forapin and Hemolysis

Naturally occurring cationic antimicrobial peptides (AMPs) and their mimics form a diverse class of antibacterial agents currently validated in preclinical and clinical settings for the treatment of infections caused by antimicrobial-resistant bacteria. Numerous studies with linear, cyclic, and diastereomeric AMPs have strongly supported the hypothesis that their physicochemical properties, rather than any specific amino acid sequence, are responsible for their microbiological activities. It is generally believed that the amphiphilic topology is essential for insertion into and disruption of the cytoplasmic membrane. In particular, the ability to rapidly kill bacteria and the relative difficulty with which bacteria develop resistance make AMPs and their mimics attractive targets for drug development. However, the therapeutic use of naturally occurring AMPs is hampered by the high manufacturing costs, poor pharmacokinetic properties, and low bacteriological efficacy in animal models. In order to overcome these problems, a variety of novel and structurally diverse cationic amphiphiles that mimic the amphiphilic topology of AMPs have recently appeared. Many of these compounds exhibit superior pharmacokinetic properties and reduced in vitro toxicity while retaining potent antibacterial activity against resistant and nonresistant bacteria. In summary, cationic amphiphiles promise to provide a new and rich source of diverse antibacterial lead structures in the years to come.

Topics: Anti-Infective Agents; Antimicrobial Cationic Peptides; Bacteria; Hemolysis; Hydrophobic and Hydrophilic Interactions; Molecular Structure; Structure-Activity Relationship; Surface-Active Agents

Novel 1-aryl-3-biphenyl-4-yl-3-hydroxy-2,5,6,7,8,9-hexahydro-3H-imidazo[1,2-a]azepin-1-ium bromides and their 2,5-dehydrogenated analogues were designed and synthesized using a reaction of aryl-(4,5,6,7-tetrahydro-3H-azepin-2-yl)-amines with 1-biphenyl-4-yl-2-bromoethanone. Among the 16 novel compounds 5 derivatives displayed in vitro antimicrobial activity; while three of them showed promising activity against Staphylococcus aureus, Cryptococcus neoformans and Candida albicans.

Topics: Anti-Bacterial Agents; Antifungal Agents; Azepines; Bacteria; Fungi; HEK293 Cells; Hemolysis; Humans; Imidazoles; Microbial Sensitivity Tests; Molecular Structure; Structure-Activity Relationship

Antimicrobial peptides (AMPs) are amphipathic molecules displaying broad-spectrum bactericidal activity, providing opportunities to develop a new generation of antibiotics. However, their use is limited either by poor metabolic stability or by high hemolytic activity. We herein addressed the potential of thiazole-based γ-peptide oligomers named ATCs as tunable scaffolds to design polycationic AMP mimetics. Knowing the side chain distribution along the backbone, we rationally designed facially amphiphilic sequences with bactericidal effect in the micromolar range. Since no hemolytic activity was detected up to 100 μM, this class of compounds has shown the potential for therapeutic development.

Topics: Anti-Bacterial Agents; Antimicrobial Cationic Peptides; Drug Design; Erythrocytes; Fungi; Gram-Negative Bacteria; Gram-Positive Bacteria; Hemolysis; Humans; Microbial Sensitivity Tests; Thiazoles

Gram-negative bacteria are becoming resistant to almost all currently available antibiotics. Systemically designed antimicrobial peptides (AMPs) are attractive agents to enhance the activities of antibiotics. We constructed a small Pro-scanning library using amphipathic model peptides. Measurements of minimum inhibitory concentration (MIC) against

Topics: Animals; Anti-Bacterial Agents; Antimicrobial Cationic Peptides; Cell Membrane; Clarithromycin; Escherichia coli; Female; Hemolysis; Humans; Hydrophobic and Hydrophilic Interactions; Linezolid; Lipid A; Membrane Fluidity; Mice, Inbred ICR; Microbial Sensitivity Tests; Proline; Protein Binding; Protein Conformation, alpha-Helical; Rifampin

The combination of increased incidence of drug-resistant strains of bacteria and a lack of novel drugs in development creates an urgency for the search for new antimicrobials. Initial screening of compounds from an in-house library identified two 6-bromoindolglyoxylamide polyamine derivatives (3 and 4) that exhibited intrinsic antimicrobial activity towards Gram-positive bacteria, Staphylococcus aureus and S. intermedius with polyamine 3 also displaying in vitro antibiotic enhancing properties against the resistant Gram-negative bacterium Pseudomonas aeruginosa. A series of 6-bromo derivatives (5-15) were prepared and biologically evaluated, identifying analogues with enhanced antibacterial activity towards Escherichia coli and with moderate to excellent antifungal properties. Polyamine 3, which includes a spermine chain, was the most potent of the series - its mechanism of action was attributed to rapid membrane permeabilization and depolarization in both Gram-positive and Gram-negative bacteria.

Topics: Anti-Bacterial Agents; Anti-Infective Agents; Cell Line; Cell Survival; Drug Resistance, Bacterial; Erythrocytes; Fungi; Gram-Negative Bacteria; Gram-Positive Bacteria; Hemolysis; Humans; Indoles; Microbial Sensitivity Tests; Polyamines

Antimicrobial peptides often show broad-spectrum activity due to a mechanism based on bacterial membrane disruption, which also reduces development of permanent resistance, a desirable characteristic in view of the escalating multidrug resistance problem. Host cell toxicity however requires design of artificial variants of natural AMPs to increase selectivity and reduce side effects. Kiadins were designed using rules obtained from natural peptides active against E. coli and a validated computational algorithm based on a training set of such peptides, followed by rational conformational alterations. In vitro activity, tested against ESKAPE strains (ATCC and clinical isolates), revealed a varied activity spectrum and cytotoxicity that only in part correlated with conformational flexibility. Peptides with a higher proportion of Gly were generally less potent and caused less bacterial membrane alteration, as observed by flow cytometry and AFM, which correlate to structural characteristics as observed by circular dichroism spectroscopy and predicted by molecular dynamics calculations.

Topics: Algorithms; Anti-Bacterial Agents; Antimicrobial Cationic Peptides; Bacteria; Cell Membrane Permeability; Drug Design; Glycine; Hemolysis; In Vitro Techniques; Lysine; Microbial Sensitivity Tests; Models, Molecular; Molecular Conformation; Molecular Dynamics Simulation; Mutagenicity Tests; Structure-Activity Relationship

Antimicrobial peptides are an important weapon against invading pathogens and are potential candidates as novel antibacterial agents, but their antifungal activities are not fully developed. In this study, a set of imperfectly amphipathic peptides was developed based on the imperfectly amphipathic palindromic structure R

Topics: Amino Acid Sequence; Animals; Antifungal Agents; Candida albicans; Cytoplasm; Drug Resistance, Fungal; HEK293 Cells; Hemolysis; Humans; Hydrophobic and Hydrophilic Interactions; Intracellular Membranes; Inverted Repeat Sequences; Mice; Models, Molecular; Peptides; Protein Conformation; RAW 264.7 Cells

Here we describe the three-dimensional structure and antimicrobial mechanism of mBjAMP1, an antimicrobial peptide (AMP) isolated from Branchiostoma japonicum. The structure of mBjAMP1 was determined by 2D solution NMR spectroscopy and revealed a novel α-hairpinin-like scaffold stabilized by an intramolecular disulfide bond. mBjAMP1 showed effective growth inhibition and bactericidal activities against pathogenic bacteria but was not cytotoxic to mammalian cells. Antimicrobial mechanism studies using fluorescence-based experiments demonstrated that mBjAMP1 did not disrupt membrane integrity. Laser-scanning confocal microscopy indicated that mBjAMP1 is able to penetrate the bacterial cell membrane without causing membrane disruption. Moreover, gel retardation assay suggested that mBjAMP1 directly binds to bacterial DNA as an intracellular target. Collectively, mBjAMP1 may inhibit biological functions by binding to DNA or RNA after penetrating the bacterial cell membrane, thereby causing cell death. These results suggest that mBjAMP1 may present a promising template for the development of peptide-based antibiotics.

Topics: Animals; Antimicrobial Cationic Peptides; Cell Membrane; Circular Dichroism; Disulfides; DNA, Bacterial; Erythrocytes; Gram-Negative Bacteria; Gram-Positive Bacteria; Hemolysis; Lancelets; Magnetic Resonance Spectroscopy; Mice; Microbial Sensitivity Tests; Microscopy, Confocal; Protein Conformation; RAW 264.7 Cells

Coiled-coil, a basic folding pattern of native proteins, was previously demonstrated to be associated with the specific spatial recognition, association, and dissociation of proteins and can be used to perfect engineering peptide model. Thus, in this study, a series of amphiphiles composed of heptads repeats with coiled-coil structures was constructed, and the designed peptides exhibited a broad spectrum of antimicrobial activities. Circular dichroism and biological assays showed that the heptad repeats and length of the linker between the heptads largely influenced the amphiphile's helical propensity and cell selectivity. The engineered amphiphiles were also found to efficiently reduce sessile P. aeruginosa biofilm biomass, neutralize endotoxins, inhibit the inflammatory response, and remain active under physiological salt concentrations. In summary, these findings are helpful for short AMP design with a highly therapeutic index to treat bacteria-induced infection.

Topics: Amino Acid Sequence; Anti-Bacterial Agents; Bacteria; Bacterial Infections; Biofilms; Circular Dichroism; Drug Design; Hemolysis; Humans; Models, Molecular; Peptides; Protein Structure, Secondary; Pseudomonas aeruginosa; Pseudomonas Infections; Surface-Active Agents

Since the bacterial resistance to antibiotics is increasing rapidly, numerous studies have contributed to the design and synthesis of potent synthetic mimics of antimicrobial peptides (AMPs). In an attempt to find the pharmacophore of short antimicrobial peptidomimetics through systematic tuning of hydrophobic and hydrophilic patterns, we have identified a set of short histidine-derived antimicrobial peptides (SAMPs) with potent and broad-spectrum activity. A combination of high antimicrobial activity against methicillin-resistant Staphylococcus aureus (MRSA), without hemolytic activity and proteolytic stability makes these molecules promising candidates for novel antimicrobial therapeutics.

Topics: Anti-Infective Agents; Hemolysis; Methicillin-Resistant Staphylococcus aureus; Microbial Sensitivity Tests; Peptidomimetics; Protein Stability

The activity of antimicrobial peptides (AMPs) that contain a large proportion of histidine residues (pK(a) ∼ 6) depends on the physiological pH environment. Advantages of these AMPs include high activity in slightly acidic areas of the human body and relatively low toxicity in other areas. Also, many AMPs are highly active in a multivalent form, but this often increases toxicity. Here we designed pH dependent amphiphilic compounds consisting of multiple ultrashort histidine lipopeptides on a triazacyclophane scaffold, which showed high activity toward Aspergillus fumigatus and Cryptococcus neoformans at acidic pH, yet remained nontoxic. In vivo, treatment with a myristic acid conjugated trivalent histidine-histidine dipeptide resulted in 55% survival of mice (n = 9) in an otherwise lethal murine lung Aspergillus infection model. Fungal burden was assessed and showed completely sterile lungs in 80% of the mice (n = 5). At pH 5.5 and 7.5, differing peptide-membrane interactions and peptide nanostructures were observed. This study underscores the potential of unique AMPs to become the next generation of clinical antimicrobial therapy.

Topics: Animals; Anti-Bacterial Agents; Antifungal Agents; Antimicrobial Cationic Peptides; Aspergillus fumigatus; Candida albicans; Cell Line; Cryptococcus neoformans; Female; Gram-Negative Bacteria; Gram-Positive Bacteria; Hemolysis; Humans; Hydrogen-Ion Concentration; Lipopeptides; Lung; Mice; Mice, Inbred ICR; Microbial Sensitivity Tests; Nanostructures; Polymers; Pulmonary Aspergillosis; Structure-Activity Relationship

De novo cyclic pseudopeptides composed of α-amino and aza-β(3)-amino acids were designed with the aim to obtain potential new antimicrobial agents. Antimicrobial cyclic pseudopeptides (ACPPs) are based on the properties of antimicrobial peptides (AMPs), so they are cationic and amphiphilic. Aza-β(3)-amino acids enhance the in vivo half-life of these compounds and offer the possibility to incorporate a large variety of side chains. Most of the 13 ACPPs exert antimicrobial activities in rich media with broad spectrum of antibacterial activities. Selectivity for bacterial over mammalian cells was determined by testing the hemolytic activities of ACPPs against sheep red blood cells (sRBC). We examined the ratio of cationic to hydrophobic residues as well as the type of hydrophobic side chains essential for biological activity of this class of ACPPs. These results will be useful for designing potential candidates for a therapeutic application.

Topics: Amino Acids; Animals; Anti-Bacterial Agents; Aza Compounds; Gram-Negative Bacteria; Gram-Positive Bacteria; Hemolysis; Hydrophobic and Hydrophilic Interactions; Microbial Sensitivity Tests; Oligopeptides; Peptides, Cyclic; Peptidomimetics; Sheep; Structure-Activity Relationship

The synthesis and screening of neutral and cationic, linear and cyclic peptoids (N-alkylglycine peptidomimetics) is described. Structure-activity relationship studies show that the in vitro activities of the tested peptoids depend on both cyclization and decoration with cationic groups. The most powerful N-lysine cyclopeptoid derivatives showed good antifungal activity against Candida albicans (ATCC90029 and L21) and Candida famata (SA550, Amph B-resistant) and low hemolytic activity. The effects of the cyclic peptoids on membrane permeabilization were evaluated by the propidium iodide exclusion assay.

Topics: Anti-Bacterial Agents; Antifungal Agents; Cations; Cell Membrane Permeability; Drug Design; Erythrocytes; Hemolysis; Humans; Microbial Sensitivity Tests; Peptides, Cyclic; Structure-Activity Relationship

Systemic bacterial infections are associated with high mortality. The access of bacteria or constituents thereof to systemic circulation induces the massive release of immunomodulatory mediators, ultimately causing tissue hypoperfusion and multiple-organ failure despite adequate antibiotic treatment. Lipid A, the "endotoxic principle" of bacterial lipopolysaccharide (LPS), is one of the major bacterial immunostimuli. Here we demonstrate the biological efficacy of rationally designed new synthetic antilipopolysaccharide peptides (SALPs) based on the Limulus anti-LPS factor for systemic application. We show efficient inhibition of LPS-induced cytokine release and protection from lethal septic shock in vivo, whereas cytotoxicity was not observed under physiologically relevant conditions and concentrations. The molecular mechanism of LPS neutralization was elucidated by biophysical techniques. The lipid A part of LPS is converted from its "endotoxic conformation," the cubic aggregate structure, into an inactive multilamellar structure, and the binding affinity of the peptide to LPS exceeds those of known LPS-binding proteins, such as LPS-binding protein (LBP). Our results thus delineate a novel therapeutic strategy for the clinical management of patients with septic shock.

Topics: Animals; Anti-Infective Agents; Bacteria; Calorimetry; Cells, Cultured; Cytokines; Female; Hemolysis; Humans; Leukocytes, Mononuclear; Lipopolysaccharides; Mice; Mice, Inbred C57BL; Microbial Sensitivity Tests; Peptides; Shock, Septic

We synthesized antibacterial pseudopeptides with less hemolytic activity by incorporation of reduced amide bond psi[CH2NH] into alpha helical antibacterial peptide with hemolytic activity. As the pKa value of reduced amide bond is 7-8, it is protonated depending on the pH. We investigated the secondary structure, the binding affinity and the leakage activity for the vesicles, and the antibacterial activity of the peptide and its pseudopeptides at neutral and basic pH. Unlike the peptide, the pseudopeptides showed a more potent leakage activity when pH increased. The peptide exhibited a lower antibacterial activity at basic pH than at neutral pH, whereas the pseudopeptide showed the same antibacterial activity at basic and neutral pH. Overall results indicated that hydrophobicity of backbone of the pseudopeptide plays an important role in the increase of leakage activity and retention of antibacterial activity at basic pH.

Topics: Amino Acid Sequence; Anti-Bacterial Agents; Erythrocytes; Hemolysis; Humans; Hydrogen-Ion Concentration; Microbial Sensitivity Tests; Peptides

Cyclotides are plant derived mini-proteins with compact folded structures and exceptional stability. Their stability derives from a head-to-tail cyclized backbone coupled with a cystine knot arrangement of three-conserved disulfide bonds. Taking advantage of this stable framework we developed novel VEGF-A antagonists by grafting a peptide epitope involved in VEGF-A antagonism onto the stable cyclotide framework. Antagonists of this kind have potential therapeutic applications in diseases where angiogenesis is an important component of disease progression, including cancer and rheumatoid arthritis. A grafted analogue showed biological activity in an in vitro VEGF-A antagonism assay at low micromolar concentration and the in vitro stability of the target epitope was markedly increased using this approach. In general, the stabilization of bioactive peptide epitopes is a significant problem in medicinal chemistry and in the current study we have provided insight into one approach to stabilize these peptides in a biological environment.

Topics: Chemistry, Pharmaceutical; Cyclotides; Cystine Knot Motifs; Drug Delivery Systems; Drug Design; Epitopes; Hemolysis; Humans; Hydrogen-Ion Concentration; Models, Chemical; Molecular Conformation; Neovascularization, Pathologic; Protein Structure, Tertiary; Vascular Endothelial Growth Factor A

Halocidin is an antimicrobial peptide found in the tunicate. A series of experiments were previously conducted in an attempt to develop a novel antibiotic derived from halocidin, as the peptide was determined to evidence profound antimicrobial activity against a variety of antibiotic-resistant microbes, with significantly less toxicity to human blood cells. In this study, we assessed the validity of one of the halocidin congeners, called Khal, as a new antibiotic for the treatment of systemic bacterial infections. Our in vitro antimicrobial tests showed that the MICs of Khal against several gram-positive bacteria were below 16 microg/ml in the presence of salt. We also determined that Khal retained sufficient target selectivity to discern microbial and human blood cells and was therefore capable of efficiently killing invading pathogens. Furthermore, Khal caused no aggregation problems upon incubation with human serum and also proved to be resistant to proteolysis by enzymes occurring in human serum. In the following experiments conducted with a mouse model of Listeria monocytogenes infection, we demonstrated that a single intravenous inoculation with Khal resulted in significant therapeutic effects on the survival of mice. In addition, our bacterial-enumeration analysis showed that after Listeria infection, livers and spleens from Khal-treated mice generated a great deal fewer recoverable CFU. Finally, the antibiotic effects of Khal were evaluated under confocal microscopy after we immunostained the liver sections with anti-Khal antibody. It was concluded that Khal bound specifically to the surfaces of bacteria colonized in the mouse liver and killed the bacteria rapidly.

Topics: Animals; Anti-Bacterial Agents; Blood Cells; Chromatography, High Pressure Liquid; Disease Models, Animal; Dose-Response Relationship, Drug; Hemolysis; Humans; Listeria monocytogenes; Listeriosis; Liver; Male; Mice; Mice, Inbred BALB C; Microbial Sensitivity Tests; Peptides; Spleen; Time Factors

Cycloviolacin H4, a new macrocyclic miniprotein comprising 30 amino acid residues, was isolated from the underground parts of the Australian native violet Viola hederaceae. Its sequence, cyclo-(CAESCVWIPCTVTALLGCSCSNNVCYNGIP), was determined by nanospray tandem mass spectrometry and quantitative amino acid analysis. A knotted disulfide arrangement, which was designated as a cyclic cystine knot motif and characteristic to all known cyclotides, is proposed for stabilizing the molecular structure and folding. The cyclotide is classified in the bracelet subfamily of cyclotides due to the absence of a cis-Pro peptide bond in the circular peptide backbone. A model of its three-dimensional structure was derived based on the template of the homologous cyclotide vhr1 (Trabi et al. Plant Cell 2004, 16, 2204-2216). Cycloviolacin H4 exhibits the most potent hemolytic activity in cyclotides reported so far, and this activity correlates with the size of a surface-exposed hydrophobic patch. This work has thus provided insight into the factors that modulate the cytotoxic properties of cyclotides.

Topics: Amino Acid Sequence; Amino Acids; Australia; Cyclotides; Erythrocytes; Hemolysis; Humans; Models, Molecular; Molecular Sequence Data; Protein Conformation; Sequence Alignment; Viola

Seven depsipeptides were synthesized by appending seven amino acids (Lys, Leu, Val, Phe, Ser, Gln, and Pro) at the N-terminus of the active fragment [TE-(33-43)], respectively corresponding to the C-terminal beta sheet domain of tenecin 1, an antibacterial protein and their activities were measured against Staphylococcus aureus. Considering the relationship between the activity and the characteristic of amino acid at the N-terminal of the peptide, novel derivatives were designed and synthesized from TE-(33-43) by introduction of fatty acids at the N-terminal. In this process, we synthesized novel lipid-peptide hybrid compounds with a potent antibacterial activity and more improved bioavailabilities. We characterized the important structural parameters of the lipid-peptide hybrid compounds for the antibacterial activities.

Topics: Amino Acid Sequence; Animals; Anti-Bacterial Agents; Antimicrobial Cationic Peptides; Hemolysis; Insect Proteins; Lipids; Mice; Microbial Sensitivity Tests; Molecular Sequence Data; Staphylococcus aureus