Activated protein C improves pial microcirculation in experimental endotoxemia in rats

Introduction: The brain is one of the first organs affected clinically in sepsis. Microcirculatory alterations are suggested to be a critical component in the pathophysiology of sepsis. The aim of this study was to investigate the effects of recombinant human activated protein C (rhAPC) on the pial microcirculation in experimental endotoxemia using intravital microscopy. Our hypothesis is rhAPC protects pial microcirculation in endotoxemia. Methods: Endotoxemia was generated in Lewis rats with intravenous injection of lipopolysaccharide (LPS, 5. mg/kg i.v.). Dura mater was removed through a cranial window to expose pial vessels on the brain surface. The microcirculation, including leukocyte-endothelial interaction, functional capillary density (FCD) and plasma extravasation of pial vessels was examined by fluorescent intravital microscopy (IVM) 2. h after administration of LPS, LPS and rhAPC or equivalent amount of saline (used as Control group). Plasma cytokine levels of interleukin 1 alpha (IL1-α), tumor necrosis factor-α (TNF-α), interferon γ (IFN-γ), Monocyte chemotactic protein-1 (MCP-1) and Granulocyte-macrophage colony-stimulating factor (GM-CSF) were evaluated after IVM. Results: LPS challenge significantly increased leukocyte adhesion (773±190 vs. 592±152n/mm ² Control), decreased FCD (218±54 vs. 418±74cm/cm ² Control) and increased proinflammatory cytokine levels (IL-1α: 5032±1502 vs. 8±21pg/ml; TNF-α: 1823±1007 vs. 168±228pg/ml; IFN-γ: 785±434 vs. 0pg/ml; GM-CSF: 54±52 vs. 1±3pg/ml) compared to control animals. rhAPC treatment significantly reduced leukocyte adhesion (599±111n/mm ²), increased FCD (516±118cm/cm ²) and reduced IL-1α levels (2134±937pg/ml) in the endotoxemic rats. Conclusion: APC treatment significantly improves pial microcirculation by reducing leukocyte adhesion and increasing FCD.