Absence of in vitro innate immunomodulation by insect-derived short proline-rich antimicrobial peptides points to direct antibacterial action in vivo

• Published in: Journal of peptide science 2012-10, Vol.18 (10), p.599-608
• Main Authors: Fritsche, Stefanie, Knappe, Daniel, Berthold, Nicole, von Buttlar, Heiner, Hoffmann, Ralf, Alber, Gottfried
• Format: Article
• Language: English
• Subjects: Animals; Anti-Bacterial Agents - chemistry; Anti-Bacterial Agents - pharmacology; Antimicrobial Cationic Peptides - chemistry; Antimicrobial Cationic Peptides - pharmacology; apidaecin; Bees - chemistry; Cells, Cultured; Cytokines - analysis; Cytokines - immunology; Dendritic Cells - drug effects; Dendritic Cells - immunology; Female; Immunity, Innate; immunomodulation; Lipopolysaccharides - pharmacology; Macrophages - drug effects; Macrophages - immunology; Mice; Mice, Inbred C57BL; oncocin; Proline - chemistry; proline-rich antimicrobial peptides
• ISSN: 1075-2617; 1099-1387
• DOI: 10.1002/psc.2440

Some antimicrobial peptides (AMPs) have been described to exert immunomodulatory effects, which may contribute to their in vivo antibacterial activity. Very recently, we could show that novel oncocin and apidaecin derivatives are potently antibacterially active in vivo. Therefore, we studied oncocin and apidaecin derivatives for their effects on murine dendritic cells (DC) and macrophages and compared them with well‐known immunomodulatory activities of murine cathelicidin‐related antimicrobial peptide (CRAMP). To characterize the immunomodulatory activity of the peptides on key cells of the innate immune system, we stimulated murine DC and macrophages with the oncocin and apidaecin derivatives alone, or in combination with lipopolysaccharide (LPS). We analyzed the secretion of pro‐inflammatory cytokines, the expression of surface activation markers, and the chemotactic activity of the AMPs. In contrast to LPS, none of the oncocin and apidaecin derivatives alone has an influence on cytokine or surface marker expression by DC and macrophages. Furthermore, the tested oncocin and apidaecin derivatives do not modulate the immune response after LPS stimulation, whereas CRAMP shows a reduction of the LPS‐mediated immune response as expected. All peptides tested are not chemotactic for DC. Together, lack of in vitro immunomodulatory effects by oncocin and apidaecin derivatives on key cells of the innate murine immune system suggests that their potent in vivo antibacterial activity relies on a direct antibacterial effect. This will simplify further pharmaceutical investigation and development of insect peptides as therapeutic compounds against bacterial infections. Copyright © 2012 European Peptide Society and John Wiley & Sons, Ltd. In this study, we show that optimized insect PrAMPs (e.g. Onc72) do not modulate activation of innate immune cells such as dendritic cells and macrophages in vitro. This includes expression of surface activation markers (e.g. CD86), cytokine secretion and induction of chemotaxis. Thus, the efficacy of the insect peptide derivatives studied in murine infection models appears to rely exclusively on a direct antibacterial effect.