T. Cyr1, P. Waltz1, S. Shiva1, S. Ofori-Acquah1, B. Zuckerbraun1 1University Of Pittsburgh,Surgery,Pittsburgh, PA, USA
Introduction. Erythroid danger associated molecular pattern molecules (eDAMPs) may amplify vascular and endothelial injury in sepsis. Free heme is a known DAMP and may be increased in sepsis to promote microvascular and subsequent organ injury. The purpose of these experiments was to test the hypothesis that sepsis results in increased available heme, which promotes vascular and organ injury.
Methods. Serum was collected from patients with intra-abdominal sources of sepsis that required source control. Free heme, HO-1, bilirubin, and hemopexin was measured. Serum from 10 patients that did and 10 patients that did not develop acute lung injury/MODS was evaluated for ability to activate cultured wild type or TLR4 knockout endothelial cells or macrophages. Additionally, the ‘available’ levels of heme were measured by a heme reporter assay system.
Results. Serum from patients taken on presentation and within 24 hours that went on to develop ALI/MODS demonstrated an increased endothelial cell or macrophage activation. TLR4 knockout cells were activated to a significantly lower extent than wild types. Lipopolysaccharide deactivation did not significantly decrease cell activation. HO-1 over-expression or hemopexin treatment ameliorated cell activation. Measurable heme levels did not show any significant differences between groups, however ‘available’ heme levels were higher in the ALI/MODS group by reporter assay.
Conclusion. Serum from sepsis patients can increase cellular injury through a TLR4 pathway independent of LPS levels and dependent upon heme signaling pathways. Further investigation is warranted to investigate this complex signaling pathway and possible therapeutic development.