Inhibition of ex-vivo PAF-induced platelet aggregation by the PAF-antagonist RP 48740: relationship to plasma concentrations in healthy volunteers

1991 ◽  
Vol 41 (2) ◽  
Author(s):  
J.L. Pinquier ◽  
P. Sedivy ◽  
R. Bruno ◽  
F. Bompart ◽  
J. Gregoire ◽  
...  
Keyword(s):  
Platelet Aggregation ◽  
Healthy Volunteers ◽  
Ex Vivo ◽  
Plasma Concentrations

INITIAL STUDIES IN MAN WITH A NOVEL THROMBOXANE RECEPTOR BLOCKING DRUG GR32191

1987 ◽  
Author(s):  
M Thomas ◽  
P Lumley ◽  
P Ballard ◽  
J R O'Brien
Keyword(s):  
Platelet Aggregation ◽  
Bleeding Time ◽  
Ex Vivo ◽  
Plasma Concentrations ◽  
Blocking Drug ◽  
Double Blind ◽  
Receptor Blocking ◽  
Thromboxane Receptor ◽  
Pre Treatment ◽  
Induced Aggregation

In-vitro GR32191 is a potent and specific thromboxane receptor blocking drug on platelets, and vascular and airways smooth muscle (Lumley et al this meeting). We have undertaken studies in healthy male subjects (n) to examine the effects of oral GR32191 upon platelet aggregation ex-vivo and template bleeding time. Platelet aggregation was monitored in whole blood by counting platelets electronically. Concentration-effect curves to U-46619 and ADP were constructed prior to and following drug or placebo. The degree of rightward displacement of a curve due to treatment was expressed as a concentration-ratio (CR) which was calculated at the 50% aggregation level (ECso post-treatment ECso pre-treatment). Plasma concentrations of GR32191 were determined by h.p.l.c. After single doses of GR32191 mean peak CR's of 8 and 80 were achieved with 0.125 and 0.25mg/kg (n=4) and values of 74 and 234 with 0.5 and lmg/kg (n=4). Peak effects were seen within 2 hours of dosing while activity was still present between 8 and 24 hours. ADP-induced aggregation was unaffected by drug (CR<2) and placebo was without significant effect upon the sensitivity to either aggregating agent (CR<2). GR32191 was rapidly absorbed and the plasma elimination half-life was about 2 hours. GR32191 17.5mg 12-hourly for 10 days (n=6) produced a progressive antagonism of U-46619 induced aggregation which resulted in a large continuous blockade in all subjects (range of 12htrough CR's 85 to 287). However, plasma concentrations of GR32191 did not accumulate on repeated administration. In a double-blind, placebo-controlled, cross-over study (n=16), a statistically significant (p= 0.002) increase in bleeding time was seen following treatment with GR32191 40mg twice daily for 7 days (pre-treatment mean 3.79 min, post-placebo mean 3.47 min, post-GR32191 mean 5.42 min). Rectal bleeding (n=l) has occurred with GR32191 but otherwise tolerability has been good. No drug related changes have been seen in routine laboratory safety screens. Clinical studies are in progress.

Inhibitory Effect of Piracetam on Platelet-rich Thrombus Formation in an Animal Model

1998 ◽  
Vol 79 (01) ◽  
pp. 222-227 ◽  
Author(s):  
F. Stockmans ◽  
W. Deberdt ◽  
Å. Nyström ◽  
E. Nyström ◽  
J. M. Stassen ◽  
...  
Keyword(s):  
Platelet Aggregation ◽  
Ex Vivo ◽  
Peak Plasma ◽  
Thrombus Formation ◽  
Plasma Concentrations ◽  
Inhibitory Effect ◽  
Human Platelets ◽  
Cell Deformability

SummaryIntravenous administration of piracetam to hamsters reduced the formation of a platelet-rich venous thrombus induced by a standardised crush injury, in a dose-dependent fashion with an IC50 of 68 ± 8 mg/kg. 200 mg/kg piracetam also significantly reduced in vivo thrombus formation in rats. However, in vitro aggregation of rat platelets was only inhibited with piracetam-concentrations at least 10-fold higher than plasma concentrations (6.2 ± 1.1 mM) obtained in the treated animals. No effects were seen on clotting tests.In vitro human platelet aggregation, induced by a variety of agonists, was inhibited by piracetam, with IC50’s of 25-60 mM. The broad inhibition spectrum could be explained by the capacity of piracetam to prevent fibrinogen binding to activated human platelets. Ex vivo aggregations and bleeding times were only minimally affected after administration of 400 mg/kg piracetam i.v. to healthy male volunteers, resulting in peak plasma levels of 5.8 ± 0.3 mM.A possible antiplatelet effect of piracetam could be due to the documented beneficial effect on red blood cell deformability leading to a putative reduction of ADP release by damaged erythrocytes. However similarly high concentrations were needed to prevent stirring-induced “spontaneous” platelet aggregation in human whole blood.It is concluded that the observed antithrombotic action of piracetam cannot satisfactorily be explained by an isolated direct effect on platelets. An additional influence of piracetam on the rheology of the circulating blood and/or on the vessel wall itself must therefore be taken into consideration.

General Medicine: Effects of Aspirin on Platelet Aggregation in Smokers and Nonsmokers

1997 ◽  
Vol 31 (3) ◽  
pp. 290-293 ◽  
Author(s):  
Clarence Chant ◽  
Susan C Fagan ◽  
Sheena K Aurora ◽  
Barry E Gidal ◽  
Rajiv Joseph
Keyword(s):  
Platelet Aggregation ◽  
Healthy Volunteers ◽  
Whole Blood ◽  
Ex Vivo ◽  
Smoking Status ◽  
Outcome Measurement ◽  
Tertiary Care ◽  
Atp Release ◽  
General Medicine ◽  
Blood Platelet

Objective To assess the relative antiaggregatory ability of aspirin on platelets of smoking and nonsmoking healthy volunteers. Design Prospective, randomized, crossover study. Setting Tertiary-care teaching institution. Subjects Eighteen healthy smoking and nonsmoking male volunteers. Interventions Each subject received aspirin 325 mg or ticlopidine 250 mg bid as an active control for 7 days in a crossover manner separated by a 1-month washout period. Whole blood platelet aggregation was measured on four occasions, twice at baseline and once after each drug treatment. Outcome Measurement Whole blood ex vivo platelet aggregation in terms of impedance (Ω) and adenosine triphosphate (ATP) release (nmol), as assessed using Lumi-aggregometry. Results Aspirin was associated with significantly less ATP release in both smokers (p = 0.01) and nonsmokers (p = 0.003). No significant differences in platelet aggregation were found between smokers and nonsmokers at baseline or with any treatment phases. Sixty-seven percent and 17% of volunteers receiving ticlopidine and aspirin, respectively, reported adverse effects. Conclusions Twice-daily administration of aspirin for 7 days to healthy volunteers was well tolerated and also reduced platelet aggregation significantly regardless of smoking status.

scholarly journals Neutrophils Isolated from Septic Patients Exhibit Elevated Uptake of Vitamin C and Normal Intracellular Concentrations despite a Low Vitamin C Milieu

Antioxidants ◽  
2021 ◽  
Vol 10 (10) ◽  
pp. 1607
Author(s):  
Anitra C. Carr ◽  
Stephanie Bozonet ◽  
Juliet Pullar ◽  
Emma Spencer ◽  
Patrice Rosengrave ◽  
...  
Keyword(s):  
Vitamin C ◽  
Healthy Volunteers ◽  
Ex Vivo ◽  
Plasma Concentrations ◽  
Dehydroascorbic Acid ◽  
Neutrophil Function ◽  
Healthy Controls ◽  
Lower Plasma ◽  
Circulating Cells ◽  
Plasma Ascorbate

Vitamin C (ascorbate) plays an important role in neutrophil function and is accumulated by the cells either directly via vitamin C transporters (SVCT) or indirectly following oxidation to dehydroascorbic acid. Septic patients are known to have significantly depleted plasma ascorbate status, but little is known about the ascorbate content of their circulating cells. Therefore, we assessed the ascorbate concentrations of plasma, leukocytes and erythrocytes from septic patients and compared these to healthy controls. Non-fasting blood samples were collected from healthy volunteers (n = 20) and critically ill patients with sepsis (n = 18). The ascorbate content of the plasma and isolated neutrophils and erythrocytes was measured using HPLC and plasma myeloperoxidase concentrations were determined using ELISA. Ex vivo uptake of ascorbate and dehydroascorbic acid by neutrophils from septic patients was also assessed. Neutrophils isolated from septic patients had comparable intracellular ascorbate content to healthy volunteers (0.33 vs. 0.35 nmol/106 cells, p > 0.05), despite significantly lower plasma concentrations than the healthy controls (14 vs. 88 µmol/L, p < 0.001). In contrast, erythrocytes from septic patients had significantly lower intracellular ascorbate content than healthy controls (30 vs. 69 µmol/L, p = 0.002), although this was 2.2-fold higher than the matched plasma concentrations in the patients (p = 0.008). Higher concentrations of myeloperoxidase, a source of reactive oxygen species, were observed in the septic patients relative to healthy controls (194 vs. 14 mg/mL, p < 0.0001). In contrast to neutrophils from healthy volunteers, the neutrophils from septic patients demonstrated elevated uptake of extracellular ascorbate. Overall, neutrophils from septic patients exhibited comparable intracellular ascorbate content to those from healthy controls, despite the patients presenting with hypovitaminosis C. The mechanisms involved are currently uncertain, but could include increased generation of dehydroascorbic acid in septic patients, enhanced basal activation of their neutrophils or upregulation of their vitamin C transporters.

Phospholipase C from Clostridium Perfringens Induces Human Platelet Aggregation in Plasma

1988 ◽  
Vol 59 (02) ◽  
pp. 236-239 ◽  
Author(s):  
Giovanna Barzaghi ◽  
Chiara Cerletti ◽  
Giovanni de Gaetano
Keyword(s):  
Platelet Aggregation ◽  
Receptor Antagonist ◽  
Phospholipase C ◽  
Clostridium Perfringens ◽  
Human Platelet ◽  
Ex Vivo ◽  
Platelet Rich Plasma ◽  
Platelet Activating Factor ◽  
Inhibitory Effect ◽  
Thromboxane Receptor Antagonist

SummaryWe studied the aggregating effect of different concentrations of phospholipase C (PLC) (extracted from Clostridium perfringens) on human platelet-rich plasma (PRP). PRP was preincubated with PLC for 3 min at 37° C and the platelet aggregation was followed for 10 min. The threshold aggregating concentration (TAG) of PLC was 3-4 U/ml.We also studied the potentiation of PLC with other stimuli on platelet aggregation. Potentiating stimuli, such as arachidonic acid (AA), ADP. Platelet Activating Factor (PAF) and U-46619 (a stable analogue of cyclic endoperoxides) were all used at subthreshold concentrations. We also studied the possible inhibitory effect of aspirin, apyrase, TMQ, a prostaglandin endoper- oxide/thromboxane receptor antagonist and BN-52021, a PAF receptor antagonist. Only aspirin and apyrase were able to reduce aggregation induced by PLC alone and PLC + AA and PLC + ADP respectively. TMQ and BN-52021 were inactive. In ex vivo experiments oral aspirin (500 mg) partially inhibited platelet aggregation induced by PLC alone, PLC + AA and PLC + ADP 2 and 24 h after administration. Aspirin 20 mg for 7 days also reduced aggregation induced by PLC + AA.

Antithrombotic Effects and Bleeding Time Prolongation with Synthetic Platelet GPIIb/llla Inhibitors in Animal Models of Platelet-Mediated Thrombosis

1994 ◽  
Vol 71 (01) ◽  
pp. 095-102 ◽  
Author(s):  
Désiré Collen ◽  
Hua Rong Lu ◽  
Jean-Marie Stassen ◽  
Ingrid Vreys ◽  
Tsunehiro Yasuda ◽  
...  
Keyword(s):  
Platelet Aggregation ◽  
Bleeding Time ◽  
Bolus Injection ◽  
Cell Injury ◽  
Ex Vivo ◽  
Thrombus Formation ◽  
Femoral Vein ◽  
Thrombotic Occlusion ◽  
Antithrombotic Effects

SummaryCyclic Arg-Gly-Asp (RGD) containing synthetic peptides such as L-cysteine, N-(mercaptoacetyl)-D-tyrosyl-L-arginylglycyl-L-a-aspartyl-cyclic (1→5)-sulfide, 5-oxide (G4120) and acetyl-L-cysteinyl-L-asparaginyl-L-prolyl-L-arginyl-glycyl-L-α-aspartyl-[0-methyltyrosyl]-L-arginyl-L-cysteinamide, cyclic 1→9-sulfide (TP9201) bind with high affinity to the platelet GPIIb/IIIa receptor.The relationship between antithrombotic effect, ex vivo platelet aggregation and bleeding time prolongation with both agents was studied in hamsters with a standardized femoral vein endothelial cell injury predisposing to platelet-rich mural thrombosis, and in dogs with a carotid arterial eversion graft inserted in the femoral artery. Intravenous administration of G4120 in hamsters inhibited in vivo thrombus formation with a 50% inhibitory bolus dose (ID50) of approximately 20 μg/kg, ex vivo ADP-induccd platelet aggregation with ID50 of 10 μg/kg, and bolus injection of 1 mg/kg prolonged the bleeding time from 38 ± 9 to 1,100 ± 330 s. Administration of TP9201 in hamsters inhibited in vivo thrombus formation with ID50 of 30 μg/kg, ex vivo platelet aggregation with an ID50 of 50 μg/kg and bolus injection of 1 mg/kg did not prolong the template bleeding time. In the dog eversion graft model, infusion of 100 μg/kg of G4120 over 60 min did not fully inhibit platelet-mediated thrombotic occlusion but was associated with inhibition of ADP-induccd ex vivo platelet aggregation and with prolongation of the template bleeding time from 1.3 ± 0.4 to 12 ± 2 min. Infusion of 300 μg/kg of TP9201 over 60 min completely prevented thrombotic occlusion, inhibited ex vivo platelet aggregation, but was not associated with prolongation of the template bleeding time.TP9201, unlike G4120, inhibits in vivo platelet-mediated thrombus formation without associated prolongation of the template bleeding time.

Comparative Arterial Antithrombotic Activity of Clopidogrel and Acetyl Salicylic Acid in the Pig

1992 ◽  
Vol 68 (05) ◽  
pp. 500-505 ◽  
Author(s):  
Ch M Samama ◽  
Ph Bonnin ◽  
M Bonneau ◽  
G Pignaud ◽  
E Mazoyer ◽  
...  
Keyword(s):  
Platelet Aggregation ◽  
Femoral Artery ◽  
Bleeding Time ◽  
Ex Vivo ◽  
Flow Reduction ◽  
Cyclic Flow ◽  
Left Femoral Artery ◽  
Before And After ◽  
The Right ◽  
Induced Aggregation

SummaryWe investigated the comparative antithrombotic properties of clopidogrel, an analogue of ticlopidine, and aspirin, using the Folts' model on femoral arteries in 22 pigs. On each animal, clopidogrel or aspirin were used to treat the thrombotic process on the left femoral artery and to prevent this process on the right femoral artery. Sequentially: an injury and stenosis were carried out on the left femoral artery; the thrombotic process was monitored with a Doppler during a 30-min observation period for cyclic flow reductions or permanent cessation of flow; after the first cyclic flow reduction occurred, clopidogrel (5 mg kg-1) or aspirin (2.5, 5, 100 mg kg-1) were injected intravenously; if cyclic flow reductions were abolished, epinephrine (0.4 µg kg-1 min-1) was injected to try to restore cyclic flow reductions and/or permanent cessation of flow; then injury and stenosis were applied on the right femoral artery. Before and after injection of clopidogrel or aspirin, ear immersion bleeding times and ex-vivo platelet aggregation were performed. Clopidogrel (n = 7) abolished cyclic flow reductions in all animals and epinephrine did not restore any cyclic flow reduction. On the right femoral artery, cyclic flow reductions were efficiently prevented, even for two injuries. Basal bleeding time (5 min 28) was lengthened (>15 min, 30 min after clopidogrel and remained prolonged even after 24 h). ADP-induced platelet aggregation was inhibited (more than 78%). Comparatively, aspirin had a moderate and no dose-dependent effect. Aspirin 2.5 mg kg-1 (n = 6) abolished cyclic flow reductions in 2 animals, CFR reoccurred spontaneously in one animal and epinephrine restored it in a second animal. Aspirin 5 mg kg-1 (n = 6) abolished cyclic flow reductions in only 3 animals and epinephrine always restored it. Aspirin 100 mg kg-1 (n = 3) was unable to abolish cyclic flow reductions. On the right femoral artery, aspirin did not significantly prevent cyclic flow reductions which occurred in all animals after one (n = 14) or two injuries (n = 1), except for one animal. Basal bleeding time was lengthened but it shortened rapidly, reaching its basal value after 24 h. ADP-induced aggregation was not significantly inhibited, whereas arachidonic acid induced aggregation was always inhibited. Clopidogrel appears as a more potent antithrombotic drug than aspirin in this model, in treating and preventing spontaneous or epinephrine-induced cyclic flow reductions and lengthening bleeding time.

Reaction of Acetaldehyde with Human Platelets

1992 ◽  
Vol 67 (01) ◽  
pp. 126-130 ◽  
Author(s):  
Olivier Spertini ◽  
Jacques Hauert ◽  
Fedor Bachmann
Keyword(s):  
Platelet Aggregation ◽  
Inhibitory Action ◽  
Ex Vivo ◽  
Platelet Rich Plasma ◽  
Shape Change ◽  
Reaction Medium ◽  
Human Platelets ◽  
Membrane Glycoproteins ◽  
Neutral Ph

SummaryPlatelet function defects observed in chronic alcoholics are not wholly explained by the inhibitory action of ethanol on platelet aggregation; they are not completely reproduced either in vivo by short-term ethanol perfusion into volunteers or in vitro by the addition of ethanol to platelet-rich plasma. As acetaldehyde (AcH) binds to many proteins and impairs cellular activities, we investigated the effect of this early degradation product of ethanol on platelets. AcH formed adducts with human platelets at neutral pH at 37° C which were stable to extensive washing, trichloracetic acid hydrolysis and heating at 100° C, and were not reduced by sodium borohydride. The amount of platelet adducts formed was a function of the incubation time and of the concentration of AcH in the reaction medium. At low AcH concentrations (<0.2 mM), platelet bound AcH was directly proportional to the concentration of AcH in the reaction medium. At higher concentrations (≥0.2 mM), AcH uptake by platelets tended to reach a plateau. The amount of adducts was also proportional to the number of exposures of platelets to pulses of 20 pM AcH.AcH adducts formation severely impaired platelet aggregation and shape change induced by ADP, collagen and thrombin. A positive correlation was established between platelet-bound AcH and inhibition of aggregation.SDS-PAGE analysis of AcH adducts at neutral pH demonstrated the binding of [14C]acetaldehyde to many platelet proteins. AcH adduct formation with membrane glycoproteins, cytoskeleton and enzymes might interfere with several steps of platelet activation and impair platelet aggregation.This in vitro study shows that AcH has a major inhibitory action on platelet aggregation and may account for the prolonged ex vivo inhibition of aggregation observed in chronic alcoholics even in the absence of alcoholemia.

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