Purification, Conformational Analysis, and Properties of a Family of Tigerinin Peptides From Skin Secretions of the Crowned Bullfrog Hoplobatrachus Occipitalis

J Nat Prod. 2016 Sep 23;79(9):2350-6. doi: 10.1021/acs.jnatprod.6b00494. Epub 2016 Aug 25.

Abstract

Four host-defense peptides belonging to the tigerinin family (tigerinin-1O: RICTPIPFPMCY; tigerinin-2O: RTCIPIPLVMC; tigerinin-3O: RICTAIPLPMCL; and tigerinin-4O: RTCIPIPPVCF) were isolated from skin secretions of the African crowned bullfrog Hoplobatrachus occipitalis. In aqueous solution at pH 4.8, the cyclic domain of tigerinin-2O adopts a rigid amphipathic conformation that incorporates a flexible N-terminal tail. The tigerinins lacked antimicrobial (MIC > 100 μM) and hemolytic (LC50 > 500 μM) activities but, at a concentration of 20 μg/mL, significantly (P < 0.05) inhibited production of interferon-γ (IFN-γ) by peritoneal cells from C57BL/6 mice without affecting production of IL-10 and IL-17. Tigerinin-2O and -4O inhibited IFN-γ production at concentrations as low as 1 μg/mL. The tigerinins significantly (P ≤ 0.05) stimulated the rate of insulin release from BRIN-BD11 clonal β-cells without compromising the integrity of the plasma membrane. Tigerinin-1O was the most potent (threshold concentration 1 nM) and the most effective (395% increase over basal rate at a concentration of 1 μM). Tigerinin-4O was the most potent and effective peptide in stimulating the rate of glucagon-like peptide-1 release from GLUTag enteroendocrine cells (threshold concentration 10 nM; 289% increase over basal rate at 1 μM). Tigerinin peptides have potential for development into agents for the treatment of patients with type 2 diabetes.

MeSH terms

  • Amphibian Proteins / chemistry
  • Amphibian Proteins / isolation & purification*
  • Amphibian Proteins / pharmacology
  • Animals
  • Antimicrobial Cationic Peptides / chemistry
  • Antimicrobial Cationic Peptides / isolation & purification*
  • Antimicrobial Cationic Peptides / pharmacology
  • Diabetes Mellitus, Type 2 / drug therapy
  • Humans
  • Hydrogen-Ion Concentration
  • Insulin / pharmacology
  • Interleukin-10 / metabolism
  • Interleukin-17 / metabolism
  • Mice
  • Mice, Inbred C57BL
  • Microbial Sensitivity Tests
  • Peptides / chemistry
  • Peptides / isolation & purification
  • Peptides / pharmacology*
  • Rana catesbeiana
  • Skin / drug effects
  • Skin / metabolism*

Substances

  • Amphibian Proteins
  • Antimicrobial Cationic Peptides
  • Insulin
  • Interleukin-17
  • Peptides
  • tigerinin 1
  • Interleukin-10