Lipopolysaccharide-Induced Hemolysis Is Abolished by Inhibition of Thrombin Generation but Not Inhibition of Platelet Aggregation
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Inflammation, Vol. 42, No. 5, October 2019 ( # 2019) DOI: 10.1007/s10753-019-01038-6 ORIGINAL ARTICLE Lipopolysaccharide-Induced Hemolysis Is Abolished by Inhibition of Thrombin Generation but Not Inhibition of Platelet Aggregation Stephan Brauckmann,1,2 Katharina Effenberger-Neidnicht,2 Michael Nagel,3 Christian Mayer,3 Jürgen Peters,1 and Matthias Hartmann 1,4 Abstract—In human sepsis, hemolysis is an independent predictor of mortality, but the mech- anisms evoking hemolysis have not been fully elucidated. Therefore, we tested the hypoth- eses that (1) lipopolysaccharide (LPS)-induced hemolysis is dependent on thrombin gener- ation or platelet aggregation and (2) red cell membranes are weakened by LPS. Anesthetized male Wistar rats were subjected to LPS or vehicle for 240 min. The effects of hemostasis inhibition on LPS-induced hemolysis were investigated by use of the thrombin inhibitor argatroban or the platelet function inhibitor eptifibatide. Free hemoglobin concentration, red cell membrane stiffness and red cell morphological changes were determined by spectropho- tometry, atomic force microscopy, and light microscopy. Efficacy of argatroban and eptifibatide was assessed by rotational thrombelastometry and impedance aggregometry, respectively. LPS markedly increased free hemoglobin concentration (20.8 μmol/l ± 3.6 vs. 3.5 ± 0.3, n =6, p < 0.0001) and schistocytes, reduced red cell membrane stiffness, and induced disseminated intravascular coagulation. Inhibition of thrombin formation with argatroban abolished the increase in free hemoglobin concentration, schistocyte formation, and disseminated intravascular coagulation in LPS-treated animals. Eptifibatide had no inhibitory effect. The LPS evoked decrease of red cell stiffness that was not affected by argatroban or eptifibatide. LPS causes hemolysis, schistocyte formation, and red cell mem- brane weakening in rats. The thrombin inhibitor argatroban but not the platelet inhibitor eptifibatide abolished hemolysis and schistocyte formation. Thus, LPS-induced hemolysis 1 Klinik für Anäesthesiologie und Intensivmedizin, Universitätsklinikum Essen, Universität Duisburg-Essen, Hufelandstraße 55, 45122 Essen, Germany 2 Institut für Physiologische Chemie, Universitätsklinikum Essen, Universität Duisburg-Essen, Hufelandstraße 55, 45122 Essen, Germany 3 Institut für Physikalische Chemie, CENIDE, Universität Duisburg-Es- sen, Universitätsstraße 2, 45141 Essen, Germany 4 To whom correspondence should be addressed at Klinik für Anäesthesiologie und Intensivmedizin, Universitätsklinikum Essen, Universität Duisburg-Essen, Hufelandstraße 55, 45122 Essen, Germany. E-mail: [email protected] Abbreviations: LPS, Lipopolysaccharide 1767 0360-3997/19/0500-1767/0 # 2019 Springer Science+Business Media, LLC, part of Springer Nature 1768 Brauckmann, Effenberger-Neidnicht, Nagel, Mayer, Peters, and Hartmann depends on disseminated intravascular coagulation, possibly enhanced by red cell membrane weakening. Clinical studies are necessary to investigate whether thrombin antagonists can decrease hemolysis and mortality in sepsis. KEY WORDS: lipopolysaccharide; hemolysis; hemostasis; red cell membrane stiffness. BACKGROUND Laboratory Animal Science Association. The experimental protocol had been approved based on the local animal We previously demonstrated that increased free he- protection act with the permit number Az.: 84- moglobin plasma concentration is an independent predictor 02.04.2013.A015. for sepsis mortality [1], and a causal role of free hemoglo- bin in the pathogenesis of sepsis has been demonstrated in Anesthesia, Analgesia, and Instrumentation animals [2]. The deleterious effects of free hemoglobin can be explained by the well-known toxicity of cell free hemo- Rats were anesthetized with isoflurane in O2 (5% – globin and its degradation products [3]. Concerning the isoflurane for induction and 1.5 2% to maintain anesthe- pathophysiological mechanisms leading to hemolysis, an sia), treated with ketamine (50 mg/kg s.c.) and lidocaine involvement of disseminated intravascular coagulation (5 mg/kg s.c.) for analgesia, and subjected to surgical (DIC), which is common in sepsis, has been suggested preparation of the right inguinal region for catheter place- [4]. Infusion of thrombin was demonstrated to form fibrin ments into the right femoral artery and vein. Catheters were ’ strands capable of slicing red blood cells leading to so- perfused with Ringer s solution (arterial 3 ml/h, venous called schistocytes in rats [5]. Such fibrin strands have also 7 ml/kg/h). Mean arterial pressure, heart rate, and respira- been demonstrated in humans with disseminated intravas- tory rate of the spontaneous breathing rats were monitored cular coagulation [6]. Furthermore, we recently demon- continuously. Body temperature was measured using a strated as another potential mechanism contributing to rectal probe and was kept above 37 °C. After 240 min, LPS-induced hemolysis in vivo, that lipopolysaccharide i.e., at the end of the experiments, animals were sacrificed (LPS), the main constituent of the Gram-negative bacterial by cardiac incision under deep isoflurane anesthesia. cell membrane, is incorporated in membranes in a receptor- independent manner and decreases red cell osmotic resis- Experimental Groups and Blood Collections tance and membrane stiffness [7, 8]. Interestingly, TLR-4 Experiments were performed using 6 rats per experi- signaling and an involvement of the complement system as mental intervention over a total period of 240 min each. the mechanisms leading to the LPS-induced hemolysis LPS, argatroban, and eptifibatide were dissolved in were excluded in this latter study [7]. Ringer’s solution and administered intravenously using a In the present study, we tested in anesthetized rats the syringe pump (Perfusor-Secura FT; B. BRAUN, hypotheses that (1) LPS-induced hemolysis depends on Melsungen, Germany). thrombin generation or platelet aggregation and (2) red cell The experimental interventions were as follows: infu- membranes are weakened by the endotoxin. sion of Ringer’s solution as a time control, infusion of LPS alone (1 mg/kg/h), infusion of LPS (1 mg/kg/h) and argatroban (50 μg/kg/min) combined, and LPS (1 mg/kg/ METHODS h) and eptifibatide (180 μg/kg bolus and 2 μg/kg/min) combined. At different time points (baseline, 60, 120, 180, and Animals 240 min), the blood was collected from the femoral artery Male Wistar rats (430 to 470 g) were obtained from into a self-filling arterial sampler (0.7 ml) containing 80 IU the central animal care unit of the University Hospital electrolyte-balanced heparin (PICO50) Radiometer Medi- Essen and kept under standardized conditions of tempera- cal (Brønshøj, Denmark) for measurements of free hemo- ture (22 °C ± 1), humidity (55% ± 5), and 12-h/12-h light/ globin concentration, platelet function, red cell stiffness dark cycles with free access to food (ssniff-Spezialdiäten, and volume, or into a syringe containing sodium citrate Soest, Germany) and water. All animals received humane (0.3 ml; 3.13% Eifelfango, Bad Neuenahr-Ahrweiler, Ger- care according the standards of the Federation of European many) for thromboelastometry examinations. To Lipopolysaccharide-Induced Hemolysis 1769 compensate for the blood sample-induced blood loss, 1 ml Red Cell Morphology and Schistocyte Formation of Ringer’s solution was infused after taking each blood Peripheral blood smears were prepared by the wedge sample. Hematocrit decreased from 42.7% ± 2.4 at base- slide technique. To assess red cell morphology, light mi- line to 32.7% ± 3.7 at 240 min. No changes in arterial croscopy was performed on an inverted microscope (Zeiss pressure and heart rate were observed with this procedure. IM35, Carl Zeiss AG, Oberkochen, Germany) using a magnification of × 400. Images were taken using a Canon Free Hemoglobin Concentration 1000D single-lens reflex camera (Canon, Krefeld, Germa- For the measurement of free hemoglobin concentra- ny). Changes in red cell morphology were compared with tion, platelet poor plasma was obtained by centrifugation time-related samples between the different experimental (3000g, 15 min) and stored at − 80 °C. Free hemoglobin interventions. Definition of schistocytes was according to concentration was measured spectrophotometrically from the International Council for Standardization in Hematol- the absorption of the hemoglobin Soret band (μQuant, Bio- ogy (ICSH). Schistocytes were quantified as the percent- Tek Instruments GmbH, Friedrichshall, Germany) [9]. age of undamaged red cells per 1000 counted cells at the end of the series in a blinded manner [10, 11]. Assessment of Coagulation and Platelet Function Red Cell Membrane Stiffness and Red Cell Volume Sufficient inhibition of coagulation by argatroban was monitored by thromboelastometry of citrated whole blood Red cell membrane stiffness was measured using samples (ROTEM®, TEM International, München, Ger- the atomic force microscopy nanoindentation technique many) according to the manufacturer’s recommendations. (BNano Wizard^, JPK Instruments, Berlin, Germany) Coagulation was initiated by recalcification with 20 μl and noncontact/tapping mode high resonance frequen- 0.2 M CaCl2. For evaluation of consumption of hemostatic cy (NCH) cantilevers (NanoWorld, Neuchatel, Switzer- factors, the maximum clot firmness (MCF) was land) [7]. An intermittent contact mode at a frequency determined. of 240–270 kHz was used for the imaging. The scan Efficacy of platelet aggregation inhibition was