Search

The recent pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) has highlighted how urgent and necessary the discovery of new antiviral compounds is for novel therapeutic approaches. Among the various classes of molecules with antiviral activity, antimicrobial peptides (AMPs) of innate immunity are among the most promising ones, mainly due to their different mechanisms of action against viruses and additional biological properties. In this review, the main physicochemical characteristics of AMPs are described, with particular interest toward peptides derived from amphibian skin. Living in aquatic and terrestrial environments, amphibians are one of the richest sources of AMPs with different primary and secondary structures. Besides describing the various antiviral activities of these peptides and the underlying mechanism, this review aims at emphasizing the high potential of these small molecules for the development of new antiviral agents that likely reduce the selection of resistant strains. [ABSTRACT FROM AUTHOR]

The host‐defense peptide ocellatin‐3N (GIFDVLKNLAKGVITSLAS.NH2), first isolated from the Caribbean frog Leptodactylus nesiotus, inhibited growth of clinically relevant Gram‐positive and Gram‐negative bacteria as well as a strain of the major emerging yeast pathogen Candida parapsilosis. Increasing cationicity while maintaining amphipathicity by the substitution Asp4→Lys increased potency against the microorganisms by between 4‐ and 16‐fold (MIC ≤3 μM) compared with the naturally occurring peptide. The substitution Ala18→Lys and the double substitution Asp4→Lys and Ala18→Lys had less effects on potency. The [D4K] analog also showed 2.5‐ to 4‐fold greater cytotoxic potency against non‐small‐cell lung adenocarcinoma A549 cells, breast adenocarcinoma MDA‐MB‐231 cells, and colorectal adenocarcinoma HT‐29 cells (LC50 values in the range of 12–20 μM) compared with ocellatin‐3N but was less hemolytic to mouse erythrocytes. However, the peptide showed no selectivity for tumor‐derived cells [LC50 = 20 μM for human umbilical vein endothelial cells (HUVECs)]. Ocellatin‐3N and [D4K]ocellatin‐3N stimulated the release of insulin from BRIN‐BD11 clonal β‐cells at concentrations ≥1 nM, and [A18K]ocellatin‐3N, at concentrations ≥0.1 nM. No peptide stimulated the release of lactate dehydrogenase at concentrations up to 3 μM, indicating that plasma membrane integrity had been preserved. The three peptides produced an increase in intracellular [Ca2+] in BRIN‐BD11 cells when incubated at a concentration of 1 μM. In view of its high insulinotropic potency and relatively low hemolytic activity, the [A18K] ocellatin analog may represent a template for the design of agents with therapeutic potential for the treatment of patients with type 2 diabetes. [ABSTRACT FROM AUTHOR]

Pseudomonas aeruginosa is a pathogenic bacterium known to cause serious human infections, especially in immune‐compromised patients. This is due to its unique ability to transform from a drug‐tolerant planktonic to a more dangerous and treatment‐resistant sessile life form, called biofilm. Recently, two derivatives of the frog skin antimicrobial peptide esculentin‐1a, i.e. Esc(1‐21) and its D‐amino acids containing diastereomer Esc(1‐21)‐1c, were characterized for their powerful anti‐Pseudomonal activity against both forms. Prevention of biofilm formation already in its early stages could be even more advantageous for counteracting infections induced by this bacterium. In this work, we studied how the diastereomer Esc(1‐21)‐1c can inhibit Pseudomonas biofilm formation in comparison to the parent peptide and two clinically‐used conventional antibiotics, i.e. colistin and aztreonam, when applied at dosages below the minimal growth inhibitory concentration. Biofilm prevention was correlated to the peptides' ability to inhibit Pseudomonas motility and to reduce the production of virulent metabolites, for example, pyoverdine and rhamnolipids. Furthermore, the molecular mechanism underlying these activities was evaluated by studying the peptides' effect on the expression of key genes involved in the virulence and motility of bacteria, as well as by monitoring the peptides' binding to the bacterial signaling nucleotide ppGpp. Our results demonstrate that the presence of only two D‐amino acids in Esc(1‐21)‐1c is sufficient to downregulate ppGpp‐mediated expression of biofilm‐associated genes, presumably as a result of higher peptide stability and therefore prolonged interaction with the nucleotide. Overall, these studies should assist efficient design and optimization of new anti‐infective agents with multiple pharmacologically beneficial properties. [ABSTRACT FROM AUTHOR]

Pseudomonas aeruginosa is a pathogenic bacterium known to cause serious human infections, especially in immune‐compromised patients. This is due to its unique ability to transform from a drug‐tolerant planktonic to a more dangerous and treatment‐resistant sessile life form, called biofilm. Recently, two derivatives of the frog skin antimicrobial peptide esculentin‐1a, i.e. Esc(1‐21) and its D‐amino acids containing diastereomer Esc(1‐21)‐1c, were characterized for their powerful anti‐Pseudomonal activity against both forms. Prevention of biofilm formation already in its early stages could be even more advantageous for counteracting infections induced by this bacterium. In this work, we studied how the diastereomer Esc(1‐21)‐1c can inhibit Pseudomonas biofilm formation in comparison to the parent peptide and two clinically‐used conventional antibiotics, i.e. colistin and aztreonam, when applied at dosages below the minimal growth inhibitory concentration. Biofilm prevention was correlated to the peptides' ability to inhibit Pseudomonas motility and to reduce the production of virulent metabolites, for example, pyoverdine and rhamnolipids. Furthermore, the molecular mechanism underlying these activities was evaluated by studying the peptides' effect on the expression of key genes involved in the virulence and motility of bacteria, as well as by monitoring the peptides' binding to the bacterial signaling nucleotide ppGpp. Our results demonstrate that the presence of only two D‐amino acids in Esc(1‐21)‐1c is sufficient to downregulate ppGpp‐mediated expression of biofilm‐associated genes, presumably as a result of higher peptide stability and therefore prolonged interaction with the nucleotide. Overall, these studies should assist efficient design and optimization of new anti‐infective agents with multiple pharmacologically beneficial properties. [ABSTRACT FROM AUTHOR]

Temporin A (FLPLIGRVLSGIL-NH2), temporin F (FLPLIGKVLSGIL-NH2), and temporin G (FFPVIGRILNGIL-NH2), first identified in skin secretions of the frog Rana temporaria, produced concentration-dependent stimulation of insulin release from BRIN-BD11 rat clonal β-cells at concentrations ≥1 nM, without cytotoxicity at concentrations up to 3 µM. Temporin A was the most effective. The mechanism of insulinotropic action did not involve an increase in intracellular Ca2+ concentrations. Temporins B, C, E, H, and K were either inactive or only weakly active. Temporins A, F, and G also produced a concentration-dependent stimulation of insulin release from 1.1B4 human-derived pancreatic β-cells, with temporin G being the most potent and effective, and from isolated mouse islets. The data indicate that cationicity, hydrophobicity, and the angle subtended by the charged residues in the temporin molecule are important determinants for in vitro insulinotropic activity. Temporin A and F (1 µM), but not temporin G, protected BRIN-BD11 cells against cytokine-induced apoptosis (P < 0.001) and augmented (P < 0.001) proliferation of the cells to a similar extent as glucagon-like peptide-1. Intraperitoneal injection of temporin G (75 nmol/kg body weight) together with a glucose load (18 mmol/kg body weight) in C57BL6 mice improved glucose tolerance with a concomitant increase in insulin secretion whereas temporin A and F administration was without significant effect on plasma glucose levels. The study suggests that combination therapy involving agents developed from the temporin A and G sequences may find application in Type 2 diabetes treatment. [ABSTRACT FROM AUTHOR]

ABSTRACT In this article, we report novel and additional results, both experimental and computational, obtained in our laboratories on the peptide P-113. In particular, our experimental results indicate that this peptide is endowed with a high target-cell selectivity towards yeast species, suggesting its potential development as a new drug against oral microbial infections. To provide additional structural insights, we performed several Molecular Dynamics simulations in different conditions. Results suggest that P-113 is a rather compact species presumably because of its highly charged state as emerged from the dramatic increase of internal fluctuation occurring upon point-mutation. The peptide turns out to adopt, in water, a beta-hairpin-like conformation and, in a more hydrophobic environment, is found to be in a (probably slow) equilibrium between α-helix and hairpin conformations. Complexation with Zn2+ induces a drastic mechanical stabilization, which prevents any conformational organization of the peptide into a biologically active state. © 2013 Wiley Periodicals, Inc. Biopolymers (Pept Sci) 102: 159-167, 2014. [ABSTRACT FROM AUTHOR]

Contact lens (CL) wear is a risk factor for development of microbial keratitis, a vision threatening infection of the eye. Adverse events associated with colonization of lenses, especially by the multi‐drug resistant and biofilm forming bacterium Pseudomonas aeruginosa remain a major safety issue. Therefore, novel strategies and compounds to reduce the onset of CL‐associated ocular infections are needed. Recently, the activity of the frog skin‐derived antimicrobial peptide Esc(1‐21) and its diastereomer Esc(1‐21)‐1c was evaluated against both planktonic and sessile forms of this pathogen. Furthermore, Esc(1‐21) was found to significantly reduce the severity of P. aeruginosa keratitis in a mouse model and preserve antipseudomonal activity in the presence of human basal tears. Here, we have analyzed the activity of the peptides on P. aeruginosa biofilm formed on soft CLs. Microbiological assays and scanning electron microscopy analysis indicated that the peptides were able to disrupt the bacterial biofilm, with the diastereomer having the greater efficacy (up to 85% killing vs no killing at 4 μM for some strains). Furthermore, upon covalent immobilization to the CL, the two peptides were found to cause more than four log reduction in the number of bacterial cells within 20 minutes and to reduce bacterial adhesion to the CL surface (77%–97% reduction) in 24 hours. Importantly, peptide immobilization was not toxic to mammalian cells and did not affect the lens characteristics. Overall, our data suggest that both peptides have great potential to be developed as novel pharmaceuticals for prevention and treatment of CL‐associated P. aeruginosa keratitis. [ABSTRACT FROM AUTHOR]