Abstract
Several pathologic conditions are associated with hemolysis, i.e. release of ferrous (Fe(II)) hemoglobin from red blood cells. Oxidation of cell-free hemoglobin produces (Fe(III)) methemoglobin. More extensive oxidation produces (Fe(III)/Fe(IV) O) ferryl hemoglobin. Both cell-free methemoglobin and ferryl hemoglobin are thought to contribute to the pathogenesis of hemolytic disorders. We show hereby that ferryl hemoglobin, but not hemoglobin or methemoglobin, acts as a potent proinflammatory agonist that induces vascular endothelial cells in vitro to rearrange the actin cytoskeleton, forming intercellular gaps and disrupting the integrity of the endothelial cell monolayer. Furthermore, ferryl hemoglobin induces the expression of proinflammatory genes in endothelial cells in vitro, e.g. E-selectin, Icam-1, and Vcam-1, through the activation of the nuclear factor kappaB family of transcription factors. This proinflammatory effect, which requires actin polymerization, involves the activation of the c-Jun N-terminal kinase and the p38 mitogen-activated protein kinase signal transduction pathways. When administered to naïve mice, ferryl hemoglobin induces the recruitment of polymorphonuclear cells, demonstrating that it acts as a proinflammatory agonist in vivo. In conclusion, oxidized hemoglobin, i.e. ferryl hemoglobin, acts as a proinflammatory agonist that targets vascular endothelial cells.
Highlights
Hemoglobin (Hb) is a tetrameric (␣22) hemoprotein that accounts for 97% of the total dry content of red blood cells in mammals, where it acts essentially as a gas sensor/carrier
Under inflammatory conditions endothelial cells (EC) become activated, promoting vasoconstriction and thrombosis as well as leukocyte chemotaxis, adhesion, and transmigration. This proinflammatory response results from the expression of immediate-early responsive genes encoding vasoconstrictive, pro-thrombotic, proinflammatory, and chemotactic as well as adhesive (e.g. intercellular adhesion molecule 1 (ICAM-1/CD54), vascular cell adhesion molecule 1 (VCAM-1/CD106), E-selectin/
FerrylHb led to similar levels of PMN cell influx into the peritoneal cavity of Tlr4Ϫ/Ϫ versus wild type Tlr4ϩ/ϩ mice (Fig. 10, C and D), which discards the possibility that the proinflammatory effect of ferrylHb is because of a putative endotoxin contamination and, supports the notion that ferrylHb is a bona fide proinflammatory agonist
Summary
CD62E, and P-selectin/CD62P molecules (for review, see Ref. 12). Expression of these genes is regulated primarily at the transcriptional level via activation of the nuclear factor B (NF-B) family of transcription factors [13, 14]. NF-B comprises five family members, i.e. NF-B1/p105, NF-B2/p100, RelA/p65, RelB, and c-Rel that can form active homo- or heterodimers (for review, see Ref. 15). Most proinflammatory agonists that elicit EC activation target IB molecules for phosphorylation [17], ubiquitination [18], and proteolytic degradation by the 26 S proteasome pathway [19, 20]. This allows for rapid nuclear translocation and binding of the NF-B dimers to DNA “B motifs” in the promoter of NF-B-dependent genes (for review, see Ref. 15). Based on this observation we propose that oxidized cell-free Hb might contribute to the pathologic outcome of hemolytic disorders
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
