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Effects of Heparin and Bivalirudin on Thrombin-Induced Platelet Activation: Differential Modulation of PAR Signaling Drives Divergent Prothrombotic Responses

ABSTRACT: Heparin and bivalirudin are widely used as anticoagulants in the setting of acute thrombosis. In this study, we investigated how these drugs affect the ability of thrombin to generate a prothrombotic platelet response via activation of the protease-activated receptors (PARs) 1 and 4. We examined the effects of heparin/antithrombin and bivalirudin on PAR1- and PAR4-mediated intracellular calcium mobilization, aggregation, α-granule release, and procoagulant membrane exposure in platelets exposed to thrombin concentrations likely to be encountered in the thrombus microenvironment during thrombosis. At physiological antithrombin levels, heparin treatment resulted in complete and sustained inhibition of thrombin-induced PAR4-mediated platelet activation, but transient PAR1 signaling was sufficient to elicit significant α-granule release and platelet aggregation. In contrast, bivalirudin treatment resulted in rapid and profound inhibition of signaling from both PAR receptors, followed by a delayed phase of PAR4-mediated platelet activation, resulting in a robust prothrombotic response. Combination treatment with bivalirudin and subtherapeutic concentrations of heparin completely inhibited the residual platelet activation observed with single drug treatment at all time-points. Our results show that heparin and bivalirudin have different and complementary inhibitory effects on the activation of PAR1 and PAR4 by thrombin.

SUBMITTER: Lund M

PROVIDER: S-EPMC8511449 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:BackgroundThe family of 4 related protease-activated receptors (PAR-1, 2, 3 & 4) expressed by mammalian cells allow to sense for and react to extracellular proteolytic activity. Since major human bacterial pathogens secret a wide array of protease(-s) we investigated whether they interfere with human PAR function.Methodology/principal findingsSupernatants from cultures of major human bacterial pathogens were assayed for the presence of protease(-s) capable to cleave overexpressed human PAR-1, 2, 3 and 4 reporter constructs. Group A streptococcus (GAS) was found to secret a PAR-1-cleaving protease. Experiments involving genetical and pharmacological gain and loss of function identified streptococcal pyrogenic exotoxin B SpeB as the protease responsible. On the host's side analysis of overexpressed PAR-1 carrying alanine substitutions and deletions showed the amino acid residue leucine44 on PAR-1's extracellular N-terminus to be the only cleavage site. Complementary studies on endogenously expressed PAR-1 using PAR-1 blocking antibodies further supported our conclusion. Through PAR-1 cleavage SpeB efficiently blunted thrombin-induced induction of the ERK-pathway in endothelial cells and prevented platelets aggregation in response to thrombin.Conclusions/significanceOur results identify a novel function of the streptococcal virulence factor SpeB. By cleaving human PAR-1 at the N-terminal amino acid residue leucine44 SpeB rendered endothelial cells unresponsive to thrombin and prevented human platelets from thrombin-induced aggregation. These results suggest that by blunting PAR-1 signaling, SpeB modulates various innate host responses directed against invasive GAS potentially helping the invasive bacteria to escape. This may allow to tailor additional treatments in the future since upon invasion of the blood stream endothelial cells as well as platelets and mononuclear cells respond to PAR-1 agonists aiming to prevent further bacterial dissemination.

Project description:Extracorporeal membrane oxygenation is a potentially life-saving intervention in refractory cardiopulmonary failure, but it requires anticoagulation to prevent circuit thromboses, which exposes the patient to hemorrhagic complications. Heparin has traditionally been the anticoagulant of choice, but the direct thrombin inhibitor bivalirudin is routinely used in cases of heparin-induced thrombocytopenia and has been suggested as a superior choice. We sought to examine the timing of hemorrhagic and thrombotic complications after extracorporeal membrane oxygenation cannulation and to compare the rates of such complications between patients anticoagulated with heparin versus bivalirudin.DesignRetrospective cohort study.SettingJohns Hopkins Hospital patients between January 2016 and July 2019.PatientsAdult (> 18 yr) extracorporeal membrane oxygenation patients.InterventionsPatients were anticoagulated either with heparin or bivalirudin.Measurements and main resultsWe compared rates of hemorrhagic and thrombotic complications by time on heparin versus bivalirudin and characterized the average time to each complication. Of 144 extracorporeal membrane oxygenation patients (mean age 55.3 yr; 58% male), 41% were on central venoarterial extracorporeal membrane oxygenation, 40% on peripheral venoarterial extracorporeal membrane oxygenation, and 19% on venovenous extracorporeal membrane oxygenation. Thirteen patients (9%) received bivalirudin during their extracorporeal membrane oxygenation run, due to concern for (n = 8) or diagnosis of (n = 4) heparin-induced thrombocytopenia or for heparin resistance (n = 1). The rate of hemorrhagic or thrombotic complications did not differ between heparin (0.13/d) and bivalirudin (0.06/d; p = 0.633), but patients on bivalirudin received significantly fewer blood transfusions (1.0 U of RBCs/d vs 2.9/d on heparin; p < 0.001).ConclusionsOur results confirm the safety and efficacy of bivalirudin as an alternative anticoagulant in extracorporeal membrane oxygenation and suggest a potential benefit in less blood product transfusion, although prospective studies are needed to evaluate the true effect of bivalirudin versus the disease processes that prompted its use in our study population.

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Effects of Heparin and Bivalirudin on Thrombin-Induced Platelet Activation: Differential Modulation of PAR Signaling Drives Divergent Prothrombotic Responses

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