Coenzyme Q10 Attenuates Platelet Integrin αIIbβ3 Outside-in Signaling through Targeting cAMP/PKA Pathway and Inhibits Atherosclerosis

Abstract Introduction: Platelet integrin αIIbβ3 outside-in signaling is crucial for platelet adhesion and aggregation, and contributes to atherogenesis. Coenzyme Q10 (CoQ10) has been implicated as a protective factor against cardiovascular diseases (CVDs), particularly atherosclerosis. However, whether CoQ10 attenuates atherosclerosis through inhibiting platelet function and αIIbβ3 outside-in signaling is unknown. The aim of this study was to explore whether CoQ10 affects platelet function and αIIbβ3 outside-in signalling and thus inhibiting the progress of atherosclerosis in vivo and the underlying mechanisms in vitro. Methods: In vitro study, The murine platelet rich plasma (PRP) from C57BL/6J wild-type (WT) mice or human PRP and gel-filtered platelets were incubated with different concentrations (1, 10 or 100 μM) of CoQ10 or the vehicle control for 50 min. Platelet aggregation, spreading on fibrinogen (Fg) and clot retraction were determined. In addition, the effects of CoQ10 on platelet integrin αIIbβ3 inside-out signalling (e.g., talin-1 and kindlin-3 binding to integrin β3) were determined by immunoprecipitation, and outside-in signalling (e.g., phosphorylation of sarcoma tyrosine-protein kinase (c-Src), focal adhesion kinase (FAK), and β3 cytoplasmic tail, myosin light chain (MLC)) were determined by Western blotting. The levels of platelet ATP and cAMP were measured by ELISA assays. In vivo study, male homozygous apolipoprotein E-deficient (apoE-/-) mice (C57BL/6 genetic background) were fed either a standard normal AIN-93G diet (NC group), a Western-type diet (HFD group) or a Western-type diet supplemented with CoQ10 (1800 mg/kg diet) (CoQ10 group) for 12 weeks. Platelet aggregation, granule secretion, platelet spreading, clot retraction, integrin αIIbβ3 outside-in signalling, platelet-leukocyte interactions and carotid artery plaque area were also examined. In our randomized, double-blind, placebo-controlled trial, 101 hypercholesterolemic subjects were randomly administrated to 120 mg CoQ10 or placebo daily for 24 weeks. Platelet intracellular CoQ10 levels, platelet aggregation in PRP, platelet platelet factor 4 (PF-4) and C-C motif ligand 5 (CCL5) release, and platelet integrin αIIbβ3 outside-in signalling were also evaluated before and after 24 weeks of intervention. Results: We found that CoQ10 inhibited human and WT mouse platelet aggregation, platelet spreading, granule secretion, and clot retraction in vitro and apoE-/- mice on a high fat diet. CoQ10 also reduced atherosclerosis and platelet-monocyte aggregation in apoE-/- mice. The inhibitory effects of CoQ10 is mediated by attenuated αIIbβ3 outside-in signalling pathway (e.g., attenuation of phosphorylation of c-Src, FAK, and β3 cytoplasmic tail, and MLC in thrombin-activated platelets or platelets exposed to immobilized Fg), which requires up-regulation of the cAMP/PKA pathway, where CoQ10 inhibited phosphodiesterase 3A activity and activated the A2A adenosine receptor. However, CoQ10 did not affect platelet integrin αIIbβ3 inside-out signalling pathway, platelet cellular ATP, or platelet apoptosis (the mitochondrial membrane potential and phosphatidylserine exposure). Moreover, our clinical trial in dyslipidemic patients demonstrated that CoQ10 supplementation attenuated platelet aggregation, which was positively correlated with the increased platelet CoQ10 concentrations, inhibited αIIbβ3 outside-in signalling and decreased platelet PF-4 and CCL5 secretion. Conclusions: We present new data to suggest that CoQ10 plays a novel role in attenuating platelet function and integrin αIIbβ3 outside-in signalling though targeting cAMP/PKA signalling cascade and thus inhibiting the progress of atherosclerosis. CoQ10 is therefore a promising agent for the prevention and/or treatment for cardiovascular disease. Disclosures No relevant conflicts of interest to declare.

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Impaired “outside-in” integrin αIIbβ3 signaling and thrombus stability in TSSC6-deficient mice

Blood ◽

10.1182/blood-2006-02-004267 ◽

2006 ◽

Vol 108 (6) ◽

pp. 1911-1918 ◽

Cited By ~ 69

Author(s):

Matt W. Goschnick ◽

Lai-Man Lau ◽

Janet L. Wee ◽

Yong S. Liu ◽

P. Mark Hogarth ◽

...

Keyword(s):

Ex Vivo ◽

Fluorescein Isothiocyanate ◽

Clot Retraction ◽

In Vivo Evaluation ◽

Integrin Αiibβ3 ◽

Normal Platelet ◽

Granule Secretion ◽

Platelet Spreading ◽

Deficient Mice

AbstractWe investigated the role of the hematopoietic-specific tetraspanin superfamily member, TSSC6, in platelet function using wild-type mice and TSSC6-deficient mice. TSSC6 is expressed on the surface of murine platelets and is up-regulated by thrombin stimulation, indicating an intracellular pool of TSSC6. Immunoprecipitation/Western blot studies reveal a constitutive physical association of TSSC6 with the integrin αIIbβ3 complex under strong detergent conditions. In vivo evaluation of hemostasis by tail bleeding revealed increased bleeding time, volume of blood lost, and evidence of tail rebleeds in TSSC6 null mice, indicating unstable hemostasis. Using ex vivo techniques, we showed that TSSC6-deficient platelets exhibited impaired kinetics of clot retraction, platelet aggregation at lower doses of PAR-4, and collagen and platelet spreading on fibrinogen in the presence of normal integrin αIIbβ3 expression. TSSC6-deficient platelets showed normal alpha granule secretion, normal “insideout” integrin αIIbβ3 signaling (fluorescein isothiocyanate [FITC]–fibrinogen and JON/A binding), and normal platelet adhesion on fibrinogen. Furthermore, we show that absence of platelet TSSC6 affects the secondary stability of arterial thrombi in vivo upon vascular injury. These data demonstrate that TSSC6 appears to regulate integrin αIIbβ3 “outside-in” signaling events in platelets and is necessary for stability of arterial thrombi in vivo.

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Effect of propranolol on platelet function

Blood ◽

10.1182/blood.v49.2.185.185 ◽

1977 ◽

Vol 49 (2) ◽

pp. 185-196 ◽

Cited By ~ 192

Author(s):

BB Weksler ◽

M Gillick ◽

J Pink

Keyword(s):

Platelet Aggregation ◽

Platelet Function ◽

Direct Action ◽

Blood Platelets ◽

Adenosine Diphosphate ◽

Ionophore A23187 ◽

Atherosclerotic Vascular Disease ◽

Clot Retraction

Abstract Excessive reactivity of blood platelets may contribute to atherosclerotic vascular disease. Hence drugs which alter platelet function may be protective. Prompted by findings that propranolol therapy normalized hyperactive platelet aggregation in patients with coronary artery disease, we studied propranolol in vitro to assess its action on platelets. At concentrations similar to those achieved in vivo (0.1–1 muM), propranolol raised the thresholds for aggregation of some normal paltelets by adenosine diphosphate (ADP). At higher concentrations (10-50 muM), propranolol abolished the second wave of platelet aggregation induced by ADP and epinephrine, and inhibited aggregation induced by collagen, thrombin, and the ionophore A23187. Propanolol blocked the release of 14C-serotonin from platelets, inhibited platelet adhesion to collagen, and interfered with clot retraction. Propranolol blocked ionophore-induced uptake of 45Ca by platelets. Inhibition appeared unrelated to beta-adrenergic blockage, as d(+) propranolol (which lacks beta-blocking activity) was equipotent with 1(-) propranolol. Moreover, practolol, a beta-blockading drug which is nonlipophilic, did not inhibit platelet function. These studies suggested that propranolol, like local anesthetics, decreased platelet responsiveness by a direct action on the platelet membrane, possibly by interfering with calcium availability. Modulation of platelet function by propranolol may occur at concentrations achieved at usual clinical doses of the drug.

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CIB1 Is Required for FAK Activation during Outside-in Signaling through Platelet Integrin αIIbβ3

Blood ◽

10.1182/blood.v112.11.2873.2873 ◽

2008 ◽

Vol 112 (11) ◽

pp. 2873-2873 ◽

Cited By ~ 1

Author(s):

Ulhas Pandurang Naik ◽

Meghna Ulhas Naik

Keyword(s):

Resting State ◽

Ex Vivo ◽

Clot Retraction ◽

Integrin Αiibβ3 ◽

High Affinity ◽

Fibrinogen Binding ◽

Platelet Spreading ◽

Inside Out ◽

Dependent Interaction

Abstract Platelets play an important role in the processes of hemostasis and thrombosis. Platelet integrin αIIbβ3 mediates bi-directional signaling during these processes. Agonist-dependent activation of integrin αIIbβ3 through inside-out signaling results in high-affinity binding of soluble ligands, such as fibrinogen. Fibrinogen binding induces a cascade of signaling through the integrin, termed outside-in signaling that results in platelet aggregation and clot retraction. Previously, we have characterized CIB1, a calcium- and integrin-binding protein that specifically interacts with the cytoplasmic domain of αIIb. Previous reports using in vitro and ex vivo studies implicated that CIB1 is involved in maintaining αIIbβ3 in its resting state, agonist-induced activation of the integrin, and outside-in signaling resulting in platelet spreading. Here, we show that platelet filopodia formation induced by fibrinogen binding to integrin αIIbβ3 needs Ca2+, but is independent of the Ca2+-dependent interaction of CIB1 with αIIb. Additionally, dynamic rearrangement of the cytoskeleton is required for the recruitment of FAK to the CIB1-αIIb complex at the filopodia and FAK activation. Moreover, disruption of the association of CIB1 and αIIb by incorporation of αIIb peptide or CIB1 antibody inhibited FAK activation. Furthermore, Cib1 null platelets acquired a spiky morphology and failed to fully spread on immobilized fibrinogen. Interestingly, FAK activation was significantly reduced in Cib1 null platelets exposed to immobilized fibrinogen. Our results suggest that during outside-in signaling, a rise in the intracellular Ca2+ level and filopodia formation occurs prior to the interaction of CIB1 with αIIb. Additionally, Ca2+ bound CIB1 recruits FAK to the αIIbβ3 complex at the filopodia, where FAK is activated, resulting in platelet spreading. Thus, our results have provided a mechanism through which CIB1 regulates outside-in signaling through integrin αIIbβ3.

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The tetraspanin superfamily member CD151 regulates outside-in integrin αIIbβ3 signaling and platelet function

Blood ◽

10.1182/blood-2003-12-4430 ◽

2004 ◽

Vol 104 (8) ◽

pp. 2368-2375 ◽

Cited By ~ 86

Author(s):

Lai-Man Lau ◽

Janet L. Wee ◽

Mark D. Wright ◽

Gregory W. Moseley ◽

P. Mark Hogarth ◽

...

Keyword(s):

Platelet Function ◽

Fluorescein Isothiocyanate ◽

Dense Granule ◽

Free Calcium ◽

Clot Retraction ◽

Altered Expression ◽

Integrin Αiibβ3 ◽

Normal Platelet ◽

Granule Secretion

Abstract The tetraspanin family member CD151 forms complexes with integrins and regulates cell adhesion and migration. While CD151 is highly expressed in megakaryocytes and to a lesser extent in platelets, its physiologic role in platelets is unclear. In this study, we investigate the physical and functional importance of CD151 in murine platelets. Immunoprecipitation/Western blot studies reveal a constitutive physical association of CD151 with integrin αIIbβ3 complex under strong detergent conditions. Using CD151-deficient mice, we show that the platelets have impaired “outside-in” integrin αIIbβ3 signaling with defective platelet aggregation responses to protease-activated receptor 4 (PAR-4) agonist peptide, collagen, and adenosine diphosphate (ADP); impaired platelet spreading on fibrinogen; and delayed kinetics of clot retraction in vitro. This functional integrin αIIbβ3 defect could not be attributed to altered expression of integrin αIIbβ3. CD151–/– platelets displayed normal platelet alpha granule secretion, dense granule secretion, and static platelet adhesion. In addition, CD151–/– platelets displayed normal “inside-out” integrin αIIbβ3 signaling properties as demonstrated by normal agonist-induced binding of soluble fluorescein isothiocyanate (FITC)–fibrinogen, JON/A antibody binding, and increases in cytosolic-free calcium and inositol 1,4,5 triphosphate (IP3) levels. This study provides the first direct evidence that CD151 is essential for normal platelet function and that disruption of CD151 induced a moderate outside-in integrin αIIbβ3 signaling defect.

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Effect of propranolol on platelet function

Blood ◽

10.1182/blood.v49.2.185.bloodjournal492185 ◽

1977 ◽

Vol 49 (2) ◽

pp. 185-196

Author(s):

BB Weksler ◽

M Gillick ◽

J Pink

Keyword(s):

Platelet Aggregation ◽

Platelet Function ◽

Direct Action ◽

Blood Platelets ◽

Adenosine Diphosphate ◽

Ionophore A23187 ◽

Atherosclerotic Vascular Disease ◽

Clot Retraction

Excessive reactivity of blood platelets may contribute to atherosclerotic vascular disease. Hence drugs which alter platelet function may be protective. Prompted by findings that propranolol therapy normalized hyperactive platelet aggregation in patients with coronary artery disease, we studied propranolol in vitro to assess its action on platelets. At concentrations similar to those achieved in vivo (0.1–1 muM), propranolol raised the thresholds for aggregation of some normal paltelets by adenosine diphosphate (ADP). At higher concentrations (10-50 muM), propranolol abolished the second wave of platelet aggregation induced by ADP and epinephrine, and inhibited aggregation induced by collagen, thrombin, and the ionophore A23187. Propanolol blocked the release of 14C-serotonin from platelets, inhibited platelet adhesion to collagen, and interfered with clot retraction. Propranolol blocked ionophore-induced uptake of 45Ca by platelets. Inhibition appeared unrelated to beta-adrenergic blockage, as d(+) propranolol (which lacks beta-blocking activity) was equipotent with 1(-) propranolol. Moreover, practolol, a beta-blockading drug which is nonlipophilic, did not inhibit platelet function. These studies suggested that propranolol, like local anesthetics, decreased platelet responsiveness by a direct action on the platelet membrane, possibly by interfering with calcium availability. Modulation of platelet function by propranolol may occur at concentrations achieved at usual clinical doses of the drug.

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Integrin αIIb cytoplasmic Tail Is Essential for Integrin Outside-in Signaling and Regulation of in Vivo Thrombosis

Blood ◽

10.1182/blood.v124.21.4160.4160 ◽

2014 ◽

Vol 124 (21) ◽

pp. 4160-4160

Author(s):

Meghna Ulhas Naik ◽

Ulhas P Naik

Keyword(s):

Platelet Aggregation ◽

Conflicts Of Interest ◽

Cytoplasmic Tail ◽

Cytoplasmic Domain ◽

P38 Map Kinase ◽

Clot Retraction ◽

Integrin Αiibβ3 ◽

Signaling Events ◽

Inside Out

Abstract Platelet aggregation plays an important role in physiological hemostasis and pathological thrombosis. Platelet agonists induce a series of events called inside-out signaling that lead to the activation of integrin αIIbβ3. Fibrinogen binding to the activated integrin relay signals termed as outside-in signaling that regulate thrombus growth and stability. Talin and kindlin bind to the integrin β3 cytoplasmic tail to induce inside-out signaling. Although, integrin αIIb cytoplasmic domain also bind to a number of proteins, its importance in hemostasis or thrombosis is not well understood. Previously, we have identified a calcium- and integrin-binding protein (CIB1) that specifically interacts with the integrin αIIb cytoplasmic tail. Using a novel technique to inhibit interaction of CIB1 with integrin αIIb in intact human platelets, we have shown that CIB1 regulates outside-in signaling through integrin αIIbβ3. Recently, using Cib1-/- mice, we showed that CIB1 is a key regulator of thrombosis in vivo. Interestingly, agonist-induced platelet aggregation and secretion was normal in Cib1-/- platelets. Furthermore, expression or activation of integrin αIIbβ3 was also not affected by Cib1 deficiency, suggesting that integrin inside-out signaling is not affected in Cib1-/- platelets. However, adhesion and spreading on immobilized fibrinogen (Fg) was severely affected in Cib1-/- platelets. When we analyzed the rate of clot retraction, we found that significantly (P<0.001) delayed clot retraction was observed in Cib1-/- platelets compared to WT littermates, suggesting that integrin outside-in signaling is impaired in the absence of Cib1. To delineate the molecular mechanism regulated by CIB1 during platelet spreading and clot retraction, we analyzed the known signaling events activated during outside-in signaling. We found that Fg-dependent activation of ERK1 and p38 MAP kinase was significantly reduced in Cib1-/- null platelets. Furthermore, phosphorylation of the myosin light chain was also blocked in Cib1-/- platelets adhered to immobilized Fg. Furthermore, outside-in signaling-dependent tyrosine phosphorylation of β3 was greatly reduced in Cib1-/- platelets. When analyzed for the candidate tyrosine kinase responsible for reduced β3 phosphorylation, both Src and FAK activation was significantly reduced in Cib1-/- platelets. Furthermore, downstream signaling events such as activation of PAK1, PI3K, PDK1, as well as Akt were significantly affected in Cib1-/- platelets adhered to immobilized Fg. To test if impaired inhibition of GSK3-β is the cause of defective outside in signaling in Cib1-/- platelets we treated Cib1-/- platelets with SB216763, a specific GSK3-β inhibitor. We found that inhibition of GSK3-β rescued defective platelet adhesion and clot retraction observed in Cib1-/- platelets. It also rescued activation of p38 and Erk2 activation as well as MLC phosphorylation. However, activation of FAK, Src, PAK1, PI3K, PDK1, and Akt was not rescued, suggesting that these are upstream of GSK3-β. Furthermore, we found that outside-in dependent recruitment of FAK to the integrin-c-Src complex is greatly reduced in the absence of Cib1 suggesting that integrin αIIb cytoplasmic domain serves as a docking site for CIB1 so that it can recruit FAK to the integrin-c-Src complex and propagate outside-in signaling leading to GSK3-β inhibition, which is crucial for thrombus growth and stability. These in vivo and in vitro results clearly show that CIB1 regulates thrombosis by regulating outside-in signaling without affecting inside-out signaling through integrin αIIbβ3. Our results highlight an essential function to integrin αIIb cytoplasmic tail in regulating integrin outside-in signaling and thus thrombus growth and stability. Disclosures No relevant conflicts of interest to declare.

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A Comparison of the Effect of Decorsin and Two Disintegrins, Albolabrin and Eristostatin, on Platelet Function

Thrombosis and Haemostasis ◽

10.1055/s-0038-1649933 ◽

1995 ◽

Vol 74 (05) ◽

pp. 1316-1322 ◽

Cited By ~ 13

Author(s):

Mary Ann McLane ◽

Jagadeesh Gabbeta ◽

A Koneti Rao ◽

Lucia Beviglia ◽

Robert A Lazarus ◽

...

Keyword(s):

Platelet Aggregation ◽

Platelet Function ◽

Sequence Similarity ◽

Platelet Aggregation Inhibitors ◽

Antiplatelet Drug ◽

Rgd Sequence ◽

Fibrinogen Receptor ◽

Activated Platelets

SummaryNaturally-occurring fibrinogen receptor antagonists and platelet aggregation inhibitors that are found in snake venom (disintegrins) and leeches share many common features, including an RGD sequence, high cysteine content, and low molecular weight. There are, however, significant selectivity and potency differences. We compared the effect of three proteins on platelet function: albolabrin, a 7.5 kDa disintegrin, eristostatin, a 5.4 kDa disintegrin in which part of the disintegrin domain is deleted, and decorsin, a 4.5 kDa non-disintegrin derived from the leech Macrobdella decora, which has very little sequence similarity with either disintegrin. Decorsin was about two times less potent than albolabrin and six times less potent than eristostatin in inhibiting ADP- induced human platelet aggregation. It had a different pattern of interaction with glycoprotein IIb/IIIa as compared to the two disintegrins. Decorsin bound with a low affinity to resting platelets (409 nM) and to ADP-activated platelets (270 nM), and with high affinity to thrombin- activated platelets (74 nM). At concentrations up to 685 nM, it did not cause expression of a ligand-induced binding site epitope on the (β3 subunit of the GPIIb/IIIa complex. It did not significantly inhibit isolated GPIIb/IIIa binding to immobilized von Willebrand Factor. At low doses (1.5-3.0 μg/mouse), decorsin protected mice against death from pulmonary thromboembolism, showing an effect similar to eristostatin. This suggested that decorsin is a much more potent inhibitor of platelet aggregation in vivo than in vitro, and it may have potential as an antiplatelet drug.

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The Effect of Barbituric Acid Derivatives on Platelet Function in Vitro and in Vivo

Thrombosis and Haemostasis ◽

10.1055/s-0038-1649080 ◽

1973 ◽

Vol 30 (02) ◽

pp. 315-326

Author(s):

J. Heinz Joist ◽

Jean-Pierre Cazenave ◽

J. Fraser Mustard

Keyword(s):

Platelet Aggregation ◽

Platelet Function ◽

Barbituric Acid ◽

Platelet Rich Plasma ◽

Inhibitory Effect ◽

Primary Response ◽

Sodium Pentobarbital ◽

Barbituric Acid Derivatives

SummarySodium pentobarbital (SPB) and three other barbituric acid derivatives were found to inhibit platelet function in vitro. SPB had no effect on the primary response to ADP of platelets in platelet-rich plasma (PRP) or washed platelets but inhibited secondary aggregation induced by ADP in human PRP. The drug inhibited both phases of aggregation induced by epinephrine. SPB suppressed aggregation and the release reaction induced by collagen or low concentrations of thrombin, and platelet adherence to collagen-coated glass tubes. The inhibition by SPB of platelet aggregation was readily reversible and isotopically labeled SPB did not become firmly bound to platelets. No inhibitory effect on platelet aggregation induced by ADP, collagen, or thrombin could be detected in PRP obtained from rabbits after induction of SPB-anesthesia.

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Abstract 13598: The G-protein BetaGamma Subunits Regulate Platelet Function

Circulation ◽

10.1161/circ.142.suppl_3.13598 ◽

2020 ◽

Vol 142 (Suppl_3) ◽

Author(s):

Ahmed Alarabi ◽

Zubair Karim ◽

Victoria Hinojos ◽

Patricia A Lozano ◽

Keziah Hernandez ◽

...

Keyword(s):

G Protein ◽

Platelet Function ◽

Thrombus Formation ◽

Human Platelets ◽

Inhibitory Effects ◽

Clot Retraction ◽

Betagamma Subunits

Platelet activation involves tightly regulated processes to ensure a proper hemostasis response, but when unbalanced, can lead to pathological consequences such as thrombus formation. G-protein coupled receptors (GPCRs) regulate platelet function by interacting with and mediating the response to various physiological agonists. To this end, an essential mediator of GPCR signaling is the G protein Gαβγ heterotrimers, in which the βγ subunits are central players in downstream signaling pathways. While much is known regarding the role of the Gα subunit in platelet function, that of the βγ remains poorly understood. Therefore, we investigated the role of Gβγ subunits in platelet function using a Gβγ (small molecule) inhibitor, namely gallein. We observed that gallein inhibits platelet aggregation and secretion in response to agonist stimulation, in both mouse and human platelets. Furthermore, gallein also exerted inhibitory effects on integrin αIIbβ3 activation and clot retraction. Finally, gallein’s inhibitory effects manifested in vivo , as documented by its ability to modulate physiological hemostasis and delay thrombus formation. Taken together, our findings demonstrate, for the first time, that Gβγ directly regulates GPCR-dependent platelet function, in vitro and in vivo . Moreover, these data highlight Gβγ as a novel therapeutic target for managing thrombotic disorders.

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Comparison of the effect of coagulation and platelet function impairments on various mouse bleeding models

Thrombosis and Haemostasis ◽

10.1160/th13-11-0919 ◽

2014 ◽

Vol 112 (08) ◽

pp. 412-418 ◽

Cited By ~ 15

Author(s):

Nima Vaezzadeh ◽

Ran Ni ◽

Paul Y. Kim ◽

Jeffrey I. Weitz ◽

Peter L. Gross

Keyword(s):

Platelet Aggregation ◽

Platelet Function ◽

Saphenous Vein ◽

Ex Vivo ◽

Arterial Injury ◽

Inhibitory Antibody ◽

Study Objective ◽

Tail Tip

SummaryHaemostatic impairments are studied in vivo using one of several murine bleeding models. However it is not known whether these models are equally appropriate for assessing coagulation or platelet function defects. It was our study objective to assess the performance of arterial, venous and combined arterial and venous murine bleeding models towards impaired coagulation or platelet function. Unfractionated heparin (UFH) or αIIbβ3 inhibitory antibody (Leo.H4) were administered to mice, and their effects on bleeding in saphenous vein, artery, and tail tip transection models were quantified and correlated with their effects on plasma clotting and ADP-induced platelet aggregation, respectively. All models exhibited similar sensitivity with UFH (EC50 dose = 0.19, 0.13 and 0.07 U/g, respectively) (95% CI = 0.14 – 0.27, 0.08 – 0.20, and 0.03 – 0.16 U/g, respectively). Maximal inhibition of ex vivo plasma clotting could be achieved with UFH doses as low as 0.03 U/g. In contrast, the saphenous vein bleeding model was less sensitive to αIIbβ3 inhibition (EC50 = 6.9 µg/ml) than tail transection or saphenous artery bleeding models (EC50 = 0.12 and 0.37 µg/ml, respectively) (95% CI = 2.4 – 20, 0.05 – 0.33, and 0.06 – 2.2 µg/ml, respectively). The EC50 of Leo.H4 for ADP-induced platelet aggregation in vitro (8.0 µg/ml) was at least 20-fold higher than that of the tail and arterial, but not the venous bleeding model. In conclusion, venous, arterial and tail bleeding models are similarly affected by impaired coagulation, while platelet function defects have a greater influence in models incorporating arterial injury.

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