Increased platelet microvesicle formation is associated with mortality in a porcine model of endotoxemia

Decrease of exosomal miR-21-5p and the increase of CD62p+ exosomes are associated with the development of sepsis in polytraumatized patients

Sepsis as a severe systemic inflammation leads oftentimes to organ dysfunction and subsequently to death. In polytrauma patients, septic complications represent with 45% the predominant cause of late death and are responsible for extremely high costs in the healthcare system. Therefore, clinicians have to detect as early as possible the begin of sepsis to improve the patient's outcome. One new promising diagnostic tool to diagnose septic complications in polytraumatized patients are exosomes. Plasma samples from polytraumatized patients (Injury Severity Score (ISS) ≥16) which developed sepsis (n = 10) and without sepsis (n = 10), were collected at emergency room (ER), 24h and 5 days after trauma. The EVs subpopulations were investigated by a bead-based multiplex flow cytometry measurement of surface epitopes and were compared with plasma EVs from healthy controls (n = 10). Moreover, exosomal cytokine concentrations were measured via high-sensitive ELISA and were correlated with systemic concentrations. For miRNA cargo analysis, we analysed the miRNAs miR-1298-5p, miR-1262, miR-125b-5p, miR-92a-3p, miR-93-5p, miR-155-5p and miR-21-5p and compared their exosomal concentrations by means of RT-qPCR. CD62p + exosomes were significantly increased in septic polytrauma-patients (p ≤ 0.05), while CD40+exosomes, as well as CD49e + exosomes were diminished (p ≤ 0.05). Furthermore, we observed that the exosomal IL-6 concentration reflects the systemic IL-6 concentration (r2 = 0.63) and did not significantly alter between patients with and without sepsis. The exosomal IL-10 concentration seemed to be constant in all patients and healthy controls. We observed that a decrease of miR-21-5p in exosomes was associated with the development of sepsis (p ≤ 0.05), while exosomal miR-93-5p, miR-155-5p and miR-92a-3p were not specifically altered in septic patients. Taken together, the present study in polytraumatized patients demonstrated that the development of sepsis is associated with an increase of CD62p + exosomes. Furthermore, the exosomal cargo was changed in septic patients: miR-21-5p was diminished.

Large extracellular vesicle (EV) and neutrophil extracellular trap (NET) interaction captured in vivo during systemic inflammation

Extracellular vesicles (EVs) and neutrophil extracellular traps (NETs) are pivotal bioactive structures involved in various processes including inflammation. Herein we report the interactions between EVs and NETs during murine endotoxemia studied in situ directly in the vasculature (cremaster muscle, liver sinusoids) using intravital microscopy (IVM). We captured NETs and EV release in real time by both non- and polarized neutrophils in liver but not in cremaster vasculature. When comparing numbers of circulating EVs of various origin (nanoparticle tracking analysis-NTA, flow cytometry) with those interacting with endothelium and NETs (IVM) we observed that whereas platelet and monocyte/macrophage-derived EVs dominate in blood and peritoneal lavage, respectively, mostly neutrophil-derived EVs interact with the vascular lining, NETs and leukocytes. Despite the interaction, NETs do not affect EV formation as NET release inhibition did not alter EV release. However, EVs inhibit NETs formation and in particular, erythrocyte-derived EVs downregulate NET release and this effect is mediated via Siglec-E-dependent interactions with neutrophils. Overall, we report that EVs are present in NETs in vivo and they do modulate their release but the process in not bidirectional. Moreover, EVs isolated from body fluids might not reflect their importance in direct endothelial- and leukocyte-related interactions.

THE ROLES OF EXTRACELLULAR VESICLES IN SEPSIS AND SYSTEMIC INFLAMMATORY RESPONSE SYNDROME

ABSTRACT

Sepsis is a life-threatening organ dysfunction, caused by dysregulation of the host response to infection. To understand the underlying mechanisms of sepsis, the vast spectrum of extracellular vesicles (EVs) is gaining importance in this research field. A connection between EVs and sepsis was shown in 1998 in an endotoxemia pig model. Since then, the number of studies describing EVs as markers and mediators of sepsis increased steadily. Extracellular vesicles in sepsis could be friends and foes at the same time depending on their origin and cargo. On the one hand, transfer of EVs or outer membrane vesicles can induce sepsis or systemic inflammatory response syndrome with comparable efficiency as well-established methods, such as cecal ligation puncture or lipopolysaccharide injection. On the other hand, EVs could provide certain therapeutic effects, mediated via reduction of reactive oxygen species, inflammatory cytokines and chemokines, influence on macrophage polarization and apoptosis, as well as increase of anti-inflammatory cytokines. Moreover, EVs could be helpful in the diagnosis of sepsis. Extracellular vesicles of different cellular origin, such as leucocytes, macrophages, platelets, and granulocytes, have been suggested as potential sepsis biomarkers. They ensure the diagnosis of sepsis earlier than classical clinical inflammation markers, such as C-reactive protein, leucocytes, or IL-6. This review summarizes the three roles of EVs in sepsis-mediator/inducer, biomarker, and therapeutic tool.

Therapeutic Potential of Extracellular Vesicles for Sepsis Treatment

Sepsis is a deadly condition lacking a specific treatment despite decades of research. This has prompted the exploration of new approaches, with extracellular vesicles (EVs) emerging as a focal area. EVs are nanosized, cell-derived particles that transport bioactive components (i.e., proteins, DNA, and RNA) between cells, enabling both normal physiological functions and disease progression depending on context. In particular, EVs have been identified as critical mediators of sepsis pathophysiology. However, EVs are also thought to constitute the biologically active component of cell-based therapies and have demonstrated anti-inflammatory, anti-apoptotic, and immunomodulatory effects in sepsis models. The dual nature of EVs in sepsis is explored here, discussing their endogenous roles and highlighting their therapeutic properties and potential. Related to the latter component, prior studies involving EVs from mesenchymal stem/stromal cells (MSCs) and other sources are discussed and emerging producer cells that could play important roles in future EV-based sepsis therapies are identified. Further, how methodologies could impact therapeutic development toward sepsis treatment to enhance and control EV potency is described.

Extracellular vesicles as mediators and markers of acute organ injury: current concepts

Due to the continued high incidence and mortality rate worldwide, there is a need to develop new strategies for the quick, precise, and valuable recognition of presenting injury pattern in traumatized and poly-traumatized patients. Extracellular vesicles (EVs) have been shown to facilitate intercellular communication processes between cells in close proximity as well as distant cells in healthy and disease organisms. miRNAs and proteins transferred by EVs play biological roles in maintaining normal organ structure and function under physiological conditions. In pathological conditions, EVs change the miRNAs and protein cargo composition, mediating or suppressing the injury consequences. Therefore, incorporating EVs with their unique protein and miRNAs signature into the list of promising new biomarkers is a logical next step. In this review, we discuss the general characteristics and technical aspects of EVs isolation and characterization. We discuss results of recent in vitro, in vivo, and patients study describing the role of EVs in different inflammatory diseases and traumatic organ injuries. miRNAs and protein signature of EVs found in patients with acute organ injury are also debated.

Circulating microparticles are associated with clinical severity of persistent ST-segment elevation myocardial infarction complicated with cardiogenic shock

BACKGROUND

Cardiogenic shock (CS) is the leading cause of death in patients admitted for acute myocardial infarction (MI). Despite the recent advances in reperfusion and medical treatment mortality remains unacceptably high. Whether cells of the blood compartment in CS-patients are activated and release microparticles (cMPs) that may be both messengers and biomarkers of cell damage is not known. We aimed to investigate the cMP subtypes and parental activated cells of ST-elevation MI (STEMI)-patients complicated by CS and that of non-CS STEMI-patients (non-CS) in order to identify a cMP signature that could aid CS patient's risk stratification.

METHODS

Clinically-characterized STEMI-patients with and without CS (36/group) were included. Treatment was delivered according to guidelines and included primary percutaneous coronary intervention. cMPs were characterized by triple-labeling flow cytometry using Annexin V and cell surface-specific monoclonal antibodies.

RESULTS

Increased levels of leukocyte-derived (neutrophil and granulocyte origin) and platelet-derived cMPs were detected in CS compared to non-CS patients. A signature of cMPs derived from platelets, leukocytes, and endothelium discriminated CS-patients (AUC of 0.743±0.059 [95% CI: 0.628-0.859], P<0.0001) and predicted mortality in CS (AUC of 0.869±0.06 [95% CI: 0.750-0.988], P<0.0001). In CS-patients, a higher number of platelet- and monocyte-cMPs and of tissue factor-rich cMPs associated to worse myocardial blush grade and thrombolysis in myocardial infarction flow.

CONCLUSIONS

cMPs derived from proinflammatory and prothrombotic cells were found to be elevated in CS-patients. In treated as per guidelines CS patients, granulocytes and neutrophils remained activated and actively shed cMPs. These cMPs were biomarkers of adverse prognosis in CS.

TRANSLATIONAL ASPECT

Increased levels of leukocyte and platelet-derived circulating microparticles (cMPs) are found in cardiogenic shock (CS) patients as compared to non-CS patients. In CS-patients, a higher number of platelet- and monocyte-cMPs and a higher number of tissue factor-rich cMPs were associated to worse myocardial reperfusion. A specific prothrombotic and proinflammatory cMPs signature in cardiogenic shock (CS) patients is a potential discriminator and survival prognostic biomarker for CS, which could aid management and improve clinical outcomes.

Extracellular Vesicles as Markers and Mediators in Sepsis

Sepsis is defined as life-threatening organ dysfunction caused by a dysregulated host response to infection. It remains a highly lethal condition in which current tools for early diagnosis and therapeutic decision-making are far from ideal. Extracellular vesicles (EVs), 30 nm to several micrometers in size, are released from cells upon activation and apoptosis and express membrane epitopes specific for their parental cells. Since their discovery two decades ago, their role as biomarkers and mediators in various diseases has been intensively studied. However, their potential importance in the sepsis syndrome has gained attention only recently. Sepsis and EVs are both complex fields in which standardization has long been overdue. In this review, several topics are discussed. First, we review current studies on EVs in septic patients with emphasis on their variable quality and clinical utility. Second, we discuss the diagnostic and therapeutic potential of EVs as well as their role as facilitators of cell communication via micro RNA and the relevance of micro-organism-derived EVs. Third, we give an overview over the potential beneficial but also detrimental roles of EVs in sepsis. Finally, we focus on the role of EVs in selected intensive care scenarios such as coagulopathy, mechanical ventilation and blood transfusion. Overall, the prospect for EV use in septic patients is bright, ranging from rapid and precise (point-of-care) diagnostics, prevention of harmful iatrogenic interventions, to using EVs as guides of individualized therapy. Before the above is achieved, however, the EV research field requires reliable standardization of the current methods and development of new analytical procedures that can close the existing technological gaps.

HMGB1/IL-1β complexes in plasma microvesicles modulate immune responses to burn injury

Modulating immune responses to sepsis and trauma remain one of the most difficult challenges in modern medicine. Large burn injuries (LBI) are a severe form of trauma associated with sepsis, immune impairment, and mortality. Immune dysfunction after LBI is complex, involving both enhanced and impaired immune activation. The release of Damage-Associated Molecular Patterns (DAMPs), such as HMGB1, and cytokines (e.g. IL-1β) creates an environment of immune dysfunction often leading to end organ failure and death. Both HMGB1 and IL-1β have been found to play critical roles in sepsis and post-burn immune dysfunction. HMGB1 and IL-1β have been shown previously to form potent complexes in vitro. We recently identified the presence of HMGB1/IL-1β heterocomplexes in human tissue. We now find HMGB1/IL-1β complexes in human and mouse plasma, and identify a synergistic role of HMGB1/IL-1β complexes in post-burn immune dysfunction. In both humans and mice, we found that HMGB1 was enriched in plasma microvesicles (MVs) after LBI. HMGB1 was found form complexes with IL-1β. Using flow cytometry of mouse plasma MVs, we identified an increase in an HMGB1+/IL-1β+ MVs. Using co-IP, HMGB1 was found to bind the pro-form of IL-1β in mouse and human plasma. Pro-IL-1β, which is traditionally considered inactive, became active when complexed with HMGB1. Human THP-1 monocytes treated with HMGB1-pro-IL-1β complexes showed increased transcription of LBI associated cytokines IL-6 and IFNβ along with suppression of iNOS, mimicking findings associated with LBI. These findings identify that HMGB1/IL-1β complexes released after burn injuries can modulate immune responses, and microvesicles are identified as a novel reservoir for these immune mediators. These complexes might serve as novel immune targets for the treatment of systemic immune responses due to LBI or other causes of sepsis.

Technological Advances in Cardiovascular Safety Assessment Decrease Preclinical Animal Use and Improve Clinical Relevance

Cardiovascular (CV) safety liabilities are significant concerns for drug developers and preclinical animal studies are predominately where those liabilities are characterized before patient exposures. Steady progress in technology and laboratory capabilities is enabling a more refined and informative use of animals in those studies. The application of surgically implantable and telemetered instrumentation in the acute assessment of drug effects on CV function has significantly improved historical approaches that involved anesthetized or restrained animals. More chronically instrumented animals and application of common clinical imaging assessments like echocardiography and MRI extend functional and in-life structural assessments into the repeat-dose setting. A growing portfolio of circulating CV biomarkers is allowing longitudinal and repeated measures of cardiac and vascular injury and dysfunction better informing an understanding of temporal pathogenesis and allowing earlier detection of undesirable effects. In vitro modeling systems of the past were limited by their lack of biological relevance to the in vivo human condition. Advances in stem cell technology and more complex in vitro modeling platforms are quickly creating more opportunity to supplant animals in our earliest assessments for liabilities. Continuing improvement in our capabilities in both animal and nonanimal modeling should support a steady decrease in animal use for primary liability identification and optimize the translational relevance of the animal studies we continue to do.

Microparticles: a new perspective in central nervous system disorders

Microparticles (MPs) are a heterogeneous population of small cell-derived vesicles, ranging in size from 0.1 to 1 μm. They contain a variety of bioactive molecules, including proteins, biolipids, and nucleic acids, which can be transferred between cells without direct cell-to-cell contact. Consequently, MPs represent a novel form of intercellular communication, which could play a role in both physiological and pathological processes. Growing evidence indicates that circulating MPs contribute to the development of cancer, inflammation, and autoimmune and cardiovascular diseases. Most cell types of the central nervous system (CNS) have also been shown to release MPs, which could be important for neurodevelopment, CNS maintenance, and pathologies. In disease, levels of certain MPs appear elevated; therefore, they may serve as biomarkers allowing for the development of new diagnostic tools for detecting the early stages of CNS pathologies. Quantification and characterization of MPs could also provide useful information for making decisions on treatment options and for monitoring success of therapies, particularly for such difficult-to-treat diseases as cerebral malaria, multiple sclerosis, and Alzheimer's disease. Overall, studies on MPs in the CNS represent a novel area of research, which promises to expand the knowledge on the mechanisms governing some of the physiological and pathophysiological processes of the CNS.

Microvesicles at the crossroads between infection and cardiovascular diseases

Observational and experimental studies continue to support the association of infection and infection-stimulated inflammation with development of cardiovascular disease (CVD) including atherosclerosis and thrombosis. Microvesicles (MV) are heterogeneous populations of sealed membrane-derived vesicles shed into circulation by activated mammalian cells and/or pathogenic microbes that may represent an interface between bacterial/microbial infection and increased risk of CVD. This review evaluates how MV act to modulate and intersect immunological and inflammatory responses to infection with particular attention to progression of CVD. Although infection-related stimuli provoke release of MV from blood and vascular cells, MV express phosphatidylserine and other procoagulant factors on their surface, which initiate and amplify blood coagulation. In addition, MV mediate cell-cell adhesion, which may stimulate production of pro-inflammatory cytokines in vascular cells, which in turn aggravate progression of CVD and propagate atherothrombosis. MV transfer membrane receptors, RNA and proteins among cells, and present auto-antigens from their cells of origin to proximal or remote target cells. Because MV harbor cell surface proteins and contain cytoplasmic components of the parent cell, they mediate biological messages and play a pivotal role in the crossroad between infection-stimulated inflammation and CVDs.

Leukocyte- and platelet-derived microvesicle interactions following in vitro and in vivo activation of toll-like receptor 4 by lipopolysaccharide

Background

Pro-coagulant membrane microvesicles (MV) derived from platelets and leukocytes are shed into the circulation following receptor-mediated activation, cell-cell interaction, and apoptosis. Platelets are sentinel markers of toll-like receptor 4 (TLR4) activation. Experiments were designed to evaluate the time course and mechanism of direct interactions between platelets and leukocytes following acute activation of TLR4 by bacterial lipopolysaccharide (LPS).

Methodology/Principal Findings

Blood from age-matched male and female wild type (WT) and TLR4 gene deleted (dTLR4) mice was incubated with ultra-pure E. coli LPS (500 ng/ml) for up to one hour. At designated periods, leukocyte antigen positive platelets, platelet antigen positive leukocytes and cell-derived MV were quantified by flow cytometry. Numbers of platelet- or leukocyte-derived MV did not increase within one hour following in vitro exposure of blood to LPS. However, with LPS stimulation numbers of platelets staining positive for both platelet- and leukocyte-specific antigens increased in blood derived from WT but not dTLR4 mice. This effect was blocked by inhibition of TLR4 signaling mediated by My88 and TRIF. Seven days after a single intravenous injection of LPS (500 ng/mouse or 20 ng/gm body wt) to WT mice, none of the platelets stained for leukocyte antigen. However, granulocytes, monocytes and apoptotic bodies stained positive for platelet antigens.

Conclusions/Significance

Within one hour of exposure to LPS, leukocytes exchange surface antigens with platelets through TLR4 activation. In vivo, leukocyte expression of platelet antigen is retained after a single exposure to LPS following turn over of the platelet pool. Acute expression of leukocyte antigen on platelets within one hour of exposure to LPS and the sustained expression of platelet antigen on leukocytes following a single acute exposure to LPS in vivo explains, in part, associations of platelets and leukocytes in response to bacterial infection and changes in thrombotic propensity of the blood.

Early endotoxin-mediated haemostatic and inflammatory responses in the clopidogrel-treated pig

We have previously shown that the thrombin inhibiting agent melagatran markedly prolongs aPTT and counteracts creatinine increase in endotoxemic pigs. Against this background the effects of the platelet-inhibiting agent, clopidogrel on basic haemostatic, inflammatory and physiological variables were evaluated during porcine endotoxemia. Clopidogrel (10 mg/kg) or saline was randomly injected i.v. 30 min before start of a 6-h continuous infusion of endotoxin in 12 anaesthetised pigs. Another three pigs were given clopidogrel but not endotoxin. Clopidogrel did not affect physiological variables, formation of activated platelet microparticles, PK, aPTT, platelet count, plasma fibrinogen, TNF-alpha, or IL-6 during porcine endotoxemia. Although renal function, as evaluated by creatinine clearance (CLcr) deteriorated significantly (P = 0.01) in the saline-endotoxin, but not in the clopidogrel-endotoxin group, there was no significant difference between the saline-endotoxin and the clopidogrel-endotoxin groups. Renal biopsies were marked with a FITC-labelled chicken anti-fibrinogen antibody detecting fibrinogen and platelet bound fibrinogen, as a marker of porcine platelet activation, and examined by light microscopy. Evaluation of these immunohistochemical slides did not indicate that clopidogrel, significantly reduced the amount of intrarenal fibrin or fibrinogen depositions. Besides a trend to preserve renal function, clopidogrel did not affect haemodynamics or the coagulatory and inflammatory responses in porcine endotoxemia.

Ringer's solution but not hydroxyethyl starch or modified fluid gelatin enhances platelet microvesicle formation in a porcine model of septic shock †

BACKGROUND

Sepsis is associated with volume deficit and clotting system activation. Platelet activation in sepsis results in an increased formation of microvesicles, which in turn, have been associated with increased mortality. We hypothesized an effect of different volume replacement solutions on platelet-derived microvesicle formation in septic shock.

METHODS

Anaesthetized, mechanically ventilated and multi-catheterized pigs received 1 g kg(-1) body weight faeces into the abdominal cavity to induce sepsis and were observed over 8 h. Five animals in each group received volume replacement therapy with modified fluid gelatin 4% or 8% (MFG4%, MFG8%), 6% hydroxyethylstarch (HES) 200/0.5 or Ringer's solution (RS) to maintain a central venous pressure of 12 mm Hg. Flow cytometry was used for determination of microvesicles before induction of sepsis (baseline) and after 8 h. Platelets and microvesicles were identified with an anti-platelet monoclonal Ab and a secondary antibody. Microvesicles were determined as the smallest 1-3% positive cells in forward scatter. Intergroup comparisons were performed using Wilks-Lambda and Ryan-Einot-Gabriel-Welsh F-test. Differences within groups were compared using a two-tailed Student's t-test.

RESULTS

Baseline values were considered as 100%. While microvesicle formation was reduced in HES (73 (sd 19)%), MFG4% (63 (41)%) and MFG8% groups (53 (17)%), an increase in the RS-group (210 (121)%) was observed. Eight hours after induction of sepsis, formation of microvesicles was significantly higher in the RS group compared to all colloid-treated groups.

CONCLUSION

In this porcine septic shock model the formation of platelet-derived microvesicles was significantly increased by volume replacement with Ringer's solution in comparison to colloid solutions.

Effects of mechanical ventilation on platelet microparticles in bronchoalveolar lavage fluid

INTRODUCTION

Mechanical ventilation (MV) is considered to contribute to lung injury. Platelet membrane-derived microparticles (PMPs) are procoagulant and participate in the inflammatory process. The bronchoalveolar space could, besides plasma, be a site of origin of these microparticles. We evaluated the presence of these PMPs and two prostaglandin-derived metabolites in bronchoalveolar lavage fluid (BALF) regarding their possible relation to MV.

MATERIALS AND METHODS

Before and after 1 h of MV, PMPs and prostaglandin metabolites were analyzed, in BALF from 14 anesthetized pigs, by flow cytometry and RIA, respectively. Tracheal mucus from five humans was analyzed for PMPs at extubation after surgery.

RESULTS

Activated PMPs and prostaglandin metabolites were present in all BALF samples. The time needed to count 5000 cellular events was prolonged six-fold after 1 h of mechanical ventilation (p<0.001). The relative content of PMPs was constant in all samples. The PMPs were thrombogenic, i.e. they were fibrinogen, p-selectin and von Willebrand factor positive. Lavage did not per se affect the period necessary to count 5000 cellular events. PMPs in human tracheal mucus were in the same range as in the pig after 1 h of MV aiming at a PaCO(2) between 5.0 and 5.5 kPa.

CONCLUSIONS

Activated PMPs are present in the pulmonary air-liquid interface. The prolongation of the time needed to count 5000 cellular events in BALF after MV indicates activation and adherence. Adherent microparticles bind neutrophils, which may aggravate pathological processes leading to pulmonary dysfunction. Evaluation of PMPs in BALF may be useful in evaluating strategies for lung-protective ventilator treatment.

[Chronic experimental bacteremia in Yucatan micropigs]

The Yucatan micropig has been used to develop an experimental model of chronic bacteremia. This animal exhibits clinical and biological characteristics that are close to those in humans, and the pharmacokinetic behaviours of many classes of drugs in this model are similar to those in man. Six adult female were intravenously inoculated with a mean Escherichia coli inoculum of 5.1 x 10(9) bacteria. During five days of spontaneous evolution, the medical follow-up includes biological, clinical and bacteriological parameters. A systemic inflammatory syndrome, a sepsis, an organ insufficiency and positive blood cultures mimic the human disease. In all animals there is an adynamia, a lack of motor coordination, an anorexia, a tachypnea, a fever, a leuconeutropenia followed by an hyperleucocytosis, an anemia, a thrombopenia, an acute tubulonephritis and an elevated sedimentation rate. In some cases, there is an increase of the C reactive protein, in others, an increase of IL-6 and IL-8. At day five, all animals are alive, and five micropigs have positive blood cultures. This chronic, reproducible model is thus suitable for further antibacterial treatments evaluations.

Propofol (Diprivan-EDTA) counteracts oxidative injury and deterioration of the arterial oxygen tension during experimental septic shock

PURPOSE

Human septic shock can be replicated in the endotoxaemic pig. Endotoxaemia causes a multitude of events, including reduced PaO(2) and increased lipid peroxidation. This study was designed to evaluate the possible effects of a commonly used anaesthetic drug with known antioxidant properties (propofol) during porcine endotoxaemia.

METHODS

Ten pigs were anaesthetised and given a 6 h E. coli endotoxin infusion. The animals received, randomly, a supplementary continuous infusion of propofol emulsion (containing 0.005% EDTA) or the corresponding volume of vehicle (controls). Pathophysiologic responses were determined. Non-enzymatic (by measuring plasma 8-iso-PGF(2 alpha) and enzymatic (by measuring plasma 15-keto-dihydro-PGF(2 alpha)) lipid peroxidations were evaluated. Plasma levels of the endogenous antioxidants alpha- and gamma-tocopherols, were also analysed.

RESULTS

Endotoxaemia increased plasma levels of 8-iso-PGF(2 alpha) (1st-4th h) and 15-keto-dihydro-PGF(2 alpha) (1st-4th h) significantly more in controls than in the propofol+endotoxin group. PaO(2) was significantly less affected by endotoxin in the propofol treated animals (2nd-4th h). Mean arterial pressure (4th-6th h) and systemic vascular resistance (6th h) were reduced significantly more by endotoxin among the propofol-treated animals. Vitamin E (alpha-tocopherol) increased in all animals, significantly more in the propofol+endotoxin group (1/2-6th h) than in the control group.

CONCLUSIONS

Propofol reduced endotoxin-induced free radical mediated and cyclooxygenase catalysed lipid peroxidation significantly. The implication is that propofol counteracts endotoxin-induced deterioration of PaO(2).

Effects of melagatran, a novel direct thrombin inhibitor, during experimental septic shock

Sepsis and endotoxaemia initiate the generation of thrombin, which is responsible for the conversion of fibrinogen to fibrin, platelet aggregation and acts as an inflammatory mediator affecting numerous types of cells, including myocardial, smooth muscle and endothelial cells. Human Gram-negative septic shock, frequently seen in intensive care units, is a condition with high mortality. This condition can be replicated in the endotoxaemic pig. As many of the toxic effects of sepsis are due to thrombin generation, it was of interest to study, using this porcine experimental septic shock model, whether inhibition of thrombin could alleviate the effects of endotoxaemia. For this purpose melagatran, a direct synthetic thrombin inhibitor with a molecular weight of 429 Da, was employed. Melagatran does not significantly interact with any other enzymes in the coagulation cascade or fibrinolytic enzymes aside from thrombin. Furthermore, melagatran does not require endogenous co-factors such as antithrombin or heparin co-Factor II for its antithrombin effect, which is important, as these inhibitors are often consumed in septic patients. We have shown that melagatran exerts a beneficial effect on renal function, as evaluated by plasma creatinine and urinary output, during experimental septic shock. These effects were most pronounced during the later phase of the experimental period, after the infusion of melagatran had been discontinued. Prevention of intrarenal coagulation may be attributable to this finding. In addition, melagatran had beneficial effects on systemic haemodynamics (left ventricular stroke work index, pulmonary capillary wedge pressure and systemic vascular resistance index) in endotoxaemic pigs. This result may be explained by the ability of melagatran to inhibit thrombin, thereby counteracting thrombin's cellular effects. Thus, it can be seen, using this experimental model of septic shock, that melagatran may help to alleviate some of the damaging effects of endotoxaemia, although more research is required to test this further.

Vitamin E in relation to lipid peroxidation in experimental septic shock

Lipid peroxidation and antioxidant balance in the body is a crucial factor in the pathophysiology of various diseases. This study investigates the circulatory alpha-tocopherol levels and its relationship with 8-iso-prostaglandin F2alpha (8-iso-PGF2alpha), a non-enzymatic and, 15-keto-13,14-dihydro-PGF2alpha (15-K-DH-PGF2alpha), a cyclooxygenase catalysed oxidation product of arachidonic acid in experimental septic shock in pigs. A steady decrease in alpha-tocopherol levels in plasma was observed in both survivor and non-survivor animals. A simultaneous increase of oxidative injury indicator, plasma 8-iso-PGF2alpha was seen in both groups but with a different fashion. 8-Iso-PGF2alpha levels increased steadily in the animals that died during the experiment. An early and rapid increase of plasma 15-K-DH-PGF2alpha, an inflammatory response indicator, was also observed in all animals. There was a significant difference in the kinetics of decrement of alpha-tocopherol levels and a concomitant increase in 15-K-DH-PGF2alpha levels among the non-survivors. Thus, a successive disappearance of circulatory vitamin E in conjunction with the surge of plasma isoprostanes and prostaglandins impairs the oxidant-antioxidant balance in favour of the former and may possibly have an effect on the survivality during experimental porcine septicaemia.

Lipid peroxidation induced by an early inflammatory response in endotoxaemia

BACKGROUND

Endotoxaemic challenge promptly causes lipid peroxidation. Porcine endotoxaemia can be used to replicate severe human septic shock. This model was used to evaluate non-enzymatic [8-Iso-prostaglandin F2alpha (8-Iso-PGF2alpha)] and enzymatic [15-keto-13,14-dihydro-prostaglandin F2alpha (15-K-DH-PGF2alpha)] lipid peroxidation, respectively, in relation to survival. The aim of this study was to correlate, if possible, pathophysiologic events during endotoxaemia to the levels of these arachidonic acid metabolites.

METHODS

Nineteen pigs were anaesthetised, monitored (circulatory and respiratory variables in relation to lipid peroxidation) and given a continuous 6 h E. coli endotoxin (10 microg x kg(-1) x h(-1)) infusion. All animals were mechanically ventilated at constant tidal volumes and the inspired oxygen fraction was kept constant during the experimental period.

RESULTS

This endotoxin infusion caused expressed derangements in all pigs and death in 9 of them. The levels of 8-Iso-PGF2alpha, indicating oxidative injury, were different in time course, magnitude and fashion between survivors and non-survivors. The levels of 15-K-DH-PGF2alpha, indicating inflammatory response, showed a similar pattern. At 1 h the CO2 partial pressure in arterial blood was significantly higher in non-surviving pigs and correlated (r: 0.7; P<0.05) to the levels of 15-K-DH-PGF2alpha. Prostaglandin F2alpha is mainly metabolised in the lung. The lung weights were significantly (P<0.05) higher in non-surviving than in surviving animals. Both free radical and cyclooxygenase catalysed oxidative modification occurs during endotoxaemia.

CONCLUSION

Increased metabolism and inflammation, as evaluated by 15-K-DH-PGF2alpha, in the group of non-survivors may mediate the increase in arterial CO2. Thus, increased lipid peroxidation seems to be associated with endotoxaemic organ dysfunction and increased mortality.

Oxidative injury and survival during endotoxemia

This study investigates the plasma levels of 8-iso-PGF2alpha, a non-enzymatic, and 15-K-DH-PGF2alpha, a cyclooxygenase catalyzed oxidation product of arachidonic acid in an experimental porcine endotoxemic shock model. A significant (P < 0.001) and rapid appearance and disappearance of PGF2alpha metabolite after endotoxin infusion was very similar in both non-survival and survival groups indicating an acute progression and recession of inflammation. When oxidative injury was assessed by measuring free 8-iso-PGF2alpha the levels in plasma increased significantly up to 2 h and remained at this level until death among the non-survivors. This was apparently different from the survivors where the 8-iso-PGF2alpha levels increased to its height at 1 h, then decreased to the basal levels after 5 h. Thus, free radical and cyclooxygenase catalyzed oxidation of arachidonic acid occurs during endotoxemia. Free radical dependent oxidative injury following endotoxin induced inflammation may be the major cause of organ failure and increased mortality.

Radioimmunoassay of 15-keto-13,14-dihydro-prostaglandin F2alpha: an index for inflammation via cyclooxygenase catalysed lipid peroxidation

The metabolism of PGF2alpha in human and other species results initially in the formation of 15-keto-dihydro-PGF2alpha and later to several beta-oxidized metabolites, which are species-specific. Since the discovery of cyclooxygenase-2 (COX-2), the importance of measuring various arachidonic acid metabolites during inflammatory conditions is on focus. This study presents the development and validation of a new radioimmunoassay of 15-keto-dihydro-PGF2alpha as an index of lipid peroxidation via cyclooxygenase (COX-1 and COX-2) pathway. Furthermore, its application in endotoxin-induced acute inflammation in pigs is presented. An antibody was raised in rabbits by immunization with 15-keto-dihydro-PGF2alpha coupled to BSA at the carboxylic acid by 1,1'-carbonyldiimidazole method. The cross-reactivity of the antibody with PGF2alpha, 15-keto-PGF2alpha, PGE2, 15-keto-13,14-dihydro-PGE2, 8-iso-15-keto-13,14-dihydro-PGF2alpha, 11beta-PGF2alpha, 9beta-PGF2alpha, TXB2 and 8-iso-PGF3alpha was 0.02, 0.43, < 0.001, 0.5, 1.7, < 0.001, < 0.001, < 0.001, 0.01%, respectively. The intra-assay precision was 12.2% (CV) at the level of 64 pg/0.1 ml and 14.0% with 512 pg/0.1 ml in the human plasma. Similarly, intra-assay accuracy was 108.6% and 103.3% for the low and the high standards, respectively. The detection limit was about 45 pmol/L. 15-keto-dihydro-PGF2alpha levels in plasma from normal human volunteers were evaluated and found to correlate with the obtained values by GC-MS methods from other studies. The levels of 15-keto-dihydro-PGF2alpha in the plasma increased several-fold after endotoxin infusion (10 microg/kg/h over 6 h) to the pigs. Thus, this 1 5-keto-dihydro-PGF2alpha radioimmunoassay method is relevant to apply in inflammatory injury, and other physiological and pathophysiological studies, as an index of in vivo enzymatic lipid peroxidation.