A family of antimicrobial and immunomodulatory peptides related to the frenatins from skin secretions of the Orinoco lime frog Sphaenorhynchus lacteus (Hylidae)

• Published in: Peptides (New York, N.Y. : 1980) Vol. 56; pp. 132 - 140
• Main Authors: Conlon, J. Michael, Mechkarska, Milena, Radosavljevic, Gordana, Attoub, Samir, King, Jay D., Lukic, Miodrag L., McClean, Stephen
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01-06-2014
• Subjects: Amphibian Proteins - chemistry; Animals; Anti-Infective Agents - chemistry; Anti-Infective Agents - pharmacology; Antiinfectives and antibacterials; Antimicrobial; Antineoplastic Agents - pharmacology; Anura; Bacteria; Cell Survival - drug effects; Cytokine; Cytokines; Discoglossus; Frenatin; Frog skin; Frogs; Humans; Hylidae; Hylinae; Immunologic Factors - chemistry; Immunologic Factors - pharmacology; Immunomodulatory; Interleukin-10 - metabolism; Interleukin-1beta - metabolism; Interleukin-23 - metabolism; Lime; Lipopolysaccharides - pharmacology; Litoria; Macrophages; Macrophages - drug effects; Macrophages - metabolism; Methicillin-Resistant Staphylococcus aureus - drug effects; Mice; Peptides; Peptides - chemistry; Peptides - pharmacology; Secretions; Skin - secretion; Sphaenorhynchus; Staphylococcus aureus; Staphylococcus epidermidis; Tumor Necrosis Factor-alpha - metabolism; Antimicrobial; Frenatin; Immunomodulatory; Hylidae; Frog skin; Cytokine
• ISSN: 0196-9781; 1873-5169
• DOI: 10.1016/j.peptides.2014.03.020

•Three frenatin-related peptides were isolated from Sphaenorhynchus lacteus skin secretions.•Frenatin 2.1S and 2.2S show potent bactericidal activity against MRSA.•Frenatin 2.1S and 2.2S are cytotoxic to lung adenocarcinoma A549 cells.•Frenatin 2.1S and 2.2S enhance production of TNF-α, IL-1β, and IL23 by mouse macrophages.•Frenatin 2.2S inhibits production of IL-10 by lipopolysaccharide-stimulated macrophages.
Peptidomic analysis of norepinephrine-stimulated skin secretions of the Orinoco lime tree frog Sphaenorhynchus lacteus (Hylidae, Hylinae) revealed the presence of three structurally related host-defense peptides with limited sequence similarity to frenatin 2 from Litoria infrafrenata (Hylidae, Pelodryadinae) and frenatin 2D from Discoglossus sardus (Alytidae). Frenatin 2.1S (GLVGTLLGHIGKAILG.NH2) and frenatin 2.2S (GLVGTLLGHIGKAILS.NH2) are C-terminally α-amidated but frenatin 2.3S (GLVGTLLGHIGKAILG) is not. Frenatin 2.1S and 2.2S show potent bactericidal activity against clinical isolates of methicillin-resistant Staphylococcus aureus (MRSA) and Staphylococcus epidermidis (MIC ≤16μM) but are less active against a range of Gram-negative bacteria. Frenatin 2.1S (LC50=80±6μM) and 2.2S (LC50=75±5μM) are cytotoxic against non-small cell lung adenocarcinoma A549 cells but are less hemolytic against human erythrocytes (LC50=167±8μM for frenatin 2.1S and 169±7μM for 2.2S). Weak antimicrobial and cytotoxic potencies of frenatin 2.3S demonstrate the importance of C-terminal α-amidation for activity. Frenatin 2.1S and 2.2S significantly (P<0.05) increased production of proinflammatory cytokines IL-1β and IL-23 by lipopolysaccharide (LPS)-stimulated mouse peritoneal macrophages and frenatin 2.1S also enhanced production of TNF-α. Effects on IL-6 production were not significant. Frenatin 2.2S significantly downregulated production of the anti-inflammatory cytokine IL-10 by LPS-stimulated cells. The data support speculation that frenatins act on skin macrophages to produce a cytokine-mediated stimulation of the adaptive immune system in response to invasion by microorganisms. They may represent a template for the design of peptides with therapeutic applications as immunostimulatory agents.