BackgroundRecent studies have suggested that excessive formation of neutrophil extracellular traps (NETs) plays a critical role in the pathogenesis of sepsis. Although elevation of the plasma level of cell-free DNA (cf-DNA) has been reported in sepsis patients, there has been little direct measurement of circulating free NETs such as myeloperoxidase-conjugated DNA (MPO-DNA). The objectives of this study were to detect NETs in the bloodstream of patients with septic shock, and to assess the correlations of circulating NET levels with organ dysfunction, disease severity, and mortality.MethodsFifty-five patients with septic shock admitted to the intensive care units (ICUs) of 35 Japanese hospitals were studied. Septic shock was diagnosed according to the 1997 definition of the American College of Chest Physicians/Society of Critical Care Medicine. To detect circulating NETs, plasma levels of MPO-DNA and cf-DNA were measured by sandwich enzyme-linked immunosorbent assay and by fluorometric assay on days 1, 3, and 7 after the onset of septic shock. Physiological and mortality data were collected from the clinical database.ResultsOn days 1, 3, and 7, the patients showed a marked increase in plasma MPO-DNA levels compared with healthy volunteers, whereas the plasma cf-DNA level was only increased significantly on day 1 and then decreased rapidly. A high MPO-DNA level on days 3 and 7 were associated with 28-day mortality.On days 3 and 7, the MPO-DNA levels were inversely correlated with both the mean arterial pressure and the PaO2/FIO2 ratio, whereas the cf-DNA level was not correlated with either parameter. There was a positive correlation between the plasma MPO-DNA level and the sepsis-related organ failure assessment score on days 3 and 7. Neither cf-DNA nor MPO-DNA levels were correlated with the disseminated intravascular coagulation (DIC) score or the platelet count.ConclusionThe increase in circulating MPO-DNA in patients with septic shock indicates acceleration of NET formation in the early stages of sepsis. High MPO-DNA levels are associated with the severity of organ dysfunction and 28-day mortality due to septic shock, but not with the DIC score. These results suggest that excessive NET formation contributes to the pathogenesis of septic shock.Electronic supplementary materialThe online version of this article (10.1186/s13054-018-2109-7) contains supplementary material, which is available to authorized users.

Components of neutrophil extracellular traps (NETs) are released into the circulation by neutrophils and contribute to microcirculatory disturbance in sepsis. Removing NET components (DNA, histones, and proteases) from the circulation could be a new strategy for counteracting NET-dependent tissue damage. We evaluated the effect of hemoperfusion with a polymyxin B (PMX) cartridge, which was originally developed for treating gram-negative infection, on circulating NET components in patients with septic shock, as well as the effect on phorbol myristate acetate (PMA)-stimulated neutrophils obtained from healthy volunteers. Ex vivo closed loop hemoperfusion was performed through PMX filters in a laboratory circuit. Whole blood from healthy volunteers (incubated with or without PMA) or from septic shock patients was perfused through the circuit. For in vivo experiment blood samples were collected before and immediately after hemoperfusion with PMX to measure the plasma levels of cell-free NETs. The level of cell-free NETs was assessed by measuring myeloperoxidase-associated DNA (MPO-DNA), neutrophil elastase-associated DNA (NE-DNA), and cell-free DNA (cf-DNA). Plasma levels of MPO-DNA, NE-DNA, and cf-DNA were significantly increased after 2 h of PMA stimulation. When the circuit was perfused with blood from septic shock patients or PMA-stimulated neutrophils from healthy volunteers, circulating levels of MPO-DNA, NE-DNA, and cf-DNA were significantly reduced after 1 and 2 h of perfusion with a PMX filter compared with perfusion without a PMX filter. In 10 patients with sepsis, direct hemoperfusion through filters with immobilized PMX significantly reduced plasma levels of MPO-DNA and NE-DNA. These ex vivo and in vivo findings demonstrated that hemoperfusion with PMX removes circulating NET components. Selective removal of circulating NET components from the blood could be effective for prevention/treatment of NET-related inappropriate inflammation and thrombogenesis in patients with sepsis.

No abstract