The insect peptide CopA3 inhibits lipopolysaccharide-induced macrophage activation

We recently demonstrated that the insect peptide CopA3 (LLCIALRKK), a disulfide‐linked dimeric peptide, exerts antimicrobial and anti‐inflammatory activities in a mouse colitis model. Here, we examined whether CopA3 inhibited activation of macrophages by LPS. Exposure of an unseparated mouse peritoneal cell population or isolated peritoneal macrophages to LPS markedly increased secretion of IL‐6 and TNF‐α; these effects were significantly inhibited by CopA3 treatment. The inhibitory effect of CopA3 was also evident in murine macrophage cell line, RAW 264.7. Western blotting revealed that LPS‐induced activation of STAT1 and STAT5 in macrophages was significantly inhibited by CopA3. Inhibition of JAK (STAT1/STAT5 kinase) with AG490 markedly reduced the production of IL‐6 and TNF‐α in macrophages. Collectively, these observations suggest that CopA3 inhibits macrophage activation by inhibiting activating phosphorylations of the transcription factors, STAT1 and STAT5, and blocking subsequent production of IL‐6 and TNF‐α and indicate that CopA3 may be useful as an immune‐modulating agent. Copyright © 2012 European Peptide Society and John Wiley & Sons, Ltd. The α‐helical domain of the natural insect peptide (coprisin) possesses antibacterial activity. We have synthesized a nine‐mer dimeric D‐type peptide (CopA3), derived from this domain, finding it to have anti‐inflammatory activity against Clostridium difficile‐induced animal colitis. Here, we report that CopA3 inhibits the LPS‐induced activation of macrophages and that this inhibitory effect is associated with inactivation of JAK/STAT pathways involved in proinflammatory cytokine production. This suggests that CopA3 could be used against hyper‐immune responses mediated by abnormally activated macrophages.