In vitro studies on the effect of activated protein C on platelet activation and thrombin generation

Mathematical Modeling of Severe Acute Respiratory Syndrome Coronavirus 2 Infection Network with Cytokine Storm, Oxidative Stress, Thrombosis, Insulin Resistance, and Nitric Oxide Pathways

Coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection is a systemic disease affecting not only the lungs but also multiple organ systems. Clinical studies implicate that SARS-CoV-2 infection causes imbalance of cellular homeostasis and immune response that trigger cytokine storm, oxidative stress, thrombosis, and insulin resistance. Mathematical modeling can offer in-depth understanding of the SARS-CoV-2 infection and illuminate how subcellular mechanisms and feedback loops underpin disease progression and multiorgan failure. We report here a mathematical model of SARS-CoV-2 infection pathway network with cytokine storm, oxidative stress, thrombosis, insulin resistance, and nitric oxide (NO) pathways. The biochemical systems theory model shows autocrine loops with positive feedback enabling excessive immune response, cytokines, transcription factors, and interferons, which can imbalance homeostasis of the system. The simulations suggest that changes in immune response led to uncontrolled release of cytokines and chemokines, including interleukin (IL)-1β, IL-6, and tumor necrosis factor α (TNFα), and affect insulin, coagulation, and NO signaling pathways. Increased production of NETs (neutrophil extracellular traps), thrombin, PAI-1 (plasminogen activator inhibitor-1), and other procoagulant factors led to thrombosis. By analyzing complex biochemical reactions, this model forecasts the key intermediates, potential biomarkers, and risk factors at different stages of COVID-19. These insights can be useful for drug discovery and development, as well as precision treatment of multiorgan implications of COVID-19 as seen in systems medicine.

Recombinant human soluble thrombomodulin and mortality in sepsis-induced disseminated intravascular coagulation

Recombinant human soluble thrombomodulin (rhTM) is a novel class of anticoagulants for treating disseminated intravascular coagulation (DIC). Although rhTM is widely used in clinical settings throughout Japan, there is limited clinical evidence supporting the use of rhTM in patients with sepsis-induced DIC. Furthermore, rhTM is not approved for DIC treatment in other countries. This study aimed to clarify the survival benefits of rhTM administration in critically ill patients. Data from 3,195 consecutive adult patients who were admitted to 42 intensive care units for the treatment of severe sepsis or septic shock between January 2011 and December 2013 were retrospectively analysed, and 1,784 patients were diagnosed with DIC based on the scoring algorithm from the Japanese Association for Acute Medicine DIC (n = 645, rhTM group; n = 1,139, control group). Propensity score matching created 452 matched pairs, and logistic regression analysis revealed a significant association between rhTM administration and lower in-hospital all-cause mortality in the propensity score-matched groups (odds ratio, 0.757; 95 % confidence interval, 0.574–0.999, p = 0.049). Inverse probability of treatment weighted and quintile-stratified analyses also revealed significant associations between rhTM administration and lower in-hospital all-cause mortality. Survival time in the propensity score-matched rhTM group was significantly longer than that in the propensity score-matched control group (hazard ratio, 0.781; 95 % confidence interval, 0.624–0.977, p = 0.03). Bleeding complications were not more frequent in the rhTM groups. In conclusion, this study demonstrated that rhTM administration is associated with reduced in-hospital all-cause mortality among patients with sepsis-induced DIC.

Activated Protein C Drives the Hyperfibrinolysis of Acute Traumatic Coagulopathy

BACKGROUND

Major trauma is a leading cause of morbidity and mortality worldwide with hemorrhage accounting for 40% of deaths. Acute traumatic coagulopathy exacerbates bleeding, but controversy remains over the degree to which inhibition of procoagulant pathways (anticoagulation), fibrinogen loss, and fibrinolysis drive the pathologic process. Through a combination of experimental study in a murine model of trauma hemorrhage and human observation, the authors' objective was to determine the predominant pathophysiology of acute traumatic coagulopathy.

METHODS

First, a prospective cohort study of 300 trauma patients admitted to a single level 1 trauma center with blood samples collected on arrival was performed. Second, a murine model of acute traumatic coagulopathy with suppressed protein C activation via genetic mutation of thrombomodulin was used. In both studies, analysis for coagulation screen, activated protein C levels, and rotational thromboelastometry (ROTEM) was performed.

RESULTS

In patients with acute traumatic coagulopathy, the authors have demonstrated elevated activated protein C levels with profound fibrinolytic activity and early depletion of fibrinogen. Procoagulant pathways were only minimally inhibited with preservation of capacity to generate thrombin. Compared to factors V and VIII, proteases that do not undergo activated protein C-mediated cleavage were reduced but maintained within normal levels. In transgenic mice with reduced capacity to activate protein C, both fibrinolysis and fibrinogen depletion were significantly attenuated. Other recognized drivers of coagulopathy were associated with less significant perturbations of coagulation.

CONCLUSIONS

Activated protein C-associated fibrinolysis and fibrinogenolysis, rather than inhibition of procoagulant pathways, predominate in acute traumatic coagulopathy. In combination, these findings suggest a central role for the protein C pathway in acute traumatic coagulopathy and provide new translational opportunities for management of major trauma hemorrhage.

Comparative response of platelet fV and plasma fV to activated protein C and relevance to a model of acute traumatic coagulopathy

Background

Acute traumatic coagulopathy (ATC) has been linked to an increase in activated protein C (aPC) from 40 pM in healthy individuals to 175 pM. aPC exerts its activity primarily through cleavage of active coagulation factor Va (fVa). Platelets reportedly possess fVa which is more resistant to aPC cleavage than plasma fVa; this work examines the hypothesis that normal platelets are sufficient to maintain coagulation in the presence of elevated aPC.

Methods

Coagulation responses of normal plasma, fV deficient plasma (fVdp), and isolated normal platelets in fVdp were conducted: prothrombin (PT) tests, turbidimetry, and thromboelastography (TEG), including the dose response of aPC on the samples.

Results

PT and turbidimetric assays demonstrate that normal plasma is resistant to aPC at doses much higher than those found in ATC. Additionally, an average physiological number of washed normal platelets (200,000 platelets/mm³) was sufficient to eliminate the anti-coagulant effects of aPC up to 10 nM, nearly two orders of magnitude above the ATC concentration and even the steady-state pharmacological concentration of human recombinant aPC, as measured by TEG. aPC also demonstrated no significant effect on clot lysis in normal plasma samples with or without platelets.

Conclusions

Although platelet fVa shows slightly superior resistance to aPC's effects compared to plasma fVa in static models, neither fVa is sufficiently cleaved in simulations of ATC or pharmacologically-delivered aPC to diminish coagulation parameters. aPC is likely a correlative indicator of ATC or may play a cooperative role with other activity altering products generated in ATC.

Anticoagulant properties of drotrecogin alfa (activated) during hemofiltration in patients with severe sepsis

In a retrospective study among 35 severely septic patients treated with drotrecogin alfa (activated) (DrotAA) and renal replacement therapy (RRT), Camporota and colleagues demonstrated that the addition of heparin, epoprostenol, or both to DrotAA during RRT did not improve filter survival. Furthermore, in a multivariate logistic regression analysis, they identified the minimum value in platelet count as the only predictive factor of filter clotting during DrotAA infusion. These findings are in line with the previously formulated suggestion that DrotAA alone is as effective as heparin in the prevention of coagulation in the extracorporeal circuit. They also confirm the importance of baseline platelet count in the pathogenesis of extracorporeal circuit thrombosis. In the study by Camporata and colleagues, DrotAA treatment was not associated with an increase in red blood cell requirements. The results of this study supply a background to clinical decision making when choosing an anticoagulant for RRT in septic patients.

Effect of Drotrecogin alfa (activated) on platelet receptor expression in vitro

Thrombocytopenia is a common problem in critically ill patients, which is associated with increased mortality. Recently, Drotrecogin alfa (activated) (recombinant human activated protein C (APC)) was shown to reduce mortality in patients with severe sepsis. Only minimal effect of APC on coagulation markers was demonstrated. Nevertheless, low platelet count was identified as a risk factor for bleeding with use of this drug. We conducted this study to evaluate possible influence of APC on in vitro expression of platelet receptors at therapeutic and supra-therapeutic concentrations. Blood samples of volunteers and patients with severe sepsis were adjusted with APC to final concentrations of 0.045 microg mL(-1) APC (APC-45, therapeutic dose) and 0.225 microg mL(-1) APC (APC-225, five-fold therapeutic dose), respectively. The activation of platelets was mediated by two different agonists. APC had no significant influence on platelet activation, with or without stimulation at both concentrations. In group APC-225, CD62P showed a non-significant decrease. This in vitro study demonstrates that therapeutic plasma concentrations of Drotrecogin alfa (activated) have neither influence on expression of platelet activation markers nor on platelet-granulocyte complexes in blood of volunteers and patients with severe sepsis. Thus, a direct drug-platelet interaction seems unlikely.

Releasing growth factors from activated human platelets after chitosan stimulation: a possible bio-material for platelet-rich plasma preparation

INTRODUCTION

Thrombin is commonly used for activating the platelets and releasing the growth factors on the application of platelet-rich plasma (PRP). We have previously reported that chitosan can enhance rabbit platelet aggregation. In this study, the effects of chitosan on the subsequent growth factors release after human platelets activation were examined to evaluate the possibility of chitosan being used as a substitute for thrombin during PRP preparation.

MATERIAL AND METHODS

Human platelet activation was determined by aggregation, adhesion and alpha-granule membrane glycoprotein expression. Platelet aggregation was measured by the turbidimetric method, the adhesion was directly examined on chitosan-coated glass plates under light microscope and scanning electron microscope (SEM), and the alpha-granule membrane glycoprotein was detected by fluorescent isothiocyanate (FITC)-conjugated anti-CD61 antibody through flow cytometry. The subsequent epidermal growth factor (EGF), platelet-derived growth factor (PDGF)-AB and transforming growth factor (TGF)-beta1 release from platelets were assayed by ELISA after mixing with chitosan.

RESULTS

The enhancing effects on the platelet adhesion and the aggregation from chitosan were observed. Under both microscopes, the adhesive platelets on the chitosan-coated plates were not only greater in number but also earlier in activation than those on the control plates. With flow cytometry, increased glycoprotein IIIa expression in platelets was detected after chitosan treatment. Greater concentrations of growth factors were measured from PRP after chitosan treatment than after the solvent treatment.

CONCLUSION

Because of the observations of growth factors releasing from activated human platelets after chitosan stimulation, we suggest that chitosan may be an appropriate substitute for thrombin in PRP preparation.

Effect of recombinant activated protein C and low-dose heparin on neutrophil-endothelial cell interactions in septic shock

OBJECTIVE

To examine the effects of recombinant activated protein C (rhAPC) and low-dose heparin on neutrophil-platelet-endothelial cell interactions in septic shock.

DESIGN

Controlled experiments using phase contrast microscopy to study neutrophil, platelet, and endothelial cell interactions in flowing cell suspensions under simulated physiologic conditions.

SETTING

University research laboratory.

PATIENTS

Adult patients with septic shock and normal volunteers.

INTERVENTIONS

Neutrophils and platelets removed from control subjects were stimulated with plasma and serum from 21 patients in septic shock and perfused over endothelial cells. Activated protein C, low-dose heparin, and low-dose heparin with rhAPC were added to cells suspended in septic plasma. Neutrophil rolling velocity and the number of neutrophils adherent to endothelial cells and in aggregates were determined. Flow cytometric analysis of CD11b/CD63 cells was used to identify platelet-neutrophil aggregates.

MEASUREMENTS AND MAIN RESULTS

Activated protein C significantly decreased neutrophil adhesion and aggregation and increased rolling velocity in cells stimulated with both septic serum and septic plasma. Significant decreases in platelet-neutrophil aggregates induced by septic plasma were also observed. Low-dose heparin alone had no effects on these variables. The addition of low-dose heparin to cells suspended in septic plasma and rhAPC attenuated the benefits observed with rhAPC alone in each of these variables.

CONCLUSIONS

These data suggest that the in vitro addition of rhAPC decreases sepsis-induced interactions between isolated platelets, neutrophils, and endothelial cells. Low-dose heparin attenuates the benefits observed with rhAPC. The changes in neutrophil-endothelial cell interactions demonstrated with rhAPC may play a role in preserving microvascular patency in patients with septic shock.

Drotrecogin Alfa

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