Bacterial susceptibility and resistance to modelin-5

Modelin-5 (M5-NH2) killed Pseudomonas aeruginosa with a minimum lethal concentration (MLC) of 5.86 μM and strongly bound its cytoplasmic membrane (CM) with a Kd of 23.5 μM. The peptide adopted high levels of amphiphilic α-helical structure (75.0%) and penetrated the CM hydrophobic core (8.0 mN m-1). This insertion destabilised CM structure via increased lipid packing and decreased fluidity (ΔGmix < 0), which promoted high levels of lysis (84.1%) and P. aeruginosa cell death. M5-NH2 showed a very strong affinity (Kd = 3.5 μM) and very high levels of amphiphilic α-helical structure with cardiolipin membranes (96.0%,) which primarily drove the peptide's membranolytic action against P. aeruginosa. In contrast, M5-NH2 killed Staphylococcus aureus with an MLC of 147.6 μM and weakly bound its CM with a Kd of 117.6 μM, The peptide adopted low levels of amphiphilic α-helical structure (35.0%) and only penetrated the upper regions of the CM (3.3 mN m-1). This insertion stabilised CM structure via decreased lipid packing and increased fluidity (ΔGmix > 0) and promoted only low levels of lysis (24.3%). The insertion and lysis of the S. aureus CM by M5-NH2 showed a strong negative correlation with its lysyl phosphatidylglycerol (Lys-PG) content (R2 > 0.98). In combination, these data suggested that Lys-PG mediated mechanisms inhibited the membranolytic action of M5-NH2 against S. aureus, thereby rendering the organism resistant to the peptide. These results are discussed in relation to structure/function relationships of M5-NH2 and CM lipids that underpin bacterial susceptibility and resistance to the peptide.

Temporin B Forms Hetero-Oligomers with Temporin L, Modifies Its Membrane Activity, and Increases the Cooperativity of Its Antibacterial Pharmacodynamic Profile

The pharmacodynamic profile of antimicrobial peptides (AMPs) and their in vivo synergy are two factors that are thought to restrict resistance evolution and ensure their conservation. The frog Rana temporaria secretes a family of closely related AMPs, temporins A–L, as an effective chemical dermal defense. The antibacterial potency of temporin L has been shown to increase synergistically in combination with both temporins B and A, but this is modest. Here we show that the less potent temporin B enhances the cooperativity of the in vitro antibacterial activity of the more potent temporin L against EMRSA-15 and that this may be associated with an altered interaction with the bacterial plasma membrane, a feature critical for the antibacterial activity of most AMPs. Addition of buforin II, a histone H2A fragment, can further increase the cooperativity. Molecular dynamics simulations indicate temporins B and L readily form hetero-oligomers in models of Gram-positive bacterial plasma membranes. Patch-clamp studies show transmembrane ion conductance is triggered with lower amounts of both peptides and more quickly when used in combination, but conductance is of a lower amplitude and pores are smaller. Temporin B may therefore act by forming temporin L/B hetero-oligomers that are more effective than temporin L homo-oligomers at bacterial killing and/or by reducing the probability of the latter forming until a threshold concentration is reached. Exploration of the mechanism of synergy between AMPs isolated from the same organism may therefore yield antibiotic combinations with advantageous pharmacodynamic properties.

Impacts of Metabolism and Organic Acids on Cell Wall Composition and Pseudomonas aeruginosa Susceptibility to Membrane Active Antimicrobials

Reliable antimicrobial susceptibility testing is essential in informing both clinical antibiotic therapy decisions and the development of new antibiotics. Mammalian cell culture media have been proposed as an alternative to bacteriological media, potentially representing some critical aspects of the infection environment more accurately. Here, we use a combination of NMR metabolomics and electron microscopy to investigate the response of Escherichia coli and Pseudomonas aeruginosa to growth in differing rich media to determine whether and how this determines metabolic strategies, the composition of the cell wall, and consequently susceptibility to membrane active antimicrobials including colistin and tobramycin. The NMR metabolomic approach is first validated by characterizing the expected E. coli acid stress response to fermentation and the accompanying changes in the cell wall composition, when cultured in glucose rich mammalian cell culture media. Glucose is not a major carbon source for P. aeruginosa but is associated with a response to osmotic stress and a modest increase in colistin tolerance. Growth of P. aeruginosa in a range of bacteriological media is supported by consumption of formate, an important electron donor in anaerobic respiration. In mammalian cell culture media, however, the overall metabolic strategy of P. aeruginosa is instead dependent on consumption of glutamine and lactate. Formate doping of mammalian cell culture media does not alter the overall metabolic strategy but is associated with polyamine catabolism, remodelling of both inner and outer membranes, and a modest sensitization of P. aeruginosa PAO1 to colistin. Further, in a panel of P. aeruginosa isolates an increase between 2- and 3-fold in sensitivity to tobramycin is achieved through doping with other organic acids, notably propionate which also similarly enhances the activity of colistin. Organic acids are therefore capable of nonspecifically influencing the potency of membrane active antimicrobials.

Antimicrobial peptides with pH dependent activity and alkaline optima: their origins, mechanisms of action and potential applications

A number of disorders and diseases are associated with conditions of high pH and many conventional antibiotics lose their efficacy under these pH conditions, generating a need for novel antimicrobials, and a potential solution to fulfil this need is antimicrobial peptides (AMPs) with high pH optima. This review shows that a variety of anionic and cationic AMPs with this pH dependency are produced by creatures across the eukaryotic kingdom, including humans, rabbits, cattle, sheep, fish and frogs. These AMPs exhibit activity against viruses, bacteria and fungi that involves membrane interactions and appear to be facilitated by a variety of mechanisms that generally promote passage across membranes to attack intracellular targets, such as DNA or protein synthesis, and / or membrane lysis. Some of these mechanisms are unknown but those elucidated include the use of bacterial pores and transporters, the self-promoted uptake pathway and established models of membrane interaction, such as the carpet mechanism, toroidal pore formation, the adoption of tilted peptide and the SHM model. A variety of potential roles have been proposed for these AMPs, including use as antivirals, antibacterials, antifungals, adjuvants to antimicrobial therapy, biomarkers of disease and probes for pathogenic microbes. In this review, these properties are described and discussed, with an emphasis on the antimicrobial mechanisms used by these AMPs and the pH dependency of these mechanisms.

A pleurocidin analogue with greater conformational flexibility, enhanced antimicrobial potency and in vivo therapeutic efficacy

Antimicrobial peptides (AMPs) are a potential alternative to classical antibiotics that are yet to achieve a therapeutic breakthrough for treatment of systemic infections. The antibacterial potency of pleurocidin, an AMP from Winter Flounder, is linked to its ability to cross bacterial plasma membranes and seek intracellular targets while also causing membrane damage. Here we describe modification strategies that generate pleurocidin analogues with substantially improved, broad spectrum, antibacterial properties, which are effective in murine models of bacterial lung infection. Increasing peptide-lipid intermolecular hydrogen bonding capabilities enhances conformational flexibility, associated with membrane translocation, but also membrane damage and potency, most notably against Gram-positive bacteria. This negates their ability to metabolically adapt to the AMP threat. An analogue comprising D-amino acids was well tolerated at an intravenous dose of 15 mg/kg and similarly effective as vancomycin in reducing EMRSA-15 lung CFU. This highlights the therapeutic potential of systemically delivered, bactericidal AMPs.

Biophysical studies on the antimicrobial activity of linearized esculentin 2EM

Linearized esculentin 2 EM (E2EM-lin) from the frog, Glandirana emeljanovi was highly active against Gram-positive bacteria (minimum lethal concentration ≤ 5.0 μM) and strongly α-helical in the presence of lipid mimics of their membranes (>55.0%). The N-terminal α-helical structure adopted by E2EM-lin showed the potential to form a membrane interactive, tilted peptide with an hydrophobicity gradient over residues 9 to 23. E2EM-lin inserted strongly into lipid mimics of membranes from Gram-positive bacteria (maximal surface pressure changes ≥5.5 mN m^-1), inducing increased rigidity (C_s^-1 ↑), thermodynamic instability (ΔG_mix < 0 → ΔG_mix > 0) and high levels of lysis (>50.0%). These effects appeared to be driven by the high anionic lipid content of membranes from Gram-positive bacteria; namely phosphatidylglycerol (PG) and cardiolipin (CL) species. The high levels of α-helicity (60.0%), interaction (maximal surface pressure change = 6.7 mN m^-1) and lysis (66.0%) shown by E2EM-lin with PG species was a major driver in the ability of the peptide to lyse and kill Gram-positive bacteria. E2EM-lin also showed high levels of α-helicity (62.0%) with CL species but only low levels of interaction (maximal surface pressure change = 2.9 mN m^-1) and lysis (21.0%) with the lipid. These combined data suggest that E2EM-lin has a specificity for killing Gram-positive bacteria that involves the formation of tilted structure and appears to be primarily driven by PG-mediated membranolysis. These structure/function relationships are used to help explain the pore forming process proposed to describe the membranolytic, antibacterial action of E2EM-lin.

Biophysical investigation into the antibacterial action of modelin-5-NH2

Modelin-5-CONH2 (M5-NH2) is a synthetic antimicrobial peptide, which was found to show potent activity against Bacillus subtilis (minimum lethal concentration = 8.47 μM) and to bind strongly to membranes of the organism (Kd = 10.44 μM). The peptide adopted high levels of amphiphilic α-helical structure in the presence of these membranes (>50%), which led to high levels of insertion (Δπ ≥ 8.0 mN m-1). M5-NH2 showed high affinity for anionic lipid (Kd = 7.46 μM) and zwitterionic lipid (Kd = 14.7 μM), which drove insertion into membranes formed from these lipids (Δπ = 11.5 and 3.5 mN m-1, respectively). Neutron diffraction studies showed that M5-NH2 inserted into B. subtilis membranes with its N-terminal residue, L16, located 5.5 Å from the membrane centre, in the acyl chain region of these membranes, and promoted a reduction in membrane thickness of circa 1.8 Å or 5% of membrane width. Insertion into B. subtilis membranes by the peptide also promoted other effects associated with membrane thinning, including increases in membrane surface area (Cs-1 decreases) and fluidity (ΔGmix > 0 to ΔGmix < 0). Membrane insertion and thinning by M5-NH2 induced high levels of lysis (>55%), and it is speculated that the antibacterial action of the peptide may involve the toroidal pore, carpet or tilted-type mechanism of membrane permeabilization.

Liposome mediated-CYP1A1 gene silencing nanomedicine prepared using lipid film-coated proliposomes as a potential treatment strategy of lung cancer

The occurrence of lung cancer is linked with tobacco smoking, mainly through the generation of polycyclic aromatic hydrocarbons (PAHs). Elevated activity of cytochrome P4501A1 (CYP1A1) plays an important role in the metabolic processing of PAHs and its carcinogenicity. The present work aimed to investigate the role of CYP1A1 gene in PAH-mediated growth and tumor development in vitro and using an in vivo animal model. RNAi strategy was utilized to inhibit the overexpression of CYP1A1 gene using cationic liposomes generated using a lipid film-coated proliposome microparticles. Treatment of PAH-induced human alveolar adenocarcinoma cell line with cationic liposomes carrying CYP1A1 siRNA resulted in down regulation of CYP1A1 mRNA, protein as well as its enzymatic activity, triggering apoptosis and inhibiting multicellular tumor spheroids formation in vitro. Furthermore, silencing of CYP1A1 gene in BALB/c nude xenografts inhibited tumor growth via down regulation of CYP1A1 expression. Altogether, our findings showed that liposome-based gene delivery technology is a viable and stable approach for targeting cancer causing genes such as CY1PA1. This technology facilitated by the use of sugar particles coated with lipid films has demonstrated ability to generate anticancer effects that might be used in the future for therapeutic intervention and treatment of lung cancer.

An Atlas of Anionic Antimicrobial Peptides from Amphibians

Anionic antimicrobial peptides (AAMPs) with net charges ranging from -1 to -8 have been identified in frogs, toads, newts and salamanders across Africa, South America and China. Most of these peptides show antibacterial activity and a number of them are multifunctional, variously showing antifungal activity, anticancer action, neuropeptide function and the ability to potentiate conventional antibiotics. Antimicrobial mechanisms proposed for these AAMPs, include toroidal pore formation and the Shai-Huang-Matsazuki model of membrane interaction along with pH dependent amyloidogenesis and membranolysis via tilted peptide formation. The potential for therapeutic and biotechnical application of these AAMPs has been demonstrated, including the development of amyloid-based nanomaterials and antiviral agents. It is concluded that amphibian AAMPs represent an untapped potential source of biologically active agents and merit far greater research interest.

Minor sequence modifications in temporin B cause drastic changes in antibacterial potency and selectivity by fundamentally altering membrane activity

Antimicrobial peptides (AMPs) are a potential source of new molecules to counter the increase in antimicrobial resistant infections but a better understanding of their properties is required to understand their native function and for effective translation as therapeutics. Details of the mechanism of their interaction with the bacterial plasma membrane are desired since damage or penetration of this structure is considered essential for AMPs activity. Relatively modest modifications to AMPs primary sequence can induce substantial changes in potency and/or spectrum of activity but, hitherto, have not been predicted to substantially alter the mechanism of interaction with the bacterial plasma membrane. Here we use a combination of molecular dynamics simulations, circular dichroism, solid-state NMR and patch clamp to investigate the extent to which temporin B and its analogues can be distinguished both in vitro and in silico on the basis of their interactions with model membranes. Enhancing the hydrophobicity of the N-terminus and cationicity of the C-terminus in temporin B improves its membrane activity and potency against both Gram-negative and Gram-positive bacteria. In contrast, enhancing the cationicity of the N-terminus abrogates its ability to trigger channel conductance and renders it ineffective against Gram-positive bacteria while nevertheless enhancing its potency against Escherichia coli. Our findings suggest even closely related AMPs may target the same bacterium with fundamentally differing mechanisms of action.

pH Dependent Antimicrobial Peptides and Proteins, Their Mechanisms of Action and Potential as Therapeutic Agents

Antimicrobial peptides (AMPs) are potent antibiotics of the innate immune system that have been extensively investigated as a potential solution to the global problem of infectious diseases caused by pathogenic microbes. A group of AMPs that are increasingly being reported are those that utilise pH dependent antimicrobial mechanisms, and here we review research into this area. This review shows that these antimicrobial molecules are produced by a diverse spectrum of creatures, including vertebrates and invertebrates, and are primarily cationic, although a number of anionic examples are known. Some of these molecules exhibit high pH optima for their antimicrobial activity but in most cases, these AMPs show activity against microbes that present low pH optima, which reflects the acidic pH generally found at their sites of action, particularly the skin. The modes of action used by these molecules are based on a number of major structure/function relationships, which include metal ion binding, changes to net charge and conformational plasticity, and primarily involve the protonation of histidine, aspartic acid and glutamic acid residues at low pH. The pH dependent activity of pore forming antimicrobial proteins involves mechanisms that generally differ fundamentally to those used by pH dependent AMPs, which can be described by the carpet, toroidal pore and barrel-stave pore models of membrane interaction. A number of pH dependent AMPs and antimicrobial proteins have been developed for medical purposes and have successfully completed clinical trials, including kappacins, LL-37, histatins and lactoferrin, along with a number of their derivatives. Major examples of the therapeutic application of these antimicrobial molecules include wound healing as well as the treatment of multiple cancers and infections due to viruses, bacteria and fungi. In general, these applications involve topical administration, such as the use of mouth washes, cream formulations and hydrogel delivery systems. Nonetheless, many pH dependent AMPs and antimicrobial proteins have yet to be fully characterized and these molecules, as a whole, represent an untapped source of novel biologically active agents that could aid fulfillment of the urgent need for alternatives to conventional antibiotics, helping to avert a return to the pre-antibiotic era.

Low pH Enhances the Action of Maximin H5 against Staphylococcus aureus and Helps Mediate Lysylated Phosphatidylglycerol-Induced Resistance

Maximin H5 (MH5) is an amphibian antimicrobial peptide specifically targeting Staphylococcus aureus. At pH 6, the peptide showed an improved ability to penetrate (ΔΠ = 6.2 mN m(-1)) and lyse (lysis = 48%) Staphylococcus aureus membrane mimics, which incorporated physiological levels of lysylated phosphatidylglycerol (Lys-PG, 60%), compared to that at pH 7 (ΔΠ = 5.6 mN m(-1) and lysis = 40% at pH 7) where levels of Lys-PG are lower (40%). The peptide therefore appears to have optimal function at pH levels known to be optimal for the organism's growth. MH5 killed S. aureus (minimum inhibitory concentration of 90 μM) via membranolytic mechanisms that involved the stabilization of α-helical structure (approximately 45-50%) and showed similarities to the "Carpet" mechanism based on its ability to increase the rigidity (Cs(-1) = 109.94 mN m(-1)) and thermodynamic stability (ΔGmix = -3.0) of physiologically relevant S. aureus membrane mimics at pH 6. On the basis of theoretical analysis, this mechanism might involve the use of a tilted peptide structure, and efficacy was noted to vary inversely with the Lys-PG content of S. aureus membrane mimics for each pH studied (R(2) ∼ 0.97), which led to the suggestion that under biologically relevant conditions, low pH helps mediate Lys-PG-induced resistance in S. aureus to MH5 antibacterial action. The peptide showed a lack of hemolytic activity (<2% hemolysis) and merits further investigation as a potential template for development as an antistaphylococcal agent in medically and biotechnically relevant areas.

The effect of amidation on the behaviour of antimicrobial peptides

Aurein 2.6-COOH and aurein 3.1-COOH were studied along with their naturally occurring C-terminally amidated analogues. Circular dichroism (CD) and molecular dynamic (MD) simulations were used to study the effects of amidation on the interaction of antimicrobial peptides (AMPs) with lipid bilayers. CD measurements and MD analysis suggested that both peptide analogues were predominantly random coil and adopted low levels of \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\alpha$$\end{document}α-helical structure in solution (<30 %) and in the presence of a lipid bilayer the peptides formed a stable \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\alpha$$\end{document}α-helical structure. In general, amidated analogues have a greater propensity than the non-amidated peptides to form a \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\alpha$$\end{document}α-helical structure. MD simulations predicted that aurein 2.6-COOH and aurein 3.1-CHOOH destabilised lipid bilayers from 1,2-dimyristoyl-sn-glycero-3-phosphocholine and 1,2-dimyristoyl-sn-glycero-3-phosphoserine via angled bilayer penetration. They also showed that aurein 2.6-CONH\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$_2$$\end{document}2 and aurein 3.1-CONH\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$_2$$\end{document}2 formed a helix horizontal to the plane of an asymmetric interface.

The increasing role of phosphatidylethanolamine as a lipid receptor in the action of host defence peptides

Host defence peptides (HDPs) are antimicrobial agents produced by organisms across the prokaryotic and eukaryotic kingdoms. Many prokaryotes produce HDPs, which utilise lipid and protein receptors in the membranes of bacterial competitors to facilitate their antibacterial action and thereby survive in their niche environment. As a major example, it is well established that cinnamycin and duramycins from Streptomyces have a high affinity for phosphatidylethanolamine (PE) and exhibit activity against other Gram-positive organisms, such as Bacillus. In contrast, although eukaryotic HDPs utilise membrane interactive mechanisms to facilitate their antimicrobial activity, the prevailing view has long been that these mechanisms do not involve membrane receptors. However, this view has been recently challenged by reports that a number of eukaryotic HDPs such as plant cyclotides also use PE as a receptor to promote their antimicrobial activities. Here, we review current understanding of the mechanisms that underpin the use of PE as a receptor in the antimicrobial and other biological actions of HDPs and describe medical and biotechnical uses of these peptides, which range from tumour imaging and detection to inclusion in topical microbicidal gels to prevent the sexual transmission of HIV.

PEGylated graphene oxide for tumor-targeted delivery of paclitaxel

Aim: The graphene oxide (GO) sheet has been considered one of the most promising carbon derivatives in the field of material science for the past few years and has shown excellent tumor-targeting ability, biocompatibility and low toxicity. We have endeavored to conjugate paclitaxel (PTX) to GO molecule and investigate its anticancer efficacy. Materials & Methods: We conjugated the anticancer drug PTX to aminated PEG chains on GO sheets through covalent bonds to get GO-PEG-PTX complexes. The tissue distribution and anticancer efficacy of GO-PEG-PTX were then investigated using a B16 melanoma cancer-bearing C57 mice model. Results: The GO-PEG-PTX complexes exhibited excellent water solubility and biocompatibility. Compared with the traditional formulation of PTX (Taxol®), GO-PEG-PTX has shown prolonged blood circulation time as well as high tumor-targeting and -suppressing efficacy. Conclusion: PEGylated graphene oxide is an excellent nanocarrier for paclitaxel for cancer targeting.

The role of C-terminal amidation in the membrane interactions of the anionic antimicrobial peptide, maximin H5

Maximin H5 is an anionic antimicrobial peptide from amphibians, which carries a C-terminal amide moiety, and was found to be moderately haemolytic (20%). The α-helicity of the peptide was 42% in the presence of lipid mimics of erythrocyte membranes and was found able to penetrate (10.8 mN m(-1)) and lyse these model membranes (64 %). In contrast, the deaminated peptide exhibited lower levels of haemolysis (12%) and α-helicity (16%) along with a reduced ability to penetrate (7.8 m Nm(-1)) and lyse (55%) lipid mimics of erythrocyte membranes. Taken with molecular dynamic simulations and theoretical analysis, these data suggest that native maximin H5 primarily exerts its haemolytic action via the formation of an oblique orientated α-helical structure and tilted membrane insertion. However, the C-terminal deamination of maximin H5 induces a loss of tilted α-helical structure, which abolishes the ability of the peptide's N-terminal and C-terminal regions to H-bond and leads to a loss in haemolytic ability. Taken in combination, these observations strongly suggest that the C-terminal amide moiety carried by maximin H5 is required to stabilise the adoption of membrane interactive tilted structure by the peptide. Consistent with previous reports, these data show that the efficacy of interaction and specificity of maximin H5 for membranes can be attenuated by sequence modification and may assist in the development of variants of the peptide with the potential to serve as anti-infectives.

Thymopentin nanoparticles engineered with high loading efficiency, improved pharmacokinetic properties, and enhanced immunostimulating effect using soybean phospholipid and PHBHHx polymer

Formulation of protein and peptide drugs with sustained release properties is crucial to enhance their therapeutic effect and minimize administration frequency. In this study, immunomodulating polymeric systems were designed by manufacturing PHBHHx nanoparticles (NPs) containing thymopentin (TP5). The release profile of the drug was studied over a period of 7 days. The PHBHHx NPs containing TP5-phospholipid (PLC) complex (TP5-PLC) displayed a spherical shape with a mean size, zeta potential, and encapsulation efficiency of 238.9 nm, -32.0 mV, and 72.81%, respectively. The cytotoxicity results showed the PHBHHx NPs had a relatively low toxicity in vitro. TP5 entrapped in the NPs could hardly release in vitro, while the NPs had longer than 7 days release duration after a single subcutaneous injection in Wistar rats. The immunodepression rat model was built to evaluate the immunomodulating effects of TP5-PLC-NPs in vivo. The results of T-lymphocyte subsets (CD3(+), CD4(+), CD8(+), and CD4(+)/CD8(+) ratio) analysis and superoxide dismutase (SOD) values suggested that TP5-PLC-NPs had stronger immunoregulation effects than TP5 solution. In conclusion, an applicable approach to markedly enhancing the loading of a water-soluble peptide into a hydrophobic polymer matrix has been introduced. Thus, TP5-PLC-NPs are promising nanomedicine systems for sustained release effects of TP5.

Sounding the death knell for microbes?

Over the past 5 years, several studies showed that ultrasound, which is sound with a frequency>20 kHz, is able to kill bacteria by activating molecules termed sonosensitizers (SS) to produce reactive oxygen species, which are toxic to microbes. It is our opinion that this work opens up the potential for the development of a novel form of ultrasound-mediated antimicrobial therapy. Termed sonodynamic antimicrobial chemotherapy (SACT), we define this therapy as a regime where a SS is selectively delivered to target microbial cells and activated by ultrasound to induce the death of those microbial cells. Here, we review recent work on SACT, current understanding of its mechanisms, and future prospects for SACT as a therapeutically viable antimicrobial regime.

Reliability of HSP70 (HSPA) expression as a prognostic marker in glioma

Production of heat shock protein 70 (HSP70/HSPA) is induced by a wide range of cellular stress conditions, such as cancer and hypoxia, with production also being linked to tumourigenesis. HSPA mRNA transcripts and proteins were examined in three human glioma cell lines, representing astrocytoma, oligodendroglioma and glioblastoma, plus 18 clinical brain tissue samples. GAPDH was used as a control gene throughout these studies and exhibited a consistent level of expression in a normal astrocyte cell line, tumourous cell lines and tissue samples. In contrast, the average HSPA mRNA copy numbers detected in glioblastoma tissue were between 1.8- and 8.8-fold higher than in lower grade glioma and control tissue, respectively, which is suggestive of a grade-related transcription profile. Similar patterns of grade-related expression were also observed in glioma cell lines. This study indicates for the first time that HSPA expression in glioma cells may possibly be grade related, and hence could have potential as a prognostic marker.

The effects of suspension particle size on the performance of air-jet, ultrasonic and vibrating-mesh nebulisers

Using latex microspheres as model suspensions, the influence of suspension particle size (1, 4.5 and 10 μm) on the properties of aerosols produced using Pari LC Sprint (air-jet), Polygreen (ultrasonic), Aeroneb Pro (actively vibrating-mesh) and Omron MicroAir NE-U22 (passively vibrating-mesh) nebulisers was investigated. The performance of the Pari nebuliser was independent of latex spheres particle size. For both Polygreen and Aeroneb Pro nebulizers, total aerosol output increased when the size of latex spheres increased, with highest fine particle fraction (FPF) values being recorded. However, following nebulisation of 1 or 4.5 μm suspensions with the Polygreen device, no particles were detected in the aerosols deposited in a two-stage impinger, suggesting that the aerosols generated from this device consisted mainly of the continuous phase while the dispersed microspheres were excluded and remained in the nebuliser. The Omron nebuliser efficiently nebulised the 1 μm latex spheres, with high output rate and no particle aggregation. However, this device functioned inefficiently when delivering 4.5 or 10 μm suspensions, which was attributed to the mild vibrations of its mesh and/or the blockage of the mesh apertures by the microspheres. The Aeroneb Pro fragmented latex spheres into smaller particles, but uncontrolled aggregation occurred upon nebulisation. This study has shown that the design of the nebuliser influenced the aerosol properties using latex spheres as model suspensions. Moreover, for the recently marketed mesh nebulisers, the performance of the Aeroneb Pro device was less dependent on particle size of the suspension compared with the Omron MicroAir nebuliser.

Stability of parenteral nanoemulsions loaded with paclitaxel: the influence of lipid phase composition, drug concentration and storage temperature

Paclitaxel was loaded into licensed parenteral nutrition nanoemulsions (Clinoleic® and Intralipid®) using bath sonication, and the stability of the formulations was investigated following storage for two weeks at room temperature or at 4 °C. In general, Clinoleic droplets were smaller than Intralipid droplets, being around 255 and 285 nm, respectively, for blank and freshly loaded emulsions. Regardless of storage temperature, the Clinoleic exhibited a very slight or no increase in droplet size upon storage, whilst the droplet size of the Intralipid emulsion increased significantly. The droplet size of both emulsions was minimally affected by paclitaxel concentration within the range of 0, 1, 3 and 6 mg/ml. The pH of both emulsions markedly decreased upon storage at room temperature, which was possibly attributed to the production of fatty acids resulting from phospholipid hydrolysis. However, at 4 °C, the pH of Clinoleic emulsion was unaffected by storage or paclitaxel concentration while the Intralipid emulsion demonstrated a trend for pH reduction. Both nanoemulsions had a negative zeta potential, with the Clinoleic formulations having the highest charge, possibly explaining the better size stability of this emulsion. Overall, this study has shown that paclitaxel was successfully loaded into clinically licensed parenteral emulsions and that Clinoleic showed greater stability than the Intralipid.

A novel form of bacterial resistance to the action of eukaryotic host defense peptides, the use of a lipid receptor

Host defense peptides show great potential for development as new antimicrobial agents with novel mechanisms of action. However, a small number of resistance mechanisms to their action are known, and here, we report a novel bacterial resistance mechanism mediated by a lipid receptor. Maximin H5 from Bombina maxima bound anionic and zwitterionic membranes with low affinity (Kd > 225 μM) while showing a strong ability to lyse (>55%) and penetrate (π > 6.0 mN m(-1)) these membranes. However, the peptide bound Escherichia coli and 1,2-dimyristoyl-sn-glycero-3-phosphoethanolamine (DMPE) membranes with higher affinity (Kd < 65 μM) and showed a very low ability for bilayer lysis (<8%) and partitioning (π > 1.0 mN m(-1)). Increasing levels of membrane DMPE correlated with enhanced binding by the peptide (R(2) = 0.96) but inversely correlated with its lytic ability (R(2) = 0.98). Taken with molecular dynamic simulations, these results suggest that maximin H5 possesses membranolytic activity, primarily involving bilayer insertion of its strongly hydrophobic N-terminal region. However, this region was predicted to form multiple hydrogen bonds with phosphate and ammonium groups within PE head-groups, which in concert with charge-charge interactions anchor the peptide to the surface of E. coli membranes, inhibiting its membranolytic action.

Antimicrobial activity of aurein 2.5 against yeasts

Fungal infections with multiple resistance to conventional antifungals are increasingly becoming a medical problem, and there is an urgent need for new antifungal compounds with novel mechanisms of action. Here, we show that aurein 2.5, a naturally occurring peptide antibiotic, displays activity against the fungal strains: Rhodotorula rubra and Schizosaccharomyces pombe (MICs < 130 μM). The peptide adopted high levels of membrane-interactive α-helical structure (> 65%) in the presence of lipid membranes derived from these organisms and showed strong propensities to penetrate (π ≥ 13 mN m(-1) ) and lyse them (> 70%). Based on these data, we suggest that aurein 2.5 kills yeasts via membranolytic mechanisms and may act as a template for the development of therapeutically useful antifungal agents.

Aurein 2.3 functionality is supported by oblique orientated α-helical formation

In this study, an amphibian antimicrobial peptide, aurein 2.3, was predicted to use oblique orientated α-helix formation in its mechanism of membrane destabilisation. Molecular dynamic (MD) simulations and circular dichroism (CD) experimental data suggested that aurein 2.3 exists in solution as unstructured monomers and folds to form predominantly α-helical structures in the presence of a dimyristoylphosphatidylcholine membrane. MD showed that the peptide was highly surface active, which supported monolayer data where the peptide induced surface pressure changes>34 mNm(-1). In the presence of a lipid membrane MD simulations suggested that under hydrophobic mismatch the peptide is seen to insert via oblique orientation with a phenylalanine residue (PHE3) playing a key role in the membrane interaction. There is evidence of snorkelling leucine residues leading to further membrane disruption and supporting the high level of lysis observed using calcein release assays (76%). Simulations performed at higher peptide/lipid ratio show peptide cooperativity is key to increased efficiency leading to pore-formation.

Effect of salt on the interaction of Hal18 with lipid membranes

One of the major obstacles in the development of new antimicrobial peptides as novel antibiotics is salt sensitivity. Hal18, an α-helical subunit of Halocidin isolated from Halocynthia aurantium, has been previously shown to maintain its antimicrobial activity in high salt conditions. The α-helicity of Hal18 in the presence and absence of salt was demonstrated by circular dichroism spectroscopy, which showed that the peptide was mainly unordered containing β-strands and β-turns. However, in the presence of dimyristoylphosphatidylcholine (DMPC) and dimyristoylphosphatidylserine (DMPS) vesicles, Hal18 folded to form α-helices (circa 42 %). Furthermore, the structure was not significantly affected by pH or the presence of metal ions. These data were supported by monolayer results showing Hal18 induced stable surface pressure changes in monolayers composed of DMPC (5 mN m(-1)) and DMPS (8.5 mN m(-1)), which again were not effected by the presence of metal ions or pH. It is proposed that the hydrophobic groove within its molecular architecture enables the peptide to form stable associations with lipid membranes. The balance of hydrophobicity along the Hal18 long axis would also support oblique orientation of the peptide at the membrane interface. Hence, this model of membrane interaction would enable the peptide to penetrate deep into the membrane. This concept is supported by lysis data. Overall, it would appear that this peptide is a potential candidate for future AMP design for use in high salt environments.

Aberrant action of amyloidogenic host defense peptides: a new paradigm to investigate neurodegenerative disorders?

Host defense peptides (HDPs) are components of the innate immune system with activity against a broad range of microbes. In some cases, it appears that this activity is mediated by the ability of these peptides to permeabilize microbial membranes via the formation of amyloid associated structures. Recent evidence suggests that the naturally occurring function of the Aβ40 and Aβ42 peptides, which are causative agents of Alzheimer's disease, may be to serve as amyloidogenic HDPs. Here, it is hypothesized that the neurotoxicity of these peptides is related to aberrant use of their amyloid-mediated antimicrobial mechanisms, which provides the as yet unexplored paradigm of a relationship among HDPs, neurodegenerative disorders, and other conditions that could contribute to their understanding and remediation.

Effect of cholesterol on the membrane interaction of Modelin-5 isoforms

Modelin-5 isoforms were used to gain an insight into the effects of amidation on antimicrobial selectivity. When tested against Escherichia coli, amidation increased toxicity 10-fold (MIC = 31.25 μM) while showing limited increased hemolytic activity (2% lysis). Our results show that both the amidated and non-amidated peptides had a disordered structure in aqueous solution (<18% helical) and folded to form helices at the membrane interface (for example, >43% in the presence of DMPC). The stabilization of the helical structure by amidation has previously been shown to play a key role in increasing antibacterial efficacy. The presence of cholesterol in the membrane increases the packing density (C(s)(-1) values 25-33 mN m(-1)) and so prevents the peptide from forming stable association with the membrane, which is evidenced by the higher binding coefficient (K(d)) in the presence of cholesterol: 57.70 μM for Modelin-5-COOH and 35.64 μM for Modelin-5-CONH(2) compared to the presence of E. coli lipid extract (10 μM), which would prevent local concentration of the peptide at the bilayer interface as seen by reduction in monolayer interaction. This in turn would be predicted to inhibit activity.

On the selectivity and efficacy of defense peptides with respect to cancer cells

Here, we review potential determinants of the anticancer efficacy of innate immune peptides (ACPs) for cancer cells. These determinants include membrane-based factors, such as receptors, phosphatidylserine, sialic acid residues, and sulfated glycans, and peptide-based factors, such as residue composition, sequence length, net charge, hydrophobic arc size, hydrophobicity, and amphiphilicity. Each of these factors may contribute to the anticancer action of ACPs, but no single factor(s) makes an overriding contribution to their overall selectivity and toxicity. Differences between the anticancer actions of ACPs seem to relate to different levels of interplay between these peptide and membrane-based factors.

Uptake and cell-killing activities of a series of Victoria blue derivatives in a mouse mammary tumour cell line

The triarylmethane dye Victoria blue BO (VBBO) is a known photosensitizer which has been shown to induce a cytotoxic response in vitro. Several novel Victoria blue derivatives, with varying physicochemical properties, have been compared to VBBO, with respect both to dark toxicity and phototoxicity, on a mouse mammary tumour cell line, EMT6. Photosensitizer uptake was observed using confocal fluorescence microscopy. The chemical differences, particularly in the naphthyl substitution of the derivatives were shown to alter the light:dark toxicity differential and the uptake of the photosensitizers.

A Langmuir approach using on monolayer interactions to investigate surface active peptides

The Langmuir Blodgett apparatus provides a versatile system for studying the interfacial properties of peptides and peptide-membrane interactions under controlled conditions. Using amphiphilic α-helical peptides to highlight studies undertaken, here we discuss the use of this system to provide information on the surface activity of peptides and describe the insights these studies give into biological function.

Influence of C-terminal amidation on the efficacy of modelin-5

To gain insight into the effects of amidation on the mechanism of membrane interaction, we studied two peptides modelin-5-COOH and modelin-5-CONH(2) and found they exhibit high surface activities (23.2 and 27.1 mN/m, respectively). When they were tested against Escherichia coli, amidation was seen to increase efficacy approximately 10-fold. Our results demonstrated that both peptides adopted low levels of α-helix in solution (<20%); however, in the presence of E. coli lipid extract, modelin-5-CONH(2) had a greater propensity (69%) than modelin-5-COOH (32%) to generate α-helical structure. The binding coefficient for both peptides was ∼10 μM, and the Hill coefficient approximated 1, suggesting that for both peptides the interactions with E. coli membranes were monomeric and comparable in strength. The peptides showed a clear preference for anionic lipid, with monolayer data showing that enhanced levels of helicity were associated with a greater pressure change (∼6 mN/m). Use of fluorescein-phosphatidylethanolamine showed the amidated version was able to generate greater levels of membrane disruption, which was confirmed by thermodynamic analysis. The data would imply that both peptides are able to initially bind to bilayer structures, but upon binding, the amidation stabilizes helix formation. This would be expected to help overcome a key rate-limiting step and generate higher local concentrations of peptide at the bilayer interface, which in turn would be predicted to increase efficacy.

Anionic antimicrobial peptides from eukaryotic organisms

Anionic antimicrobial peptides / proteins (AAMPs) were first reported in the early 1980s and since then, have been established as an important part of the innate immune systems of vertebrates, invertebrates and plants. These peptides are active against bacteria, fungi, viruses and pests such as insects. AAMPs may be induced or expressed constitutively and in some cases, antimicrobial activity appears to be a secondary role for these peptides with other biological activities constituting their primary role. Structural characterization shows AAMPs to generally range in net charge from -1 to -7 and in length from 5 residues to circa 70 residues and for a number of these peptides, post-translational modifications are essential for antimicrobial activity. Membrane interaction appears key to the antimicrobial function of AAMPs and to facilitate these interactions, these peptides generally adopt amphiphilic structures. These architectures vary from the alpha-helical peptides of some amphibians to the cyclic cystine knot structures observed in some plant proteins. Some AAMPs appear to use metal ions to form cationic salt bridges with negatively charged components of microbial membranes, thereby facilitating interaction with their target organisms, but in many cases, the mechanisms underlying the antimicrobial action of these peptides are unclear or have not been elucidated. Here, we present an overview on current research into AAMPs, which suggests that these peptides are an untapped source of putative antimicrobial agents with novel mechanisms of action and possess potential for application in the medical and biotechnological arenas.

A theoretical analysis of secondary structural characteristics of anticancer peptides

Here, cluster analysis showed that a database of 158 anticancer peptides formed 21 clusters based on net positive charge, hydrophobicity and amphiphilicity. In general, these clusters showed similar median toxicities (P = 0.176) against eukaryotic cell lines and no single combination of these properties was found optimal for efficacy. The database contained 14 peptides, which showed selectivity for tumour cell lines only (ACP(CT)), 123 peptides with general toxicity to eukaryotic cells (ACP(GT)) and 21 inactive peptides (ACP(I)). Hydrophobic arc size analysis showed that there was no significant difference across the datasets although peptides with wide hydrophobic arcs (>270 degrees) appeared to be associated with decreased toxicity. Extended hydrophobic moment plot analysis predicted that over 50% of ACP(CT) and ACP(GT) peptides would be surface active, which led to the suggestion that amphiphilicity is a key driver of the membrane interactions for these peptides but probably plays a role in their efficacy rather than their selectivity. This analysis also predicted that only 14% of ACP(CT) peptides compared to 45% of ACP(GT) peptides were candidates for tilted peptide formation, which led to the suggestion that the absence of this structure may support cancer cell selectivity. However, these analyses predicted that ACP(I) peptides, which possess no anticancer activity, would also form surface active and tilted alpha-helices, clearly showing that other factors are involved in determining the efficacy and selectivity of ACPs.

Investigations into the ability of the peptide, HAL18, to interact with bacterial membranes

Halocidin was isolated from hemocytes, Halocynthia aurantium as a heterodimeric peptide consisting of two alpha-helical subunits, Hal15 and Hal18. Hal18 was shown to have antibacterial properties against Bacillus subtilis (MLC = 15 microM) and Escherichia coli (MLC = 100 microM). The peptide was shown to produce stable monolayers, which were characteristic of alpha-helical peptides predicted to orientate parallel to the surface of the interface. Constant area assays showed that Hal18 was surface active (4 microM) inducing surface pressure changes >30 mN m(-1) characteristic of membrane interactive peptides. The peptide induced stable surface pressure changes in monolayers that were mimetic of B. subtilis membranes (circa 7 mN m(-1)) and E. coli membrane-mimics (circa 4 mN m(-1)). Hal18 inserted readily into zwitterionic DOPE and anionic DOPG monolayers inducing surface pressure changes circa 8 mN m(-1) in both cases, providing evidence that interaction is not headgroup specific. Thermodynamic analysis of compression isotherms showed that the presence of Hal18 destabilised B. subtilis membranes (DeltaG (Mix) > 0), which is in contrast to its stabilising effect on E. coli lipid extract implying the differential antimicrobial efficacy may be driven by lipid packing.

Interactions of cell penetrating peptide Tat with model membranes: A biophysical study

The protein transduction domain of the HIV-1 transactivator of transcription, Tat (Tat((48-60))), has been shown to transport P10, a cytotoxic peptide mimic of the cyclin dependent kinase inhibitor p21WAF1/CIP1, into the nucleus of cancerous cells and induce apoptosis. Here, monolayer studies were used to investigate the membrane interactions of Tat((48-60)), P10 and the construct Tat((48-60))P10. It was found that Tat((48-60)) showed no significant surface activity but that both P10 and Tat((48-60))P10, were highly surface active, inducing surface pressure changes of 9.7 and 8.9mNm(-1), respectively, with DMPS monolayers. The comparison of Tat((48-60))P10 and P10 surface interactions would be consistent with a hypothesis that the cargo attachment influences the capacity of the Tat-protein transduction domain to mediate transport across membranes either directly or via localisation of the construct at the membrane interface.

Antimicrobial properties of a lipid interactive alpha-helical peptide VP1 against Staphylococcus aureus bacteria

Theoretical analysis indicates that peptide VP1 forms a membrane interactive amphiphilic alpha-helix with antibacterial properties. Fourier transform infra-red based analyses showed VP1 to be alpha-helical (45%) in the presence of vesicle mimics of membranes from Staphylococcus aureus and to induce increases in the fluidity of these vesicles, as indicated by a rise in wavenumber of circa 0.5 to 1.0 cm(-1). The peptide induced surface pressure increases of 5 mN m(-1) in monolayer mimics of S. aureus membranes confirm the formation of a membrane interactive alpha-helix. These interactions appeared to involve significant hydrophobic and electrostatic contributions as VP1 induced comparable surface pressure changes in anionic (5.5 mN m(-1)) and zwitterionic (4 mN m(-1)) lipid monolayers. It is suggested that whilst efficacy requires further sequence specific information, the peptides generic structure provides the basis for its broad antimicrobial activity.

The interactions of aurein 1.2 with cancer cell membranes

Here, the interactions of aurein 1.2, a defence peptide, with T98G glioblastoma cell membranes are studied. The peptide induced maximal surface pressure changes of circa 9 mN m(-1) in monolayers of endogenous T98G membrane lipid. Reducing monolayer anionic lipid showed a positive correlation (R(2)>0.91) with decreases in maximal surface pressure changes induced by aurein 1.2 (circa 3 mN m(-1) in the absence of this lipid). Cancer cell membrane invasion by the peptide therefore appears not to be mediated by lipid receptors or specific lipid requirements but rather a general requirement for anionic lipid and/or other negatively charged membrane components.