Unfractionated heparin attenuates histone-mediated cytotoxicity in vitro and prevents intestinal microcirculatory dysfunction in histone-infused rats.

Background: Extracellular histones are major mediators of organ dysfunction and death in sepsis, and they may cause microcirculatory dysfunction. Heparins have beneficial effects in sepsis and have been reported to bind to histones and neutralize their cytotoxicity. The aim of this study was to investigate the impact of histones on intestinal microcirculation and the intestinal endothelium and to discuss the protective effect of unfractionated heparin (UFH) on the endothelial cytotoxicity and microcirculatory dysfunction induced by histones.
Methods: Anesthetized rats were infused with 30 mg/kg calf thymus histones, and UFH was administered intravenously at a concentration of 100 IU/kg per hour. The intestinal microcirculation was visualized and measured with incident dark field microscope. Plasma von Willebrand factor (vWF) and soluble thrombomodulin were detected, and structural changes in the rat intestinal microvascular endothelium were examined. The effects of histones and UFH on cell survival rates, vWF release and calcium influx were investigated in human intestinal microvascular endothelial cells (HIMECs).
Results: Histone infusion caused severe intestinal microcirculatory dysfunction in the absence of obvious hemodynamic changes, and UFH protected intestinal microcirculation in histone-infused rats. Concentrations of the plasma endothelial injury markers vWF and soluble thrombomodulin were elevated, and structural abnormalities were found in the intestinal microvascular endothelium in the histone-infused rats. These events were attenuated by UFH. In vitro, UFH significantly reduced the histone-induced cytotoxicity of HIMECs, reduced the release of vWF from the cytoplasm into the culture medium, and inhibited calcium influx into HIMECs.
Conclusion: Histones induce intestinal microcirculatory dysfunction followed by direct injury to the endothelial cells; UFH protects the intestinal microcirculation partly by antagonizing the endothelial toxicity of histones.