Anne W. Young

Bio: Anne W. Young is an academic researcher from New York University. The author has contributed to research in topics: Antimicrobial peptides & Antimicrobial. The author has an hindex of 7, co-authored 12 publications receiving 454 citations. Previous affiliations of Anne W. Young include L'Oréal.

Length Effects in Antimicrobial Peptides of the (RW)n Series

Abstract: A class of antimicrobial peptides involved in host defense consists of sequences rich in Arg and Trp-R and -W. Analysis of the pharmacophore in these peptides revealed that chains as short as trimers of sequences such as WRW and RWR have antimicrobial activity (M. B. Strom, B. E. Haug, M. L. Skar, W. Stensen, T. Stiberg, and J. S. Svendsen, J. Med. Chem. 46:1567-1570, 2003). To evaluate the effect of chain length on antimicrobial activity, we synthesized a series of peptides containing simple sequence repeats, (RW)n-NH2 (where n equals 1, 2, 3, 4, or 5), and determined their antimicrobial and hemolytic activity. The antimicrobial activity of the peptides increases with chain length, as does the hemolysis of red blood cells. Within the experimental error, longer peptides (n equals 3, 4, or 5) show similar values for the ratio of hemolytic activity to antibacterial activity, or the hemolytic index. The (RW)3 represents the optimal chain length in terms of the efficacy of synthesis and selectivity as evaluated by the hemolytic index. Circular dichroism spectroscopy indicates that these short peptides appear to be unfolded in aqueous solution but acquire structure in the presence of phospholipids. Interaction of the peptides with model lipid vesicles was examined using tryptophan fluorescence. The (RW)n peptides preferentially interact with bilayers containing the negatively charged headgroup phosphatidylglycerol relative to those containing a zwitterionic headgroup, phosphatidylcholine.

Tuning the membrane selectivity of antimicrobial peptides by using multivalent design.

Abstract: Rapid emergence of antibacterial drug resistance poses a critical problem for the treatment of infectious diseases. The number of new classes of antibiotics approved by the FDA has declined in recent years. Since their discovery in the early 1980s, antimicrobial peptides (AMPs, also called host defense peptides) have stimulated interest as prospective antibiotic agents because they rapidly inactivate a wide range of microorganisms including Gram-positive and negative bacteria, fungi, and some viruses. In many cases they are indifferent to current multidrug-resistant (MDR) strains. Naturally occurring AMPs span a wide range of size, sequence, and structure. They generally share only amphiphilicity and positive charge. Different chemical approaches have been pursued in efforts to increase the effectiveness of AMPs, including incorporation of unnatural dor b-amino acids, cyclization of peptides, and screening of synthetic AMP combinatorial libraries. Despite recent progress, the diversity and lack of structural homology among known AMPs make it difficult to predict the activity of a peptide or to design AMPs with desired activities in vivo. In a recent study, a linguistic model was applied to the rational design of AMPs. To date, classical drug R&D approaches have not been successfully applied to derive novel antibiotics from AMPs. The amino acids Arg (R) and Trp (W) occur in natural AMPs that span a range of sizes and secondary structures, including indolicidin and tritrpticin, which have a broad spectrum of antibacterial activity but lyse erythrocytes. QSAR analysis of Rand W-rich peptides suggested that the order of amino acids is not crucial whereas R and W content correlates most strongly with activity. Strom et al. proposed that simple combinations of R and W side chains constitute one type of pharmacophore for AMPs. We recently investigated the length requirement for antimicrobial activity of RW peptides. Even short repeats of RW are active, providing a starting point for de novo design of AMPs. The hypothesis we test in this work is that multi/polyvalent RW peptide display can enhance the effectiveness of antibacterials against MDR bacterial strains. Application of multivalency to cell surface receptors has been demonstrated previously. Our thinking was originally based on the two-state model of AMP action proposed by Huang, which is broadly consistent with other current ideas. The model assumes that AMPs act at the level of the cell membrane via electrostatic interactions with the negatively charged head groups of bacterial lipids. At peptide-to-lipid ratios (P/L) above a threshold value, the peptides form clusters that lead to permeation of the cell membrane. The susceptibility of a cell to an AMP depends on the value of P/L determined by the lipid composition of the cell membrane. Huang ascribes this to an elastic perturbation of the surface. However alternative physical mechanisms can be invoked. A consequence of assembly models is that prenucleating AMP monomers might reduce the critical concentration for cluster formation as AMPs bind to the bacterial membrane. Initial attachment of AMPs to bacterial surfaces or membranes is salt sensitive, consistent with electrostatic interactions. General arguments suggest that covalently tethering a number of weakly interacting ligands can enhance overall avidity for targets such as cell surfaces. We recently applied this strategy to create new antimicrobial agents by linking tetrapeptides RWRW and RRWW to a polydisperse polymer scaffold. These constructs enhanced antimicrobial activity, with an increase of roughly tenfold in potency against both Gram-negative and positive strains. At the same time the hemolytic activity of the polymers increased, but the ratio of antimicrobial to hemolytic activity remained roughly constant. To further explore multivalent AMP designs, we have synthesized a variety of dendrimeric AMPs containing multiple RW dipeptides. Of these the most successful is (RW)4D (Scheme 1). A detailed account of the constructs based on alternative scaffolds will be presented elsewhere. Dendrimeric peptide displays were first developed in the 1980s as multiple antigenic peptides. They consist of a core formed by radially branched lysines or other residues. Peptide sequences are grafted to the core by standard solid-phase chemistry. Herein, we report the antibacterial and hemolytic activity of (RW)4D compared to the natural AMP indolicidin (ILPWKWPWWPWRR-NH2) from bovine

Effects of Trp- and Arg-containing antimicrobial-peptide structure on inhibition of Escherichia coli planktonic growth and biofilm formation

Abstract: Biofilms are sessile microbial communities that cause serious chronic infections with high morbidity and mortality. In order to develop more effective approaches for biofilm control, a series of linear cationic antimicrobial peptides (AMPs) with various arginine (Arg or R) and tryptophan (Trp or W) repeats [(RW)n-NH2, where n = 2, 3, or 4] were rigorously compared to correlate their structures with antimicrobial activities affecting the planktonic growth and biofilm formation of Escherichia coli. The chain length of AMPs appears to be important for inhibition of bacterial planktonic growth, since the hexameric and octameric peptides significantly inhibited E. coli growth, while tetrameric peptide did not cause noticeable inhibition. In addition, all AMPs except the tetrameric peptide significantly reduced E. coli biofilm surface coverage and the viability of biofilm cells, when added at inoculation. In addition to inhibition of biofilm formation, significant killing of biofilm cells was observed after a 3-hour treatment of preformed biofilms with hexameric peptide. Interestingly, treatment with the octameric peptide caused significant biofilm dispersion without apparent killing of biofilm cells that remained on the surface; e.g., the surface coverage was reduced by 91.5 ± 3.5% by 200 μM octameric peptide. The detached biofilm cells, however, were effectively killed by this peptide. Overall, these results suggest that hexameric and octameric peptides are potent inhibitors of both bacterial planktonic growth and biofilm formation, while the octameric peptide can also disperse existing biofilms and kill the detached cells. These results are helpful for designing novel biofilm inhibitors and developing more effective therapeutic methods.

Describing the mechanism of antimicrobial peptide action with the interfacial activity model.

Abstract: Antimicrobial peptides (AMPs) have been studied for three decades, and yet a molecular understanding of their mechanism of action is still lacking. Here we summarize current knowledge for both synthetic vesicle experiments and microbe experiments, with a focus on comparisons between the two. Microbial experiments are done at peptide to lipid ratios that are at least 4 orders of magnitude higher than vesicle-based experiments. To close the gap between the two concentration regimes, we propose an “interfacial activity model”, which is based on an experimentally testable molecular image of AMP–membrane interactions. The interfacial activity model may be useful in driving engineering and design of novel AMPs.

Membrane Active Antimicrobial Peptides: Translating Mechanistic Insights to Design.

Abstract: Antimicrobial peptides (AMPs) are promising next generation antibiotics that hold great potential for combating bacterial resistance. AMPs can be both bacteriostatic and bactericidal, induce rapid killing and display a lower propensity to develop resistance than do conventional antibiotics. Despite significant progress in the past 30 years, no peptide antibiotic has reached the clinic yet. Poor understanding of the action mechanisms and lack of rational design principles have been the two major obstacles that have slowed progress. Technological developments are now enabling multidisciplinary approaches including molecular dynamics simulations combined with biophysics and microbiology toward providing valuable insights into the interactions of AMPs with membranes at atomic level. This has led to increasingly robust models of the mechanisms of action of AMPs and has begun to contribute meaningfully toward the discovery of new AMPs. This review discusses the detailed action mechanisms that have been put forward, with detailed atomistic insights into how the AMPs interact with bacterial membranes. The review further discusses how this knowledge is exploited towards developing design principles for novel AMPs. Finally, the current status, associated challenges and future directions for the development of AMP therapeutics are discussed.

Bacterial Biofilm Eradication Agents: A Current Review.

Abstract: Most free-living bacteria can attach to surfaces and aggregate to grow into multicellular communities encased in extracellular polymeric substances called biofilms. Biofilms are recalcitrant to antibiotic therapy and a major cause of persistent and recurrent infections by clinically important pathogens worldwide (e.g., Pseudomonas aeruginosa, Escherichia coli, and Staphylococcus aureus). Currently, most biofilm remediation strategies involve the development of biofilm-inhibition agents, aimed at preventing the early stages of biofilm formation, or biofilm-dispersal agents, aimed at disrupting the biofilm cell community. While both strategies offer some clinical promise, neither represents a direct treatment and eradication strategy for established biofilms. Consequently, the discovery and development of biofilm eradication agents as comprehensive, stand-alone biofilm treatment options has become a fundamental area of research. Here we review our current understanding of biofilm antibiotic tolerance mechanisms and provide an overview of biofilm remediation strategies, focusing primarily on the most promising biofilm eradication agents and approaches. Many of these offer exciting prospects for the future of biofilm therapeutics for a large number of infections that are currently refractory to conventional antibiotics.