Abstract Number: PB1784
Meeting: ISTH 2020 Congress
Background: Emerging in vitro studies have shown that heparin, an anticoagulant, possesses anti-inflammatory properties. Recently this was demonstrated by reduction of toxicity exhibited by neutrophil extracellular traps (NETs) in the presence of heparin and modified heparin, but the exact mechanism for this anti-inflammatory activity remains to be elucidated. It has also been established that negatively-charged heparin can bind to positively-charged histones, a major component of NETs which can cause complement activation.
Aims: To investigate the anti-complement effects of heparin on whole blood stimulated by histones.
Methods: Selectively desulfated heparins and molecular weight fractions of heparin were investigated. Histones (50 µg/mL) spiked in whole blood were incubated with 200 µg/mL of heparin for 6 hours and levels of C3a, a marker of complement activation, were then measured by ELISA. Data were analysed by Dunnett’s multiple comparison (* = p< 0.05) relative to histones only, and across samples.
Results: Heparin reduced histone induced C3a by 90% (figure 1). 2-O-desulfated, N-acetyl and 6-O-desulfated heparins significantly lowered C3a levels by 83%, 71% and 70% respectively. Of these heparins there was no difference in reduction for 2-O-desulfated heparin when compared to heparin. N-desulfated and N-acetyl-O-desulfated heparin had no effect. Molecular weight heparin fractions significantly reduced C3a production (figure 2), with fractions ≤Mw1900 less effective than fractions ≥Mw3450. However, increase in Mw above 3450 did not further reduce observed C3a.
Conclusions: All heparin tested attenuated histone induced C3a production. This effect was charge dependent as both fully desulfated (N-acetyl-O-desulfated heparin with complete loss of negative-charge) and N-desulfated (which exposes positively charged amine groups) heparins had no effect, whilst selective desulfation retained some of heparin’s activity. There was a molecular weight dependence, with a threshold of fractions ˃ Mw3450 g/mole (~10 saccharides) showing no further decrease in C3a levels induced by histones.
To cite this abstract in AMA style:Hogwood J, Qiao Y, Pitchford S, Page C, Mulloy B, Gray E. Anti-complement Effect of Heparin in Stimulated Whole Blood [abstract]. Res Pract Thromb Haemost. 2020; 4 (Suppl 1). https://abstracts.isth.org/abstract/anti-complement-effect-of-heparin-in-stimulated-whole-blood/. Accessed August 15, 2022.
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