Effect of New Synthetic Heparin Mimetics on Whole Blood Thrombin Generation In Vivo and In Vitro in Rats

2002 ◽  
Vol 87 (02) ◽  
pp. 238-244 ◽  
Author(s):  
J.P. Hérault ◽  
A. Bernat ◽  
C. Gaich ◽  
J.M. Herbert
Keyword(s):  
Venous Thrombosis ◽  
Charge Density ◽  
Whole Blood ◽  
Thrombin Generation ◽  
Platelet Rich Plasma ◽  
Lag Time ◽  
Drug Candidate ◽  
Platelet Factor

SummaryThe effect of new heparin mimetics (synthetic oligosaccharides) was studied in vitro with regard to thrombin generation (TG) in rat platelet rich plasma (PRP) and whole blood (WB) and in vivo on stasis-induced venous thrombosis in the rat.TG in PRP and in WB was highly dependent on platelet count and strongly influenced by the haematocrit. The peak of TG appeared to be significantly higher in WB than in PRP whereas the endogenous thrombin potential (ETP) was not significantly different under either condition.The effect of hirudin, the synthetic pentasaccharide SR90107/ Org31540 (SP) and heparin were measured on TG in PRP and WB. We then compared the effect of two new synthetic heparin mimetics (SR121903A and SanOrg123781) with potent and comparable antithrombin (AT) mediated activity against factor Xa and thrombin. These two compounds were made of a pentasaccharide with a high affinity to AT, prolonged at the non-reducing end by an oligosaccharide chain recognised by thrombin. In SR121903A, the charge density and charge distribution was analogous to that of heparin whereas in SanOrg123781 the charges were only located on the last 5 saccharides of the non-reducing end of the molecule. In PRP and in WB, SR121903A acted on the lag time and on the AUC whereas SanOrg123781 inhibited thrombin formation with no effect on the lag time. SanOrg123781 was more potent in inhibiting TG than SR121903A. This difference was due to the structures of the compounds that differed in their ability to be neutralised by platelet factor 4. The antithrombotic effect of the two compounds was examined in a venous thrombosis model in rats. We observed that SanOrg123781 was more active than SR121903A and heparin.Taken together, these results indicate that the activity of oligosaccharides is greatly influenced by the global charge density of the molecule and show that SanOrg123781 is a potent and promising antithrombotic drug candidate.

Effect of SR121566A, a Potent GP IIb-IIIa Antagonist on Platelet-mediated Thrombin Generation In Vitro and In Vivo

1998 ◽  
Vol 79 (02) ◽  
pp. 383-388 ◽  
Author(s):  
J. P. Herault ◽  
V. Peyrou ◽  
P. Savi ◽  
A. Bernat ◽  
J. M. Herbert
Keyword(s):  
Arachidonic Acid ◽  
Platelet Aggregation ◽  
Venous Thrombosis ◽  
Thrombin Generation ◽  
Platelet Rich Plasma ◽  
Venous Stasis ◽  
Lag Phase ◽  
Dependent Manner

SummaryThe effect of SR121566A, a new non-peptide GP IIb-IIIa antagonist was studied in vitro with regard to thrombin generation in platelet rich plasma and in vivo on stasis-induced venous thrombosis in the rabbit. SR121566A inhibited ADP-, arachidonic acid- and collagen-induced human platelet aggregation with IC50 values of 46 ± 7.5, 56 ± 6 and 42 ± 3 nM, respectively. In the same experimental conditions, SR121566A strongly inhibited thrombin generation triggered by low concentrations of tissue factor. SR121566A reduced in a dose-dependent manner both the area under the curve and the thrombin peak concentration but did not affect the lag phase (defined as the time until 10 nM thrombin was generated). Aspirin (100 µg/ml) did not affect thrombin generation.One hour after intravenous administration to rabbits, SR121566A exhibited a potent ex vivo inhibitory effect against ADP-, arachidonic acid- and collagen-induced platelet aggregation. The ID50 were 0.6 ± 0.25, 0.7 ± 0.08 and 0.13 ± 0.08 mg/kg, respectively. The ability of aspirin and SR121566A to affect venous stasis was determined in a stasis-induced venous thrombosis model in rabbits under high and low thrombogenic challenges. While aspirin was ineffective in both conditions, SR121566A significantly inhibited thrombus formation under low thrombogenic challenge demonstrating for the first time that a potent non-peptide platelet GP IIb-IIIa antagonist inhibits thrombin generation in vivo and exhibits a strong antithrombotic effect with regard to stasis-induced venous thrombosis. These results therefore confirm the existence of a close relationship between platelet activation and thrombin generation leading to blood coagulation but also emphasise the key role of platelets in the development of venous thrombosis, most likely through activation of the GP IIb-IIIa complex.

Comparison of the effect of fondaparinux and enoxaparin on thrombin generation during in-vitro clotting of whole blood and platelet-rich plasma

2004 ◽  
Vol 15 (2) ◽  
pp. 149-156 ◽  
Author(s):  
Grigoris T Gerotziafas ◽  
François Depasse ◽  
Tahar Chakroun ◽  
Patrick Van Dreden ◽  
Meyer M Samama ◽  
...  
Keyword(s):  
Whole Blood ◽  
Thrombin Generation ◽  
Platelet Rich Plasma

scholarly journals Candida: Platelet Interaction and Platelet Activity in vitro

2018 ◽  
Vol 11 (1) ◽  
pp. 52-62 ◽  
Author(s):  
Claudia Eberl ◽  
Cornelia Speth ◽  
Ilse D. Jacobsen ◽  
Martin Hermann ◽  
Magdalena Hagleitner ◽  
...  
Keyword(s):  
Whole Blood ◽  
Candida Species ◽  
Platelet Rich Plasma ◽  
Yeast Cells ◽  
Small Subset ◽  
High Morbidity ◽  
Platelet Activity ◽  
Secretory Products

Over the last 2 decades, platelets have been recognized as versatile players of innate immunity. The interaction of platelets with fungal pathogens and subsequent processes may critically influence the clinical outcome of invasive mycoses. Since the role of platelets in Candida infections is poorly characterized and controversially discussed, we studied interactions of human platelets with yeast cells, (pseudo-)hyphae, biofilms and secretory products of human pathogenic Candida species applying platelet rich plasma and a whole blood model. Incubation of Candida with platelets resulted in moderate mutual interaction with some variation between different species. The rate of platelets binding to ­Candida (pseudo-) hyphae and candidal biofilm was comparably low as that to the yeast form. Candida-derived secretory products did not affect platelet activity – neither stimulatory nor inhibitory. The small subset of platelets that bound to Candida morphotypes was consequently activated. However, this did not result in reduced growth or viability of the different Candida species. A whole blood model simulating in vivo conditions confirmed platelet activation in the subpopulation of Candida-bound platelets. Thus, the inability of platelets to efficiently react on Candida presence might favor fungal survival in the blood and contribute to high morbidity of Candida sepsis.

scholarly journals Lipolysis generates platelet dysfunction after in vivo heparin administration

2002 ◽  
Vol 103 (4) ◽  
pp. 433-440 ◽  
Author(s):  
Elijah W. MURIITHI ◽  
Philip R. BELCHER ◽  
Stephen P. DAY ◽  
Mubarak A. CHAUDHRY ◽  
Muriel J. CASLAKE ◽  
...  
Keyword(s):  
Superoxide Dismutase ◽  
Cardiopulmonary Bypass ◽  
Lipoprotein Lipase ◽  
Whole Blood ◽  
Ex Vivo ◽  
Hepatic Lipase ◽  
Platelet Factor 4 ◽  
Platelet Factor

Heparin, when administered to patients undergoing operations using cardiopulmonary bypass, induces plasma changes that gradually impair platelet macroaggregation, but heparinization of whole blood in vitro does not have this effect. The plasma changes induced by heparin in vivo continue to progress in whole blood ex vivo. Heparin releases several endothelial proteins, including lipoprotein lipase, hepatic lipase, platelet factor-4 and superoxide dismutase. These enzymes, which remain active in plasma ex vivo, may impair platelet macroaggregation after in vivo heparinization and during cardiopulmonary bypass. In the present study, proteins were added in vitro to hirudin (200units·ml-1)-anticoagulated blood from healthy volunteers, and the platelet macroaggregatory responses to ex vivo stimulation with collagen (0.6μg·ml-1) were assessed by whole-blood impedance aggregometry. Over a 4h period, human lipoprotein lipase and human hepatic lipase reduced the platelet macroaggregatory response from 17.0±2.3 to 1.5±1.3 and 1.2±0.6Ω respectively (means±S.D.) (both P<0.01; n = 6). Other lipoprotein lipases also impaired platelet macroaggregation, but platelet factor-4 and superoxide dismutase did not. Platelet macroaggregation showed an inverse linear correlation with plasma concentrations of non-esterified fatty acids (r2 = 0.69; two-sided P<0.0001; n = 8), suggesting that heparin-induced lipolysis inhibits platelet macroaggregation. Lipoprotein degradation products may cause this inhibition by interfering with eicosanoids and other lipid mediators of metabolism.

Generic and Branded Versions of Argatroban Exhibit Differential Anticoagulant Effects In Whole Blood, Plasma Based Assays and Thrombin Generation Assays

Blood ◽  
2010 ◽  
Vol 116 (21) ◽  
pp. 5129-5129
Author(s):  
Jawed Fareed ◽  
Debra Hoppensteadt ◽  
Omer Iqbal ◽  
Jeanine M. Walenga ◽  
Bruce E Lewis
Keyword(s):  
Protein Interactions ◽  
Whole Blood ◽  
Thrombin Generation ◽  
Conflicts Of Interest ◽  
Anticoagulant Effect ◽  
Thrombin Time ◽  
Clotting Time ◽  
Generic Products

Abstract Abstract 5129 Several generic versions of argatroban) (Mitsubishi; Tokyo, Japan) have been introduced in Japan (Argaron, Gartban, Slovastan). In addition, other generic versions of argatroban are being considered by the European and North American regulatory bodies. While the generic versions of argatroban exhibit similar antithrombin potency (Ki values), because of the differential compositional variations their anticoagulant effects in whole blood systems may differ due to their cellular and plasmatic protein interactions. Branded and generic versions of argatroban may exhibit differential anticoagulant actions in the whole blood and plasma based assays due to their differential interactions with blood cells, platelets and plasma proteins. Three generic versions of argatroban that are commercially available in Japan namely Argaron, Gartban and Slovastan and a powdered version of generic argatroban (Lundbeck) were compared with the branded argatroban. Native whole blood thrombelastographic (TEG) analysis was carried out at 0.1 ug/mL, the Activated Clotting Time (ACT) assay was carried out in a concentration range of 0–10 ug/mL, and such coagulation tests as the PT/INR, aPTT, Heptest, and calcium thrombin time were performed. Plasma retrieved from the supplemented whole blood was also assayed. Ratios of the clotting time test values from whole blood and plasma were calculated. Retrieved plasma samples were also assayed in the thrombin generation assays (TGA). All of the different versions of argatroban produced a concentration dependent anticoagulant effect in the native whole blood TEG and ACT. In the TEG, while argatroban and Slovastan showed a similar effect, Gartban, Argaron and a powdered generic showed weaker effects. Argatroban was also different in the ACT assay. At a concentration of 5 ug/ml the ACTs were, Arg 340+15.2 secs, S 297+10.5 secs, G 292.0+19.1 secs and A 285.2+21.7 secs. In the citrated whole blood systems, all agents produced a concentration dependent anticoagulant effect; however, the generic versions produced a stronger anticoagulant effect in comparison to branded argatroban (p<0.001). In the PT assay at 5 ug/mL, argatroban showed 32 ± 3 sec vs 40–50 sec for the generic products. Similarly in the aPTT, Heptest and thrombin time tests argatroban was weaker than the generic products. Differences among generic versions were also evident. Similar results were obtained in the retrieved plasma, however the ratio of whole blood over plasma varied from product to product. The IC50 of the generic and branded argatrobans in the TGA were also different. These results show that while in the thrombin inhibition assays generic and branded argatroban may show similar effects, these agents exhibit assay dependent differences in the whole blood and plasma based assays. Such differences may be more evident in the in vivo studirs where endothelial cells and other interactions may contribute to product individuality. Therefore, based on the in vitro antiprotease assays, generic argatrobans may not be considered equivalent and require a multi-parametric study. Currently available generic argatrobans may not be equivalent in the in vivo anticoagulant effects. Therefore, clinical validation of the clinical equivalence for these drugs is warranted. Disclosures: No relevant conflicts of interest to declare.

Comparison Of The Effects Of Aspirin In Humans Ex Vivo In Platelet-Rich Plasma And Whole Blood

1981 ◽  
Author(s):  
Barbara Nunn
Keyword(s):  
Whole Blood ◽  
Ex Vivo ◽  
Platelet Rich Plasma ◽  
Trisodium Citrate ◽  
Blood Platelet ◽  
Maximal Response ◽  
Blood Samples ◽  
Platelet Concentration

The effect of aspirin on human platelet function is usually assessed using platelet-rich plasma (PRP). Some preliminary results in vitro suggested that the effect of aspirin appears to be greater in PRP than whole blood. To explore this possibility further, a comparison of the effect of aspirin in humans ex vivo has been made taking measurements simultaneously in whole blood and PRP at 2 platelet concentrations. Blood samples (36ml) were drawn from 7 male volunteers after a light breakfast. Each took 300mg soluble aspirin and blood samples were drawn again 2 hours later. Blood was mixed with 0.1 volumes 129nM trisodium citrate. Some (30ml) was then centrifuged to prepare PRP and platelet -poor plasma (PPP) by standard techniques. Platelet concentration of some PRP was adjusted with PPP to equal that of the corresponding blood sample; the rest was adjusted to 350,000 per μl. Aggregation in response to collagen (Horm, Munich) was measured photometrically at 37°. Aggregation in 0.5ml aliquots of whole blood was measured after 4 min stirring with 154mM NaCl (control) or collagen at 37° as the fall in single platelet count determined using an Ultraflo- 100 whole blood platelet counter (Clay Adams). The concentrations of collagen producing a 50% maximal response (EC50) in PRP and blood were determined. Dose-ratios for each volunteer were calculated by dividing the EC50 obtained after aspirin by the corresponding value obtained before aspirin.The effect of aspirin was significantly (p<0.001) less in blood than PRP. Whether or not the results in whole blood more closely reflect the effect of aspirin in vivo remains to be determined.

scholarly journals FEIBA® and Novoseven® Neutralize the Anticoagulant Effects of a Novel Small Molecule FXIa Inhibitor BMS-986177/JNJ-70033093 in Human Plasma and Whole Blood in Vitro

Blood ◽  
2020 ◽  
Vol 136 (Supplement 1) ◽  
pp. 10-11
Author(s):  
Matthew W Bunce ◽  
Zheng Huang Devine ◽  
Madhu Chintala
Keyword(s):  
Human Plasma ◽  
Whole Blood ◽  
Thrombin Generation ◽  
Hemophilia A ◽  
Lag Time ◽  
Publicly Traded ◽  
Routine Prophylaxis ◽  
Control And Prevention ◽  
Bleeding Episodes

Background: FXIa inhibition is a promising antithrombotic drug target. BMS-986177/JNJ-70033093 (BMS-177/JNJ-3093) is a novel small molecular inhibitor of FXIa currently in Phase II clinical trials with the potential for reduced bleeding risk as compared to the currently approved oral anticoagulantsHowever, reversal of anticoagulation may still be required in patients who have uncontrolled or life-threatening bleeding or need an urgent surgical procedure. Aim: To evaluate the ability of nonspecific reversal agents (NSRAs) FEIBA®, NovoSeven®, Kcentra®, Profilnine®, BeneFix®, Novoeight®, and Cyklokapron® to neutralize the anticoagulation of BMS-177/JNJ-3093 in the activated partial thromboplastin time (aPTT), thromboelastography (TEG) and thrombin generation assay (TGA) in vitro using human plasma or whole blood. Method: aPTT and TEG were performed in human plasma and whole blood, respectively, using standard assay procedures. TGA was performed in human plasma using diluted kaolin aPTT reagent (1:10,000). JNJ-3093 was evaluated at different concentrations (0.3 -10 µM) to cover the anticipated exposures in the Phase II clinical trials. The NSRAs were evaluated at the anticipated concentrations according to the dosing information in their respective labels. Results: BMS-177/JNJ-3093 produced concentration dependent increases in aPTT (up to 4.4x at 10 μM); prolongations of lag time in TEG (2.6X); prolongations of lag time (3X) as well as reductions in peak thrombin generation (70%) in TGA. FEIBA® effectively neutralized the anticoagulant effects of JNJ-3093 in aPTT, TEG and TGA. NovoSeven® neutralized the BMS-177/JNJ-3093-induced prolongations in aPTT, prolongations in lag time in TEG and TGA assays and partially restored the peak thrombin generation in TGA. In contrast, all other NSRAs tested had negligible effects or did not show neutralization of anticoagulation induced by BMS-177/JNJ-3093 in the referenced assays Conclusion: These results demonstrate that FEIBA® and NovoSeven® can effectively neutralize the anticoagulant effects of BMS-177/JNJ-3093 in vitro. A clinical study is required to determine if these agents can reverse the anticoagulant effects of BMS-177/JNJ-3093 in patients. Table Disclosures Bunce: Johnson & Johnson: Current Employment, Current equity holder in publicly-traded company. Huang Devine:Johnson & Johnson: Current Employment, Current equity holder in publicly-traded company. Chintala:Johnson & Johnson: Current Employment, Current equity holder in publicly-traded company. OffLabel Disclosure: FEIBA: hemophilia A and B patients with inhibitors for: control and prevention of bleeding episodes; use around the time of surgery; routine prophylaxis to prevent or reduce the frequency of bleeding episodes NovoSeven: Treatment of bleeding and prevention of bleeding for surgeries and procedures in adults and children with hemophilia A or B with inhibitors, congenital Factor VII (FVII) deficiency, and Glanzmanns thrombasthenia with a decreased or absent response to platelet transfusions; treatment of bleeding and prevention of bleeding for surgeries and procedures in adults with acquired hemophilia Kcentra: urgent reversal of acquired coagulation factor deficiency induced by vitamin K antagonist therapy in adult patients with need for urgent surgery/invasive procedure or acute major bleeding Profilnine: prevention and control of bleeding in patients with Factor IX deficiency due to hemophilia B BeneFix: control and prevention of bleeding episodes or peri-operative management in adult and pediatric patients with hemophilia B Novoeight: for use in adults and children with hemophilia A for control and prevention of bleeding, perioperative management, and routine prophylaxis to prevent or reduce the frequency of bleeding episodes Cyklokapron: patients with hemophilia for short-term use to reduce or prevent hemorrhage and reduce the need for replacement therapy during and following tooth extraction)

In Vitro and In Vivo Effects of Adrenaline and Phentolamine on Platelet Function

1978 ◽  
Vol 40 (02) ◽  
pp. 428-438 ◽  
Author(s):  
Oreste Ponari ◽  
Emilio Civardi ◽  
Alessandro Megha ◽  
Mario Pini ◽  
Raffaele Poti’ ◽  
...  
Keyword(s):  
Platelet Aggregation ◽  
Platelet Rich Plasma ◽  
Threshold Concentration ◽  
Two Phase ◽  
Platelet Factor ◽  
Induce Platelet Aggregation ◽  
In Vivo Effects ◽  
In Vivo Administration

Summary In vitro and in vivo effects of adrenaline (ADR) on platelet aggregation, on platelet factor 3 (PF3) availability and on platelet factor 4 (PF4) release were studied in man. Inhibitory action of an alpha-blocker, phentolamine (PHEN) was investigated in the same conditions.The threshold concentration (TC) of ADR inducing the typical two-phase response in aggregation tests when added to platelet-rich plasma (PRP) varied in different pools of plasma, but always induced an evident PF4 release and increased PF3 availability. A further increase in both parameters was obtained with higher concentrations but without any significant dose/response correlation.Adding PHEN alone to PRP did not induce platelet aggregation or modify PF4 release induced by stirring, but it reduced PF3 availability. On the other hand, PHEN prevented the effects of ADR in different platelet tests, at appropriate concentrations.Intravenous infusion of ADR lowered the TC, and increased PF3 availability and PF4 release. In vivo administration of PHEN, in contrast, increased TC and reduced PF3 availability, while PF4 remained unchanged.

Influence of Fibrinogen Split Products on Platelets

1967 ◽  
Vol 17 (01/02) ◽  
pp. 078-098 ◽  
Author(s):  
M. I Barnhart ◽  
D. C Cress ◽  
R. L Henry ◽  
J. M Riddle
Keyword(s):  
Platelet Aggregation ◽  
Plasma Concentration ◽  
Whole Blood ◽  
Platelet Rich Plasma ◽  
Platelet Response ◽  
Transient Nature ◽  
Platelet Morphology ◽  
Platelet Aggregates

SummaryBreakdown products of fibrinogen and fibrin can play a role in hemostasis and also may be of consequence in thrombosis. β2 fibrinogen derivative D is an electropositive terminal proteolysis product of fibrinolysis which has the ability to aggregate platelets. The normal plasma concentration of such nonclottable fibrinogen relatives is 0.2 mg/ml. During fibrinolysis this concentration may reach 5 mg/ml plasma. Addition of β 2 fibrinogen D (raising the plasma concentration 0.1 to 5 mg/ml) either in vivo or in vitro induced platelet aggregations. Moreover, alterations in platelet morphology occurred which were obvious by electron microscopy.Platelet depletion was a consistent response to the infusion of purified β2 fibrinogen D (8 to 55 mg/kg body weight) into dogs. Circulating platelets decreased as much as 85% but were only temporarily aggregated and reappeared in the circulation within 1 to 5 hrs. Small platelet aggregates circulated while large aggregates were trapped in the microcirculation. Thrombin was not responsible for the platelet aggregations as neither prothrombin nor clottable fibrinogen were changed significantly. The transient nature and morphological features of the platelet response according to microscopic criteria were prominent during and after infusion of β2 fibrinogen D.In vitro studies included 3 systems; washed platelets, platelet rich plasma and whole blood. Positive results were obtained with all, but platelets in whole blood were most responsive. The magnitude of platelet aggregation and morphology correlated with the concentration of β2 fibrinogen D. Platelet aggregation induced by ADP (10~5 mg/ml) was compared with that induced by β2 fibrinogen D (0.09 to 0.72 mg/ml). With either reagent aggregates were of dendritic forms. Combination of the 2 reagents was additive but did not further change the morphology. Additional factors seem necessary for development of viscous metamorphosis.

Reverting Rivaroxaban Effect By Activated Factor X: Assessment Using Thrombin Generation Assay

Blood ◽  
2014 ◽  
Vol 124 (21) ◽  
pp. 2868-2868 ◽  
Author(s):  
Dominique Grenier ◽  
Meyer Michel Samama ◽  
Sami Chtourou ◽  
Jean-Luc Plantier
Keyword(s):  
Thrombin Generation ◽  
Lag Time ◽  
Peak Height ◽  
Factor X ◽  
Thrombin Generation Assay ◽  
Lag Times ◽  
Dose Dependent ◽  
Control Plasma

Abstract Specific anti-activated factor X molecules are currently used for the prevention and the treatment of various thromboembolic disorders. However, despite a growing use of these molecules, they are still devoid of a reliable antidote. Rivaroxaban is a specific anticoagulant targeting activated factor X (FXa). Its potential in inhibiting FXa in vitro and in vivo was demonstrated during the characterization of the molecule. However, the use of FXa to revert the effect of Rivaroxaban in plasma was never studied. To do so the measurement of thrombin generation (TG) using the calibrated automatic thrombinoscope was performed. The ability of purified human FXa (Haematologic Technologies at 10, 50, 100, 500 and 1000 ng/ml) to induce TG in a platelet-poor plasma (PPP) without the induction of the coagulation was first evaluated. There was a FXa dose-dependent TG. The TG profile at concentrations up to 50 ng/ml of FXa was similar than the control profile obtained by a PPP activated by tissue-factor (0.5 pM) and phospholipids. Above 50 ng/ml FXa, the lag time decreased and the endogeneous thrombin potential (ETP) increased with the dose. This pattern revealed the thrombogenic potential of FXa and demonstrated that a dose of 50 ng/ml (or ≈1 nM) FXa was the maximum safer dose identified by this assay. A similar experiment was performed following the activation of plasma with 0.5 pM Tissue-Factor (TF) and 4 µM phospholipids (PL) and adding FXa at 31, 62, 125, 250 and 500 ng/ml. The kinetics of TG in the presence of the different amounts of FXa differed less than when coagulation was not induced. The lag times varies from 3 to 1.83 min with the increasing concentrations of FXa and the peak heights from 120 to 212 nM, being the two most affected parameters. Following the addition of 62 ng/ml (or ≈1.25 nM) FXa, the TG was more effective than a control plasma identically stimulated. Rivaroxaban was then spiked in the PPP at the therapeutic dose of 0.35 µg/ml (or 0.8 µM). Following 0.5 pM TF/4 µM PL stimulation, this dosage completely inhibits the TG. Increasing doses of FXa (31, 62, 125, 250 and 500 ng/ml) were then added and dose-dependently restores the TG. All the parameters of the TG profile were affected by the presence of FXa. The normalization was attained at the dose of 250 ng/ml (or 5 nM) FXa. A similar set of experiment was repeated by activating the plasma with cephalin, used as a model to mimic the initiation of the contact phase coagulation. The pattern of TG was different than following FT/PL activation. With cephalin and for all FXa concentrations identical peak aspects (velocity, ETP and peak height) were obtained differing only by their lag times and times-to-peak. Lag times and times to peak were shortened by the addition of FXa from 10.7 to 3.7 min and 13.2 to 6 min respectively. Plasma were then spiked by Rivaroxaban (0.35 µg/ml) and activated by cephalin in the presence of various concentrations of FXa (31, 62, 125, 250 and 500 ng/ml). A dose-dependent TG was demonstrated with the ETP, the peak height and the velocity increasing with the amount of FXa spiked whereas the lag time and time to peak were shortened. Following the induction by cephalin, the presence of FXa systematically shortened the TG when Rivaroxaban was present or not, when compared to the TG from control plasma. This work aimed to establish the antidote potential of the natural substrate of the anti-Xa molecules and limiting the risk in promoting a thrombotic response. The calibrated thrombin generation assay was used to determine the in vitro efficiency of FXa to induce a normal thrombin generation without primary induction or following an induction by TF/PL or cephalin. The doses of FXa required to normalize coagulation in the presence of Rivaroxaban and following induction were identified. These conditions will now be assessed in vivo in Rivaroxaban treated-mice. In addition of establishing the antidote properties of FXa, this data paved the way to compare its capacities, which are optimal to inhibit such inhibitor, to further antidote in development. Disclosures Grenier: LFB BIotechnologies: Employment. Chtourou:LFB Biotechnologies: Employment. Plantier:LFB Biotechnologies: Employment.

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