Prevention of erythrocyte fragility and anaemia induced by extracellular histones

Abstract Introduction Neutrophil extracellular traps (NETs) are released from neutrophils following activation by pathogens and/or tissue injury and exhibit anti-microbial activity. Uncontrolled formation of NETs can, however, become pathogenic, particularly via their associated histones, and induce endothelial cell death, systemic vascular obstruction, multiple organ failure and initiate coagulation by both activating platelets and damaging erythrocytes such that they become pro-thrombotic. Study Objectives Recently we discovered an additional effect of histones on erythrocyte, which is to enhance their fragility when they are subjected to shear stress associated with blood flow through the vascular system and spleen in particular. Our laboratory has synthesised a family of small polyanions (SPAs) which have been screened for their ability to neutralise the pathogenic effects of histones and NETs. Methods We have used a novel mechanically-induced shear stress method as well as an in vitro spleen filtration model to investigate the effects of mammalian histones ± SPAs, on RBC fragility. The in vitro findings were mirrored in vivo with the injection of histones and SPAs in mice. Results Our results revealed that free histones bind to erythrocytes with high affinity and render erythrocytes susceptible to lysis by shear stress in a dose-dependent manner and some SPAs could totally inhibit or reverse this phenomenon. Conclusions Based on these data we propose that erythrocytes can neutralise the damaging effects of histones in the circulation and also transport them to the spleen for disposal. Overload of this disposal system could cause the unexplained anaemia associated with sepsis, cancer and other pathological conditions.