Maurizio Simmaco

Antimicrobial peptides from amphibian skin: What do they tell us?

Amphibian skin secretions contain many biologically active compounds, such as biogenic amines, complex alkaloids, or peptides. Within the latter class of molecules, a large number of peptide antibiotics has been isolated and characterized from different amphibian species. Antimicrobial peptides are considered the effector molecules of innate immunity, acting as a first line of defense against bacterial infections, by perturbing the phospholipid bilayer of the target cell membrane. These gene-encoded molecules are synthesized as inactive precursors and in several cases their proparts were shown to have highly conserved structures. It has also been demonstrated that the promoter regions of inducible peptide antibiotics are often regulated by the transcriptional control machinery NF-kappa B/I kappa B alpha. In amphibia of Rana and Bombina genera, inhibition of transcription of the genes encoding antimicrobial peptides has been obtained by glucocorticoid treatment, which causes an increase of I kappa B alpha synthesis. Moreover, determination of the structure of a number of genes coding for antimicrobial peptides in amphibia has actually shown that their promoter regions contain recognition sites for nuclear factors.

Amphibian skin: a promising resource for antimicrobial peptides.

Amphibian skin is a rich source of biologically active compounds that are assumed to have diverse physiological and defence functions. In addition to the range of pharmacologically active peptides present, some of which have mammalian homologues, skin secretions contain a broad spectrum of antimicrobial peptides. As yet, such peptides from only a few species have been studied, and screening of other species is expected to yield further new antimicrobial activities. Natural antimicrobial peptides isolated from amphibian skin could provide lead structures for either the chemical, or rDNA synthesis of novel antimicrobials.

Syringopeptins, new phytotoxic lipodepsipeptides of Pseudomonas syringae pv. syringae

The primary structure of some new lipodepsipeptides named syringopeptins, produced by plant pathogenic strains of Pseudopmonas syringae pv. syringae has been determined by a combination of chemical methods, 1H and 13C NMR spectroscopy and FAB mass spectrometry. Two syringomycin‐producing strains afforded 3‐hydroxydecanoyl‐Dhb‐Pro‐Val‐Val‐Ala‐Ala‐Val‐Val‐Dhb‐Ala‐Val‐Ala‐Ala‐Dhb‐aThr‐Ser‐Ala‐Dhb‐Ala‐Dab‐Dab‐Tyr, with Tyr acylating a Thr to form a macrolactone ring, and smaller amounts of the 3‐hydroxydodecanoyl homologue. Evidence was obtained that a third syringomycin‐producing strain and a syringotoxin‐producing strain synthesize 3‐hydroxydecanoyl‐Dhb‐Pro‐Val‐Ala‐Ala‐Val‐Leu‐Ala‐Ala‐Dhb‐Val‐Dhb‐Ala‐Val‐Ala‐Ala‐Dhb‐aThr‐Ser‐Ala‐Val‐Ala‐Dab‐Dab‐Tyr, with Tyr and aThr forming again the macrolactone ring, and smaller amounts of the 3‐hydroxydodecanoyl homologue.

The structure of syringomycins A1, E and G

By a combination of 1D and 2D 1H‐ and 13C‐NMR, FAB‐MS, and chemical and enzymatic reactions carried out at the milligram level, it has been demonstrated that syringomycin E, the major phytotoxic antibiotic produced by Pseudomonas syringae pv. syringae, is a new lipodepsipeptide. Its amino acid sequence is Ser‐Ser‐Dab‐Dab‐Arg‐Phe‐Dhb‐4(Cl)Thr‐3(OH)Asp with the β‐carboxy group of the C‐terminal residue closing a macrocyclic ring on the OH group of the N‐terminal Ser, which in turn is N‐acylated by 3‐hydroxydodecanoic acid. Syringomycins A1 and G, two other metabolites of the same bacterium, differ from syringomycin E only in their fatty acid moieties corresponding, respectively, to 3‐hydroxydecanoic and 3‐hydroxytetradecanoic acid.

Novel antimicrobial peptides from skin secretion of the European frog Rana esculenta

Three antimicrobial peptides were isolated from skin secretion of the European frog, Rana esculenta. Two of them show similarity to brevinin‐1 and brevinin‐2, respectively, two antimicrobial peptides recently isolated from a Japanese frog [Morikawa, N., Hagiwara, K. and Nakajima, T. (1992) Biochem. Biophys. Res. Commun. 189, 184‐190]. The third one, named esculentin, is 46 residues long and represents a different type of peptide. All these peptides have as a common motif an intramolecular disulfide bridge located at the COOH‐terminal end. The peptides from R. esculenta show distinctive antibacterial activity against representative Gram‐negative and Gram‐positive bacterial species. In particular, esculentin is the most active against Staphylococcus aureus, and has a much lower hemolytic activity.

L-acetylcarnitine causes rapid antidepressant effects through the epigenetic induction of mGlu2 receptors

Epigenetic mechanisms are involved in the pathophysiology of depressive disorders and are unique potential targets for therapeutic intervention. The acetylating agent L-acetylcarnitine (LAC), a well-tolerated drug, behaves as an antidepressant by the epigenetic regulation of type 2 metabotropic glutamate (mGlu2) receptors. It caused a rapid and long-lasting antidepressant effect in Flinders Sensitive Line rats and in mice exposed to chronic unpredictable stress, which, respectively, model genetic and environmentally induced depression. In both models, LAC increased levels of acetylated H3K27 bound to the Grm2 promoter and also increased acetylation of NF-ĸB-p65 subunit, thereby enhancing the transcription of Grm2 gene encoding for the mGlu2 receptor in hippocampus and prefrontal cortex. Importantly, LAC reduced the immobility time in the forced swim test and increased sucrose preference as early as 3 d of treatment, whereas 14 d of treatment were needed for the antidepressant effect of chlorimipramine. Moreover, there was no tolerance to the action of LAC, and the antidepressant effect was still seen 2 wk after drug withdrawal. Conversely, NF-ĸB inhibition prevented the increase in mGlu2 expression induced by LAC, whereas the use of a histone deacetylase inhibitor supported the epigenetic control of mGlu2 expression. Finally, LAC had no effect on mGlu2 knockout mice exposed to chronic unpredictable stress, and a single injection of the mGlu2/3 receptor antagonist LY341495 partially blocked LAC action. The rapid and long-lasting antidepressant action of LAC strongly suggests a unique approach to examine the epigenetic hypothesis of depressive disorders in humans, paving the way for more efficient antidepressants with faster onset of action.

Temporin L: antimicrobial, haemolytic and cytotoxic activities, and effects on membrane permeabilization in lipid vesicles

The temporins are a family of small, linear antibiotic peptides with intriguing biological properties. We investigated the antibacterial, haemolytic and cytotoxic activities of temporin L (FVQWFSKFLGRIL-NH2), isolated from the skin of the European red frog Rana temporaria. The peptide displayed the highest activity of temporins studied to date, against both human erythrocytes and bacterial and fungal strains. At variance with other known temporins, which are mainly active against Gram-positive bacteria, temporin L was also active against Gram-negative strains such as Pseudomonas aeruginosa A.T.C.C. 15692 and Escherichia coli D21 at concentrations comparable with those that are microbiocidal to Gram-positive bacteria. In addition, temporin L was cytotoxic to three different human tumour cell lines (Hut-78, K-562 and U-937), causing a necrosis-like cell death, although sensitivity to the peptide varied markedly with the specific cell line tested. A study of the interaction of temporin L with liposomes of different lipid compositions revealed that the peptide causes perturbation of bilayer integrity of both neutral and negatively charged membranes, as revealed by the release of a vesicle-encapsulated fluorescent marker, and that the action of the peptide is modulated to some extent by membrane lipid composition. In particular, the presence of negatively charged lipids in the model bilayer inhibits the lytic power of temporin L. We also show that the release of fluorescent markers caused by temporin L is size-dependent and that the peptide does not have a detergent-like effect on the membrane, suggesting that perturbation of bilayer organization takes place on a local scale, i.e. through the formation of pore-like openings.

Phytotoxic properties of Pseudomonas syringae pv. syringae toxins

Abstract Syringomycin E, syringomycin G and syringopeptin 25A, the main components of the Pseudomonas syringae pv. syringae toxin mixture, were assayed for their phytotoxicity, determined as electrolyte leakage from carrot tissues, necrosis of tobacco leaves, and death of potato tissues, and for their antimicrobial activity on Rhodotorula pilimanae. p]In the antimicrobial assay, syringomycins were 30 times more active than syringopeptin 25A, but, in the electrolyte leakage assay, they proved to be 40 times less active than the former since a significant effect required concentrations of 16 and 0·4 μ m respectively. A statistically identical effect on electrolyte leakage was obtained with syringopeptin 25A or with an unfractionated toxin mixture equimolar for syringopeptin 25A. A similar pattern of activity was observed in the tobacco leaf and potato disc assays. After a short incubation at pH 10, syringomycins completely lost their antimicrobial and phytotoxic activities, while syringopeptin 25A retained all its antimicrobial activity and most of its phytotoxicity. These findings indicate that syringopeptin 25A and syringomycins are mainly responsible for, respectively, the phytotoxic activity and the antimicrobial activity on R. pilimanae, characteristic of the unfractionated toxin mixture of P. s. pv. syringae. The high phytotoxicity of syringopeptin 25A is a new finding which prompts a careful examination of the role played by the individual metabolites in the disease caused by P. s. pv. syringae ecotypes.

Cardiac resynchronization therapy increases plasma levels of the endogenous inotrope apelin.

Cardiac resynchronization therapy (CRT) has been introduced to treat drug refractory chronic heart failure (CHF). Apelin, the endogenous ligand of the APJ receptor, is under evaluation for its potential role in human CHF pathophysiology. This study aims to assess whether biventricular pacing affects plasma apelin levels in patients with severe CHF.

The synthesis of antimicrobial peptides in the skin of Rana esculenta is stimulated by microorganisms

Secretions of amphibian skin glands contain numerous antimicrobial peptides that play a crucial role in the defense against microorganisms. The location of these glands on the surface of the animal makes them a useful model for in vivo studies of the relationships between the innate immune system and the natural flora. Here, we present the results of a study showing that in Rana esculenta the total antimicrobial activity of skin secretion is modulated by the presence of the natural flora. Frogs kept in a sterile environment do not produce antimicrobial peptides. This finding represents the first in vivo demonstration of the induction of defense peptides in a vertebrate. We also present data on the morphological changes in skin glands of animals kept in sterile conditions or treated with glucocorticoids. Cells from glands regenerated under normal conditions, but not those from “sterile” frogs, contain κB‐binding activity in the cytoplasm.