ATTIVITA' ANTIBATTERICA E ANTIFUNGINA DI PEPTIDI ANTIMICROBICI E LORO INIBIZIONE DA ESOPOLISACCARIDI DI PATOGENI POLMONARI

2001/2002XV Ciclo1972Versione digitalizzata della tesi di dottorato cartacea

The human cathelicidin LL-37 - A pore-forming antibacterial peptide and host-cell modulator

The human cathelicidin hCAP18/LL-37 has become a paradigm for the pleiotropic roles of peptides in host defence. It has a remarkably wide functional repertoire that includes direct antimicrobial activities against various types of microorganisms, the role of \u2018alarmin\u2019 that helps to orchestrate the immune response to infection, the capacity to locally modulate inflammation both enhancing it to aid in combating infection and limiting it to prevent damage to infected tissues, the promotion of angiogenesis and wound healing, and possibly also the elimination of abnormal cells. LL-37 manages to carry out all its reported activities with a small and simple, amphipathic, helical structure. In this review we consider how different aspects of its primary and secondary structures, as well as its marked tendency to form oligomers under physiological solution conditions and then bind to molecular surfaces as such, explain some of its cytotoxic and immunomodulatory effects. We consider its modes of interaction with bacterial membranes and capacity to act as a pore-forming toxin directed by our organism against bacterial cells, contrasting this with the mode of action of related peptides from other species. We also consider its different membrane-dependent effects on our own cells, which underlie many of its other activities in host defence

PEGylation of the peptide Bac7(1–35) reduces renal clearance while retaining antibacterial activity and bacterial cell penetration capacity

6The proline-rich antibacterial peptide Bac7(1–35) protects mice against Salmonella typhimurium infection, despite its rapid clearance. To overcome this problem the peptide was linked to a polyethylene glycol (PEG) molecule either via a cleavable ester bond or via a non-hydrolysable amide bond. Both the PEGylated conjugates retained most of the in vitro activity against S. typhimurium. In addition, the ester bond was cleaved in human serum or plasma, releasing a carboxymethyl derivative of Bac7(1–35) which accounts for a higher activity of this peptide with relative to the other, non-hydrolysable form. Both PEGylated peptides maintained the capacity of the unconjugated form to kill bacteria without permeabilizing the bacterial membranes, by penetrating into cells. They exploited the same transporter as unmodified Bac7(1–35), suggesting it has the capacity to internalize quite sizeable cargo if this is linked to Bac7 fragment. PEGylation allows the peptide to have a wide distribution in mice, and a slow renal clearance, indicating that this strategy would improve the bioavailability of Bac7, and in principle of other antimicrobial peptides. This can be an equally important issue to reducing cytotoxicity for therapeutic use of these antibacterials.partially_openopenBenincasa, Monica; Zahariev, Sotir; Pelillo, Chiara; Milan, Annalisa; Gennaro, Renato; Scocchi, MarcoBenincasa, Monica; Zahariev, Sotir; Pelillo, Chiara; Milan, Annalisa; Gennaro, Renato; Scocchi, Marc

Trichoplaxin — A new membrane-active antimicrobial peptide from placozoan cDNA

AbstractA method based on the use of signal peptide sequences from antimicrobial peptide (AMP) precursors was used to mine a placozoa expressed sequence tag database and identified a potential antimicrobial peptide from Trichoplax adhaerens. This peptide, with predicted sequence FFGRLKSVWSAVKHGWKAAKSR is the first AMP from a placozoan species, and was named trichoplaxin. It was chemically synthesized and its structural properties, biological activities and membrane selectivity were investigated. It adopts an α-helical structure in contact with membrane-like environments and is active against both Gram-negative and Gram-positive bacterial species (including MRSA), as well as yeasts from the Candida genus. The cytotoxic activity, as assessed by the haemolytic activity against rat erythrocytes, U937 cell permeabilization to propidium iodide and MCF7 cell mitochondrial activity, is significantly lower than the antimicrobial activity. In tests with membrane models, trichoplaxin shows high affinity for anionic prokaryote-like membranes with good fit in kinetic studies. Conversely, there is a low affinity for neutral eukaryote-like membranes and absence of a dose dependent response. With high selectivity for bacterial cells and no homologous sequence in the UniProt, trichoplaxin is a new potential lead compound for development of broad-spectrum antibacterial drugs

The proline-rich peptide Bac7(1-35) reduces mortality from Salmonella typhimurium in a mouse model of infection

<p>Abstract</p> <p>Background</p> <p>Bac7 is a proline-rich peptide with a potent <it>in vitro </it>antimicrobial activity against Gram-negative bacteria. Here we investigated its activity in biological fluids and <it>in vivo </it>using a mouse model of <it>S. typhimurium </it>infection.</p> <p>Results</p> <p>The efficacy of the active 1-35 fragment of Bac7 was assayed in serum and plasma, and its stability in biological fluids analyzed by Western blot and mass spectrometry. The ability of the peptide to protect mice against <it>Salmonella </it>was assayed in a typhoid fever model of infection by determination of survival rates and bacterial load in liver and spleen of infected animals. In addition, the peptide's biodistribution was evaluated by using time-domain optical imaging. Bac7(1-35) retained a substantial <it>in vivo </it>activity showing a very low toxicity. The peptide increased significantly the number of survivors and the mean survival times of treated mice reducing the bacterial load in their organs despite its rapid clearance.</p> <p>Conclusions</p> <p>Our results provide a first indication for a potential development of Bac7-based drugs in the treatment of salmonellosis and, eventually, other Gram-negative infections. The <it>in vivo </it>activity for this peptide might be substantially enhanced by decreasing its excretion rate or modifying the treatment schedule.</p

Effect of size and N-terminal residue characteristics on bacterial cell penetration and antibacterial activity of the proline-rich peptide Bac7

Bac7 is a proline-rich antimicrobial peptide, selective for Gram-negative bacteria, which acts intracellularly after membrane translocation. Progressively shortened fragments of Bac7 allowed determining the minimal sequence required for entry and antimicrobial activity as a 16-residue, N-terminal fragment, while further shortening led to a marked decrease in both functions. Furthermore, two N-terminal arginine residues were required for efficient translocation and activity. Analogues in which these residues were omitted, or where the side chain steric or physicochemical characteristics were systematically altered, were tested on different Escherichia coli strains, including a mutant with a destabilized outer membrane and one lacking the relevant SbmA membrane transport protein. H-bonding capacity, stereochemistry, and charge, in that order, played a determining role for efficient transit through both the outer and cytoplasmic membranes. Our studies allowed building a more detailed model for the mode-of-action of Bac7, and confirming its potential as an anti-infective agent, also suggesting it may be a vehicle for internalization of other antibiotic cargo

The mechanism of killing by the proline-rich peptide Bac7(1-35) against clinical strains of Pseudomonas aeruginosa differs from that against other gram-negative bacteria

Pseudomonas aeruginosa infections represent a serious threat to worldwide health. Proline-rich antimicrobial peptides (PR-AMPs), a particular group of peptide antibiotics, have demonstrated in vitro activity against P. aeruginosa strains. Here we show that the mammalian PR-AMP Bac7(1\u201335) is active against some multidrug-resistant cystic fibrosis isolates of P. aeruginosa. By confocal microscopy and cytometric analyses, we investigated the mechanism of killing against P. aeruginosa strain PAO1 and three selected isolates, and we observed that the peptide inactivated the target cells by disrupting their cellular membranes. This effect is deeply different from that previously described for PR-AMPs in Escherichia coli and Salmonella enterica serovar Typhimurium, where these peptides act intracellularly after having been internalized by means of the transporter SbmA without membranolytic effects. The heterologous expression of SbmA in PAO1 cells enhanced the internalization of Bac7(1\u201335) into the cytoplasm, making the bacteria more susceptible to the peptide but at the same time more resistant to the membrane lysis, similarly to what occurs in E. coli. The results evidenced a new mechanism of action for PRAMPs and indicate that Bac7 has multiple and variable modes of action that depend on the characteristics of the different target species and the possibility to be internalized by bacterial transporters. This feature broadens the spectrum of activity of the peptide and makes the development of peptide-resistant bacteria a more difficult process

Structure-activity relationships of the antimicrobial peptide arasin 1 - and mode of action studies of the N terminal, proline-rich region

Arasin 1 is a 37 amino acid long proline-rich antimicrobial peptide isolated from the spider crab, Hyas araneus. In this work the active region of arasin 1 was identified through structure-activity studies using different peptide fragments derived from the arasin 1 sequence. The pharmacophore was found to be located in the proline/arginine-rich NH2 terminus of the peptide and the fragment arasin 1(1–23) was almost equally active to the full length peptide. Arasin 1 and its active fragment arasin 1(1–23) were shown to be non-toxic to human red blood cells and arasin 1(1–23) was able to bind chitin, a component of fungal cell walls and the crustacean shell. The mode of action of the fully active N-terminal arasin 1(1–23) was explored through killing kinetic and membrane permeabilization studies. At the minimal inhibitory concentration (MIC), arasin 1(1–23) was not bactericidal and had no membrane disruptive effect. In contrast, at concentrations of 5×MIC and above it was bactericidal and interfered with membrane integrity. We conclude that arasin 1(1–23) has a different mode of action than lytic peptides, like cecropin P1. Thus, we suggest a dual mode of action for arasin 1(1–23) involving membrane disruption at peptide concentrations above MIC, and an alternative mechanism of action, possibly involving intracellular targets, at MIC

Selection and redesign for high selectivity of membrane-active antimicrobial peptides from a dedicated sequence/function database

Antimicrobial peptides (AMPs) are plausible candidates for the development of novel classes of antibiotics with a low tendency to elicit resistance. They often form lesions in the bacterial membrane making it hard for bacteria to develop permanent resistance. However, a potent antibacterial activity is often accompanied by excessive cytotoxicity towards host cells. Modifying known natural sequences, based on desirable biophysical properties, is expensive and time-consuming and often with limited success. \u2018Mutator\u2019 is a freely available web-based computational tool for suggesting residue variations that potentially increase a peptide's selectivity, based on the use of quantitative structure activity relationship (QSAR) criteria. Although proven to be successful, it has never been used to analyze multiple sequences simultaneously. Modifying the Mutator algorithm allowed screening of many sequences in the dedicated Database of Anuran Defense Peptides (DADP) and by implementing limited amino acid substitutions on appropriate candidates, propose 8 potentially selective AMPs called Dadapins. Two were chosen for testing, confirming the prediction and validating this approach. They were shown to efficiently inactivate bacteria by disrupting their membranes but to be non-toxic for host cells, as determined by flow cytometry and confirmed by atomic force microscopy (AFM)

Association Between Circulating CD4+ T Cell Methylation Signatures of Network-Oriented SOCS3 Gene and Hemodynamics in Patients Suffering Pulmonary Arterial Hypertension

Pathogenic DNA methylation changes may be involved in pulmonary arterial hypertension (PAH) onset and its progression, but there is no data on potential associations with patient-derived hemodynamic parameters. The reduced representation bisulfite sequencing (RRBS) platform identified N= 631 differentially methylated CpG sites which annotated to N= 408 genes (DMGs) in circulating CD4(+) T cells isolated from PAH patients vs. healthy controls (CTRLs). A promoter-restricted network analysis established the PAH subnetwork that included 5 hub DMGs (SOCS3, GNAS, ITGAL, NCOR2, NFIC) and 5 non-hub DMGs (NR4A2, GRM2, PGK1, STMN1, LIMS2). The functional analysis revealed that the SOCS3 gene was the most recurrent among the top ten significant pathways enriching the PAH subnetwork, including the growth hormone receptor and the interleukin-6 signaling. Correlation analysis showed that the promoter methylation levels of each network-oriented DMG were associated individually with hemodynamic parameters. In particular, SOCS3 hypomethylation was negatively associated with right atrial pressure (RAP) and positively associated with cardiac index (CI) (vertical bar r vertical bar &gt;= 0.6). A significant upregulation of the SOCS3, ITGAL, NFIC, NCOR2, and PGK1 mRNA levels (qRT-PCR) in peripheral blood mononuclear cells from PAH patients vs. CTRLs was found (P &lt;= 0.05). By immunoblotting, a significant upregulation of the SOCS3 protein was confirmed in PAH patients vs. CTRLs (P &lt; 0.01). This is the first network-oriented study which integrates circulating CD4(+) T cell DNA methylation signatures, hemodynamic parameters, and validation experiments in PAH patients at first diagnosis or early follow-up. Our data suggests that SOCS3 gene might be involved in PAH pathogenesis and serve as potential prognostic biomarker