Surfactin C inhibits platelet aggregation

This study was designed to investigate the effect of surfactin C, which is derived from Bacillus subtilis, on platelet aggregation and homotypic leucocyte aggregation. Surfactin C strongly and dose-dependently inhibited platelet aggregation, which was stimulated both by thrombin (0.1 U mL(-1)), a potent agonist that activates the G protein-coupled protease receptor, and by collagen (5 microg mL(-1)), a potent ligand that activates alpha(IIb)beta(3) with IC50 values (concentration inhibiting platelet aggregation by 50%) of 10.9 and 17.0 microM, respectively. Moreover, surfactin C significantly suppressed the intracellular Ca(2+) mobilization in thrombin-activated platelets. Surfactin C, however, did not affect various integrin-mediated U937 cell aggregation, implying that the anti-platelet activity of surfactin C was not due to its detergent effect but by its action on the downstream signalling pathway. Therefore, the results suggest that surfactin C may have a beneficial therapeutic effect on aberrant platelet aggregation-mediated cardiovascular diseases.     

银杏内酯注射液和银杏内酯ABC对血小板活化因子诱导的家兔血小板聚集作用比较

目的 观察银杏内酯注射液、银杏内酯ABC以及银杏叶提取物注射液（EGb761）对家兔血小板聚集功能、超微结构及PF-4和β-TG含量的影响比较。方法 将日本大耳兔分为对照（生理盐水）组、EGb761（1.02 mL/kg）组、银杏内酯ABC （5.13 mg/kg）组、银杏内酯注射液（1.02 mL/kg,以萜内酯计5.1 mg/kg）组、白果内酯（5.13 mg/kg）组,分别iv相应药物1周。给药结束后,家兔心脏取血,观察PAF诱导下血小板聚集率;电镜观察血小板超微结构;试剂盒法观察PAF诱导下血清中血小板因子-4（PF-4）和β-血小板球蛋白（β-TG）含量。结果 与对照组比较,EGb761组、银杏内酯ABC组、银杏内酯注射液组的血小板聚集率均显著降低（P<0.05、0.01）,白果内酯组无显著变化;血小板聚集抑制率：银杏内酯注射液（43.76%） > 银杏内酯ABC （35.3%） > EGb761（26.52%） > 白果内酯（5.48%）。与对照组比较,EGb761、银杏内酯ABC、银杏内酯注射液均能减少聚集型血小板数量,使树突型血小板突起变少变短。与对照组比较,银杏内酯注射液和银杏内酯ABC均使PF-4和β-TG表达显著降低（P<0.01）,EGb761仅显著降低β-TG表达（P<0.05）。结论 银杏内酯注射液通过PAF途径发挥抗血小板聚集作用,其作用强于银杏内酯ABC,可能是白果内酯发挥了协同增效作用。     

Cordycepin (3'-deoxyadenosine) inhibits human platelet aggregation in a cyclic AMP- and cyclic GMP-dependent manner

Cordycepin (3'-deoxyadenosine) is isolated from Cordyceps militaris, a species of the fungal genus Cordyceps. Cordycepin is an ingredient used in traditional Chinese medicine and is prescribed for various diseases, such as cancer and chronic inflammation. In this study, we investigated the novel effect of cordycepin (3'-deoxyadenosine) on collagen-induced human platelet aggregation. Cordycepin inhibited dose-dependently collagen-induced platelet aggregation in the presence of various concentrations of exogenous CaCl(2). Of two aggregation-inducing molecules, cytosolic free Ca(2+) ([Ca(2+)](i)) and thromboxane A(2) (TXA(2)), cordycepin (500 microM) blocked the up-regulation of [Ca(2+)](i), by up to 74%, but suppressed TXA(2) production by 46%. Subsequently, Ca(2+)-dependent phosphorylation of both 47-kDa and 20-kDa proteins in collagen-treated platelets was potently diminished by cordycepin. However, upstream pathways for producing these two inducers, such as the activation of phospholipase C-gamma2 (PLC-gamma2) (assessed by the phosphotyrosine level) and the formation of inositol 1,4,5-trisphosphate (IP(3)), were not altered by cordycepin. Cordycepin increased the level of second messengers adenosine 3',5'-cyclic monophosphate (cAMP) and guanosine 3',5'-cyclic monophosphate (cGMP) in collagen-stimulated platelets. Whereas the NO-sensitive guanylyl cyclase inhibitor ODQ did not alter the cordycepin-induced up-regulation of cGMP, the adenylyl cyclase inhibitor SQ22536 completely blocked the cAMP enhancement mediated by cordycepin, indicating that cordycepin had different modes of action. Therefore, our data suggest that the inhibitory effect of cordycepin on platelet aggregation might be associated with the down-regulation of [Ca(2+)](i) and the elevation of cAMP/cGMP production.     

血小板活化因子和肾上腺素对人血小板凝集的钙依赖性协同作用(英文)

AIM: To investigate the mechanism (s) involved in the synergistic interaction of platelet activating factor (PAF) and epinephrine. METHODS: Blood was obtained from healthy human subjects reported to be free of medications for at least two weeks before sampling. Aggregation was monitored at 37℃ using Dual-channel Lumi-aggregometer.The resulting aggregation was recorded for 5 min by the measurement of light transmission as a function of time.RESULTS: Platelet aggregation mediated by subthreshold concentrations of PAF (5-8 nmol/L) plus epinephrine(0.5-2 μmol/L) was inhibited by α_2-receptor blocker, yohimbine, and PAF receptor antagonist WEB 2086. This synergism was inhibited by calcium channel blockers, verapamil and diltiazem. In addition, platelet aggregation by co-addition of PAF and epinephrine was also inhibited by very low concentrations of phospholipase C (PLC) inhibitor (U73122; IC_(50)=0.2 μmol/L), the MAP kinase inhibitor, PD 98059 (IC_(50)=3 μmol/L), and cyclooxygenase(COX-1) inhibitors in     

粉防己碱对兔血小板聚集和血小板活化因子生成的影响(英文)

目的:探讨粉防己碱(Tet)对兔血小板聚集和PAF生成的影响.方法:卡西霉素(Cal)和PAF诱导血小板聚集的聚集率和Tet对血小板聚集的抑制率被测定;给予或未给予Tet处理之血小板用Cal刺激释放PAF的量也被测定.结果:在4—64 μmol·L~(-1)浓度范围,Tet明显抑制Cal和PAF诱导的血小板聚集.IC_(50)值分别为8.6μmol·L~(-1)和14.0μmol·L~(-1).Tet也浓度依赖性的抑制Cal诱导血小板释放PAF,IC_(50)值为21.0μmol·L~(-1).结论:Tet抑制血小板聚集作用与抑制内源性PAF生成有关.     

CV3988 inhibits in vivo platelet aggregation induced by PAF-acether and collagen

Platelet activating factor (PAF-acether) was shown to cause a fall in the circulating platelet count and blood pressure (BP) in anaesthetised rabbits. CV3988 caused a dose-dependent inhibition of these responses to a low dose of PAF-acether (150 ng · kg⁻¹). CV3988 itself was found to cause a fall in both BP and platelet count in vivo. Collagen (40 μg · kg⁻¹) i.v. caused sudden death in rabbits and pretreatment with CV3988 (5 mg · kg⁻¹) caused a 62% inhibition of the platelet count response to collagen without significantly increasing the survival rate. In the rat, collagen (40 μg · kg⁻¹) was not lethal and CV3988 caused a dose-dependent inhibition of the fall in platelet count due to collagen, but this action was short-lived. CV3988 also caused agonist actions in the rat. These results show that CV3988 inhibits the effects of PAF-acether in vivo and suggests that PAF-acether may play a role in mediating collagen-induced platelet aggregation in vivo.     

LB30057 inhibits platelet aggregation and vascular relaxation induced by thrombin

Previous study showed that an amidrazonophenylalanine derivative, LB30057, which has high water solubility, inhibited the catalytic activity of thrombin potently by interaction with the active site of thrombin. In the current investigation, we examined whether LB30057 inhibited platelet aggregation and vascular relaxation induced by thrombin. Treatment with LB30057 to platelet-rich plasma (PRP) isolated from human blood resulted in a concentration-dependent inhibition of thrombin-induced aggregation. Values for IC50 and IC100 were 54 +/- 4 nM and 96 +/- 3 nM, respectively. This inhibition was agonist (thrombin) specific, since IC50 values for collagen and ADP were much greater than those for thrombin. In addition, concentration-dependent inhibitory effects were observed on the serotonin secretion induced by thrombin in PRP. Consistent with these findings, thrombin-induced increase in cytosolic calcium levels was inhibited in a concentration-dependent manner. When LB30057 was treated with aortic rings isolated from rats, LB30057 resulted in a concentration-dependent inhibition of thrombin-induced vascular relaxation. All these results suggest that LB30057 is a potent inhibitor of platelet aggregation and blood vessel relaxation induced by thrombin.     

Endothelium-derived relaxing factor inhibits in vitro platelet aggregation

We studied the effects of endothelium-derived relaxing factor (EDRF), bovine retractor penis muscle inhibitory factor and sodium nitroprusside, three stimulants of guanylate cyclase, on the in vitro aggregation of washed human platelets. Platelet aggregation induced either by collagen or by the thromboxane A2 analogue U46619 was inhibited by all three agents. The anti-aggregatory effect of each agent was inhibited by haemoglobin. The anti-aggregatory effect of EDRF was potentiated by superoxide dismutase. These findings are discussed in relation to a potential role for EDRF in haemostasis.     

Levamisole inhibits in vivo rat platelet aggregation by a release of prostacyclin-like factor

1. The anti-thrombotic effect of levamisole (LMS) and acetylsalicylic acid (ASA) were examined in vitro and in vivo models. 2. LMS inhibits rat platelet aggregation induced by either adenosine 5'-diphosphate (ADP) or collagen (CLG) in vitro and in vivo. 3. LMS is more active in vivo than in vitro while acetylsalicylic acid (ASA) is more active in vitro than in vivo. It seems that in vivo LMS does not act by blocking thromboxane A2 formation only, but via participation of an endogenous factor. 4. The release of LMS-induced anti-thrombotic factor is inhibited by ASA pretreatment, indicating to be a cyclooxygenase metabolite of arachidonic acid. 5. The LMS-induced anti-thrombotic factor has a t1/2 of 3.6 +/- 0.8 min that is similar to the t1/2 of synthetic prostacyclin (PGI2) tested in our system (3.9 +/- 0.5 min; P = NS). 6. The release of PGI2-like substance from vascular tissue is LMS dose-dependent.     

Atrial natriuretic peptide inhibits glomerular contraction induced by angiotensin II and platelet activating factor

Isolated rat glomeruli were incubated with angiotensin II, PAF and atrial natriuretic peptide (ANP). Angiotensin II and PAF produced a significant glomerular contraction as evidenced by the decrease in glomerular cross-sectional area. The addition of ANP abolished this effect. These results suggest that ANP could modulate glomerular filtration rate, not only by inducing changes in intrarenal hemodynamics, but also by preventing the effect of some hormones on the filtration surface and subsequently on the ultrafiltration coefficient.     

Study of platelet aggregation induced by platelet activating factor (PAF) after administration of ticlopidine or aspirin

Platelet aggregation induced by platelet activating factor (PAF) was studied in 95 subjects: 39 controls, 23 patients receiving aspirin and 33 receiving ticlopidine. Potentiation of aggregation by concentrations of adrenaline unable to induce aggregation when used alone was also assessed. The 33 patients treated with ticlopidine showed a highly significant fall of platelet aggregation (p less than 0.001) at the three concentrations of PAF used. The 23 subjects receiving aspirin showed a diminution of platelet aggregation induced by PAF due to inhibition of ADP release. In these last two groups, adrenaline often potentiated platelet aggregation. However, this phenomenon was absent in subjects having taken aspirin in the hours before blood was drawn. This study demonstrates ticlopidine's inhibitory action on PAF-induced aggregation and confirms ticlopidine's role in reducing platelet aggregation by ADP, which has previously been demonstrated.     

Modulation of in vitro immune reactions by platelet activating factor and a platelet activating factor antagonist

Platelet activating factor (PAF) was found to suppress primary and secondary mixed lymphocyte reactions and BN52021, a naturally occurring PAF antagonist, blocked PAF-mediated suppression and enhanced the mixed lymphocyte reactions. The effect of delayed addition of PAF or BN52021 24 h or later after the initiation of cultures reduced the suppressive and enhancing effects, respectively. The removal of the antagonist BN52021 from mixed lymphocyte cultures up to 72 h after their initiation also was found to eliminate the potentiating effect of this antagonist. The continuous presence of PAF in mixed lymphocyte cultures used to generate cytotoxic lymphocytes suppressed the generation of effector cells while the addition of BN52021 elicited an enhanced level of cell-mediated cytotoxicity in such cultures. BN52021 enhanced the cytotoxic activity in such cultures irrespective of the presence of exogenous interleukin-2, suggesting that the antagonist-mediated enhancement is not due to the enhanced production of interleukin-2 by cells in the mixed cultures. The experiments reported here provide evidence for a role of PAF in modulating the complex interactions that take place in the initiation of cellular immune reactions. Furthermore, the results of these experiments indicate that the immunoregulatory action of PAF can be modulated by an antagonist that exerts its action independently of the production of the lymphocyte growth factor, interleukin-2.     

Oncocalyxone A inhibits human platelet aggregation by increasing cGMP and by binding to GP Ibalpha glycoprotein

BACKGROUND AND PURPOSE: Oncocalyxone A (OncoA) has a concentration-dependent anti-platelet activity. The present study aimed to further understand the mechanisms related to this effect. EXPERIMENTAL APPROACH: Human platelet aggregation was measured by means of a turbidimetric method. OncoA (32-256 microM) was tested against several platelet-aggregating agents, such as adenosine diphosphate (ADP), collagen, arachidonic acid (AA), ristocetin and thrombin. KEY RESULTS: OncoA completely inhibited platelet aggregation with a calculated mean inhibitory concentration (IC50-microM) of 122 for ADP, 161 for collagen, 159 for AA, 169 for ristocetin and 85 for thrombin. The anti-aggregatory activity of OncoA was not inhibited by 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ). OncoA, at a concentration that caused no significant anti-aggregatory activity, potentiated sodium nitroprusside (SNP) anti-aggregatory activity (18.8+/-2.9%-SNP vs 85.0+/-8.2%-SNP+OncoA). The levels of nitric oxide (NO) or cAMP were not altered by OncoA while cGMP levels were increased more than 10-fold by OncoA in resting or ADP-activated platelets. Flow cytometry revealed that OncoA does not interact with receptors for fibrinogen, collagen or P-selectin. Nevertheless, OncoA decreased the binding of antibodies to GP Ibalpha, a glycoprotein that is related both to von Willebrand factor and to thrombin-induced platelet aggregation. CONCLUSION AND IMPLICATIONS: OncoA showed anti-aggregatory activity in platelets that was associated with increased cGMP levels, not dependent on NO and with blocking GP Ibalpha glycoprotein. This new mechanism has the prospect of leading to new anti-thrombotic drugs.     

Cryptolepine inhibits platelet aggregation in vitro and in vivo and stimulates fibrinolysis ex vivo

1. Cryptolepine--the methylquindolanol alkaloid of Cryptolepsis sanguinolenta was evaluated for its antiplatelet and fibrinolytic effects. 2. It exhibited antiplatelet effects in vitro in human, rabbit and rat PRP with EC50 values ranging between 8.1 x 10(-8) M and 1.7 x 10(-7) M for ADP, AA and thrombin. 3. In the rat, it inhibited ADP-aggregation in vivo with delayed onset and prolonged action. 4. In vitro, cryptolepine disaggregated (dose-dependently) platelets aggregated by ADP, AA and thrombin. 5. In addition, it exhibited an indirect fibrinolytic action in the rat possibly by causing the release of plasminogen activators from the vascular endothelium.     

Hispidulin, a natural flavone, inhibits human platelet aggregation by increasing cAMP levels

Hispidulin, a natural flavone, and theophylline inhibited platelet aggregation triggered by adenosine-5'-monophosphate, arachidonic acid, paf-acether and collagen. Hispidulin was 100-fold more potent than theophylline. A threshold concentration of PGE1 did not modify the anti-aggregatory effect of hispidulin but potentiated the effect of theophylline. A threshold concentration of hispidulin had no effect on the inhibitory action of theophylline. Hispidulin (100 microM) and theophylline (10 mM) increased the control cAMP level in platelets 4-fold. A threshold concentration of PGE1 had a small effect on hispidulin-induced cAMP levels but increased the theophylline-induced cAMP levels 3-fold. Theophylline (10 mM)-induced cAMP levels were not modified by hispidulin. We demonstrate a correlation between the inhibition of platelet aggregation and the increase in cAMP levels induced by hispidulin. These data suggest that hispidulin could inhibit platelet aggregation by elevating cAMP levels by a mechanism different from that of theophylline or PGE1.