The prevention and treatment of acute chest syndrome (ACS) is a major clinical concern in sickle cell disease (SCD). However, the mechanism underlying the pathogenesis of ACS remains elusive. We tested the hypothesis that the hemolysis byproduct hemin elicits events that induce ACS. Infusion of a low dose of hemin caused acute intravascular hemolysis and autoamplification of extracellular hemin in transgenic sickle mice, but not in sickle-trait littermates. The sickle mice developed multiple symptoms typical of ACS and succumbed rapidly. Pharmacologic inhibition of TLR4 and hemopexin replacement therapy prior to hemin infusion protected sickle mice from developing ACS. Replication of the ACS-like phenotype in nonsickle mice revealed that the mechanism of lung injury due to extracellular hemin is independent of SCD. Using genetic and bone marrow chimeric tools, we confirmed that TLR4 expressed in nonhematopoietic vascular tissues mediated this lethal type of acute lung injury. Respiratory failure was averted after the onset of ACS-like symptoms in sickle mice by treating them with recombinant hemopexin. Our results reveal a mechanism that helps to explain the pathogenesis of ACS, and we provide proof of principle for therapeutic strategies to prevent and treat this condition in mice.

Although factor VII/factor VIIa (FVII/FVIIa) is known to interact with many non-vascular cells, activated monocytes, and endothelial cells via its binding to tissue factor (TF), the interaction of FVII/FVIIa with unperturbed endothelium and the role of this interaction in clearing FVII/FVIIa from the circulation are unknown. To investigate this, in the present study we examined the binding of radiolabeled FVIIa to endothelial cells and its subsequent internalization. 125 I-FVIIa bound to non-stimulated human umbilical vein endothelial cells (HUVEC) in time-and dose-dependent manner. The binding is specific and independent of TF and negatively charged phospholipids. Protein C and monoclonal antibodies to endothelial cell protein C receptor (EPCR) blocked effectively 125 I-FVIIa binding to HUVEC. FVIIa binding to EPCR is confirmed by demonstrating a marked increase in 125 I-FVIIa binding to CHO cells that had been stably transfected with EPCR compared with the wild-type. Binding analysis revealed that FVII, FVIIa, protein C, and activated protein C (APC) bound to EPCR with similar affinity. FVIIa binding to EPCR failed to accelerate FVIIa activation of factor X or protease-activated receptors. FVIIa binding to EPCR was shown to facilitate FVIIa endocytosis. Pharmacological concentrations of FVIIa were found to impair partly the EPCR-dependent protein C activation and APC-mediated cell signaling. Overall, the present data provide convincing evidence that EPCR serves as a cellular binding site for FVII/FVIIa. Further studies are needed to evaluate the pathophysiological consequences and relevance of FVIIa binding to EPCR.Despite the progress that has been made in understanding the biochemistry and pathophysiology of the coagulation cascade events, the clearance mechanism of the various coagulation proteins from the circulation is still unclear. The marked differences in circulating half-lives of factor VII (FVII) 4 and FVIIa compared with those of zymogen and the enzyme forms of other vitamin K-dependent coagulation proteins (1-7) suggest that there may be a specific and distinct clearance mechanism for FVII/FVIIa. Although tissue factor (TF), the * This work was supported by Grants HL 58869 and HL 65500 from the National Institutes of Health. 4 The abbreviations used are: FVII, factor VII; FVIIa, activated factor VII; TF, tissue factor; EPCR, endothelial cell protein C receptor; APC, activated protein C; PAR, protease-activated receptor; AP, alkaline phosphatase; TFPI, tissue factor pathway inhibitor; AT, antithrombin; FACS, fluorescence-activated cell sorter; TNF, tumor necrosis factor; IL, interleukin. NIH Public Access Cell CulturePrimary human umbilical vein endothelial cells (HUVEC) were purchased from Cambrex Bio Science (Walkersville, MD). The cells were cultured to confluency at 37 °C and 5% CO 2 in a humidified incubator in EBM-2 basal media supplemented with growth supplements (Cambrex Bio Science) and 5% fetal bovine serum. Endothelial cell passages between 3 and 10 were used in the present stud...

Meta-analysis and comparative systematic review confirm that FNAC is highly effective in the diagnosis of head and neck masses, with some limitations.

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