A Nonbactericidal Anionic Antimicrobial Peptide Provides Prophylactic and Therapeutic Efficacies against Bacterial Infections in Mice by Immunomodulatory-Antithrombotic Duality.

Although bactericidal cationic antimicrobial peptides (AMPs) have been well characterized, less information is available about the antibacterial properties and mechanisms of action of nonbactericidal AMPs, especially nonbactericidal anionic AMPs. Herein, a novel anionic antimicrobial peptide (Gy-CATH) with a net charge of -4 was identified from the skin of the frog Glyphoglossus yunnanensis. Gy-CATH lacks direct antibacterial effects but exhibits significantly preventive and therapeutic capacities in mice that are infected with Staphylococcus aureus, Enterobacteriaceae coli, methicillin-resistant Staphylococcus aureus (MRSA), or carbapenem-resistant E. coli (CREC). In vitro and in vivo investigations proved the regulation of Gy-CATH on neutrophils and macrophages involved in the host immune defense against infection. Moreover, Gy-CATH significantly reduced the extent of pulmonary fibrin deposition and prevented thrombosis in mice, which was attributed to the regulatory role of Gy-CATH in physiological anticoagulants and platelet aggregation. These findings show that Gy-CATH is a potential candidate for the treatment of bacterial infection.

Tree Frog-Derived Cathelicidin Protects Mice against Bacterial Infection through Its Antimicrobial and Anti-Inflammatory Activities and Regulatory Effect on Phagocytes.

Due to excessive use or abuse in the food industry, agriculture, and medicine, many pathogens are developing resistance against conventional antibiotics. Antimicrobial peptides (AMPs) hold promise as effective therapeutic options for the treatment of bacterial infections. Herein, a novel cathelicidin antimicrobial peptide (Zs-CATH) was identified from the tree frog Zhangixalus smaragdinus. Zs-CATH mainly adopted an amphipathic ß-sheet structure in a membrane-mimetic environment. It showed broad-spectrum antibacterial activity against Gram-positive and Gram-negative bacteria in vitro and significantly protected mice from lethal infections induced by Gram-negative bacteria Escherichia coli ATCC 25922 or Gram-positive bacteria Staphylococcus aureus ATCC 25923 in vivo. In addition, Zs-CATH exerted a strong anti-inflammatory effect by neutralizing lipopolysaccharide (LPS) and lipoteichoic acid (LTA) and promoting macrophage M2 polarization, thus inhibiting the secretion of proinflammatory cytokines (TNF-α, IL-6, and IL-1ß) and enhancing the production of M2 macrophage markers IL-10, IL-4, and CD206. The MAPK and NF-κB inflammatory signaling pathways and transcriptional activator 6 (STAT6) were involved in this effect. In mice, Zs-CATH rapidly recruited neutrophils and monocytes/macrophages to the abdominal cavity but not T and B lymphocytes. Zs-CATH did not exhibit a direct chemoattractant effect on phagocytes but significantly promoted phagocyte migration in the presence of macrophages. Zs-CATH stimulated macrophages to secrete chemokines CXCL1, CXCL2, and CCL2, which mediated the recruitment of phagocytes. Furthermore, Zs-CATH promoted the production of reactive oxygen species (ROS) and neutrophil extracellular traps (NETs), which are oxygen-dependent and oxygen-independent mechanisms of the microbicidal activity of neutrophils, respectively. Zs-CATH exhibited no toxic side effects on mammalian cells and mice. These findings show that in addition to direct antibacterial activity, Zs-CATH also possesses the ability to modulate immune and inflammatory processes during bacterial infection, showing potential for development as anti-infective and/or anti-inflammatory agents.