Sepsis is a major clinical problem, caused by a hyperactive immune response following infection. Worldwide prevalence is estimated at 1.8 m/year and mortality at around 40%1. Protective effects of the endogenous anti-inflammatory protein annexin A1 have previously been shown in many models, including sepsis2. We therefore chose to investigate the role of the annexin A1 peptide mimetic, Ac226, in murine experimental endotoxaemia, and to ascertain whether this is mediated by the formyl peptide receptor (FPR) family.
We have previously profiled differences in leukocyte-endothelium interactions following LPS injection over time3 and found that optimal responses for further study occurred 2 h after treatment. Male C57BL/6 mice were treated with LPS (10 μg/mouse, i.p.) and 20 min later with peptide Ac226 (100 μg/mouse), the pan-FPR antagonist Boc2 (10 μg/mouse), or Ac226 and Boc2 together; controls received the relevant vehicles. The mice were then anaesthetised, the mesentery was exteriorised and leukocyte-endothelium interactions in post-capillary venules were quantified by intravital microscopy 2 h after the injection of LPS.
All animals treated with vehicle or drug showed a reduction in rolling leukocyte flux compared to LPS alone, indicating a small effect of second injection. No differences were seen between groups in leukocyte rolling velocity or emigration. However, animals given LPS+Ac226 showed significantly fewer adherent leukocytes than those given LPS alone, LPS+Boc2 or LPS+Ac226+Boc2.
For the first time we demonstrate that Boc2 blocks the effects of Ac226 in this model, and therefore suggest that Ac226 is acting by an FPR-dependent mechanism to afford protection in experimental endotoxaemia. Further work is now required to establish whether a single-family member may be responsible.
1. Daniels, R. Available from: http://www.library.nhs.uk/emergency/viewresource.aspx?resID=269230tabID=290catID=1870, 2007.
2. Damazo, A. et al. Cardiovascular, Pulmonary and Renal Pathology, 2005 166 1607.
3. Hughes, E. et al. Available from: http://www.pa2online.org/abstracts/vol7issue3abst068P.pdf, 2009.