Formamidine-mediated inhibition of rat platelet aggregation

The formamidine pesticide chlordimeform (CDF) was a strong inhibitor of aggregation of rat platelets induced by collagen and arachidonic acid and was a weak inhibitor of that induced by ADP. With the exception of 4-chloro-o-formotoluidide which was an inhibitor of arachidonic acid-induced aggregation only, the CDF metabolites were without discernible effect on aggregation induced by these agents. Amitraz, another formamidine pesticide, inhibited arachidonic acid-induced aggregation but was without effect on that induced by collagen or ADP. Inhibition of collagen- and/or arachidonic acid-induced aggregation by formamidines was concentration-dependent. Although platelets underwent shape change, primary aggregation was markedly inhibited, and secondary aggregation was abolished in some cases. CDF, its two N-desmethyl metabolites, and octopamine, but not amitraz, caused significantly elevated levels of cyclic AMP in platelet rich plasma as compared to controls; however, this effect did not fully account for the action of formamidines on aggregation.     

Endothelium-dependent inhibition of platelet aggregation.

In cascade perfusion and superfusion experiments on rabbit tissues, when acetylcholine (ACh) was introduced into the circuit so as to perfuse the aorta under perfusion with noradrenaline (NA), the effluent relaxed the transverse aortic strip which had been denuded of endothelium. The effluent from the perfused aorta which was capable of relaxing the transverse aortic strip also significantly inhibited platelet aggregation induced by arachidonic acid (AA) in a volume-related manner. The inhibitory activity was decreased by the prolongation of transit time before addition of the effluent to platelet-rich plasma. Neither the inhibition of AA-induced aggregation nor the relaxation of the transverse strip by the effluent could be observed after the removal of endothelium from the aorta, or after pretreatment of aorta with mepacrine or nordihydroguaiaretic acid (NDGA). The AA-induced platelet aggregation was unaffected by pretreatment of platelets with mepacrine or NDGA at the concentration tested. Pretreatment of aorta with indomethacin failed to modify the relaxation of the transverse strip induced by the effluent. These results strongly suggest that endothelium-derived vascular relaxant factor (EDRF) possesses inhibitory activity on AA-induced aggregation in addition to its vasodilator activity.     

氯吡格雷对二磷酸腺苷诱导的血小板聚集的影响

目的 :探讨氯吡格雷对血小板聚集率的影响。方法 :血小板聚集率增高病人 2 4例 ,男性 1 4例 ,女性 1 0例 ,年龄 (5 9±s 1 0 )a。给予氯吡格雷5 0mg ,po,qd×4wk。在服药后 8d,4wk后用光学法测定血小板聚集率 (ADP诱导法 ) ,Duke法测定出、凝血时间 ,凝血因子Ⅰ及血小板计数。结果 :高血小板聚集率的病人使用氯吡格雷后血小板聚集率明显下降 ,治疗后 8d,4wk分别下降 (3 1±2 5 ) % ,(3 2± 2 1 ) % ,(P <0 .0 1 )。但出、凝血时间 ,血小板计数及凝血因子Ⅰ含量在使用氯吡格雷后无明显变化。结论 :氯吡格雷可有效拮抗ADP诱导的血小板聚集作用     

N-ethylmaleimide inhibition of thrombin-induced platelet aggregation.

The data presented in this report show that N-ethylmaleimide (NEM) is a powerful inhibitor of thrombin-induced platelet aggregation. NEM increased guanosine 3', 5'-cyclic monophosphate (cGMP) and adenosine 3', 5'-cyclic monophosphate (cAMP) levels in intact cells. The inhibition of cAMP high-affinity phosphodiesterase and cGMP phosphodiesterase was implicated in the elevation of the cyclic nucleotides. NEM dose dependently blocked the thrombin-stimulated, but not the phorbol myristate acetate-dependent phosphorylation of the protein kinase C substrate pleckstrin. Myosin light chain phosphorylation was also inhibited by NEM. In addition, the sulphydryl reagent inhibited Ca2+ mobilisation induced by thrombin. The data indicate that phospholipase C activation by thrombin is interrupted by NEM at the level of receptor-mediated signal transduction.     

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.     

Miconazole inhibition of platelet aggregation by inhibiting cyclooxygenase

Platelet dysfunction was found in rabbits to which a dose of miconazole nitrate (1.6 mg/kg body wt) therapeutic for human subjects had been given intravenously. The present experiments were conducted to elucidate the mechanism of inhibitory effects of miconazole on platelet function. After administration of a single dose of miconazole, rabbit platelet aggregation induced by collagen and sodium arachidonate was inhibited significantly for approximately 24 hr. On the other hand, hypertriglycemia, one of the major side effects of this drug, was not seen during 2 days of observations, nor were any other outstanding manifestations observed. In in vitro experiments, miconazole nitrate (10 μm) also significantly inhibited rabbit and human platelet aggregation (P < 0.01). Biochemical analyses revealed that the stimulant-induced formation of prostaglandin E₂ (PGE₂) and thromboxane B₂ (TXB₂), metabolites via cyclooxygenase, was inhibited by miconazole nitrate in both human and rabbit platelets in vitro. PGE₂ production was decreased dose-dependently with the increase of micronazole concentration (10 to 100 μM), and the decrease was in parallel with a decrease of TXB₂ production. In addition, malondialdehyde (MDA) production of human and rabbit platelets induced by exogenous arachidonate and collagen was also inhibited significantly by miconazole. Chromatographic studies showed that the amount of 12-l-hydroxy-5,8,10,14-eicosatetraenoic acid (HETE), a metabolite via lipoxygenase, was increased markedly in accordance with the miconazole-induced decrease of TXB₂ and 12-l-hydroxy-5,8,10-heptadecatrienoic acid (HHT) formation in both human and rabbit platelets. These results indicate that miconazole nitrate inhibits platelet cyclooxygenase, without affecting the stimulant-induced release of arachidonic acid from platelet phospholipids. Use of this drug in the treatment of sytemic fungal infection appears to be increasing. Careful attention should be paid to the inhibitory effects of miconazole on platelet function, especially in the case of intravenous treatment.     

Specific inhibition of ADP-induced platelet aggregation by clopidogrel in vitro

1. The thienopyridine clopidogrel is a specific inhibitor of ADP-induced platelet aggregation ex vivo. No direct effects of clopidogrel (< or = 100 microM) on platelet aggregation in vitro have been described so far. 2. Possible in vitro antiaggregatory effects (turbidimetry) of clopidogrel were studied in human platelet-rich plasma and in washed platelets. 3. Incubation of platelet-rich plasma with clopidogrel (< or = 100 microM) for up to 8 h did not result in any inhibition of ADP (6 microM)-induced platelet aggregation. 4. Incubation of washed platelets with clopidogrel resulted in a time- (maximum effects after 30 min) and concentration-dependent (IC50 1.9+/-0.3 microM) inhibition of ADP (6 microM)-induced platelet aggregation. Clopidogrel (30 microM) did not inhibit collagen (2.5 microg ml(-1))-, U46619 (1 microM)- or thrombin (0.1 u ml(-1))-induced platelet aggregation. The inhibition of ADP-induced aggregation by clopidogrel (30 microM) was insurmountable indicating a non-equilibrium antagonism of ADP actions. The R enantiomer SR 25989 C (30 microM) was significantly less active than clopidogrel (30 microM) in inhibiting platelet aggregation (32+/-5% vs 70+/-1% inhibition, P < 0.05, n = 5). 5. In washed platelets, clopidogrel (< or = 30 microM) did not significantly reverse the inhibition of prostaglandin E1 (1 microM)-induced platelet cyclic AMP formation by ADP (6 microM). 6. The antiaggregatory effects of clopidogrel were unchanged when the compound was removed from the platelet suspension. However, platelet inhibition by clopidogrel was completely abolished when albumin (350 mg ml(-1)) was present in the test buffer. 7. It is concluded that clopidogrel specifically inhibits ADP-induced aggregation of washed platelets in vitro without hepatic bioactivation. Inhibition of ADP-induced platelet aggregation by clopidogrel in vitro occurs in the absence of measurable effects on the reversal of PGE1-stimulated cyclic AMP by ADP.     

Enhanced inhibition of platelet aggregation in-vitro by niosome-encapsulated indomethacin

In order to achieve sustained antiplatelet effect from indomethacin, it was incorporated in a non-ionic surfactant vesicle (niosome). The objective was to study the effect of niosomal-encapsulated indomethacin on platelet function such as inhibition of aggregation and ATP release induced by a variety of agonists (adenosine 5'-diphosphate (ADP), epinephrine, arachidonic acid, ristocetine) and to explore the feasibility of carrier-mediated drug delivery to the platelets. Multilamellar vesicles (niosomes) were prepared from Tween-60 by the lipid hydration method. Freshly prepared human platelet rich plasma (PRP) was used for aggregation/inhibition studies, the extent of which was observed as a change in light transmission measured by the Chronolog Aggregometer. The percent inhibition of aggregation induced by the agonist ADP ranged from 28. 21+/-0.28 at the 2.0 micromol level to 92.6+/-1.20 at 12.7 micromol of the encapsulated drug while the same concentrations of the drug inhibited aggregation only to the extent of 13.75+/-0.13 and 36. 82+/-0.57%, respectively. A 100% inhibition of aggregation induced by arachidonic acid was achieved by niosomal indomethacin while inhibition by the free drug was 41.9% at equimolar concentrations. ATP release study showed that 100% inhibition was achieved by 8 micromol of the encapsulated drug while inhibition by the free drug was 40.00+/-1.82%. Therefore, at equimolar doses, the niosomal drug proved to be more efficient in inhibiting platelet aggregation than the free drug, probably due to greater quantity of the drug reaching the specific site of inhibition in the interior of the platelets and acting directly on the cyclo-oxygenase system to prevent thromboxane formation.     

Blood levels of ditazole and inhibition of platelet aggregation in man

5 healthy volunteers (3 males, 2 females, aged 22-35 years) were given 600 mg ditazole (Ageroplas) every 12 h (9.00 a.m. and 9.00 p.m.) for 10 days. Venous blood was collected from all volunteers at 9.00 and 11.00 a.m. on days 0, 3, 5, 7 and 10. The threshold concentrations of adrenaline inducing two distinct waves of platelet aggregation (Born's method) within 3 min were determined each time. Blood levels of ditazole were measured by a gas-chromatographic technique using a nitrogen-phosphorus selective detector. The average blood levels of the drug ranged between 0.84 and 1.30 microgram/ml at 9.00 a.m., and between 1.93 and 2.85 microgram/ml at 11.00 a.m. Inhibition of platelet aggregation (expressed by a grading system in arbitrary units) ranged between 1.6 and 2.0 at 9.00 a.m. and between 2.0 and 2.4 at 11.00 a.m. The fluctuations of blood levels and platelet aggregation inhibitory activity of ditazole observed during the study period were virtually the same. It is suggested that the treatment schedule used in the present study results in blood levels of ditazole sufficient to reveal any consistent alteration of platelet function in normal subjects.     

Free fatty acid-induced platelet aggregation: studies with solubilized and nonsolubilized fatty acids

The aggregation response of washed porcine platelets to the sodium salts of stearic, oleic, palmitic, and myristic acids was analyzed turbidometrically. The fatty acids were prepared as aqueous suspensions and as taurocholate- or albumin-solubilized systems. The final concentration of fatty acid in the platelet preparation varied between 70 and 600 microM. This range was within or below the normal physiological limits of 300-1200 microM. Platelet aggregation was observed with both the suspended and taurocholate-solubilized fatty acids. The extent of platelet aggregate formation increased with the fatty acid concentration and chain length. With the exception of stearate, the taurocholate-solubilized fatty acids were more active than the suspensions. Albumin-solubilized fatty acids were devoid of platelet aggregating activity. Particle-size analysis of the solubilized fatty acids indicated that fatty acid precipitation had occurred subsequent to the addition of taurocholate-solubilized fatty acids to the platelets. This precipitation did not occur with the albumin-solubilized systems, suggesting that the fatty acids must assume a particulate physical state to induce aggregation. Platelet aggregation induced by fatty acids was not inhibited by 80 nM epoprostenol, 75 microM alprostadil, or 150 microM indomethacin. This finding indicated that the fatty acid-induced platelet aggregation was independent of cyclic AMP-related calcium shift, cyclooxygenase-arachidonate, or granular nucleotide release mechanisms.     

Study of inhibition of platelet aggregation of 1,8-naphthyridine derivatives

The antiplatelet activity of some 1,8-naphthyridine derivatives was studied. The compounds displayed different abilities in blocking the effects of ADP, collagen and arachidonic acid. Four of them showed an in vitro remarkable activity similar to that of dipyridamole and papaverine.     

Effects of ADP-receptor antagonism beyond traditional inhibition of platelet aggregation

Atherothrombosis, or thrombus formation, at the site of a disrupted atherosclerotic plaque is the common pathophysiology related to myocardial infarction, ischaemic stroke and peripheral arterial disease. A growing body of evidence demonstrates an important role for vascular inflammation in the pathophysiology of atherosclerosis/atherothrombosis and the importance of the platelet as a mediator of inflammation. Clopidogrel is an ADP receptor antagonist that is superior to acetylsalicylic acid (ASA) for the prevention of ischaemic stroke, myocardial infarction and vascular death in patients with symptomatic atherosclerosis. The use of clopidogrel as well as ASA provides sustained, incremental benefit in patients with coronary manifestations of atherothrombosis. Recent evidence indicates that clopidogrel reduces markers of vascular inflammation across the cerebrovascular, coronary and peripheral circulations. These effects are not observed after treatment with ASA alone. Further studies have revealed that clopidogrel may have potential anticoagulant effects and may inhibit arterial vasoconstriction. These broader effects may contribute to the protective benefits of clopidogrel and should be considered when evaluating antiplatelet agents and optimising antiplatelet regimens.     

Platelet release reaction and aggregation induced by canatoxin, a convulsant protein: evidence for the involvement of the platelet lipoxygenase pathway.

Canatoxin is a toxic protein isolated from Canavalia ensiformis seeds. It induces death preceded by convulsions of spinal cord origin and also produces in vitro aggregation of platelets in rabbit, human and guinea-pig plasma. The aggregating effect is dose-dependent at nanomolar concentrations. Rabbit platelets pretreated with canatoxin became refractory to a second exposure to this protein or to collagen, but were still responsive to ADP, Paf-acether or arachidonic acid. [14C]-5-hydroxytryptamine was released from pre-labelled platelets on stimulation with canatoxin. Washed rabbit platelets, but not thrombin-degranulated ones, aggregated on stimulation with canatoxin provided that fibrinogen was added before the toxin. Canatoxin's pro-aggregating activity was inhibited by mepacrine, EDTA, caffeine, prostacyclin, adenosine monophosphate and also by the ADP scavenger system, creatine phosphokinase/creatine phosphate. Furthermore, 3-amino-1-[m-(trifluoromethyl)-phenyl]-2-pyrazoline (BW 755C), eicosatetraynoic acid (ETYA) and nordihydroguaiaretic acid (NDGA) were potent inhibitors of canatoxin-induced aggregation. In contrast, no inhibition was seen with indomethacin. The data indicate that canatoxin is mainly a release-reaction-promoting agent, being devoid of any direct aggregating activity. Thus the aggregation is totally dependent on the release of ADP. Furthermore, canatoxin-induced platelet activation is probably dependent on platelet phospholipase A2 and lipoxygenase activity but is not dependent on cyclo-oxygenase products or the release of Paf-acether.     

Effects of ADP-receptor antagonism beyond traditional inhibition of platelet aggregation

Atherothrombosis, or thrombus formation, at the site of a disrupted atherosclerotic plaque is the common pathophysiology related to myocardial infarction, ischaemic stroke and peripheral arterial disease. A growing body of evidence demonstrates an important role for vascular inflammation in the pathophysiology of atherosclerosis/atherothrombosis and the importance of the platelet as a mediator of inflammation. Clopidogrel is an ADP receptor antagonist that is superior to acetylsalicylic acid (ASA) for the prevention of ischaemic stroke, myocardial infarction and vascular death in patients with symptomatic atherosclerosis. The use of clopidogrel as well as ASA provides sustained, incremental benefit in patients with coronary manifestations of atherothrombosis. Recent evidence indicates that clopidogrel reduces markers of vascular inflammation across the cerebrovascular, coronary and peripheral circulations. These effects are not observed after treatment with ASA alone. Further studies have revealed that clopidogrel may have potential anticoagulant effects and may inhibit arterial vasoconstriction. These broader effects may contribute to the protective benefits of clopidogrel and should be considered when evaluating antiplatelet agents and optimising antiplatelet regimens.     

哒嗪酮类新衍生物的合成及其对血小板聚集的抑制作用

目的研究引入取代仲胺类基团对6-(4-取代乙酰氨基苯基)-5-甲基-4,5-二氢-3(2H)-哒嗪酮类化合物抗血小板凝集活性的影响。方法设计合成未见报道的目标化合物10个,所有化合物均经过1H-NMR谱等确证;参考文献方法进行体外药理实验。结果所有化合物都具有抗血小板凝集的活性,其中化合物9c,9f和9j的抗血小板凝集活性明显优于对照药MCI-154和CCI-17910。结论取代仲胺基团的空间位阻和亲水性对化合物抗血小板凝集的活性有影响。     

蛇床子素抑制血栓形成和血小板聚集的实验研究

目的　观察蛇床子素抑制血栓形成和血小板聚集的作用。方法　利用大鼠动-静脉旁路血栓形成模型和小鼠尾静脉注射胶原-肾上腺素合剂诱导血栓形成模型,分别测定给蛇床子素10、20、40mg·kg-1后血栓湿重和干重, 5min内小鼠死亡数和15min内偏瘫恢复数;分别采用ADP、凝血酶、花生四烯酸钠为诱导剂,测定经不同浓度蛇床子素处理后1、3、5min时血小板聚集率及最大聚集率的改变。结果　蛇床子素可以抑制大鼠动-静脉旁路血栓形成,减轻血栓湿重及干重;抑制胶原-肾上腺素合剂诱导的血栓形成,降低5min内的小鼠死亡率,提高15min内偏瘫小鼠的恢复率;蛇床子素在体外可抑制ADP、凝血酶、花生四烯酸钠诱导的血小板聚集,其IC50分别为0 .44、0 .186、0 .421g·L-1。结论　蛇床子素可明显抑制血栓形成和血小板的聚集。