Abdominal aortic aneurysm (AAA) rupture is associated with a systemic inflammatory response syndrome, characterized by increased microvascular permeability and neutrophil sequestration, leading to multiorgan dysfunction. We examined the role of a novel complement factor 5a (C5aR) receptor antagonist, the cyclic peptide AcF-(OpdChaWR), in attenuation of pathologic complement activation and tissue injury in a model of AAA rupture.

Anesthetized rats were randomized to sham (control) or shock and clamp (s+c) groups. Animals in the s+c group underwent 1 hour of hemorrhagic shock (mean arterial blood pressure ≤50 mm Hg), followed by 45 minutes of supramesenteric aortic clamping, then 2 hours of resuscitated reperfusion. Animals in the s+c group were randomized to receive an intravenous bolus of C5aR antagonist at 1 mg/kg or saline solution control at the end of hemorrhagic shock. Intestinal and pulmonary permeability to iodine 125–labeled albumin was measured as an indicator of microvascular permeability. Tissue myeloperoxidase activity, proinflammatory cytokine tissue necrosis factor-α (TNF-α) protein and mRNA, and C5aR mRNA levels were measured as indicators of neutrophil sequestration and inflammatory signaling, respectively.

Lung permeability index was significantly increased in the s+c group compared with the sham group (4.43 ± 0.96 vs 1.30 ± 0.17; P < .01), and prevented with treatment with C5aR antagonist (1.74 ± 0.50; P < .03). Lung myeloperoxidase activity was significantly increased in the the s+c group compared with the sham group (2.41 ± 0.34 U/mg vs 1.03 ± 0.29 U/mg; P < .009), and significantly attenuated with treatment with C5aR antagonist (1.11 ± 0.09 U/mg; P < .006). Lung TNF-α protein levels were significantly elevated in both s+c groups, whereas lung TNF-α mRNA expression was significantly downregulated in both s+c groups compared with the sham group. Intestinal permeability index was significantly increased in animals in the s+c groups during reperfusion, compared with sham (P < .001), which was attenuated in early reperfusion with treatment with C5a receptor antagonist. Data represent mean ± SEM, group comparisons with analysis of variance and post hoc Scheffé test.

These results indicate that a potent antagonist of C5a receptor protects the rat intestine and lung from neutrophil-associated injury in a model of AAA rupture. These data suggest that complement-mediated inflammation can be modulated at the C5a receptor level, independent of proinflammatory TNF-α production, and prevent acute local and remote organ injury.