Targeted in vitro synthesis of microparticles
Cell line and cultivation for EDMP production
Human ECV304 cells (Sigma-Aldrich, Steinheim, Germany) were used to investigate endothelial MP generation properties. Cultivated in Dulbecco’s Modified Eagle Medium (DMEM) and incubated under constant conditions at 37 °C, 5 % CO2 and 90 % humidity, cells were subcultured by trypsinization (0.25 % trypsin, Sigma-Aldrich, Steinheim, Germany).
For generating particles, ECV304 cells were incubated with 1 mM hydrogen peroxide (Sigma-Aldrich, Steinheim, Germany); platelets with 1.5 µg/ml bacterial lipopolysaccharide (LPS) (Sigma-Aldrich, Steinheim, Germany) – both for 22 hours at 37 °C maintaining established cultivation conditions. Subsequently, a first centrifugation step was performed to remove cells (10 min at 1.000 x g, 4 °C) followed by a second step to sediment particles from transferred supernatant (45 min at 10.000 x g, 4 °C). After removing residual supernatant, pellets were resuspended in 1x phosphate buffered saline (PBS), pooled and stored at -80 °C until analysis.
Platelet concentrates and PDMP production
Human platelets were obtained from platelet apheresis concentrates of the Institute of Transfusion Medicine (ITM) of the Cologne-Merheim Medical Centre that were not being authorised for transfusion.
For in vitro synthesis of PDMP, 40 mls of platelet concentrates were stimulated with 1.5 µg/ml LPS for 22 h at 37 °C in a humidified incubator with 5 % CO2 (ThermoFisher, Marietta, USA). Subsequently, the platelet suspension was centrifuged at 1.000xg for 10 min at 4 °C (Heraeus, Hanau, Germany). Cell-free supernatant was centrifuged twice at 10.000xg for 45 min at 4 °C (Heraeus, Hanau, Germany) for PDMP pellet sedimentation, which was resuspended in the following in PBS obtaining pure PDMP. PDMP pellets were pooled, aliquoted and stored at -80 °C until analysis.
Blood donation and processing for inducing coagulopathic conditions
Study approval was given by the ethical committee of Witten/Herdecke University (#182/2016). Eleven healthy volunteers, fulfilling the ITM criteria for blood donation (age ≥18 years; no preexisting history of coagulation disorders, anticoagulant and/or platelet-inhibiting medication or viral infection), consented to participate and donated 60 mls blood, which was collected in citrated monovettes (Sarstedt, Nümbrecht, Germany)
Coagulopathic conditions such as haemodilution (HD) and lethal triad (LT) were simulated in vitro as previously described [18,19]. In brief, conditions were either induced by diluting whole blood (WB) by replacing ⅓ by crystalloids (Sterofundin® ISO Infusionslösung, B. Braun Melsungen AG, Melsungen, Germany) only (hereafter be referred to as haemodilution, HD) or in combination with lowering the pH value to 6.8 using 2 M HCl and decreasing the temperature from 37 to 32 °C (hereafter be referred to as lethal triad, LT). Constant temperature was realized by continuous storage of samples in an appropriate tempered water bath (Thermolab1070, GFL, Burgwedel, Germany).
Application of PDMP and EDMP to the experimental HD and LT approaches
After introducing the conditions of HD and LT, either no MP (untreated controls) or EDMP/PDMP were supplemented in distinct concentrations of 1000 (1k), 10.000 (10k) or 15.000 (15k) MP/µl (Figure 1). Exact microparticle quantities required for the experimental approaches had been determined shortly before flow cytometric analysis by using the BD AccuriTM C6 (BD, Heidelberg, Germany). For this purpose, particles were defined by size (0.5 to 0.9 µm) [21] and by typical surface marker originated from the parental cell such as CD42b for platelets and CD144 for endothelial cells, respectively (BD, Heidelberg, Germany). In addition, Annexin V dye was used as marker for the externalisation of phosphatidylserine (PS). After a microparticle incubation of 5 min, samples were processed for subsequent coagulation analysis.
Extended coagulation analysis
Detection of activated platelets
For measuring platelet activation, cells were fixed according to Cyfix III protocol [20] and P-selectin expression was flow cytometric measured by using CD42b and CD62p antibodies (BD. Heidelberg, Germany) and the BD AccuriTM C6 device (BD, Heidelberg, Germany). Results are presented as relative changes of CD42b+/CD62p+ stained platelets referring to the respective unstimulated approach of each experimental group (set as 100%).
Thrombodynamics® (TD)
Differential centrifugation was applied for TD analysis (1.600 x g for 15 minutes followed by a spin of plasma for 5 minutes at 10.000 x g) and platelet-poor plasma (PPP) was immediately shock-frozen in liquid nitrogen and stored at -80 °C until analysis.
For TD analysis, PPP samples of WB and HD were thawed at 37°C and those of LT were thawed accordingly at 32°C in a water bath. The corresponding temperatures for WB, HD and LT were maintained during the TD measurements.
For the determination of spatial clot growth, the TDX kit consisting of reagent I (lyophilized protein of FXIIa inhibitor) and reagent II (CaCl2) was used according to the manufacturer’s recommendation (HemaCore, Moscow, Russia). Briefly, 120 µl of PPP were supplemented with reagent I and incubated in the device thermostat for 15 min (HemaCore, Moscow, Russia). Subsequently, the PPP samples were treated with reagent II and directly placed into the micro chamber. By inserting a with immobilized tissue factor coated insert, the reaction had been initiated and clot growth and spontaneous clot formation was recorded over 45 min. The following parameters were measured: lag-time (Tlag, min), rate of clot growth (V, µm/min), initial rate of clot growth (Vi, µm/min), clot density (D, a.u.) and clot size (Cs, µm). In addition to these parameters, Cs was measured in five minutes intervals (0-20 min) to estimate the influence of MP on the dynamics of clot growth. In order to statistically record the changed Cs over time, the individual areas under the curve (AUC) of each donor was calculated.
Statistical analysis
Statistics and graphical data analyses were performed using GraphPad Prism version 7.00 for Windows (GraphPad Software, La Jolla, USA). Non-parametric Friedman test and Dunn's post-hoc test to correct for multiple comparisons were applied to determine significant differences across the collected parameters in the groups of HD and LT.
In a first step, the MP-untreated samples in the groups of WB, HD and LT were pairwise compared as follows: WB vs. HD, WB vs. LT and HD vs. LT. Secondly, the effects of dose-specific application of PDMP or EDMP were tested in the HD and LT groups by comparing. Finally, untreated WB samples a non-parametric Wilcoxon test revealed potential effects between untreated and MP-supplemented samples (C vs. 1k). P-values with a significance level <0.05 were considered statistically significant.
Values with respect to platelet count and TD temporal course of clot growth (Cs) are presented as arithmetical mean and standard deviation.