires platelet integrity, supporting the concept of a multistep/multicompartmental process. Hypotension and death due to carrageenan result from this release of platelet mediators, which is suppressed by aspirin and by indomethacin, despite concurrent aspirin-resistant platelet aggregation.     

Inhibitory effect of tiaramide of aggregation in vivo and on electrophoresis of rabbit platelets

Effects of tiaramide, aspirin an indomethacin were studied on rabbit platelet aggregation in vivo and on platelet electrophoretic mobility. When tiaramide (6 mg/kg), aspirin (30 mg/kg) or indomethacin (1.3 mg/kg) was injected into the ear vein of rabbit during 60 sec, tiaramide only inhibited ADP-induced aggregation, 20 min after the injection. All three drugs prevented collagen-induced aggregation 20 and 120 min after the injection. Tiaramide and aspirin prevented aggregation 24 hours later. The inhibitory effects on the aggregation of tiaramide are presumably independent of prostaglandin synthesis, because malondialdehyde (a metabolite of PGG2) production was not influenced. Tiaramide reduced cyclic AMP levels in platelets after 20 min incubation, despite the ability of this agent to inhibit platelet aggregation. Tiaramide, aspirin and indomethacin per se has no effect on platelet electrophoretic mobility, while tiaramide prevented the decrease in the mobility produced by ADP. Tiaramide and aspirin also depressed the decrease in the mobility produced by collagen.     

Effects of vinblastine on malondialdehyde formation, serotonin release and aggregation in human platelets

Effects of the microtubular agent vinblastine on human platelet malondialdehyde formation, [14C]serotonin release and aggregation were studied in suspensions of [14C]serotonin-labelled platelets. Vinblastine caused dose-dependent inhibition of malondialdehyde formation and aggregation in platelet suspensions stimulated with thrombin, ADP or palmitaldehyde acetal phosphatidic acid (PGAP). Malondialdehyde formation, aggregation and [14C]serotonin release caused by threshold doses of thrombin were reduced but not abolished by 100 muM vinblastine; 30-100 muM vinblastine abolished ADP- and PGAP-induced malondialdehyde formation and [14C]serotonin released and transformed ADP- and PGAP-induced irreversible aggregation to a diminished reversible response. Arachidonate conversion to malondialdehyde catalysed by human platelet microsomes was inhibited by vinblastine and the cyclooxygenase inhibitors indomethacin and aspirin, but not by salicylate. Vinblastine inhibited the microsome-catalysed formation of malondialdehyde from prostaglandin H2. It is concluded that vinblastine inhibits the thromboxane pathway of arachidonate metabolism in stimulated platelets, consequently inhibiting release and aggregation, and that this effect of vinblastine may be, at least in part, independent of its antimicrotubular actions.     

Role of platelets in aspirin-sensitive bronchoconstriction in the guinea-pig; interactions with salicylic acid

1 The bronchoconstriction caused in the guinea-pig by arachidonic acid (AA), bradykinin, adenosine diphosphate (ADP) and adenosine triphosphate (ATP) was correlated with effects on platelets. ATP and ADP produced a brief thrombocytopenia and AA a more prolonged one. Bradykinin had no effect on platelets.2 Aspirin inhibited bronchoconstriction and thrombocytopenia produced by AA and part of the bronchoconstriction produced by ATP, but had no effect against ADP. Thrombocytopenia produced by ADP and ATP was not affected by aspirin or indomethacin.3 Platelet depletion by antiserum prevented bronchoconstriction in response to ADP and to ATP, but not in response to bradykinin or to AA, showing that platelets are not involved in aspirin-sensitive bronchoconstriction. Infusions of ADP reduced bronchoconstriction and thrombocytopenia in response to ADP itself and to ATP, but not to AA. Bronchoconstriction by ADP or ATP involves an action on platelets. Only that due to ATP is partially dependent on the activity of prostaglandin synthetase.4 ATP induced aggregation in vitro in guinea-pig platelet-rich plasma (PRP). Rabbit PRP responded only when ATP was first incubated with guinea-pig plasma. The aggregating compound formed was probably ADP, since it was destroyed by apyrase. Its formation was not inhibited by aspirin or indomethacin, indicating that aspirin inhibits ATP-induced bronchoconstriction by a different mechanism.5 The aggregating effect of ATP on guinea-pig platelets was inhibited by concentrations of apyrase that block ADP-induced aggregation, and potentiated by lower concentrations of apyrase.6 Adenosine 5'-tetraphosphate did not aggregate platelets in vivo or in vitro. In vitro aggregation occurred when apyrase was added, suggesting transformation into ADP. Adenosine 5'-tetraphosphate and apyrase inhibited aggregation due to ADP, but failed to affect that due to AA. This suggests that aggregation involving products of prostaglandin synthesis does not require ADP.7 Salicylic acid did not interfere with bronchoconstriction or aggregation due to AA, but prevented inhibition by aspirin when the weight ratio, salicylic acid:aspirin was 4:1. Salicyclic acid may be useful in studies of potential inhibitors of thromboxane A2 synthesis and of thromboxane A2-dependent processes in vivo and in vitro.     

Antiplatelet effects of piplartine,an alkamide isolated from Piper tuberculatum: possible involvement of cyclooxygenase blockade and antioxidant activity

Objectives Piplartine (piperlongumine; 5,6‐dihydro‐1‐[1‐oxo‐3‐(3,4,5‐trimethoxyphenyl]‐2(1H) pyridinone) is an alkaloid amide isolated from Piper species (Piperaceae). It has been reported to show multiple pharmacological activities in vitro and in vivo. Methods We evaluated the in‐vitro antiplatelet effect of piplartine isolated from the roots of P. tuberculatum, on human platelet aggregation induced in platelet‐rich plasma by the agonists collagen, adenosine 5′‐diphosphate (ADP), arachidonic acid (AA) and thrombin. Key findings Piplartine (100μg/ml) caused a 30% inhibition in platelet aggregation when collagen was the agonist. At 200 μg/ml, piplartine significantly inhibited the aggregation induced by arachidonic acid (100%), collagen (59%) or ADP (52%) but not that induced by thrombin. The highest concentration of piplartine (300 μg/ml) inhibited thrombin‐ (37%), ADP‐ (71%) and collagen‐ (98%) induced aggregation. The inhibitory effect of piplartine on ADP‐induced platelet aggregation was not modified by pretreatment with pentoxifylline (a phosphodiesterase inhibitor), l ‐arginine (a substrate for nitric oxide synthase) or ticlopidine (a P2Y₁₂ purinoceptor antagonist). However, aspirin, a well‐known inhibitor of cyclooxygenase, greatly increased the inhibitory effect of piplartine on arachidonic‐acid‐induced platelet aggregation. Conclusions The mechanism underlying the piplartine antiplatelet action is not totally clarified. It could be related to the inhibition of cyclooxgenase activity and a decrease in thromboxane A₂ formation, similar to that occurring with aspirin. This and other possible mechanisms require further study.     

Prostaglandin endoperoxides, thromboxane A2 and adenosine diphosphate in collagen-induced aggregation of rabbit platelets

1 A bioassay technique is described for simultaneously monitoring rabbit platelet aggregation with measurement of thromboxane A₂ (TxA₂) and prostaglandins released in response to collagen or arachidonic acid (AA).

2 Five imidazole derivatives were examined as inhibitors of thromboxane synthetase and compared with the effect of the cyclo-oxygenase inhibitor indomethacin; 1-(7-carboxyheptyl) imidazole was identified as the most potent and selective inhibitor of thromboxane synthetase and was used with indomethacin to investigate the relative contribution of the prostaglandin endoperoxides prostaglandin G₂ (PGG₂)/PGH₂ and TxA₂ in mediating platelet aggregation induced by collagen or AA.

3 Platelet aggregation induced by a low concentration of collagen was abolished by indomethacin and carboxyheptylimidazole whilst in response to a high concentration or collagen only partial inhibition of aggregation occurred.

4 The contribution of adenosine diphosphate (ADP) released from platelets during collagen or AA-induced aggregation was examined using the substrate/enzyme complex creatine phosphate/creatine phosphokinase (CP/CPK). The CP/CPK complex abolished aggregation induced by a low dose of collagen whilst aggregation to a high dose of collagen was only partially inhibited.

5 Aggregation induced by a high dose of collagen was abolished by a combination of CP/CPK with indomethacin or carboxyheptylimidazole.

6 AA-induced aggregation was abolished by indomethacin. Carboxyheptylimidazole abolished aggregation induced by a low dose of AA but inhibition was surmounted with increasing concentrations of AA in the absence of TxA₂ formation.

7 PGH₂-induced aggregation was unaffected by indomethacin and only partially inhibited by carboxyheptylimidazole. AA or PGH₂-induced platelet aggregation was unaffected by CP/CPK.

8 In conclusion, aggregation of rabbit platelets induced by a low concentration of collagen was dependent on synergism between TxA₂ and ADP whilst at high concentrations of collagen, sufficient TxA₂ and ADP were released to induce aggregation independently of each other.

9 The small amounts of prostaglandin endoperoxides produced from endogenous arachidonate have apparently no direct pro-aggregatory role. However, the relatively large amount which can be produced by a high concentration of exogenous AA when TxA₂ formation is prevented can cause aggregation of rabbit platelets.

     

烙铁头蛇毒血小板聚集素对血小板聚集和抑制剂关系的研究

研究山莨菪碱(654-2)、阿斯匹林(ASA)、前列环素(PGI_2)样物质对二磷酸腺苷(ADP)、花生四烯酸(AA)以及烙铁头蛇毒血小板聚集素(TMVA)诱导的阻抗法全血血小板聚集(简称全血聚集)的影响。结果表明:ADP.AA.TMVA诱导的全血聚集随剂量增加而增强.阻抗技术对于估价生理条件下的血小板功能较为敏感。654-2促进ADP诱导的全血聚集.而ASA和PGI_2样物质对ADP和AA诱导的聚集均有抑制作用.但不能防止TMVA诱导的聚集。提示TMVA可能通过第3途径(类似于血小板活化因子.PAF)诱导血小板聚集.经ADP和AA作用过的血小板对TMVA的活化仍有反应,其机理值得研究。     

Characterization of a new compound, S35b, as a guanylate cyclase activator in human platelets.

The effects of S35b (4-methyl-3-phenyl sulfonylfuroxan), a new phenyl sulfonylfuroxan compound, were investigated on human platelets activated by different agonists. Platelet aggregation evoked by arachidonic acid (AA), collagen, ADP and thrombin was inhibited by the drug in a dose-dependent manner. S35b inhibited the AA-induced increase of cytosolic free Ca2+ ([Ca2+]i) and production of malondialdehyde. A primary action of the compound on cyclooxygenase is unlikely since: (1) U-46619 (15s-hydroxy-11,9-[epoxymethano]-prosta-5Z,13E-dienoic acid, a stable epoxymethano analog of prostaglandin H2) could not reverse the inhibitory effect of S35b on AA-induced aggregation and [Ca2+]i increase; (2) U-46619-induced aggregation and [Ca2+]i rise were inhibited by S35b; and (3) at high collagen concentrations platelet aggregation (which is unresponsive to aspirin under such conditions) was blocked by S35b as well. Thus the drug action is likely to be exerted at an early step of the platelet activation pathway. The elevation in the platelet cGMP level evoked by S35b in a time- and concentration-dependent manner can account for the inhibitory effect: increased cGMP levels could interfere, for instance, with G protein-phospholipase C coupling and subsequent phosphoinositide hydrolysis.     

Differential effect of platelet inhibitors in normal and in hypercholesterolaemic subjects.

Dibutyryl cyclic AMP, forskolin, dipyridamole and butyl imidazole inhibited platelet aggregation (induced by ADP or collagen) in washed platelets more than in platelet-rich plasma preparations. Aspirin, indomethacin and epoprostenol (prostacyclin, PGI2) showed no preferential inhibition of these platelet preparations. When platelet-rich plasma from either normal or familial hypercholesterolaemic (FH) subjects was used, aspirin, indomethacin and dipyridamole (but not forskolin) inhibited platelet aggregation in normal subjects more than in FH patients. When low doses of aspirin (75 mg daily for 7 days) or dipyridamole (250 mg, single dose) were administered in vivo, platelet aggregation was inhibited more in the normal subjects in comparison to the patient group.     

Design,Synthesis and Pharmacological Evaluation of Novel Piperlongumine derivatives as Potential Antiplatelet Aggregation Candidate

A series of novel piperlongumine derivatives ( 4a‐i , 6a‐i ) were designed and synthesized. The inhibitory activities of platelet aggregation induced by ADP and AA in vitro have been evaluated by bron turbidimetry and liver microsomal incubated assay. The assay results show that compounds 4e and 6e exhibited remarkable potency to that of the positive control piplartine and aspirin.     

奥扎格雷抗血小板聚集作用的临床观察

目的比较奥扎格雷与阿司匹林对血小板聚集作用的影响,分析二者抵抗概率。方法脑梗死患者120例,随机分为奥扎格雷组与阿司匹林组(各60例),分别用二磷酸腺苷(ADP)、花生四烯酸(AA)诱导,进行血小板聚集试验,检测最大血小板聚集率(MAR)。各组患者均于入院当天、治疗第14天检测血小板聚集率。结果奥扎格雷组与阿司匹林组血小板聚集功能在同一诱导剂作用下,差异无统计学意义,都存在抵抗、半抵抗现象。结论奥扎格雷、阿司匹林对血小板聚集率影响的差异无统计学意义,均可作为抗血小板聚集药物,但也存在抵抗现象。奥扎格雷抗血小板聚集的长期临床效果、与其他抗血小板聚集药物联合应用能否解决抵抗问题,还需进一步的大规模临床实验研究。     

Mechanism of action of novel anti-inflammmatory drugs diflumidone and R-805.

Two novel nonsteroidal anti-inflammatory drugs (NSAID), R-805 (4-nitro-2-phenoxymethane sulfonanilide) and R-807 (3-benzoyldinuoromethane sultonanilide, diflumidonel, inhibit the biosynthesis of prostaglandin by bovine seminal vesicle microsomes and arachidonic acid-induced aggregation of human platelets in a concentration-dependent manner. Comparison of these sulfonanilides with NSAID indicates the following order of potency: (1) vs prostaglandin synthetase: indomethacin > flufenamic acid > R-807 > R-805 > phenylbutazone ? aspirin and (2) vs platelet aggregation: indomethacin > R-807 > R-805 > flufenamic acid > phenylbutazone ? aspirin. Time-dependent, irreversible inhibition of prostaglandin synthetase can be demonstrated for both R-805 and R-807. These compounds also inhibit equally the formation of PGE₂ and PGF_2α, which suggests blockade of endoperoxide formation. This is the first report of inhibition of prostaglandin synthetase and platelet aggregation by drugs of this class.     

融斑通脉颗粒对家兔血小板聚集的影响

目的观察融斑通脉颗粒对家兔血小板聚集的影响。方法使用二磷酸腺苷(ADP),花生四烯酸和胶原等促凝剂促进血小板凝聚,采用Born氏比浊法,观察融斑通脉颗粒对家兔血小板聚集的影响,并与对照组及阿司匹林组比较。结果家兔连续7 d灌胃给药,融斑通脉颗粒明显降低胶原,ADP诱导的家兔血小板聚集率(P<0.05~0.01),对花生四烯酸诱导的家兔血小板聚集率有降低趋势。结论融斑通脉颗粒具有抑制血小板聚集的作用,为其临床治疗缺血性心脏病提供了实验依据。     

蝙蝠葛碱对血小板聚集及花生四烯酸代谢的影响

蝙蝠葛碱(Dau) 抑制AA及ADP诱导的大鼠血小板聚集,也能抑制AA,ADP及Adr诱导的人血小板聚集。这种抑制作用与Dau剂量呈依赖关系。Dau抑制大鼠洗涤血小板对[1-¹⁴C]AA经环氧酶途径的代谢,TXB₂与HHT的形成均呈剂量依赖性减少。当Dau浓度达到0.1 mmol/L时亦能抑制12-HETE的形成。Dau对AA代谢的上述影响可能是其抑制血小板聚集的机理之一。     

Effect of oral aspirin dose on platelet aggregation and vascular prostacyclin (PGI2) synthesis in humans and rabbits

Large doses of oral aspirin inhibit platelet aggregation and vascular synthesis of the antiaggregatory vasodilator prostaglandin I2 (PGI2) by irreversibly acetylating the cyclooxygenase enzyme. In order to determine if one can achieve selective inactivation of platelet cyclooxygenase using oral doses of aspirin, we studied human and rabbit platelet aggregation and rabbit aortic synthesis of PGI2 before and 3 hr after various doses of aspirin. In rabbits, lower doses of aspirin produced a major inhibition of platelet aggregation and a minor inhibition of PGI2 synthesis, while higher doses of aspirin inhibited both platelet aggregation and vascular PGI2 synthesis. In humans, we found that a dose equivalent to approximately 1/4 of one 300 mg aspirin tablet consistently produced a major inhibition of cyclooxygenase-dependent platelet aggregation in a pattern similar to the inhibition of rabbit platelet aggregation where the majority of rabbit PGI2 synthetic capacity was not inhibited. In another rabbit study, we found that it takes the vasculature over 24 hr to return to control PGI2 synthetic capacity following a single, high dose of oral aspirin. In conclusion, we speculate that approximately 1/4 of an aspirin tablet, which inhibits a major portion of cyclooxygenase-dependent human platelet aggregation, may not inhibit a major portion of vascular cyclooxygenase-dependent PGI2 synthesis and may be more efficacious as an antithrombotic agent in man than are higher doses of aspirin.     

Regulation of human platelet activation--analysis of cyclooxygenase and cyclic AMP-dependent pathways

We have studied the regulation of human platelet activation by cyclic AMP (cAMP), and the cyclooxygenase products by examining the effect of prostacyclin (PGI2) and indomethacin on platelet aggregation, release reaction and thromboxane B2 (TxB2) generation induced by the full dose range of common platelet agonists in both platelet-rich plasma and washed platelets. Platelet aggregation, [14C]-5HT and TxB2 release induced by "threshold" and "supramaximal" concentrations of ADP, adrenaline, platelet-activating factor (PAF) and U46619 were totally abolished by low concentrations of PGI2 (3-6 nM). In contrast, platelet activation induced by submaximal concentrations of collagen, thrombin and the calcium ionophore A23187 was only partially inhibited by PGI2 (3-3000 nM). PAF-induced release reaction like that induced by ADP and adrenaline was totally dependent on the cyclooxygenase products and aggregation, while U46619-induced release reaction was only partially dependent on aggregation and the cyclooxygenase products. While both PGI2 (18-3000 nM) and indomethacin (10 microM) abolished collagen-induced aggregation and the aggregation-mediated release reaction, neither inhibitor significantly inhibited platelet adhesion or the adhesion-mediated release reaction. Maximal thrombin-induced aggregation and release reaction was also not significantly inhibited by PGI2 (300 nM) or indomethacin (10 microM). Thromboxane (TxB2) generation induced by sub-maximal to maximal concentrations of collagen, thrombin and A23187 was, although significantly inhibited, not abolished by PGI2. These results demonstrate that PAF is a "weak" agonist similar to ADP and adrenaline, U46619 is an agonist intermediate between weak and strong which induces a release reaction that is only partially dependent on aggregation, but unlike the strong agonists, is totally susceptible to inhibition by PGI2, PGI2 is an indirect inhibitor of phospholipase activation, which does not significantly inhibit non-aggregation-mediated arachidonate mobilization, induced by the strong agonists, and the so-called third pathway in the collagen and thrombin-induced release reaction, which is insensitive to indomethacin, is also insensitive to elevators of cAMP such as PGI2.     

Role of Platelets in Inflammation and Cancer: Novel Therapeutic Strategies

Platelets play a central role in inflammation through their direct interaction with other cell types, such as leucocytes and endothelial cells, and by the release of many factors, that is, lipids [such as thromboxane (TX)A₂] and proteins (a wide number of angiogenic and growth factors) stored in α‐granules, and adenosine diphosphate (ADP), stored in dense granules. These platelet actions trigger autocrine and paracrine activation processes that lead to leucocyte recruitment into different tissues and phenotypic changes in stromal cells which contribute to the development of different disease states, such as atherosclerosis and atherothrombosis, intestinal inflammation and cancer. The signals induced by platelets may cause pro‐inflammatory and malignant phenotypes in other cells through the persistent induction of aberrant expression of cyclooxygenase (COX)‐2 and increased generation of prostanoids, mainly prostaglandin (PG)E₂. In addition to cardiovascular disease, enhanced platelet activation has been detected in inflammatory disease and intestinal tumourigenesis. Moreover, the results of clinical studies have shown that the antiplatelet drug aspirin reduces the incidence of vascular events and colorectal cancer. All these pieces of evidence support the notion that colorectal cancer and atherothrombosis may share a common mechanism of disease, that is, platelet activation in response to epithelial (in tumourigenesis) and endothelial (in tumourigenesis and atherothrombosis) injury. Extensive translational medicine research is necessary to obtain a definitive mechanistic demonstration of the platelet‐mediated hypothesis of colon tumourigenesis. The results of these studies will be fundamental to support the clinical decision to recommend the use of low‐dose aspirin, and possibly other antiplatelet agents, in primary prevention, that is, even for individuals at low cardiovascular risk.     

Mechanisms of aggregation inhibition by aspirin and nitrate-aspirin prodrugs in human platelets

Objectives Aspirin is the mainstay of anti‐platelet therapy in the secondary prevention of cardiovascular disease. However, problems with aspirin safety and resistance demand clinical strategies based on multiple pharmacological approaches. Prodrugs of aspirin may offer beneficial effects in terms of gastro‐intestinal safety and multiple pharmacological approaches. However, the pharmacological profile of aspirin prodrugs in human platelets has not been completed yet. We aimed to compare the effects of aspirin and prodrugs of aspirin ( 1 – 5 ) on human platelet aggregation stimulated by ADP and collagen and associated receptor expression (GPIIb/IIIa and P‐selectin) in platelet‐rich plasma (PRP) and washed platelets (WP). Methods As aspirin is released from prodrugs following esterase hydrolysis we studied the expression and activity of butyrylcholineterase (BuChE) and carboxyesterase (CE) in plasma and platelets. The mechanism of prodrug‐induced platelet aggregation inhibition was explored by studying the effects of plasma and purified human BuChE on aggregation. Finally, the relative contribution of nitric oxide (NO) bioactivity to nitrate‐containing prodrugs of aspirin‐induced inhibition of aggregation was determined using 1H‐[1,2,4]oxadiazolo[4,3‐a]quinoxalin‐1‐one (ODQ,) a selective inhibitor of the soluble guanylyl cyclase. Key findings ST0702, 2 , a nicotinic acid‐aspirin codrug was equipotent with aspirin with respect to inhibition of collagen‐induced platelet aggregation. Compound 4 , a NO releasing aspirin was the most potent inhibitor of ADP‐induced platelet aggregation, an effect partially reversed by ODQ. The platelet inhibitory effects of aspirin prodrugs were time‐dependent as the maximal inhibitory effects against collagen‐induced aggregation were achieved by aspirin at 2 min, 1 at 5 min and ST0702 at 15 min. The aspirin prodrugs were significantly less potent in WP than in PRP and the reverse was true of aspirin. In the presence of complete BuChE inhibition in PRP, there was almost complete loss of aspirin prodrug, but not aspirin anti‐aggregatory activity. Interestingly, CE activity was observed in WP and platelet lysate with pNPA substrate. Accordingly, 1 and ST0702 retained 50% and 100% anti‐aggregatory activity at maximal concentrations in WP, which was attenuated in the presence of esterase inhibitor phenylmethylsulphonyl fluoride. Conclusions The inhibitory effect of aspirin prodrugs in PRP is due to prodrug activation by BuChE. In contrast, the platelet‐inhibitory effects of aspirin prodrugs in WP may be mediated through the activity of platelet CE. Compound 4 , a NO‐containing aspirin prodrug, may exert dual inhibitory effects in platelets. Thus, aspirin prodrugs effectively inhibit human platelet aggregation and as such may be an alternative to conventional aspirin.     

Dicentrine, a novel antiplatelet agent inhibiting thromboxane formation and increasing the cyclic AMP level of rabbit platelets.

Dicentrine is an antiplatelet agent isolated from the Chinese herb Lindera megaphylla. We examined the in vitro effects of dicentrine on various aspects of platelet reactivity. Dicentrine inhibited the aggregation and ATP release of washed rabbit platelets induced by arachidonic acid (AA), collagen, ADP, platelet-activating factor (PAF), thrombin and U46619. Dicentrine also inhibited the thromboxane B2 formation caused by AA, collagen and thrombin in washed intact platelets or that induced by AA in lysed platelet homogenate, while prostaglandin D2 formation caused by AA was not increased. The generation of inositol monophosphates (in the presence of indomethacin) caused by thrombin, collagen and PAF was not suppressed significantly, nor did dicentrine suppress fibrinogen-induced aggregation of elastase-treated platelets. Dicentrine inhibited the intracellular Ca2+ increase in quin-2/AM-loaded platelets caused by thrombin, PAF, collagen and AA. The cyclic AMP level was elevated by dicentrine in a concentration-dependent manner. These data indicate that the inhibitory effect of dicentrine on platelet aggregation and ATP release was due to the inhibition of thromboxane formation and the elevation of the level of cyclic AMP.