Contributions
Abstract: S1587
Type: Oral Presentation
Presentation during EHA23: On Sunday, June 17, 2018 from 08:30 - 08:45
Location: Room A9
Background
In hemolytic diseases like sickle cell disease (SCD), intravascular hemolysis results in the release of hemoglobin, heme and heme-loaded membrane microvesicles in the bloodstream. Intravascular hemolysis is then associated with inflammation and organ injury. Our previous studies have demonstrated that the complement system can be activated by heme in vitro. However, the interrelation of intravascular hemolysis, complement activation and tissue damage remains unknown.
Aims
Our objective was to investigate the mechanisms by which hemolysis and red blood cells degradation products trigger complement activation in vivo.
Methods
We evaluated the deposits of C3 activation fragments and C5b-9 in kidneys of SCD patients (n=11) and two transgenic mouse models (SAD and Townes) by immunofluorescence and immunohistochemistry. Intravascular hemolysis was induced in C57Bl/6 mice by injection of phenylhydrazine in presence or not of hemopexin. The complement deposits in the kidneys were followed. RBC microvesicles were generated in vitro from erythrocytes of SCD patients or healthy donors. Complement activation (Ba, sC5b-9) in normal human serum was measured by ELISA. Complement deposits on cultured endothelial cells and their activation status was evaluated by flow cytometry.
Results
We analyzed kidney biopsies of patients with SCD nephropathy and model mice with SCD. We detected significant tissue deposits of complement C3 and C5b-9. Moreover, drug-induced intravascular hemolysis or injection of heme in mice triggered C3 deposition, primarily in the kidneys. Red blood cells degradation products like heme-loaded microvesicles and free heme induced alternative and terminal complement pathway activation in normal serum and on EC surfaces, contrary to hemoglobin. Heme triggered rapid P-selectin, C3aR and C5aR expression and down-regulated CD46 expression on EC. Importantly, complement deposition was attenuated in vivo and in vitro by hemopexin, the potent heme scavenger.
Conclusion
In conclusion, we describe for the first time that intravascular hemolysis triggers complement activation in vivo, and is associated with SCD nephropathy. Conversely, heme inhibition using hemopexin may provide a novel therapeutic opportunity to limit complement activation in hemolytic diseases.
Session topic: 27. Sickle cell disease
Keyword(s): Complement, heme, Microvesicles, sickle cell disease
Abstract: S1587
Type: Oral Presentation
Presentation during EHA23: On Sunday, June 17, 2018 from 08:30 - 08:45
Location: Room A9
Background
In hemolytic diseases like sickle cell disease (SCD), intravascular hemolysis results in the release of hemoglobin, heme and heme-loaded membrane microvesicles in the bloodstream. Intravascular hemolysis is then associated with inflammation and organ injury. Our previous studies have demonstrated that the complement system can be activated by heme in vitro. However, the interrelation of intravascular hemolysis, complement activation and tissue damage remains unknown.
Aims
Our objective was to investigate the mechanisms by which hemolysis and red blood cells degradation products trigger complement activation in vivo.
Methods
We evaluated the deposits of C3 activation fragments and C5b-9 in kidneys of SCD patients (n=11) and two transgenic mouse models (SAD and Townes) by immunofluorescence and immunohistochemistry. Intravascular hemolysis was induced in C57Bl/6 mice by injection of phenylhydrazine in presence or not of hemopexin. The complement deposits in the kidneys were followed. RBC microvesicles were generated in vitro from erythrocytes of SCD patients or healthy donors. Complement activation (Ba, sC5b-9) in normal human serum was measured by ELISA. Complement deposits on cultured endothelial cells and their activation status was evaluated by flow cytometry.
Results
We analyzed kidney biopsies of patients with SCD nephropathy and model mice with SCD. We detected significant tissue deposits of complement C3 and C5b-9. Moreover, drug-induced intravascular hemolysis or injection of heme in mice triggered C3 deposition, primarily in the kidneys. Red blood cells degradation products like heme-loaded microvesicles and free heme induced alternative and terminal complement pathway activation in normal serum and on EC surfaces, contrary to hemoglobin. Heme triggered rapid P-selectin, C3aR and C5aR expression and down-regulated CD46 expression on EC. Importantly, complement deposition was attenuated in vivo and in vitro by hemopexin, the potent heme scavenger.
Conclusion
In conclusion, we describe for the first time that intravascular hemolysis triggers complement activation in vivo, and is associated with SCD nephropathy. Conversely, heme inhibition using hemopexin may provide a novel therapeutic opportunity to limit complement activation in hemolytic diseases.
Session topic: 27. Sickle cell disease
Keyword(s): Complement, heme, Microvesicles, sickle cell disease