No description available.

acase@tulane.edu / Development of antimicrobial peptides (AMPs) as next generation clinical antibiotics has been a pursuit of the scientific community for several decades. AMPs are attractive drug candidates because of their potent antibacterial activity and a low propensity for eliciting antibiotic resistant bacterial phenotypes. However, despite substantial efforts and myriad development approaches, AMPs have yet to make inroads in the clinic due to toxicity concerns and activity loss in vivo. We hypothesized that eukaryotic cytotoxicity and antibacterial activity loss are intricately related in that peptide-induced tissue or host cell damage corresponds to depletion of free peptide available to target bacterial cells. Using human red blood cells (RBCs) as a model eukaryotic cell, we demonstrate that a cross-section of AMPs lose appreciable antibacterial activity when preincubated with concentrated eukaryotic cells (1x109 red blood cells/mL) and that this behavior can be explained by plasma membrane binding. To approach this problem in a unique manner, we synthesized a combinatorial peptide library based on the potent AMP, ARVA, and screened the library for activity in the presence of concentrated RBCs. We isolated nine unique, but similar sequences from the screen. During the screening program, we discovered that RBC-peptide interactions lead to peptide degradation through the release of cytosolic proteases. We used this knowledge to design a consensus sequence based on the nine peptides isolated from the library screen and synthesized it using only D-isomer amino acids. The novel peptide displays excellent antimicrobial activity against several human pathogens in the presence and absence of concentrated RBCs, has reduced toxicity towards eukaryotic cells, and is not susceptible to cleavage by cellular proteases. We attempted to use this peptide, D-NOGCON, to combat P. aeruginosa in a mouse model of acute pneumonia, but were unable to ameliorate the negative outcomes associated with infection. We ultimately suggest alternative models of bacterial infection in which the peptide may be more effective and future approaches to further refining the sequence of D-NOGCON. / 1 / Charles Starr

No description available.

Antimicrobial (cationic) proteins play an important role in innate imunity. Such proteins can possess antibacterial, antiendotoxic or fungicidal abilities. The rising resistence of microbes to common antibiotics evokes acute need of studying more endogenous proteins to reveal new potential antibiotics. Ticks, the blood-feeding ectoparasites with effectual defense system, present an endless source of newly described and unknown antimicrobial peptides/proteins with significant theurapeutic potential. This study represents identification of histidine-rich proteins detected in Ixodes ricinus and Ixodes scapularis, that are related to recently described new family of proteins isolated from Rhipicephalus microplus (protein microplusin) and Amblyomma hebraeum (protein heraein). Analysis and characterization of newly identified histidine rich proteins, study of their antimicrobial and protease inhibitory effect are the main goals of this study.

A research report submitted to the Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, in partial fulfilment of the requirements for the degree of Master of Science in Medicine ( Pharmacotherapy) / Species of the genus Plectranthus, a member of the mint family ( Lamiaceae ), have been used in alternative medicines in third world countries dating back to the early Chinese empire. Plectranthus species have been used in the past for coughs and colds (P. ambiguus) and as a mouth-wash for loose and bleeding teeth (P. laxiflorus). The crushed leaves of P. madagascariensis are used by Xhosa as an ointment for scabies P. hadiensis is used orally as a cough mixture. Eight species from the genus were chosen to study the essential oil composition and antimicrobial activity. / IT2018

Antimicrobial peptides (AMPs) are relatively-short chain molecules that living organisms use to defend themselves against a wide range of invading microorganisms such as bacteria and viruses. They selectively bind to and kill microbes over host cells by permeabilizing cell membranes or by inhibiting the biological functions of intra-cellular components. Despite its significance in determining their cell selectivity, however, the cell-concentration dependence of AMP's membrane-perturbing activity has not been criticality examined. In this thesis, we present a physical model for cell selectivity of AMPs, especially its cell-concentration dependence. To this end, we use a coarse-grained model that captures essential molecular details such as lipid composition (e.g., fraction of anionic lipids) and peptide amphiphilicity and charge. In particular, we calculate the surface coverage of peptides in the membrane-perturbing mode as a function of peptide and cell densities: those that bind to the interface between lipid headgroups and tails. This allows us to extract the minimum inhibitory concentration (MIC) and the minimum hemolytic concentration (MHC) of the peptides. Our results show that both MIC and MHC increase as the cell density increases so that the peptide selectivity (given by MHC/MIC) decreases with increasing cell density. Our results will help resolve conflicting interpretations of peptide-selectivity experiments.

<p>Antimicrobial peptides (AMPs) are part of the innate immune system that is widely distributed in nature, acting as a defense mechanism against invading microorganisms. AMPs have potent antimicrobial activity against a range of microorganisms including fungi, bacteria and viruses. In view of growing multidrug resistance, AMPs are increasingly being viewed as potential therapeutic agents with a novel mechanism of action. Mastoparan is a natural, highly positively charged AMP derived from the venom of wasps. It was originally of interest based on its inherent mast cell degranulation activity. Previously, mastoparan has been shown to exhibit antimicrobial activity in vitro however these studies have been limited in scope. Here we hypothesize that mastoparan possess the capacity to be a potent broad spectrum antibacterial agent including activity against multidrug resistant bacteria. </p><p>We examined the scope of antibacterial activity exhibited by mastoparan using a variety of antimicrobial susceptibility tests and have utilized a bacterial skin infection (S. aureus) model to determine the potential of mastoparan to serve as a therapeutic agent. We tested mastoparan against 4 Gram-positive clinical isolates (e.g., S. aureus, and E. faecium), 9 Gram-negative clinical isolates (e.g., E. coli, P. aeruginosa, and B. cepacia), and 4 multidrug resistant clinical isolates (e.g., MRSA, ESBL E.coli, and ESBL K. pneumonia). These studies reveal that mastoparan exhibits broad spectrum activity against both Gram-negative (MIC: 1.9 - 125 &mug/ml) and Gram-positive (MIC: 15.6 - 125 &mug/ml) bacteria and against multidrug resistant bacteria (MIC: 7.8 - 125 &mug/ml). We also demonstrated that mastoparan disrupts the bacterial membrane, exhibits fast acting antibacterial activity and is highly effective against both multiplying and non-multiplying bacteria. Furthermore, we have shown that mastoparan demonstrates efficacy as a topical antimicrobial agent reducing lesion size by up to 79% and the amount of bacteria recovered from skin lesions by up to a 98% reduction. Based on these results we conclude that mastoparan is a highly effective antibacterial agent and is therefore a potential alternative to currently antibiotics. Mastoparan offers a promising new therapeutic option for treating bacterial infections.</p> / Dissertation

Cationic antimicrobial peptides (CAPs) are small peptides that constitute an important defence against microbial pathogens. Certain CAPs also possess anticancer properties. NRC-03 and NRC-07 are pleurocidins derived from winter and yellowtail flounder, respectively. The purpose of this investigation was to study the anticancer properties of NRC-03 and NRC-07. NRC-03 and NRC-07 killed breast cancer cells, including P-glycoprotein-overexpressing cells, in a time-dependent manner that peaked at 4 h. NRC-03 and NRC-07 lysed breast cancer cells by a mechanism that involved cell binding, mitochondrial destabilization, nuclear localization, and significant membrane damage. Interestingly, NRC-07, but not NRC-03, caused DNA fragmentation. NRC-03 and NRC-07 killed normal human epithelial cells, but did not kill endothelial cells or fibroblasts, or lyse human erythrocytes. NRC-03, and to a lesser extent NRC-07, had chemo-sensitizing properties, suggesting promise for their inclusion in combinational treatment regimens. Importantly, intratumoural injections of NRC-03 or NRC-07 inhibited tumour growth in a mouse model of breast cancer. Fetal bovine serum dose-dependently reduced cell killing by NRC-03. NRC-03 was degraded in human and mouse serum, which limited its potency. NRC-03- and NRC-07-induced cytotoxicity correlated with expression of several different negatively-charged molecules, rationalizing the generation of [D]-NRC-03, which carries the same positive charge as NRC-03, and was more potent but less selective for cancer cells than NRC-03. [D]-NRC-03 was also cytolytic and exhibited in vivo anticancer properties. To further test the clinical potential of NRC-03- and NRC-07-resistant cells were generated. NRC-03 and NRC-07 bound to resistant cells to a lesser extent than parental cells and were phenotypically distinct. Importantly, NRC-03- and NRC-07-resistant cells were killed by chemotherapeutic drugs, as well as [D]-NRC-03. These studies demonstrate that NRC-03, NRC-07, and [D]-NRC-03 are cytolytic peptides that kill breast cancer cells in vitro and in vivo. While more potent than NRC-03, [D]-NRC-03 requires further modification to minimize its toxicity toward normal cells. Although cancer cells may become resistant to NRC-03 and NRC-07 over time, resistant cells are still killed by other cytotoxic drugs, thereby reinforcing the value of adding these peptides to combinational regimens for the treatment of breast cancer.

Antimicrobial peptides (AMPs) are relatively-short chain molecules that living organisms use to defend themselves against a wide range of invading microorganisms such as bacteria and viruses. They selectively bind to and kill microbes over host cells by permeabilizing cell membranes or by inhibiting the biological functions of intra-cellular components. Despite its significance in determining their cell selectivity, however, the cell-concentration dependence of AMP's membrane-perturbing activity has not been criticality examined. In this thesis, we present a physical model for cell selectivity of AMPs, especially its cell-concentration dependence. To this end, we use a coarse-grained model that captures essential molecular details such as lipid composition (e.g., fraction of anionic lipids) and peptide amphiphilicity and charge. In particular, we calculate the surface coverage of peptides in the membrane-perturbing mode as a function of peptide and cell densities: those that bind to the interface between lipid headgroups and tails. This allows us to extract the minimum inhibitory concentration (MIC) and the minimum hemolytic concentration (MHC) of the peptides. Our results show that both MIC and MHC increase as the cell density increases so that the peptide selectivity (given by MHC/MIC) decreases with increasing cell density. Our results will help resolve conflicting interpretations of peptide-selectivity experiments.

The microbial contamination of biomedical devices is a leading cause of hospital- acquired infection. A number of strategies aimed at developing device coatings that are refractory to microbial adhesion, colonisation and biofilm formation have been developed, but the problem remains. The incorporation of biocides into biomedical device surface coatings has shown promising results in preventing the establishment of infection. Current controversy over the possibility that extensive use of biocides could potentially lead to antimicrobial resistance has fuelled the search for new actives with good antimicrobial activity and low cytotoxicity, that maintain marked efficacy after prolonged use. This doctoral thesis aims to evaluate the antimicrobial potential of a novel peptide based on human apolipoprotein E receptor binding region (apoEdpL-W). The spectrum of antimicrobial activity and anti-biofilm efficacy of apoEdpL-W was compared to that of common biocides polyhexamethylene biguanide, triclosan, cetrimide and chlorhexidine. The potential to induce bacterial insusceptibility towards these agents after long-term sub-lethal level exposure was assessed. Initial examination against 18 test microorganisms, commonly associated with device infection, showed that apoEdpL-W displayed broad-range antimicrobial and anti-biofilm efficacy. ApoEdpL-W also maintained marked antibacterial activity after incorporation onto various biomaterial polymers, often used in device surface coatings. Alterations in bacterial susceptibility after prolonged exposure to apoEdpL-W, as well as to the other biocides, were often temporary and partially reverted once the bacteria had been grown in the absence of the antimicrobial agent. The adaption of Staphylococcus aureus to the presence of triclosan resulted in the formation of small colony variants (SVCs) with reduced triclosan susceptibility. Analysis of the physiological characteristics of the triclosan induced SCVs revealed the loss of virulence determinants and potentially reduced pathogenic capability, when compared to the parent strain. The biocompatibility index values of the test actives were determined by the parallel assessment of their antibacterial activity and in vitro cytotoxicity. ApoEdpL-W showed good antibacterial efficacy whilst remaining relatively less toxic to mammalian cells than triclosan or chlorhexidine. We studied the interactions of the test antimicrobials with a preformed phospholipid bilayer using the quartz crystal microbalance device and dual polarisation interferometry, to better understand potential mode of action. Analysis revealed that ApoEdpL-W and PHMB induced the highest level of bilayer disruption, of all the antimicrobials tested. These data suggest that apoEdpL-W demonstrates antibacterial activity; biocompatibility and long-term efficacy on a level that compares favourably to that of currently used biocides. The peptide demonstrates good antimicrobial efficacy when incorporated into a range of biomaterial polymers and shows the potential to be developed as an effective coating for the reduction of device associated infections.