阿司匹林、肝素对血小板活化及表达CD40L的影响

目的探讨血小板活化与表达CD40L的关系以及阿司匹林、肝素对此过程的影响.方法体外分离健康人血小板,经不同浓度二磷酸腺苷(ADP)、凝血酶诱导后,应用流式细胞术测定血小板活化指标P选择素和炎性标志CD40L表达水平,观察二者随诱导时间延长的变化过程,并分析阿司匹林、普通肝素、低分子肝素对血小板活化及表达CD40L的影响.结果 ADP、凝血酶均呈浓度依赖方式增加血小板P选择素、CD40L表达,二者表达水平随诱导时间延长而同步增减,呈显著正相关(P<0.05).阿司匹林(2.5 μg/ml)对ADP(4 μmol/L)和凝血酶(1U/ml)诱导的血小板活化及CD40L表达无任何影响(P>0.05);普通肝素(2.5U/ml)和低分子肝素(2.5U/ml)单独或与阿司匹林合用,均能极显著地抑制凝血酶诱导的血小板活化及CD40L表达(P＜0.001),但对ADP的诱导过程无影响(P>0.05).结论炎性介质CD40L可表达在活化血小板表面,在多种诱导剂存在的情况下,阿司匹林及肝素能部分抑制血小板的活化及CD40L表达.     

三氧化二砷抑制血小板聚集功能的研究

目的:分析三氧化二砷(ATO)对血小板聚集功能的影响。方法:用不同浓度的ATO(0、0.25、0.5、1、1.5、2、2.5、5和10μmol/L)孵育富血小板血浆(PRP)0、3、15、30、45和60 min,在2 mg/L胶原或2μmol/L腺苷二磷酸(ADP)刺激下,检测血小板聚集功能。结果:在刺激剂为2 mg/L胶原时,ATO(≥5μmol/L)孵育PRP 60 min,可显著抑制血小板聚集,在相应的时间梯度实验中,ATO浓度从5μmol/L上升到10μmol/L,抑制血小板聚集所需要的孵育时间从45 min下降到30 min,ATO对胶原诱导的血小板聚集具有浓度(r=-0.902,P=0.001)和时间(r=-0.964,P=0.002;r=-0.910,P=0.032)依赖性;在刺激剂为2μmol/L ADP时,ATO(≥2μmol/L)孵育PRP 60 min,可显著抑制血小板聚集,在相应的时间梯度实验中,ATO浓度从5μmol/L上升到10μmol/L,抑制血小板聚集所需要的孵育时间从45 min下降到15 min,ATO对ADP诱导的血小板聚集亦具有浓度(r=-0.815,P=0.007)和时间(r=-0.921,P=0.009;r=-0.963,P=0.009)依赖性。结论:低浓度的ATO对血小板聚集功能没有明显的作用,但是高浓度ATO(≥2μmol/L)可抑制血小板的聚集功能,并且该抑制作用具有浓度和时间依赖性。     

三氧化二砷抑制血小板聚集功能的研究

目的:分析三氧化二砷(ATO)对血小板聚集功能的影响。方法:用不同浓度的ATO(0、0.25、0.5、1、1.5、2、2.5、5和10μmol/L)孵育富血小板血浆(PRP)0、3、15、30、45和60 min,在2 mg/L胶原或2μmol/L腺苷二磷酸(ADP)刺激下,检测血小板聚集功能。结果:在刺激剂为2 mg/L胶原时,ATO(≥5μmol/L)孵育PRP 60 min,可显著抑制血小板聚集,在相应的时间梯度实验中,ATO浓度从5μmol/L上升到10μmol/L,抑制血小板聚集所需要的孵育时间从45 min下降到30 min,ATO对胶原诱导的血小板聚集具有浓度(r=-0.902,P=0.001)和时间(r=-0.964,P=0.002;r=-0.910,P=0.032)依赖性;在刺激剂为2μmol/L ADP时,ATO(≥2μmol/L)孵育PRP 60 min,可显著抑制血小板聚集,在相应的时间梯度实验中,ATO浓度从5μmol/L上升到10μmol/L,抑制血小板聚集所需要的孵育时间从45 min下降到15 min,ATO对ADP诱导的血小板聚集亦具有浓度(r=-0.815,P=0.007)和时间(r=-0.921,P=0.009;r=-0.963,P=0.009)依赖性。结论:低浓度的ATO对血小板聚集功能没有明显的作用,但是高浓度ATO(≥2μmol/L)可抑制血小板的聚集功能,并且该抑制作用具有浓度和时间依赖性。     

野木瓜多糖对家兔血小板聚集的影响

目的研究野木瓜多糖(SCP)对血小板聚集的影响及可能机制。方法选择成年家兔30只,随机分为空白对照组、SCP 17 g/L组、SCP 34 g/L组、SCP 68 g/L组、阿司匹林组,每组6只。制备家兔富血小板及贫血小板血浆,用Born's比浊法检测17、34、68 g/LSCP对胶原、花生四烯酸(AA)、二磷酸腺苷(ADP)及凝血酶诱导的血小板聚集的影响。检测SCP对胶原诱导后血小板中5-羟色胺含量、肝素凝血酶凝固时间(HTCT)及对凝血酶作用后血小板释放丙二醛含量的影响。结果与空白对照组比较,不同浓度SCP组、阿司匹林组的胶原、ADP、凝血酶诱导的血小板聚集明显降低(P<0.05,P<0.01),SCP 1 7 g/L组AA诱导的血小板聚集无明显变化(P>0.05),SCP34 g/L组、SCP 68 g/L组、阿司匹林组AA诱导的血小板聚集明显降低(P<0.05,P<0.01)。与空白对照组比较,不同浓度SCP组丙二醛含量明显降低、HTCT延长,呈浓度依赖性(P<0.01),除SCP 1 7 g/L组外,其余各组5羟色胺明显降低,呈浓度依赖性(P<0.05,P<0.01)。结论 SCP可以抑制由胶原、ADP、AA和凝血酶诱导的血小板聚集,其机制与抑制血小板释放5-羟色胺、血小板因子Ⅳ及减少丙二醛生成有关。     

辛伐他汀可增强阿司匹林对胶原诱导的血小板活化的抑制作用

【摘要】 目的 探讨他汀类药物联合阿司匹林体外孵育对胶原诱导的血小板活化的影响。方法 采集河北医科大学第二医院门诊健康成人志愿者外周静脉血，制备血小板悬液，应用全血阻抗法、流式细胞术、Elisa等方法测定不同浓度辛伐他汀或普伐他汀单独或联合阿司匹林共同孵育对血小板聚集及活化的影响。 结果 辛伐他汀体外孵育可降低胶原诱导的血小板聚集率，联合阿司匹林，可进一步降低胶原诱导的血小板活化标志物表达及血栓素TXB2合成。结论 辛伐他汀体外孵育可抑制胶原诱导的血小板活化，与阿司匹林联合，可进一步增强后者对血小板聚集的抑制作用。     

脑梗死患者和正常人血小板表面活化相关性抗原的体内外研究

目的：观察血小板活化后表面一些抗原决定簇的改变，探讨其在血栓性疾病研究中的意义。方法：以凝血酶诱导20例正常人血小板活化，应用流式细胞仪检测其血小板膜糖蛋白GPIb,Ⅲa,P-选择素的表达，纤维蛋白原结合以及瑞斯托霉素（Risto)诱导的血小板粘附，同时用全血法测定脑梗死患者相应抗原的改变，结果：随着凝血酶浓度0.001-0.1U/ml递增瑞斯托霉素（Risto)诱导的血小板粘附及GPⅠb表达逐渐下降，P-选择素与纤维蛋白原结合则在0.01-1U/ml间逐渐上升，GPⅢa无明显变化，30例脑梗死患者GPⅠb显著下降，P-选择素的表达及纤维蛋白原结合远高于对照组，GPⅢa无变化。结论：凝血酶以剂量依赖的方式分别对血小板的粘附，聚集与释放产生影响，而血小板表面活化相关性抗原的改变是反映体内血小板活化的重要指标。     

急性冠状动脉综合征的抗血小板治疗

急性冠状动脉综合征(acute coronary syndromes,ACS)是以冠状动脉粥样硬化斑块破溃,继发完全或不完全闭塞性血栓形成为病理基础的一组临床综合征,包括不稳定型心绞痛、急性心肌梗死,其共同的发病机制是斑块破裂,斑块下脂质、胶原等暴露,使血小板黏附,激活血小板的血栓素A2(TxA2)受体、二磷酸腺苷(ADP)受体及凝血酶受体,并最终激活血小板膜糖蛋白Ⅱb/Ⅲa(GPⅡb/Ⅲa)受体,使血小板聚集并结合纤维蛋白而致不同程度血栓形成.因此抗血小板和抗凝治疗是ACS治疗的重要组成部分.     

血红蛋白在三氧化二砷抑制血小板聚集中的功能研究

目的:检测血红蛋白与砷的结合,分析血红蛋白在三氧化二砷(ATO)抑制血小板聚集功能中发挥的作用。方法:电喷雾质谱(ESI-MS)检测血红蛋白与氨基氧化苯胂酸(PAPAO)的结合。在2 mg/L胶原或2μmol/L腺苷二磷酸(ADP)刺激下,比较经10μmol/L ATO处理后,富血小板血浆(PRP)和全血血小板聚集的差异。PRP中加入0、40、60、80、100、120 g/L的血红蛋白经10μmol/L的ATO处理后,检测血小板聚集。结果:血红蛋白β链可与一分子有机砷PAPAO结合,并脱去一分子水。ATO处理PRP以及全血,两者血小板聚集均受到显著抑制,但是对PRP血小板聚集的抑制更加明显。在刺激剂为2 mg/L胶原时,血红蛋白≥80 g/L可逆转ATO对血小板聚集的抑制,并且具有浓度依赖性(r=0.956,P=0.003);同样的,在刺激剂为2μmol/L ADP时,血红蛋白≥80 g/L可逆转ATO对血小板聚集的抑制(r=0.940,P=0.005)。结论:在体外血红蛋白通过与砷结合,能够削弱ATO对血小板聚集的抑制,并且具有浓度依赖性。血红蛋白在ATO抑制血小板聚集过程中发挥重要作用。     

活化血小板表达CD154及其对单核细胞与内皮细胞黏附的促进作用

目的　探讨活化血小板通过表达CD15 4分子对单核细胞与内皮细胞黏附作用的影响。方法　以不同浓度二磷酸腺苷 (ADP) ,凝血酶体外诱导血小板活化 ,应用流式细胞术测定血小板CD6 2P、CD15 4表达水平 ,分析血小板表达CD15 4与其活化的关系 ;并将诱导或未经诱导的血小板与培养的人脐静脉内皮细胞 (HUVECs)共育 ,应用流式细胞术及ELISA法分别检测HUEVCs产生膜性及可溶性细胞间黏附分子 1(ICAM 1)的水平及变化 ,以孟加拉玫瑰红活细胞染色法测定单核细胞与HUVECs的黏附。结果　血小板活化程度与其CD15 4表达水平间呈显著正相关 (P <0 0 5 )。ADP(4μmol/L)或凝血酶 (1U/ml)诱导的血小板 ,均能显著增强单核细胞与HUVECs的黏附 ,并促进HUVECs产生膜性及可溶性ICAM 1(P <0 0 5、0 0 1) ,应用特异性CD15 4单抗后可阻断上述作用。静息血小板、单纯等量ADP或凝血酶 ,对HUVECs表达ICAM 1及单细胞与HUVECs的黏附均无影响 (P>0 0 5 )。结论　活化血小板可通过表达CD15 4促进单核细胞与内皮细胞的黏附 ,由此引发的炎症反应可能在动脉粥样硬化形成及不稳定斑块破裂方面发挥重要作用。     

大鼠不同部位微动脉对U46619收缩反应的差异

目的观察大鼠不同部位微动脉对U46619收缩反应的差异,并初步探讨差异产生的机制。方法用PowerLab Chart采集离体血管环张力变化,观察静息状态及孵育工具药后五种动脉对U46619的收缩反应。结果静息状态下,U46619(0.1μmol/L)明显收缩微动脉,但收缩强度不均。孵育L-NAME(0.1mmol/L)增强冠脉、大脑中动脉、肾内动脉和肺内动脉对U46619的收缩反应;孵育吲哚美辛(10μmol/L)减弱肾内动脉和肠系膜动脉对U46619的收缩反应。结论不同部位微动脉对U46619的收缩反应具有血管异质性;该异质性与一氧化氮合酶和环氧合酶有关。     

In vitro Effect of Verapamil on Platelet Activation Induced by ADP, Collagen or Thrombin

We studied the effects in Vitro of the calcium channel blocker verapamil (0.1, 0.2 or 0.3 mM) on platelet aggregation, on cytoplasmic Ca(+ +) levels and on TxB(2) production after activation of platelets with adenosine diphosphate (ADP) (100 μM), collagen (20 μg/ml) or thrombin (1 U/ml). A Platelet Ionized Calcium Aggregometer was used and washed, aequorin loaded platelets were employed. The drug was able to inhibit similarly and always significantly aggregation, Ca(+ +) fluxes and TxB(2) production when collagen was the agonist. Furthermore, inhibition of aggregation and TxB(2) production was significant at all the concentrations tested when platelets were activated by ADP or thrombin, but in this case inhibition of Ca (+ +) fluxes was observed only with the higher concentrations of the drug (0.2 or 0.3 mM). Hence, with these two last agonists inhibition of Ca(+ +) movements was less pronounced than inhibition of aggregation or TxB(2) production. These data suggest that platelet activation by collagen depends directly and almost exclusively on Ca(+ +) fluxes through biological membranes, while activation by ADP or thrombin is less strictly related to Ca(+ +) movements. Indeed, with these last two agonists verapamil may inhibit platelet activation also by calcium-independent mechanism(s).     

Prostaglandin E2 potentiates platelet aggregation by priming protein kinase C

Prostaglandin E2 (PGE2) is produced by activated platelets and by several other cells, including capillary endothelial cells. PGE2 exerts a dual effect on platelet aggregation: inhibitory, at high, supraphysiologic concentrations, and potentiating, at low concentrations. No information exists on the biochemical mechanisms through which PGE2 exerts its proaggregatory effect on human platelets. We have evaluated the activity of PGE2 on human platelets and have analyzed the second messenger pathways involved. PGE2 (5 to 500 nmol/L) significantly enhanced aggregation induced by subthreshold concentrations of U46619, thrombin, adenosine diphosphate (ADP), and phorbol 12-myristate 13-acetate (PMA) without simultaneously increasing calcium transients. At a high concentration (50 mumol/L), PGE2 inhibited both aggregation and calcium movements. PGE2 (5 to 500 nmol/L) significantly enhanced secretion of beta-thromboglobulin (beta TG) and adenosine triphosphate from U46619- and ADP-stimulated platelets, but it did not affect platelet shape change. PGE2 also increased the binding of radiolabeled fibrinogen to the platelet surface and increased the phosphorylation of the 47-kD protein in 32P- labeled platelets stimulated with subthreshold doses of U46619. Finally, the amplification of U46619-induced aggregation by PGE2 (500 nmol/L) was abolished by four different protein kinase C (PKC) inhibitors (calphostin C, staurosporine, H7, and TMB8). Our results suggest that PGE2 exerts its facilitating activity on agonist-induced platelet activation by priming PKC to activation by other agonists. PGE2 potentiates platelet activation at concentrations produced by activated platelets and may thus be of pathophysiologic relevance.     

dl-3-n-butylphthalide inhibits platelet activation via inhibition of cPLA2-mediated TXA2 synthesis and phosphodiesterase

Aberrant platelet activation plays a critical role in the pathogenesis of heart attack and stroke. dl-3-n-butylphthalide (NBP) has been approved in China to treat stroke with multiple mechanisms. The anti-stroke effects of NBP may be related to its antiplatelet effects reported in rats in addition to its antioxidative, antiapoptotic, and angiogenic effects. However, the effects and the underlying mechanisms of NBP on human platelets are not yet clear. In this study, we found that NBP concentration-dependently inhibited human platelet aggregation and ATP release induced by ADP, thrombin, U46619, arachidonic acid, or collagen. NBP also inhibited PAC-1 binding induced by ADP or thrombin and platelet spreading on immobilized fibrinogen. NBP reduced TXA₂ synthesis induced by thrombin or collagen via inhibiting cPLA2 phosphorylation, concomitantly with a marked decrease in intracellular calcium mobilization. Moreover, NBP also inhibited human platelet phosphodiesterase (PDE) and elevated 3,5-cyclic adenosine monophosphate level in platelets. In conclusion, NBP significantly inhibits human platelet activation via inhibition of cPLA2-mediated TXA₂ synthesis and PDE, and may be effective as an antiplatelet drug to treat other arterial thrombotic diseases.     

Phorbol-myristate-acetate-induced platelet aggregation in the presence of inhibitors

4 beta-Phorbol-12-myristate-13-acetate (PMA) at 100 ng/ml was able to induce platelet aggregation in the presence of agents which inhibited aggregation, triggered by other agonists such as adenosine diphosphate sodium salt (ADP), thrombin and collagen. PMA induced aggregation in acid-citrate-dextrose platelet-rich plasma. 100 microM tetracaine, 5 microM bromophenacyl bromide and 0.2 mM mepacrine decreased PMA-induced aggregation by only 10% in contrast to their high inhibitory effect on other aggregation systems. However, 0.4 mM mepacrine did inhibit PMA-induced aggregation at the same rate as the other aggregation systems. 100 mg/ml vincristine slightly affected PMA-induced platelet aggregation, whereas cytochalasin B rather enhanced it. Nordihydroguaiaretic acid, 5, 8, 11, 14-eicosatetraynoic acid and p-nitrophenyl-phosphorylcholine had no effect on PMA- or collagen-induced platelet aggregation, partially inhibited aggregation triggered by ADP and strongly inhibited aggregation caused by thrombin. It is suggested that PMA exerts its effect on platelets mainly due to its ability to alter their membranes.     

High molecular weight kininogen inhibits thrombin-induced platelet aggregation and cleavage of aggregin by inhibiting binding of thrombin to platelets.

In this study we show that high molecular weight kininogen (HK) inhibited alpha-thrombin-induced aggregation of human platelets in a dose-dependent manner with complete inhibition occurring at plasma concentration (0.67 mumol/L) of HK. HK (0.67 mumol/L) also completely inhibited thrombin-induced cleavage of aggregin (Mr = 100 Kd), a surface membrane protein that mediates adenosine diphosphate (ADP)-induced shape change, aggregation, and fibrinogen binding. The inhibition of HK was specific for alpha- and gamma-thrombin-induced platelet aggregation, because HK did not inhibit platelet aggregation induced by ADP, collagen, calcium ionophore (A23187), phorbol myristate acetate (PMA), PMA + A23187, or 9,11-methano derivative of prostaglandin H2 (U46619). These effects were explained by the ability of HK, at physiologic concentration, to completely inhibit binding of 125I-alpha-thrombin to washed platelets. As a result of this action of HK, this plasma protein also completely inhibited thrombin-induced secretion of adenosine triphosphate, blocked intracellular rise in Ca2+ in platelets exposed to alpha- and gamma-thrombin, inhibited thrombin-induced platelet shape change, and blocked the ability of thrombin to antagonize the increase in intracellular cyclic adenosine monophosphate (cAMP) levels induced by iloprost. Because elevation of cAMP is known to inhibit binding of thrombin to platelets, we established that HK did not increase the intracellular concentration of platelet cAMP. Finally, HK did not inhibit enzymatic activity of thrombin. To study the role of HK in the plasma environment, we used gamma-thrombin to avoid fibrin formation by alpha-thrombin. Platelet aggregation induced by gamma-thrombin was also inhibited by HK in a dose-dependent manner. The EC50 (concentration to produce 50% of the maximum rate of aggregation) of gamma-thrombin for washed platelets was 7 nmol/L and increased to 102 nmol/L when platelets were suspended in normal human plasma. The EC50 for platelet aggregation induced by alpha-thrombin in plasma deficient in total kininogen was 40 nmol/L. When supplemented with HK at plasma concentration (0.67 mumol/L), the EC50 increased to 90 nmol/L, a value similar to that for normal human plasma. These results indicate that (1) HK inhibits thrombin-induced platelet aggregation and cleavage of aggregin by inhibiting binding of thrombin to platelets; (2) HK is a specific inhibitor of platelet aggregation induced by alpha- and gamma-thrombin; and (3) HK plays a role in modulating platelet aggregation stimulated by alpha-thrombin in plasma.     

Potentiation by adrenaline of agonist-induced responses in normal human platelets in vitro

Adrenaline is not a true platelet agonist, but enhances aggregation, dense granule secretion, and phospholipase C induced by other agonists. In the present work we investigated the effect of adrenaline on other platelet responses. It strongly potentiated ADP-induced shape change in platelet-rich plasma, particularly when aggregation was prevented by EDTA. The degree of potentiation increased with increasing concentrations of ADP. Thrombin-induced α-granule secretion, measured by the release of fibrinogen in gel-filtered platelets, was also potentiated by adrenaline at thrombin concentrations above 0.05 U/ml. In contrast, adrenaline had little effect on thrombin-induced secretion of β-acetyl-hexosaminidase and potentiated very little liberation of arachidonate at high thrombin concentrations. When autocrine stimulation was inhibited by the removal of secreted ADP by creatine phosphate/creatine phosphate kinase and specific blocking of the thromboxane A(2) and fibrinogen receptors, the potentiation of thrombin-induced ADP?+?ATP secretion by adrenaline was reduced and this reduction was mostly due to the blocking of the thromboxane A(2) receptor. Protein tyrosine phosphorylation by both thrombin and collagen was reduced by adrenaline, and inhibitors of autocrine stimulation counteracted this reduction.     

Inhibitory mechanism of human platelet aggregation by nafamostat mesilate

We found that nafamostat mesilate (NM) inhibits platelet aggregation induced by all agonists tested, including ADP, collagen, arachidonic acid, thromboxane A analog, A23187, phorbol 12-myrisate 13-acetate (PMA), NaF and thrombin. The IC50 values were in the range of 9.3-17.8 mu M. NM inhibited agonists-induced aspirin-treated platelet aggregation at >10 mu M, suggesting that the action site lies beyond thromboxane (TXA)2 formation. However, NM inhibited thrombin (0.5 IU/ml)-induced TXB2 formation (IC50 = 1.9 +/- 0.6 mu M, mean +/- SD). Intracellular Ca2+ mobilization was also inhibited only when platelets were challenged by thrombin, but the effect was found at NM concentrations >50 mu M. This finding suggests that NM reduces the responses to thrombin by inhibiting its proteolytic activity on the platelet thrombin receptor (PAR1). NM did not affect the intracellular cAMP concentration or A-kinase activity. Agonists-induced surface expression of activated glycoprotein (GP)IIb-IIIa was inhibited by 10 mu M NM and was completely inhibited by 50 mu M NM. Since this inhibitory effect was parallel to the inhibition of platelet aggregation, the main inhibitory mechanism of NM against platelet aggregation seemed to be the suppression of activated GPIIb-IIIa expression, which makes it able to bind fibrinogen.     

The role of ADP secretion and thromboxane synthesis in factor VIII binding to platelets

Following stimulation with arachidonic acid, collagen, U-46619 (a stable analogue of prostaglandin endoperoxide/thromboxane-A2), thrombin, or adenosine diphosphate (ADP), unstirred human platelet suspensions bound labeled factor VIII in a reaction that reached equilibrium within 10 min. Apyrase inhibited binding induced by arachidonic acid, collagen, U-46619, and thrombin by less than 40%, but inhibited ADP-induced binding by 95%. Binding to aspirin-treated platelets was normal in response to U-46619, reduced by 60%-70% in response to ADP, collagen, and thrombin, and absent in response to arachidonic acid. Binding in response to U-46619 was not altered by the combination of apyrase and aspirin. Binding of factor VIII was decreased by 90% when 10 mM EDTA was added before each agonist, but it was inhibited less than 30% when EDTA was added following platelet stimulation. We conclude that arachidonic acid, collagen, and thrombin can expose binding sites for factor VIII independently of released ADP; that Ca++ is required for activation but probably not for binding of factor VIII to platelets; and that platelet thromboxane synthesis plays a major role in the binding of factor VIII to platelets induced by thrombin, ADP, or collagen.     

Comparison of the relative activities of inducing platelet apoptosis stimulated by various platelet-activating agents

Apoptosis-like events are known to occur in anuclear platelets. Although the mechanisms responsible for these events are still not completely understood, studies suggested that some platelet agonists can activate platelet apoptosis. However, the relative activities of various platelet agonists in inducing apoptosis have not yet been investigated. In the present study we explored this issue, and attempted to identify the correlation between platelet activation and apoptosis. In a platelet aggregation study, there were no significant differences respectively stimulated by arachidonic acid (AA; 100 µM), ADP (20 µM), collagen (10 µg/mL), thrombin (0.1 U/mL), U46619 (10 µM), and A23187 (5 µM). In a subsequent study, we fixed these concentrations of agonists to further compare their relative activities in inducing platelet apoptosis. Our results found that thrombin, U46619, and A23187 possess stronger activities than the other agonists in inducing platelet apoptosis (i.e., phosphatidylserine exposure, mitochondrial membrane potential depolarization, eukaryotic initiation factor (eIF)2α, and caspase activation). On the other hand, AA induced no apoptotic events in platelets. Based on this approach, we demonstrated for the first time that thrombin, U46619, and A23187, but not AA, possess stronger activity in inducing platelet apoptosis. In addition, we also found that platelet activation might not necessarily be associated with the occurrence of platelet apoptosis. The in vivo physiological function of the apoptotic machinery in platelets is not yet clearly understood, and needs to be further investigated in the future.     

Optical multichannel (optimul) platelet aggregometry in 96-well plates as an additional method of platelet reactivity testing

Platelet reactivity testing is important for the diagnosis of bleeding disorders, and increasingly to optimise anti-platelet therapy. Traditional light transmission aggregometry is considered the gold standard, whilst 96-well plate aggregometry, founded on similar principles, provides a higher throughput screening method. Despite the widespread use of both, methodologies and outputs vary widely between laboratories. We report a methodological approach towards providing a standardised optical detection of platelet aggregation (optimul method) based upon 96-well plate aggregometry. Individual wells of half-area 96-well plates were coated with gelatine and one of seven concentrations of arachidonic acid (AA), adenosine diphosphate (ADP), collagen, epinephrine (EPI), ristocetin, TRAP-6 amide or U46619, before being lyophilised, vacuum-sealed, foil-packed and stored at room temperature for up to 24 weeks. For platelet testing, 40?μl of platelet-rich plasma was added to each well. Platelet aggregation was determined by changes in light absorbance, release of ATP/ADP by luminescence and release of thromboxane (TX) A(2) by ELISA. Some experiments were conducted in the presence of aspirin (30?μM) or prasugrel active metabolite (PAM; 3?μM). Optimul plates stored for up to 12 weeks permitted reliable detection of concentration-dependent platelet aggregation, ATP/ADP release and TXA? production. PAM caused reductions in platelet responses to AA, ADP, collagen, EPI, TRAP-6 and U46619, whilst aspirin inhibited responses to AA, collagen and EPI. We conclude that the optimul method offers a viable, standardised approach, allowing platelet reactivity testing and could provide a broad platelet function analysis without the need for dedicated equipment.