Skin secretions of Leptodactylidae (Anura) and their potential applications

Abstract

The skin of anuran species is a protective barrier against predators and pathogens, showing also chemical defense by substances that represent a potential source for bioactive substances. This review describes the current chemical and biological knowledge from the skin secretions of Leptodactylidae species, one of the most diverse neotropical frog families. These skin secretions reveal a variety of substances such as amines (12), neuropeptides (16), and antimicrobial peptides (72). The amines include histamine and its methylated derivatives, tryptamine derivatives and quaternary amines. The peptides of Leptodactylidae species show molecular weight up to 3364 Da and ocellatins are the most reported. The peptides exhibit commonly glycine (G) or glycine-valine (GV) as C-terminal amino acids, and the most common N-terminal amino acids are glutamic acid (E), lysine (K), and valine (V). The substances from Leptodactylidae species have been evaluated against pathogenic microorganisms, particularly Escherichia coli and Staphylococcus aureus, and the most active peptides showed MIC of 1-15 µM. Furthermore, some compounds showed also pharmacological properties such as immunomodulation, treatment of degenerative diseases, anticancer, and antioxidant. Currently, only 9% of the species in this family have been properly studied, highlighting a large number of unstudied species such as an entire subfamily (Paratelmatobiinae). The ecological context, functions, and evolution of peptides and amines in this family are poorly understood and represent a large field for further exploration.

Keywords: Amines; Antibiotic resistance; Antimicrobial peptides; Peptides.

Figure 1.. Phylogenetic tree of Leptodactylidae species with studies of skin secretion. Leptodactylus knudseni (Photo by Diego Santana), L. fallax, L. pentadactylus, L. labyrinthicus (Photo by Diego Santana), L. vastus, L. stenodema, L. rugosus, L. rhodonotus, L. luctator, L. latrans (Photo by Diego Santana), L. macrosternum, L. insularum, L. pustulatus (Photo by Diego Santana), L. nesiotus, L. validus, L. syphax, L. laticeps (Photo by Hugo Cabral), Physalaemus signifier, P. nattereri (Photo by Diego Santana), P. cuvieri, P. centralis, P. biligonigerus, Engystomops pustulosus, Pleurodema thaul (Photo by Diego Baldo), P. somuncurensis, Paratelmatobius poecilogaster (outgroup). Colours represent species groups of Leptodactylus: L. pentadactylus group (green), L. latrans group (yellow), L. melanonotus (blue), and L. fuscus group (red).

Figure 2.. Chemical structures of the amines of Leptodactylidae species.

Figure 3.. Heatmap representing the presence (brown) and absence of antimicrobial peptides in Leptodactylidae species. Phylogenetic tree of Leptodactylidae species (up) and ClustalW2 Phylogeny of the antimicrobial peptides (left).