Distinguishing between different pathways of bilayer disruption by the related antimicrobial peptides cecropin B, B1 and B3

Processes and mechanisms underlying burst of giant unilamellar vesicles induced by antimicrobial peptides and compounds

To clarify the damage of lipid bilayer region in bacterial cell membrane caused by antimicrobial peptides (AMPs) and antimicrobial compounds (AMCs), their interactions with giant unilamellar vesicles (GUVs) of various lipid compositions have been examined. The findings revealed two main causes for the leakage: nanopore formation in the membrane and burst of GUVs. Although GUV burst has been explained previously based on the carpet model, the supporting evidence is limited. In this review, to better clarify the mechanism of GUV burst by AMPs, AMCs, and other membrane-active peptides, we described current knowledge of the conditions, characteristics, and detailed processes of GUV burst and the changes in the shape of the GUVs during burst. We identified several physical factors that affect GUV burst, such as membrane tension, electrostatic interaction, structural changes of GUV membrane such as membrane folding, and oil in the membrane. We also clarified one of the physical mechanisms underlying the instability of lipid bilayers that are associated with leakage in the carpet model. Based on these results, we propose a mechanism underlying some types of GUV burst induced by these substances: the growth of a nanopore to a micropore, resulting in GUV burst.

Antimicrobial and antitumor properties of anuran peptide temporin-SHf induce apoptosis in A549 lung cancer cells

Temporin-SHf is a linear, ultra-short, hydrophobic, α-helix, and phe-rich cationic antimicrobial peptide. The antitumor activities and mechanism of temporin-SHf-induced cancer cell death are unknown. The temporin-SHf was synthesized by solid-phase Fmoc chemistry and antimicrobial and antitumor activities were investigated. Temporin-SHf was microbiocidal, non-hemolytic, and cytotoxic to human cancer cells but not to non-tumorigenic cells. It affected the cancer cells' lysosomal integrity and caused cell membrane damage. The temporin-SHf inhibited A549 cancer cell proliferation and migration. It is anti-angiogenic and causes cancer cell death through apoptosis. The molecular mechanism of action of temporin-SHf confirmed that it kills cancer cells by triggering caspase-dependent apoptosis through an intrinsic mitochondrial pathway. Owing to its short length and broad spectrum of antitumor activity, temporin-SHf is a promising candidate for developing a new class of anticancer drugs.

Anticancer Mechanisms and Potential Anticancer Applications of Antimicrobial Peptides and Their Nano Agents

Traditional chemotherapy is one of the main methods of cancer treatment, which is largely limited by severe side effects and frequent development of multi-drug resistance by cancer cells. Antimicrobial peptides (AMPs) with high efficiency and low toxicity, as one of the most promising new drugs to replace chemoradiotherapy, have become a current research hotspot, attracting the attention of worldwide researchers. AMPs are natural-source small peptides from the innate immune system, and certain AMPs can selectively kill a broad spectrum of cancer cells while exhibiting less damage to normal cells. Although it involves intracellular mechanisms, AMPs exert their anti-cancer effects mainly through membrane destruction effect; thus, AMPs also hold unique advantages in fighting drug-resistant cancer cells. However, the poor stability and hemolytic toxicity of peptides limit their clinical application. Fortunately, functionalized nanoparticles have many possibilities in overcoming the shortcomings of AMPs, which provides a huge prospect for better application of AMPs. In this paper, we briefly introduce the characteristics and different sources of AMPs, review and summarize the mechanisms of action and the research status of AMPs used as an anticancer therapy, and finally focus on the further use of AMPs nano agents in the anti-cancer direction.

Potential of Antimicrobial Peptide-Overexpressed Tenebrio molitor Larvae Extract as a Natural Preservative for Korean Traditional Sauces

Here, we aimed to produce a natural food preservative using a crude extract from edible, immunized Tenebrio molitor larvae (iTME), injected with edible bacteria using an edible solvent. Results showed that iTME had concentration-dependent inhibitory activity against food-poisoning bacteria Escherichia coli, Bacillus cereus, and Staphylococcus aureus, as well as against harmful fungi Aspergillus flavus, Aspergillus parasiticus, and Pichia anomala. Moreover, iTME showed antimicrobial activity against beneficial microorganisms Bacillus subtilis and Aspergillus oryzae, but not Lactobacillus acidophilus. Furthermore, the minimum inhibitory concentration of iTME against E. coli, B. cereus, and S. aureus was 1 mg/mL, and iTME did not lose its inhibitory activity when treated at varying temperature, pH, and salinity. In addition, the antibacterial activity was lost after reacting the iTME with trypsin and chymotrypsin. The addition of iTME to Ganjang inoculated with harmful bacteria inhibited bacterial growth. Therefore, we propose that iTME can be used as a safe natural preservative to prolong food shelf life by inhibiting the growth of food-poisoning bacteria in a variety of foods, including traditional sauces.

An evidence of pores in phospholipid membrane induced by an antimicrobial peptide NK-2

NK-2, a peptide derived from a cationic core region of NK-lysin, has emerged as a promising candidate for new antibiotics. In contrast to classical antibiotics, antimicrobial peptides target bacterial membranes and disintegrate the membrane by forming the transmembrane pores. However, complete understanding of the precise mechanisms of cellular apoptosis and molecular basis of membrane selectivity is still in dispute. In the present study, we have shown that NK-2 forms trans-membrane pores on negatively charged phospholipid membranes using phase contrast microscopy. As bacteria mimicking membranes, we have chosen large unilamellar vesicles (LUV) and giant unilamellar vesicles (GUV) composed of negatively charged phospholipid, dioleoyl phosphatidyl glycerol (DOPG) and neutral phospholipid, dioleoyl phophatidylcholine (DOPC). Leakage of internal fluid of giant unilamellar vesicles (GUV), leading to decrease in intensity in the halo region of phase contrast micrographs, suggests the formation of transmembrane pores. No such reduction of intensity in the halo region of DOPC was observed, indicating, neutral vesicles does not exhibit pores. Rate constant reckoned from the decaying intensity in the halo region was found to be 0.007 s^-1. Further, significant interaction of NK-2 with anionic membranes has been envisaged from zeta potential and dynamic light scattering. Binding free energy and other interaction parameters have been delineated using theoretical ansatz. A proliferation of average Size of anionic LUV on increasing NK-2 concentration indicates membrane-membrane interaction leading to peptide induced large aggregates of vesicles.

Biophysical approaches for exploring lipopeptide-lipid interactions

In recent years, lipopeptides (LPs) have attracted a lot of attention in the pharmaceutical industry due to their broad-spectrum of antimicrobial activity against a variety of pathogens and their unique mode of action. This class of compounds has enormous potential for application as an alternative to conventional antibiotics and for pest control. Understanding how LPs work from a structural and biophysical standpoint through investigating their interaction with cell membranes is crucial for the rational design of these biomolecules. Various analytical techniques have been developed for studying intramolecular interactions with high resolution. However, these tools have been barely exploited in lipopeptide-lipid interactions studies. These biophysical approaches would give precise insight on these interactions. Here, we reviewed these state-of-the-art analytical techniques. Knowledge at this level is indispensable for understanding LPs activity and particularly their potential specificity, which is relevant information for safe application. Additionally, the principle of each analytical technique is presented and the information acquired is discussed. The key challenges, such as the selection of the membrane model are also been briefly reviewed.

Effect of antimicrobial peptides from Galleria mellonella on molecular models of Leishmania membrane. Thermotropic and fluorescence anisotropy study

Antimicrobial peptides are molecules of natural origin, produced by organisms such as insects, which have focused attention as potential antiparasitic agents. They can cause the death of parasites such Leishmania by interacting with their membrane. In this study, additional information was obtained on how the anionic peptide 2 and cecropin D-like peptide derived from Galleria mellonella interact with liposomes that mimic the composition of the Leishmania membrane. In order to do this, lipid bilayers consisting of dipalmitoylphosphatidylcholine, dipalmitoylphosphatidylethanolamine, dimyristoylphosphatidylserine, and dimyristoylphosphatidylglycerol were constructed. The effect of the peptides on these membranes was evaluated using calorimetry analysis and fluorescence spectroscopy. The results obtained using differential scanning calorimetry indicated a concentration-dependent effect on membranes composed of phosphatidylserine and phosphatidylglycerol, showing a preference of both peptides for anionic lipids. The binding of the peptides drastically reduced the transition enthalpy in the phosphatidylserine and phosphatidylglycerol liposomes. The results suggest that the mode of action of anionic peptide 2 and cecropin D-like peptide is different, with a higher effect of cecropin D-like on the anionic lipids, which led to changes in the main transition temperature and a complete solubilization of the vesicles. Interactions between peptides and phosphatidylcholine, which is the most abundant lipid on the surface of Leishmania cells, were evaluated using isothermal titration calorimetry and the anisotropy of fluorescence of DPH. The peptides had a slight effect on the gel phase of the phosphatidylcholine, with changes in the anisotropy correlated with that observed by DSC. The results showed a selectivity of these peptides toward some lipids, which will direct the study of the development of new drugs.

Charge-Driven Interaction of Antimicrobial Peptide NK-2 with Phospholipid Membranes

NK-2, derived from a cationic core region of NK-lysin, displays antimicrobial activity toward negatively charged bacterial membranes. We have studied the interaction of NK-2 with various phospholipid membranes, using a variety of experimental techniques, such as, isothermal titration calorimetry (ITC), ζ potential, and dynamic light scattering. As bacteria mimicking membranes, we have chosen large unilamellar vesicles (LUVs) composed of negatively charged phospholipid and neutral phospholipids. ITC and ζ potential results show the stronger binding affinity of NK-2 to negatively charged membranes than to neutral membranes. Saturation of the isotherm, obtained from ITC, at a given lipid to NK-2 ratio, was found to be consistent with the charge compensation, determined from ζ potential. A surface partition model with electrostatic contribution was used to estimate the intrinsic binding constant and other thermodynamical parameters of binding kinetics of NK-2. The size distribution of negatively charged LUV in the presence of NK-2 was found to increase drastically, indicating the presence of large aggregates. Such a large aggregate has not been observed in neutral membranes, which supports the ITC and ζ potential results.

Fusion expression of cecropin B-like antibacterial peptide in Pichia GS115 and its antibacterial mechanism

OBJECTIVES

To establish an efficient expression system for a fusion protein of glutathione S-transferase and cecropin B (GST-CB) and to clarify the antibacterial mechanism of CB.

RESULTS

The optimal incubation time and methanol concentration for induced expression of CB were 36 h and 1 % w/v, respectively. The yield of GST-CB was 2.2 g/l. The minimum inhibitory concentrations of GST-CB towards Staphylococcus aureus subsp. saprophyticus (ATCC 15305) and Escherichia coli strain CFT073 were 250 and 125 μg/ml, respectively. Notably, mutations of proline 24 (P24) in CB produced a polypeptide without antimicrobial activity.

CONCLUSION

The fusion protein GST-CB, which has a broad spectrum antimicrobial activity, can be abundantly expressed in Pichia pastoris GS115, and P24 may be an important amino acid for the antimicrobial activity of GST-CB.

The role of spontaneous lipid curvature in the interaction of interfacially active peptides with membranes

Research on antimicrobial peptides is in part driven by urgent medical needs such as the steady increase in pathogens being resistant to antibiotics. Despite the wealth of information compelling structure-function relationships are still scarce and thus the interfacial activity model has been proposed to bridge this gap. This model also applies to other interfacially active (membrane active) peptides such as cytolytic, cell penetrating or antitumor peptides. One parameter that is strongly linked to interfacial activity is the spontaneous lipid curvature, which is experimentally directly accessible. We discuss different parameters such as H-bonding, electrostatic repulsion, changes in monolayer surface area and lateral pressure that affect induction of membrane curvature, but also vice versa how membrane curvature triggers peptide response. In addition, the impact of membrane lipid composition on the formation of curved membrane structures and its relevance for diverse mode of action of interfacially active peptides and in turn biological activity are described. This article is part of a Special Issue entitled: Interfacially Active Peptides and Proteins. Guest Editors: William C. Wimley and Kalina Hristova.

Plantaricin A, a cationic peptide produced by Lactobacillus plantarum, permeabilizes eukaryotic cell membranes by a mechanism dependent on negative surface charge linked to glycosylated membrane proteins

Lactobacillus plantarum C11 releases plantaricin A (PlnA), a cationic peptide pheromone that has a membrane-permeabilizing, antimicrobial effect. We have previously shown that PlnA may also permeabilize eukaryotic cells, with a potency that differs between cell types. It is generally assumed that cationic antimicrobial peptides exert their effects through electrostatic attraction to negatively charged phospholipids in the membrane. The aim of the present study was to investigate if removal of the negative charge linked to glycosylated proteins at the cell surface reduces the permeabilizing potency of PlnA. The effects of PlnA were tested on clonal rat anterior pituitary cells (GH(4) cells) using patch clamp and microfluorometric techniques. In physiological extracellular solution, GH(4) cells are highly sensitive to PlnA, but the sensitivity was dramatically reduced in solutions that partly neutralize the negative surface charge of the cells, in agreement with the notion that electrostatic interactions are probably important for the PlnA effects. Trypsination of cells prior to PlnA exposure also rendered the cells less sensitive to the peptide, suggesting that negative charges linked to membrane proteins are involved in the permeabilizing action. Finally, pre-exposure of cells to a mixture of enzymes that split carbohydrate residues from the backbone of glycosylated proteins also impeded the PlnA-induced membrane permeabilization. We conclude that electrostatic attraction between PlnA and glycosylated membrane proteins is probably an essential first step before PlnA can interact with membrane phospholipids. Deviating glycosylation patterns may contribute to the variation in PlnA sensitivity of different cell types, including cancerous cells and their normal counterparts.

Review of immobilized antimicrobial agents and methods for testing

Antimicrobial surfaces for food and medical applications have historically involved antimicrobial coatings that elute biocides for effective kill in solution or at surfaces. However, recent efforts have focused on immobilized antimicrobial agents in order to avoid toxicity and the compatibility and reservoir limitations common to elutable agents. This review critically examines the assorted antimicrobial agents reported to have been immobilized, with an emphasis on the interpretation of antimicrobial testing as it pertains to discriminating between eluting and immobilized agents. Immobilization techniques and modes of antimicrobial action are also discussed.

Efficacy verification and microscopic observations of an anticancer peptide, CB1a, on single lung cancer cell

In this work, we introduce a new customized anti-lung cancer peptide, CB1a, with IC₅₀ of about 25.0 ± 1.6 μM on NCI-H460 lung cancer cells. Using a multi-cellular tumor spheroid (MCTS) model, results show that CB1a is potent in preventing the growth of lung cancer tumor-like growths in vitro. Additionally, atomic force microscopy (AFM) was used to examine cell surface damage of a single cancer. The mechanism for cell death under CB1a toxicity was verified as being largely due to cell surface damage. Moreover, with a treatment dosage of CB1a at 25 μM, Young's module (E) shows that the elasticity and stiffness of cancer cell decreased with time such that the interaction time for a 50% reduction of E (IT₅₀) was about 7.0min. This new single-cell toxicity investigation using IT₅₀ under AFM assay can be used to separately verify drug efficacy in support of the traditional IC₅₀ measurement in bulk solution. These results could be of special interest to researchers engaged in new drug development.

The antimicrobial peptide pheromone Plantaricin A increases antioxidant defenses of human keratinocytes and modulates the expression of filaggrin, involucrin, β-defensin 2 and tumor necrosis factor-α genes

Plantaricin A (PlnA) is a peptide with antimicrobial and pheromone activities. PlnA was synthesized chemically and used as a pure peptide or synthesized biologically using Lactobacillus plantarum DC400 co-cultured with Lactobacillus sanfranciscensis DPPMA174. Cell-free supernatant (CFS) was used as a crude PlnA preparation. As estimated using the 3-(4,5-dimethyl-2-yl)-2,5-diphenyltetrazolium bromide and the 2',7'-dichlorofluorescein diacetate assays, both PlnA preparations increased the antioxidant defenses of human NCTC 2544 keratinocytes. PlnA (10 μg/ml) had a higher activity than hyaluronic acid or 125 μg/ml α-tocopherol. Effects on the transcriptional regulation of filaggrin (FLG), involucrin (IVL), hyaluronan synthase (HAS2), human β-defensin-2 (HBD-2) and tumor necrosis factor-alpha (TNF-α) genes were assayed. Compared with the control, expression of the FLG gene in NCTC 2544 cells increased in cells treated with hyaluronic acid, 1 or 10 μg/ml PlnA. Compared with the control, the level of IVL gene expression increased in NCTC 2544 cells treated with 10 μg/ml PlnA. No significant difference was found between the level of the HAS2 gene expressed by control cells and cells treated with PlnA. Compared with chemically synthesized PlnA, the up-regulation of the HBD-2 gene by CFS was higher. Compared with the control, expression of TNF-α decreased in NCTC 2544 cells after treatment with 1 or 10 μg/ml of chemically synthesized PlnA. In contrast, the level of TNF-α was highest in the presence of 10 μg/ml CFS-PlnA. These findings suggest that the PlnA was positively sensed by human keratinocytes, promoting antioxidant defenses, barrier functions and antimicrobial activity of the skin.

Antitumor effects and cell selectivity of temporin-1CEa, an antimicrobial peptide from the skin secretions of the Chinese brown frog (Rana chensinensis)

Many antimicrobial peptides from amphibian exhibit additional anticancer properties due to a similar mechanism of action at both bacterial and cancer cells. We have previously reported the cDNA sequence of the antimicrobial peptide temporin-1CEa precursor cloned from the Chinese brown frog Rana chensinensis. In this study, we purified, synthesized and structurally characterized temporin-1CEa from the skin secretions of R. chensinensis. The cytotoxicity and cell selectivity of temporin-1CEa were further examined on twelve human carcinoma cell lines and on normal human umbilical vein smooth muscle cells (HUVSMCs). Our results indicated that temporin-1CEa has the amino acid sequence of FVDLKKIANIINSIF-NH(2), and exhibits 50-56% identity with temporin family peptides from other frog species. The CD spectra for temporin-1CEa adopted a well-defined α-helical structure in 50% TFE/water solution. The results of MTT assay showed that temporin-1CEa exhibits cytotoxicity to all tested cancer cell lines in a concentration-dependent manner, being MCF-7 cells the most sensitive. Moreover, temporin-1CEa had lower hemolytic effect to human erythrocytes and had no significant cytotoxicity to normal HUVSMCs at concentrations showed potent antitumor activity. In summary, temporin-1CEa, an amphiphilic α-helical cationic peptide, may represent a novel anticancer agent for breast cancer therapy, considering its cancer cell selectivity and relatively lower cytotoxicity to normal cells.

Differential scanning calorimetry: An invaluable tool for a detailed thermodynamic characterization of macromolecules and their interactions

Differential Scanning Calorimetry (DSC) is a highly sensitive technique to study the thermotropic properties of many different biological macromolecules and extracts. Since its early development, DSC has been applied to the pharmaceutical field with excipient studies and DNA drugs. In recent times, more attention has been applied to lipid-based drug delivery systems and drug interactions with biomimetic membranes. Highly reproducible phase transitions have been used to determine values, such as, the type of binding interaction, purity, stability, and release from a drug delivery mechanism. This review focuses on the use of DSC for biochemical and pharmaceutical applications.

Plantaricin A, a peptide pheromone produced by Lactobacillus plantarum, permeabilizes the cell membrane of both normal and cancerous lymphocytes and neuronal cells

Antimicrobial peptides produced by multicellular organisms protect against pathogenic microorganisms, whereas such peptides produced by bacteria provide an ecological advantage over competitors. Certain antimicrobial peptides of metazoan origin are also toxic to eukaryotic cells, with preference for a variety of cancerous cells. Plantaricin A (PlnA) is a peptide pheromone with membrane permeabilizing strain-specific antibacterial activity, produced by Lactobacillus plantarum C11. Recently, we have reported that PlnA also permeabilizes cancerous rat pituitary cells (GH(4) cells), whereas normal rat anterior pituitary cells are resistant. To investigate if preferential effect on cancerous cells is a general feature of PlnA, we have studied effects of the peptide on normal and cancerous lymphocytes and neuronal cells. Normal human B and T cells, Reh cells (from human B cell leukemia), and Jurkat cells (from human T cell leukemia) were studied by flow cytometry to detect morphological changes (scatter) and viability (propidium iodide uptake), and by patch clamp recordings to monitor membrane conductance. Ca(2+) imaging based on a combination of fluo-4 and fura-red was used to monitor PlnA-induced membrane permeabilization in normal rat cortical neurons and glial cells, PC12 cells (from a rat adrenal chromaffin tumor), and murine N2A cells (from a spinal cord tumor). All the tested cell types were affected by 10-100 microM PlnA, whereas concentrations below 10 microM had no significant effect. We conclude that normal and cancerous lymphocytes and neuronal cells show similar sensitivity to PlnA.

The roles of antimicrobial peptides in innate host defense

Antimicrobial peptides (AMPs) are multi-functional peptides whose fundamental biological role in vivo has been proposed to be the elimination of pathogenic microorganisms, including Gram-positive and -negative bacteria, fungi, and viruses. Genes encoding these peptides are expressed in a variety of cells in the host, including circulating phagocytic cells and mucosal epithelial cells, demonstrating a wide range of utility in the innate immune system. Expression of these genes is tightly regulated; they are induced by pathogens and cytokines as part of the host defense response, and they can be suppressed by bacterial virulence factors and environmental factors which can lead to increased susceptibility to infection. New research has also cast light on alternative functionalities, including immunomodulatory activities, which are related to their unique structural characteristics. These peptides represent not only an important component of innate host defense against microbial colonization and a link between innate and adaptive immunity, but also form a foundation for the development of new therapeutic agents.

Structure and function of a custom anticancer peptide, CB1a

Several natural antimicrobial peptides including cecropins, magainins and melittins have been found to kill cancer cells. However, their efficacy may not be adequate for their development as anticancer agents. In this study, we used a natural antimicrobial peptide, cecropin B (CB), as a template to generate a novel anticancer peptide. Cecropin B is an amphipathic and polycationic peptide derived from the hemolymph of Hyalophora cecropia with well-known antimicrobial and cytolytic properties. The signature pattern of cecropins is W-x-(0,2)-[KDN]-x-{L}-K-[KRE]-[LI]-E-[RKN] (PROSITE: PS00268), and this signature sequence is located at N-terminus of CB. CB1a was constructed by repeating the N-terminal ten amino acids of CB three times and including a hinge near C-terminus. The circular dichroism spectra showed that CB1a is unstructured in aqueous solution, but adopt a helical conformation in membrane-like environment. The solution structure of CB1a in a polar solvent was also studied by NMR. CB1a formed a helix-hinge-helix in 20% HFIP solution, and it was found the bent angle between two helical segments was induced ranging from 60 degrees to 110 degrees . A heparin-binding motif is located in the central part of helix 1. Isothermal titration calorimetry reveals the association constant of CB1a bound to low molecular weight heparin is 1.66 x 10(5)M(-1) at physiological ionic strength at 25 degrees C. Binding of CB1a to heparin produces a large conformational change toward a more structural state. CB1a demonstrated promising activity against several cancer cells but low toxicity against non-cancer cells. The IC(50) of CB1a on leukemia and stomach carcinoma cells were in the range of 2-8-fold lower than those of CB. Besides, CB1a exhibited low hemolytic activity against human red blood cells. Due to these properties, CB1a has the potential to become a promising anticancer agent.

Membrane structure and interactions of a short Lycotoxin I analogue

Lycotoxin I and Lycotoxin II are natural anti-microbial peptides that were identified in the venom of the Wolf Spider Lycosa carolinensis. These peptides were found to be potent growth inhibitors for bacteria (Escherichia coli) and yeast (Candida glabrata) at micromolar concentrations. Recently, shortened analogues of LycoI and LycoII have been reported to have decreased haemolytic effects. A shorter Lyco-I analogue studied, LycoI 1-15 (H-IWLTALKFLGKHAAK-NH2), was active only above 10 microM, but was also the least haemolytic. On the basis of these findings, we became interested in obtaining a deeper insight into the membrane activity of LycoI 1-15, as this peptide may represent the first major step for the future development of selective, i.e. non-haemolytic, Lycotoxin-based antibiotics. The interaction of this peptide with liposomes of different composition was studied by microcalorimetry [differential scanning calorimetry (DSC) and isothermal titration calorimetry (ITC)] and CD. The results obtained from the calorimetric and spectroscopic techniques were jointly discussed in an attempt to further understand the interaction of this peptide with model membranes.

Antitumor effects, cell selectivity and structure-activity relationship of a novel antimicrobial peptide polybia-MPI

A novel antimicrobial peptide, polybia-MPI, was purified from the venom of the social wasp Polybia paulista. It has potent antimicrobial activity against both Gram-positive and Gram-negative bacteria, but causing no hemolysis to rat erythrocytes. To date, there is no report about its antitumor effects on any tumor cell lines. In this study we synthesized polybia-MPI and studied its antitumor efficacy and cell selectivity. Our results revealed that polybia-MPI exerts cytotoxic and antiproliferative efficacy by pore formation. It can selectively inhibit the proliferation of prostate and bladder cancer cells, but has lower cytotoxicity to normal murine fibroblasts. In addition, to investigate the structure-activity relationship of polybia-MPI, three analogs in which Leu7, Ala8 or Asp9 replaced by L-Pro were designed and synthesized. L-Pro substitution of Leu7 or Asp9 significantly reduces the content of alpha-helix conformation, and L-Pro substitution of Ala8 can disrupt the alpha-helix conformation thoroughly. The L-Pro substitution induces a significant reduction of antitumor activity, indicating that the alpha-helix conformation of polybia-MPI is important for its antitumor activity. In summary, polybia-MPI may offer a novel therapeutic strategy in the treatment of prostate cancer and bladder cancer, considering its relatively lower cytotoxicity to normal cells.

Energetics and partition of two cecropin-melittin hybrid peptides to model membranes of different composition

The energetics and partition of two hybrid peptides of cecropin A and melittin (CA(1-8)M(1-18) and CA(1-7)M(2-9)) with liposomes of different composition were studied by time-resolved fluorescence spectroscopy, isothermal titration calorimetry, and surface plasmon resonance. The study was carried out with large unilamellar vesicles of three different lipid compositions: 1,2-dimyristoil-sn-glycero-3-phosphocholine (DMPC), 1,2-dimyristoyl-sn-glycero-3-phospho-rac-(1-glycerol) (DMPG), and a 3:1 binary mixture of DMPC/DMPG in a wide range of peptide/lipid ratios. The results are compatible with a model involving a strong electrostatic surface interaction between the peptides and the negatively charged liposomes, giving rise to aggregation and precipitation. A correlation is observed in the calorimetric experiments between the observed events and charge neutralization for negatively charged and mixed membranes. In the case of zwitterionic membranes, a very interesting case study was obtained with the smaller peptide, CA(1-7)M(2-9). The calorimetric results obtained for this peptide in a large range of peptide/lipid ratios can be interpreted on the basis of an initial and progressive surface coverage until a threshold concentration, where the orientation changes from parallel to perpendicular to the membrane, followed by pore formation and eventually membrane disruption. The importance of negatively charged lipids on the discrimination between bacterial and eukaryotic membranes is emphasized.

The bacterial peptide pheromone plantaricin A permeabilizes cancerous, but not normal, rat pituitary cells and differentiates between the outer and inner membrane leaflet

Plantaricin A (PlnA) is a 26-mer peptide pheromone with membrane-permeabilizing, strain-specific antibacterial activity, produced by Lactobacillus plantarum C11. We investigated the membrane-permeabilizing effects of PlnA on cultured cancerous and normal rat anterior pituitary cells using patch-clamp techniques and microfluorometry (fura-2). Cancerous cells displayed massive permeabilization within 5 s after exposure to 10-100 microM PlnA. The membrane depolarized to nearly 0 mV, and the membrane resistance decreased to a mere fraction of the initial value after less than 1 min. In outside-out membrane patches, 10 microM PlnA induced membrane currents reversing at 0 mV, which is compatible with an unspecific conductance increase. The D and L forms of the peptide had similar potency, indicating a nonchiral mechanism for the membrane-permeabilizing effect. Surprisingly, inside-out patches were insensitive to 1 mM PlnA. Primary cultures of normal rat anterior pituitary cells were also insensitive to the peptide. Thus, PlnA differentiates between plasma membranes and membrane leaflets. Microfluorometric recordings of [Ca(2+)](i) and cytosolic concentration of fluorochrome verified the rapid permeabilizing effect of PlnA on cancerous cells and the insensitivity of normal pituitary cells.

Interaction and lipid-induced conformation of two cecropin-melittin hybrid peptides depend on peptide and membrane composition

The interaction of two hybrid peptides of cecropin A and melittin [CA(1-8)M(1-18) and CA(1-7)M(2-9)] with liposomes was studied by differential scanning calorimetry (DSC), circular dichroism (CD), and quasi-elastic light scattering (QELS). The study was carried out with large unilamellar vesicles (LUVs) of three different lipid compositions: 1,2-dimyristoil-sn-glycero-3-phosphocholine (DMPC), 1,2-dimyristoyl-sn-glycero-3-phospho-rac-(1-glycerol) (DMPG) and a binary mixture of DMPC/DMPG, in a wide range of peptide-to-lipid (P:L) molar ratios (0 to 1:7). DSC results indicate that, for both peptides, the interaction depends on membrane composition, with very different behavior for zwitterionic and anionic membranes. CD data show that, although the two peptides have different secondary structures in buffer (random coil for CA(1-7)M(2-9) and predominantly beta-sheet for CA(1-8)M(1-18)), they both adopt an alpha-helical structure in the presence of the membranes. Overall, results are compatible with a model involving a strong electrostatic surface interaction between the peptides and the negatively charged liposomes, which gives place to aggregation in the gel phase and precipitation after a threshold peptide concentration. In the case of zwitterionic membranes, a progressive surface coverage with peptide molecules destabilizes the membrane, eventually leading to membrane disruption. Moreover, delicate modulations in behavior were observed depending on the peptide.

Investigations of antimicrobial peptides in planar film systems

Planar systems--monolayers and films--constitute a useful platform for studying membrane-active peptides. Here, we summarize varied approaches for studying peptide organization and peptide-lipid interactions at the air/water interface, and focus on three representative antimicrobial membrane--associated peptides-alamethicin, gramicidin, and valinomycin. Experimental data, specifically surface pressure/area isotherms and Brewster angle microscopy images, provided information on peptide association and the effects of the lipid monolayers on peptide surface organization. In general, film analysis emphasized the effects of lipid layers in promoting peptide association and aggregation at the air/water interface. Importantly, the data demonstrated that in many cases peptide domains are phase-separated within the phospholipid monolayers, suggesting that this behavior contributes to the biological actions of membrane-active antimicrobial peptides.

Survey of the year 2003 commercial optical biosensor literature

In the year 2003 there was a 17% increase in the number of publications citing work performed using optical biosensor technology compared with the previous year. We collated the 962 total papers for 2003, identified the geographical regions where the work was performed, highlighted the instrument types on which it was carried out, and segregated the papers by biological system. In this overview, we spotlight 13 papers that should be on everyone's 'must read' list for 2003 and provide examples of how to identify and interpret high-quality biosensor data. Although we still find that the literature is replete with poorly performed experiments, over-interpreted results and a general lack of understanding of data analysis, we are optimistic that these shortcomings will be addressed as biosensor technology continues to mature.

HB-107, a nonbacteriostatic fragment of the antimicrobial peptide cecropin B, accelerates murine wound repair

Antimicrobial peptides are essential to innate host defense as effectors of pathogen clearance and can modify host cell behaviors to promote wound repair. While these two functions appear interrelated, it is unclear whether the ability to aid in wound repair requires inherent antimicrobial function. We hypothesized that the influence of antimicrobial peptides on wound repair is not dependent on antimicrobial function. To explore this, we analyzed the microbial killing activity of peptide fragments and correlated this with the ability to influence wound repair in mice. HB-107, a peptide lacking antimicrobial activity and originally derived from the antimicrobial cecropin B, showed up to 64 percent improvement in wound repair compared to scrambled peptide and vehicle controls, an effect comparable to treatment with recombinant human platelet-derived growth factor-BB (formulated as Regranex). Wounds treated with HB-107 showed keratinocyte hyperplasia and increased leukocyte infiltration. Furthermore, HB-107 stimulated interleukin-8 secretion from cultured endothelial cells, an effect that may explain the increase in leukocyte migration. These findings confirm that antimicrobial peptides can function as effectors of cutaneous wound repair. Moreover, this study furthers our understanding of antimicrobial peptides by showing that their wound repair properties can be independent of antimicrobial function.