Compstatin control peptide

Essential role of the C5a receptor in E coli-induced oxidative burst and phagocytosis revealed by a novel lepirudin-based human whole blood model of inflammation.[Pubmed:12176911]

Blood. 2002 Sep 1;100(5):1869-77.

Complement plays an essential role in inflammation and tissue damage. However, it is largely unknown to what extent the system acts as a primary inducer of secondary mediator systems in the inflammatory network of human whole blood. Here we describe a novel in vitro model using the thrombin-specific hirudin analog lepirudin as anticoagulant, which, in contrast to heparin, did not interfere with complement activation. The model was used to study the role of complement in Escherichia coli-induced inflammatory responses. Granulocyte and monocyte oxidative burst was complement dependent as it was reduced by 85% and 70%, respectively, by the C3 [corrected] binding peptide compstatin. A similar reduction was found by inhibition of C5, C5a, and C5a receptor (C5aR). Furthermore, anti-CR3 antibodies were as efficient as the C5aR antagonist in reducing granulocyte oxidative burst, whereas blocking CD14 or C3aR had no effect. Up-regulation of granulocyte CR3 was virtually abolished by a C5aR antagonist. Opsonization and phagocytosis was completely inhibited by blocking of C5aR or CR3, whereas blocking of the FcgammaRs (CD16, CD32, CD64) had no effect. In contrast to oxidative burst and phagocytosis, cytokine secretion was largely complement independent. Thus, anti-CD14 abolished tumor necrosis factor-alpha, interleukin-6 (IL-6), and IL-10 secretion, whereas IL-8 was equally inhibited by anti-CD14 and compstatin. In conclusion, the present model is particularly useful for studying complement as part of the inflammatory network. The results emphasize a crucial role for C5a-C5aR interaction in E coli-induced up-regulation of CR3 and the subsequent oxidative burst and phagocytosis. Complement inhibition may have therapeutic implications in oxidative burst-induced tissue damage.

Compstatin, a peptide inhibitor of C3, prolongs survival of ex vivo perfused pig xenografts.[Pubmed:10355733]

Xenotransplantation. 1999 Feb;6(1):52-65.

Compstatin, a newly described C3-binding peptide, inhibits complement activation by blocking C3 convertase-mediated cleavage of C3. As the complement activation is an essential part of the rejection reaction, we evaluated the ability of Compstatin to delay or prevent hyperacute rejection in an ex vivo xenograft model. Pig kidneys were perfused with fresh human blood containing either Compstatin (n=6) or a control agent (n=6). Graft survival and activation of complement, leukocytes and platelets both in the fluid-phase and in the tissue were examined. The survival of the Compstatin-perfused kidneys (median, 380 min) was significantly (P=0.0036) longer than that of the controls (median, 90 min). The classical complement pathway (C1rs-C1inhibitor and C4bc) was significantly and equally activated in both groups during the first 60 min. C3 activation products increased fivefold and terminal complement complex eightfold in the control group, but no increase occurred in the Compstatin group during this period. Immunohistochemistry showed less C3 and fibrin deposition and immune electron microscopy showed less terminal SC5b-9 complement complex deposition in the Compstatin group. A significant change in total white cells, neutrophils, myeloperoxidase, and expression of the surface activation markers CD11b (CR3) and CD35 (CR1) and CD62L (L-selectin) was observed in both groups. Leukocyte activation was lower in the Compstatin group but the difference was not statistically significant. There were no differences in platelet counts, thrombospondin, soluble P-selectin or beta-thromboglobulin between the groups. We conclude that Compstatin prolongs graft survival and suggest that it may be a useful agent for attenuating hyperacute rejection by inhibiting C3 and thus terminal complement pathway activation.

Inhibition of human complement by a C3-binding peptide isolated from a phage-displayed random peptide library.[Pubmed:8752942]

J Immunol. 1996 Jul 15;157(2):884-91.

We have screened a phage-displayed random peptide library for binding to C3b, the proteolytically activated form of complement component C3, and have identified a novel peptide that suppresses complement activation. This phage-displayed peptide bound to C3, C3b, and C3c, but not to C3d, indicating that it binds to the C3c region of C3. A synthetic 27-amino acid peptide corresponding to the phage-displayed peptide also bound to C3 and C3 fragments and inhibited both the classical and alternative pathways of complement activation. The inhibition of complement activation was reversible. Studies with overlapping peptides indicated that the functional activity was located in the cyclic 13-amino acid N-terminal region (ICVVQDWGHHRCT) of the parent peptide. Reduction and alkylation of this 13-residue synthetic peptide destroyed its inhibitory activity. Analysis of the mechanism of inhibition revealed that the peptide inhibited C3 cleavage in normal human serum as well as when the alternative pathway was reconstituted with purified complement components, and the observed inhibition was not due to sterically hindered access to the C3a/C3b cleavage site. Further, the peptide did not inhibit the cleavage of factor B, indicating that it did not affect the interaction of CA with factor B or the formation of C3b,Bb. The peptide also had no effect on the binding of properdin to C3, demonstrating that the observed inhibition of C3 cleavage in normal human serum was not due in part to its effect on the properdin-stabilized C3 convertase, C3b,Bb,P. These results indicate that the peptide we have identified interacts with C3 to inhibit its activation.