Thromboxane B2 Formation Research Articles

Phosphatidylinositol-3,4,5-trisphosphate stimulates Ca2 + elevation and Akt phosphorylation to constitute a major mechanism of thromboxane A2 formation in human platelets

Phosphatidylinositol trisphosphate (PIP3) has been implicated in many platelet functions however many of the mechanisms need clarification. We have used cell permeable analogues of PIP3,1-O-(1,2-di-palmitoyl-sn-glyero-3-O-phosphoryl)-D-myo-inositol-3,4,5-trisphosphate (DiC16-PIP3) or 1-O-(1,2-di-octanoyl-sn-glyero-3-O-phosphoryl)-D-myo-inositol-3,4,5-trisphosphate (DiC8-PIP3) to study their effects on activation on washed human platelets. Addition of either DiC8- or DiC16-PIP3 to human platelets induced aggregation in the presence of extracellular Ca2+. This was reduced by the presence of indomethacin, the phospholipase C inhibitor U73122 and apyrase. DiC8-PIP3 induced the phosphorylation of Akt-Ser473 which was reduced by the Akt inhibitor IV, wortmannin and EGTA (suggesting a dependence on Ca2+ entry). In Fura2 loaded platelets DiC8-PIP3 was effective at increasing intracellular Ca2+ in a distinct and transient manner that was reduced in the presence of indomethacin, U73122 and 2-aminoethyl diphenylborinate (2APB). Ca2+ elevation was reduced by the non-SOCE inhibitor LOE908 and also by the SOCE inhibitor BTP2. DiC8-PIP3 induced the release of Ca2+ from stores which was not affected by the proton dissipating agent bafilomycin A1 and was more potent than the two-pore channel agonist DiC8-PI[3,5]P2 suggesting release from an endoplasmic reticulum type store. DiC8-PIP3 weakly induced the tyrosine phosphorylation of Syk but not of PLCγ2. Finally like thrombin DiC8-PIP3 induced the formation of thromboxane B2 that was inhibited by the Akt inhibitor IV. These studies suggest that PIP3 via Ca2+ elevation and Akt phosphorylation forms a central role in thromboxane A2 formation and the amplification of platelet activation.

Arachidonic acid-stimulated platelet tests: Identification of patients less sensitive to aspirin treatment

Serum thromboxane-B2 (TxB2), together with arachidonic acid (AA)-induced platelet aggregation, are, at the moment, the most used tests to identify patients displaying high on-aspirin treatment platelet reactivity (HAPR). Both tests are specific for aspirin action on cyclooxygenase-1. While the correlation between serum TxB2 assay and clinical outcome is established, data are conflicting with regard to aspirin treatment and a possible association with AA-stimulated platelet markers and clinical outcome. To understand such discrepancy, we performed a retrospective study to compare both assays. We collected data from 132 patients receiving a daily dose of aspirin (100 mg/day) and data from 48 patients receiving aspirin on alternate days. All Patients who received a daily dose of aspirin were studied for AA-induced platelet aggregation together with serum TxB2 levels and AA-induced TxB2 formation was also studied in 71 patients out of entire population. Consistent with recommendations in the literature, we defined HAPR by setting a cut-off point at 3.1 ng/ml for serum levels of thromboxane B2 and 20% for AA-induced platelet aggregation. According to this cut-off point, we divided our overall population into two groups: (1) TxB2 < 3.1 ng/ml and (2) TxB2 > 3.1 ng/ml. We found low agreement between such tests to identify patients displaying HAPR. Our results show that AA-induced platelet aggregation >20% identify a smaller number of HAPR patients in comparison with TxB2. A good correlation between serum TxB2 and arachidonic acid-induced TxB2 production was found (r = 0.76619).

Multiple daily doses of acetyl‐salicylic acid (ASA) overcome reduced platelet response to once‐daily ASA after coronary artery bypass graft surgery: a pilot randomized controlled trial

The efficacy of ASA for prevention of graft failure following CABG surgery may be limited by incomplete platelet inhibition due to increased post-operative platelet turnover. To determine whether acetyl-salicylic acid (ASA) 325mg once-daily or 81mg four-times daily overcomes the impaired response to ASA 81mg once-daily in post-operative coronary artery bypass graft (CABG) patients. We randomized 110 patients undergoing CABG surgery to either ASA 81mg once-daily, 81mg four times daily or 325mg once-daily and compared their effects on serum thromboxane B2 (TXB2 ) suppression and arachidonate-induced platelet aggregation. One hundred patients were included in the final analysis. Platelet counts fell after surgery, reached a nadir on day 2, and then gradually increased. Although there was near complete suppression of TXB2 on the second or third post-operative day, TXB2 levels increased in parallel with the rise in platelet count on subsequent days. This increase was most marked in patients receiving ASA 81mg once-daily and less evident in those receiving ASA four times daily. On post-operative day 4, (i) median TXB2 levels were lower with four times daily ASA than with either ASA 81mg once-daily (1.1ng/mL; Quartile(Q) Q1,Q3: 0.5, 2.4 and 13.3ng/mL; Q1,Q3: 7.8, 30.8ng/mL, respectively; P<0.0001) or ASA 325mg once-daily (3.4ng/mL; Q1,Q3: 2.0, 8.2ng/mL; P=0.002), and (ii) ASA given four times daily was more effective than ASA 81mg once-daily and 325mg once-daily at suppressing platelet aggregation. Four times daily ASA is more effective than ASA 81 and 325mg once-daily at suppressing serum TXB2 formation and platelet aggregation immediately following CABG surgery.

Chloroform fraction of Euphorbia maculata has antiplatelet activity via suppressing thromboxane B2 formation.

Euphorbia maculata (EM) is a traditionally used antidiarrheal, antibacterial, antifungal and antioxidant agent. However, the effects of EM on platelet activity remain to be elucidated. Therefore, the present study investigated the antiplatelet effect of various EM extract fractions on platelet aggregation in rats. The antiplatelet activity of the EM fractions on collagen or adenosine diphosphate (ADP)‑induced platelet aggregation was evaluated invitro and exvivo. ThromboxaneB2 (TXB2) formation, rat‑tail bleeding time and coagulation time were also measured. Among the fractions, the chloroform fraction of EM (CFEM) significantly inhibited ADP‑induced platelet aggregation invitro. Furthermore, oral administration of 50mg/kg CFEM to rats significantly reduced ADP‑induced platelet aggregation without increasing the tail bleeding time or coagulation time. In addition, EM significantly inhibited the level of TXB2 formation in a dose‑dependent manner. These results suggest that CFEM exhibits antiplatelet activity, without causing bleeding, via the suppression of TXB2 formation. CFEM may be a type of food which has the potential for preventing cardiovascular disease.

Ex vivo and in vivo studies of CME-1, a novel polysaccharide purified from the mycelia of Cordyceps sinensis that inhibits human platelet activation by activating adenylate cyclase/cyclic AMP

IntroductionCME-1, a novel water-soluble polysaccharide, was purified from the mycelia of Cordyceps sinensis, and its chemical structure was characterized to contain mannose and galactose in a ratio of 4:6 (27.6kDa). CME-1 was originally observed to exert a potent inhibitory effect on tumor migration and a cytoprotective effect against oxidative stress. Activation of platelets caused by arterial thrombosis is relevant to various cardiovascular diseases (CVDs). However, no data are available concerning the effects of CME-1 on platelet activation. Hence, the purpose of this study was to examine the ex vivo and in vivo antithrombotic effects of CME-1 and its possible mechanisms in platelet activation. MethodsThe aggregometry, immunoblotting, flow cytometric analysis and platelet functional analysis were used in this study. ResultsCME-1 (2.3-7.6μM) exhibited highly potent activity in inhibiting human platelet aggregation when stimulated by collagen, thrombin, and arachidonic acid but not by U46619. CME-1 inhibited platelet activation accompanied by inhibiting Akt, mitogen-activated protein kinases (MAPKs), thromboxane B2 (TxB2) and hydroxyl radical (OH●) formation. However, CME-1 interrupted neither FITC-triflavin nor FITC-collagen binding to platelets. CME-1 markedly increased cyclic AMP levels, but not cyclic GMP levels, and stimulated vasodilator-stimulated phosphoprotein (VASP) phosphorylation. SQ22536, an inhibitor of adenylate cyclase, but not ODQ, an inhibitor of guanylate cyclase, obviously reversed the CME-1-mediated effects on platelet aggregation and vasodilator-stimulated phosphoprotein (VASP), Akt, p38 MAPK phosphorylation, and TxB2 formation. CME-1 substantially prolonged the closure time of whole blood and the occlusion time of platelet plug formation. ConclusionThis study demonstrates for the first time that CME-1 exhibits highly potent antiplatelet activity that may initially activate adenylate cyclase/cyclic AMP and, subsequently, inhibit intracellular signals (such as Akt and MAPKs), ultimately inhibiting platelet activation. This novel role of CME-1 indicates that CME-1 exhibits high potential for application in treating and preventing CVDs.

Perilla oil improves blood flow through inhibition of platelet aggregation and thrombus formation

The inhibitory effects of perilla oil on the platelet aggregation in vitro and thrombosis in vivo were investigated in comparison with aspirin, a well-known blood flow enhancer. Rabbit platelet-rich plasma was incubated with perilla oil and aggregation inducers collagen or thrombin, and the platelet aggregation rate was analyzed. Perilla oil significantly inhibited both the collagen- and thrombin-induced platelet aggregations, in which the thromboxane B2 formation from collagen-activated platelets were reduced in a concentration-dependent manner. Rats were administered once daily by gavage with perilla oil for 1 week, carotid arterial thrombosis was induced by applying 35% FeCl3-soaked filter paper for 10 min, and the blood flow was monitored with a laser Doppler probe. Perilla oil delayed the FeCl3-induced arterial occlusion in a dose-dependent manner, doubling the occlusion time at 0.5 mL/kg. In addition, a high dose (2 mL/kg) of perilla oil greatly prevented the occlusion, comparable to the effect of aspirin (30 mg/kg). The results indicate that perilla oil inhibit platelet aggregation by blocking thromboxane formation, and thereby delay thrombosis following oxidative arterial wall injury. Therefore, it is proposed that perilla oil could be a good candidate without adverse effects for the improvement of blood flow.

Antiplatelet and antithrombotic effects of Morus alba leaves extract

Morus alba L. leaves has been used in fork medicine for the treatment of beriberi, edema, and diabetes and reported to have anti-obesity, anti-diabetic, anti-hypertension, liver protection, antiviral and antimicrobial activities. However, information on its anti-platelet and anti-thrombosis effects is limited. The current study was performed to examine the effects of M. alba leaves ethanol extract (MAE) in platelet aggregation and thrombosis. The anti-platelet activity of MAE was studied using rabbit platelets for in vitro determination of the extract effect on collagen-induced platelet aggregation, thromboxane B2 (TXB2) formation and serotonin secretion. The extract in vivo effects was also examined in arterio-venous shunt thrombus formation in rats. HPLC chromatographic analysis revealed that MAE contained rutin and isoquercitin. MAE significantly and dose dependently inhibited collagen-induced platelet aggregation with the 50 percent inhibitory concentration (IC50) of 0.42 mg/ml. MAE also attenuated serotonin secretion and thromboxane A2 formation. In addition, the extract in vivo activity showed that MAE at 400, 200 and 100 mg/kg significantly and dose-dependently attenuated thrombus formation in rat arterio-venous shunt model by 52.3% (p < 0.001), 28.3% (p < 0.01) and 19.1% (p < 0.05), respectively.

Antithrombotic and antiplatelet activities of Soshiho-tang extract

BackgroundSoshiho-tang (SH; Chinese name, Xiao-Chai-Hu-Tang; Japanese name, Shosaiko-to) is a traditional Korean, Chinese, and Japanese medicine, which has been used to treat various conditions, including hepatitis, liver cirrhosis, and chronic and acute liver disease. SH consists of seven herbal components, of which Scutellaria baicalensis Georgi and Zingiber officinale Roscoe, are reported to have antithrombotic and antiplatelet activities. We investigated the antithrombotic activity of SH, including S. baicalensis and Z. officinale, as an integrative therapy.MethodsTo identify the antithrombotic activity of SH, we used a FeCl3-induced thrombus formation model. The mechanism of SH-mediated antithrombotic activity was assessed by determining platelet aggregation and coagulation times ex vivo, washed platelet aggregation, serotonin secretion, and thromboxane B2 formation.ResultsSH prolonged the occlusion time of thrombus formation when applied in a FeCl3-induced thrombus formation model. SH also inhibited collagen-induced platelet aggregation ex vivo in a concentration-dependent manner; however, it did not affect coagulation. Hence, to identify the antiplatelet effect of SH, we investigated washed platelet aggregations in vitro. SH significantly inhibited various agonist-induced platelet aggregations, and it completely inhibited serotonin secretion and thromboxane B2 formation.ConclusionsThe findings suggest that SH inhibited FeCl3-induced thrombus formation through antiplatelet activity, including inhibition of platelet aggregation, and serotonin and TXB2 production. Thus, SH may be useful as an integrative herbal formula for the treatment of thrombosis.

The 2-arachidonoylglycerol effect on myosin light chain phosphorylation in human platelets

In human platelets the endocannabinoid 2-arachidonoylglycerol (2-AG) stimulates some important pathways leading to thromboxane B2 formation, calcium intracellular elevation, ATP secretion and actin polymerisation. The aim of the present study was to examine the 2-AG effect on myosin light chain (MLC) phosphorylation and to investigate the mechanisms involved. We demonstrated that 2-AG induced a rapid MLC phosphorylation, stimulating both the RhoA kinase (ROCK) and MLC kinase (MLCK) in a dose and time-dependent manner. In addition MLC phosphorylation was strengthened through the MLC phosphatase inhibition. MLC phosphatase inhibition was accomplished through the RhoA/ROCK and protein kinase C mediated phosphorylation of MLC phosphatase inhibiting subunits MYPT1 and CPI-17. The presence of CB1 receptor in human platelets and the involvement of CB1 receptor in MLC phosphorylation and MLC phosphatase inhibition was shown.

Anti‐platelet Activity of Erythro‐(7S,8R)‐7‐acetoxy‐3,4,3′,5′‐tetramethoxy‐8‐O‐4′‐neolignan from Myristica fragrans

Platelets play a critical role in pathogenesis of cardiovascular disorders and strokes. The inhibition of platelet function is beneficial for the treatment and prevention of these diseases. In this study, we investigated the anti-platelet activity of erythro-(7S,8R)-7-acetoxy-3,4,3',5'-tetramethoxy-8-O-4'-neolignan (EATN), a neolignan isolated from Myristica fragrans, using human platelets. EATN preferentially inhibited thrombin- and platelet-activating factor (PAF)-induced platelet aggregation without affecting platelet damage in a concentration-dependent manner with IC50 values of 3.2 ± 0.4 and 3.4 ± 0.3 μM, respectively. However, much higher concentrations of EATN were required to inhibit platelet aggregation induced by arachidonic acid. EATN also inhibited thrombin-induced serotonin and ATP release, and thromboxane B2 formation in human platelets. Moreover, EATN caused an increase in cyclic AMP (cAMP) levels and attenuated intracellular Ca(2+) mobilization in thrombin-activated human platelets. Therefore, we conclude that the inhibitory mechanism of EATN on platelet aggregation may increase cAMP levels and subsequently inhibit intracellular Ca(2+) mobilization by interfering with a common signaling pathway rather than by directly inhibiting the binding of thrombin or PAF to their receptors. This is the first report of the anti-platelet activity of EATN isolated from M. fragrans.

Nattokinase improves blood flow by inhibiting platelet aggregation and thrombus formation

The effects of nattokinase on the in vitro platelet aggregation and in vivo thrombosis were investigated in comparison with aspirin. Rabbit platelet-rich plasma was incubated with nattokinase and aggregation inducers collagen and thrombin, and the platelet aggregation rate was analyzed. Nattokinase significantly inhibited both the collagen- and thrombin-induced platelet aggregations. Nattokinase also reduced thromboxane B2 formation from collagen-activated platelets in a concentration-dependent manner. Rats were orally administered with nattokinase for 1 week, and their carotid arteries were exposed. Arterial thrombosis was induced by applying 35% FeCl3-soaked filter paper for 10 min, and the blood flow was monitored with a laser Doppler probe. Nattokinase delayed the FeCl3-induced arterial occlusion in a dose-dependent manner, doubling the occlusion time at 160 mg/kg. In addition, a high dose (500 mg/kg) of nattokinase fully prevented the occlusion, as achieved with aspirin (30 mg/kg). The results indicate that nattokinase extracted from fermented soybean inhibit platelet aggregation by blocking thromboxane formation, and thereby delay thrombosis following oxidative arterial wall injury. Therefore, it is suggested that nattokinase could be a good candidate without adverse effects for the improvement of blood flow.

The anti-aggregation effects of ondansetron on platelets involve IP3 signaling and MAP kinase pathway, but not 5-HT3-dependent pathway

Ondansetron is a 5-HT3 receptor antagonist with potent antiemetic, analgesic, and antiphlogistic effects. Literature concerning 5-HT3 antagonists on platelets is limited. In this report we examined the pharmacological effects of ondansetron on human washed platelets. Platelet aggregation induced by thrombin (0.1U/mL), collagen (2μg/mL), arachidonic acid (0.5mM), ADP (10μM), or U46619 (2μM) was observed. The effects of ondansetron on platelet aggregation and ATP release were investigated at different concentrations. Cytosolic Ca2+ influx concentration, TXB2, IP3, and the levels of cAMP and cGMP were monitored, and flow cytometric analysis and immunoblotting were performed to investigate downstream signaling components. Our results showed that ondansetron, in a concentration-dependent manner, inhibited agonist-induced platelet aggregation. At 75μM, ondansetron significantly attenuated intracellular Ca2+ mobilization, thromboxane B2 formation, and ATP release by human washed platelets activated by thrombin, collagen, or U46619, whereas it only partially attenuated arachidonic acid-driven platelet activation. Administration of ondansetron resulted in attenuated IP3 production in the washed platelets stimulated by thrombin, as determined by reduced IP1 levels, as well as diminished p38 and ERK2 phosphorylation in response to thrombin. No effect of ondansetron on the levels of either cAMP or cGMP in washed platelets was observed. Furthermore, ondansetron-mediated inhibition of platelet aggregation was not impacted by SR 57227A, the 5-HT3 agonist. Thus, rather than involving the 5-HT3-dependent pathway, the negative effect of ondansetron on platelet aggregation is instead manifested through the attenuation of agonist-induced IP3 production and MAPK (p38 and ERK2) phosphorylation that results in suppressed intracellular Ca2+ mobilization, TXB2 formation, and ATP release.

The antiplatelet activity of magnolol is mediated by PPAR-β/γ

Activation of peroxisome proliferator-activated receptor (PPAR) isoforms (α, β/δ, and γ) is known to inhibit platelet aggregation. In the present study, we examined whether PPARs-mediated pathways contribute to the antiplatelet activity of magnolol, a compound purified from Magnolia officinalis. Magnolol (20–60μM) dose-dependently enhanced the activity and intracellular level of PPAR-β/γ in platelets. In the presence of selective PPAR-β antagonist (GSK0660) or PPAR-γ antagonist (GW9662), the inhibition of magnolol on collagen-induced platelet aggregation and intracellular Ca2+ mobilization was significantly reversed. Moreover, magnolol-mediated up-regulation of NO/cyclic GMP/PKG pathway and Akt phosphorylation leading to increase of eNOS activity were markedly abolished by blocking PPAR-β/γ activity. Additionally, magnolol significantly inhibited collagen-induced PKCα activation through a PPAR-β/γ and PKCα interaction manner. The arachidonic acid (AA) or collagen-induced thromboxane B2 formation and elevation of COX-1 activity caused by AA were also markedly attenuated by magnolol. However, these above effects of magnolol on platelet responses were strongly reduced by simultaneous addition of GSK0660 or GW9662, suggesting that PPAR-β/γ-mediated processes may account for magnolol-regulated antiplatelet mechanisms. Similarly, administration of PPAR-β/γ antagonists remarkably abolished the actions of magnolol in preventing platelet plug formation and prolonging bleeding time in mice. Taken together, we demonstrate for the first time that the antiplatelet and anti-thrombotic activities of magnolol are modulated by up-regulation of PPAR-β/γ-dependent pathways.

Antiaggregatory effect of midazolam on human platelets during monitored anesthesia care for trans-vaginal oocyte retrieval

BackgroundMidazolam plays a major role in sedation and large doses might be used under certain circumstances. Trans-vaginal oocyte retrieval is one of the most painful procedures in which monitored anesthesia care (MAC) is needed. The mechanism by which midazolam exerts anti-aggregation of human platelets is still unclear.This work aimed to investigate the in vivo suppressing effect of midazolam on human platelet aggregation.MethodsSixty adult females ASA I–II, scheduled for trans-vaginal ultrasound oocyte retrieval by combined intravenous midazolam sedation with paracervical local nerve block were included. At the end of the procedure, it was found that the range of total midazolam consumption was 4.9–9 mg. Thereby, patients were divided into three groups according to the total consumption of midazolam: Group I (4.9–6.2 mg), Group II (6.3–7.6 mg), Group III (7.7–9 mg). Patients who needed other drugs for sedation were excluded. Pre- and post-operative Bleeding Time (BT) were recorded. Two blood samples were collected from each patient to test the inhibitory effect of midazolam on platelet aggregation. Platelet aggregation was tested using platelet-aggregometer. ELISA was used to measure thromboxane B2 formation. Flowcytometry was used to evaluate whether glycoprotein IIb–IIIa complex is the receptor site for the antiplatelet action of midazolam.ResultsOnly 51 patients completed the study: Group I (n = 16), Group II (n = 24), and Group III (n = 11). Bleeding Time (BT) showed significant prolongation in group III compared to basal levels. Midazolam suppressed platelet aggregation in a dose-dependent manner as detected by aggregometer. Glycoprotein IIb–IIIa complex is not its site of action as shown by flowcytometric analysis. Lastly, thromboxane B2 was significantly inhibited by midazolam.ConclusionThis study revealed that midazolam dose-dependently inhibits platelet aggregation by a mechanism not involving the binding of glycoprotein IIb–IIIa complex (fibrinogen receptor). It was also found that midazolam inhibits thromboxane A2 formation.

First Report of Transheterozygosity in a Patient with An Inherited Platelet Bleeding Disorder Due to Mutations in the Thromboxane A2 Receptor (TBXA2R) and cyclooxygenase1 (PTGS1),

Abstract 3260Platelet aggregation by thromboxane (TBXA2) stimulation of its G protein-coupled receptor TXA2R is initiated after conversion of arachidonic acid (AA) into prostaglandin H2 (PGH2) by cyclooxygenase1 (PTGS1) and subsequently by conversion of PGH2 into TXA2 by thromboxane synthase (TBXAS1). Hirata et al (JCI, 1994) reported the first TBXA2R mutation that resulted in reduced platelet responses to U46619 and low AA concentrations in subjects with a heterozygous R60L mutation. This functional defect in combination with mild clinical bleeding problems was only described for the one patient that was homozygous for this mutation. A second TBXA2 patient with an obvious bleeding diathesis carried a heterozygous D304N mutation but it was reported that this variant by itself could not explain the bleeding phenotype as other family members heterozygous for D304N presented with abnormal aggregation responses but no bleeding problems (Mumford, Blood, 2010). Functional SNPs in PTGS1 were described in pharmacogenetic studies including the L237M variant with 50% reduced COX1 metabolic activity but its effect on platelet function was not studied (Lee CR, Pharmacogenet Genomics, 2007).We here describe a 6-year old patient with ecchymosis, easy bruising and important post-traumatic bleeding complications after adenotonsillectomy and circumcision. The boy presents with normal coagulation parameters, normal platelet count and MPV, structurally normal platelets, normal ATP secretion by collagen, and the PFA100 closure time was normal for Col/Epi and mildly prolonged for Col/ADP. Platelet aggregation studies further showed an absent response to 1 mM AA as determined on different occasions, a reduced but not absent response to U46619 and a normal activation with ADP, ristocetin and Horm collagen. His parents and sister presented with increased sensitivity for ecchymoses but none had severe clinical bleeding problems and their platelets showed normal aggregation responses except for the father and sister with a reduced though not absent response to AA. Thromboxane B2 formation was determined and found to be normal in basal (plasma) and maximal stimulated (serum) conditions. In contrast, TXB2 levels were decreased after activation with U46619 for the patient but also for the father and sister compared to the control or mother. Activation with AA also resulted in reduced TXB2 levels for the patient and mildly reduced levels for all other family member compared to controls. This strongly suggests the presence of an autosomal recessive disorder. The TBXAS1, PTGS1 and TBXA2R genes were sequenced for the patient and we identified two heterozygous mutations in separate genes being R60H in TXBA2R and the functional L237M variant in PTGS1. Interestingly, his mother carried the L237M variant while R60H was present in father and sister with similar functional platelet defects as earlier described for the other heterogenous TBXA2R mutations but no clinical bleeding symptoms. To our knowledge, this is the first case of transheterozygosity for mutations explaining an autosomal recessive bleeding disorder. We hypothesize that this pattern of inheritance might be more common than expected and therefore this possibility should be taken into account when analyzing patients in the future using exome or genome wide sequencing platforms. Disclosures:No relevant conflicts of interest to declare.

Inhibition of platelet thromboxane formation and phosphoinositides breakdown by diisoeugenol.

Diisoeugenol inhibited the platelet aggregation and ATP release of rabbit platelets caused by ADP, arachidonic acid, platelet-activating factor (PAF), collagen and thrombin. Prolongation of the incubation time of platelets with diisoeugenol did not cause further inhibition and the aggregability of platelets could not be restored after washing. In human platelet-rich plasma, diisoeugenol inhibited the biphasic aggregation and ATP release induced by adrenaline and ADP in a concentration-dependent manner. Thromboxane B2 formation caused by arachidonic acid, collagen and thrombin was markedly inhibited by diisoeugenol in a concentration-dependent manner. Diisoeugenol also inhibited the formation of inositol monophosphate caused by collagen, PAF and thrombin. The cAMP level of washed platelets was not changed by diisoeugenol. It is concluded that the antiplatelet effect of diisoeugenol is due to the inhibition of thromboxane formation and phosphoinositides breakdown.

Antiplatelet effects of some aporphine and phenanthrene alkaloids in rabbits and man.

Two aporphines (boldine and laurolitsine) and five phenanthrene alkaloids (litebamine, secoboldine, N-cyanosecoboldine, N-methylsecoglaucine and N-methylsecopredicentrine) were evaluated in-vitro for their ability to inhibit platelet aggregation. All seven alkaloids inhibited aggregation of rabbit platelets and inhibited the release of ATP induced by arachidonic acid and collagen in rabbit platelets. Those aggregations induced by platelet-activating factor (PAF), thrombin, U46619 and ADP were inhibited by the three N-substituted secoboldine derivatives only. Thromboxane B2 formation caused by arachidonic acid was also suppressed by these compounds. They did not affect the generation of [3H]inositol monophosphate caused by collagen, PAF and thrombin in the presence of indomethacin. Platelet cyclic AMP level was unaffected by litebamine, but was increased by N-methylsecoglaucine. Litebamine suppressed the secondary aggregation, but not the primary aggregation, induced by ADP and adrenaline in platelet-rich plasma from man, whereas N-methylsecoglaucine inhibited both primary and secondary aggregation. It is concluded that the antiplatelet effect of these seven aporphine and phenanthrene alkaloids is mainly a result of inhibition of thromboxane A2 formation; N-methylsecoglaucine has additional antiplatelet activity as a result of increasing the levels of platelet cyclic AMP.

Mechanism of action of p-chlorobiphenyl on the inhibition of platelet aggregation.

p-Chlorobiphenyl (1-50 microM) concentration-dependently inhibited the aggregation and release reaction of rabbit washed platelets induced by arachidonic acid and collagen, but not those induced by platelet-activating factor (PAF), U46619 and thrombin. The IC50 values of p-chlorobiphenyl on the arachidonic acid and collagen-induced platelet aggregation were 2.9 +/- 0.5 and 12.8 +/- 2.3 microM, respectively. The formation of both platelet thromboxane B2 and prostaglandin D2 caused by arachidonic acid was inhibited by p-chlorobiphenyl concentration-dependently. In myo-[3H]inositol-labeled and fura-2-loaded platelets. [3H]inositol monophosphate generation and the rise in intracellular Ca2- stimulated by arachidonic acid were inhibited by p-chlorobiphenyl. In human platelet-rich plasma, p-chlorobiphenyl and indomethacin prevented the secondary aggregation and blocked ATP release from platelets induced by adenosine 5'-diphosphate and adrenaline without affecting the primary aggregation. It is concluded that p-chlorobiphenyl may be a cyclo-oxygenase inhibitor and its antiplatelet action is mainly due to the inhibition of thromboxane formation.

Antiplatelet effect of gingerol isolated from Zingiber officinale.

The purpose of this investigation was to determine the antiplatelet mechanism of gingerol. Gingerol concentration-dependently (0.5-20 microM) inhibited the aggregation and release reaction of rabbit washed platelets induced by arachidonic acid and collagen, but not those induced by platelet-activating factor (PAF), U46619 (9,11-dideoxy-9 alpha,11 alpha-methano-epoxy-PGF2 alpha) and thrombin. Gingerol also concentration-dependently (0.5-10 microM) inhibited thromboxane B2 and prostaglandin D2 formation caused by arachidonic acid, and completely abolished phosphoinositide breakdown induced by arachidonic acid but had no effect on that of collagen, PAF or thrombin even at concentrations as high as 300 microM. In human platelet-rich plasma, gingerol and indomethacin prevented the secondary aggregation and blocked ATP release from platelets induced by adenosine 5'-diphosphate (ADP, 5 microM) and adrenaline (5 microM) but had no influence on the primary aggregation. The maximal antiplatelet effect was obtained when platelets were incubated with gingerol for 30 min and this inhibition was reversible. It is concluded that the antiplatelet action of gingerol is mainly due to the inhibition of thromboxane formation.

Bakkenolide G, a natural PAF-receptor antagonist.

Because platelet-activating factor (PAF, 1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine) participates in many physiopathological responses, including inflammatory reaction, endotoxic shock, allergic diseases and platelet aggregation, PAF-receptor antagonists are important in the treatment of these diseases. A biologically active compound, bakkenolide G, extracted from the plant Petasites formosanus selectively and concentration-dependently inhibited PAF-induced platelet aggregation and ATP release. The IC50 of bakkenolide G for PAF (2 ng mL(-1))-induced platelet aggregation was 5.6 +/- 0.9 microM. Bakkenolide G also concentration-dependently inhibited PAF-induced intracellular signal transductions, including thromboxane B2 formation, and increased intra-cellular calcium concentration and phosphoinositide breakdown without affecting those caused by thrombin (0.1 units mL(-1)), collagen (10 microg mL(-1)), arachidonic acid (100 microM) and U46619 (1 microM). Bakkenolide G shifted the concentration-response curves of PAF-induced platelet aggregation parallel to the right; the Schild plot slope and the pA2 value were 1.31 +/- 0.31 and 6.21 +/- 0.75, respectively. Moreover, bakkenolide G concentration-dependently competed with [3H]PAF binding to platelets, with an IC50 value of 2.5 +/- 0.4 microM. These data strongly indicate that bakkenolide G is a specific PAF-receptor antagonist as an antiplatelet aggregatory agent.