Interaction of human defensins with Escherichia coli. Mechanism of bactericidal activity

Adaptation of a bacterial membrane permeabilization assay for quantitative evaluation of benzalkonium chloride as a membrane-disrupting agent

We describe the use of the ortho-nitrophenyl-β-galactoside (ONPG) assay developed by Lehrer et al. to which a new mathematical data treatment was applied. In this simplified assay, only one enzymatic assay is needed to provide direct evidence of the kinetics of Escherichia coli membrane permeabilization induced by different concentrations of benzalkonium chloride (BAC). Analysis of the data obtained from the revised ONPG assay with our adapted mathematical formula indicates that BAC induces permeabilization of the bacterial outer and inner membranes in a two-step process. The two effective concentration (EC50) values obtained in this study, combined with the results from an outer membrane permeabilization assay, suggest that the two steps observed in the permeabilization process are related to the two different bacterial membranes. We show that membrane permeabilization occurs very fast upon the addition of bacterial cells to the BAC solutions and demonstrate that sub-lethal concentrations of BAC disturb the integrity of the Gram-negative bacterial membranes. Overall, our work broadens our knowledge on the mode of action of BAC on bacterial cells and emphasizes that BAC, and quaternary ammonium compounds in general, should not be used at sub-lethal concentrations in order to lower the risk of bacterial tolerance and resistance to antibiotics.

Psoriasis-Associated Late Cornified Envelope (LCE) Proteins Have Antibacterial Activity

Terminally differentiating epidermal keratinocytes express a large number of structural and antimicrobial proteins that are involved in the physical barrier function of the stratum corneum and provide innate cutaneous host defense. Late cornified envelope (LCE) genes, located in the epidermal differentiation complex on chromosome 1, encode a family of 18 proteins of unknown function, whose expression is largely restricted to epidermis. Deletion of two members, LCE3B and LCE3C (LCE3B/C-del), is a widely-replicated psoriasis risk factor that interacts with the major psoriasis-psoriasis risk gene HLA-C*06. Here we performed quantitative trait locus analysis, utilizing RNA-seq data from human skin and found that LCE3B/C-del was associated with a markedly increased expression of LCE3A, a gene directly adjacent to LCE3B/C-del. We confirmed these findings in a 3-dimensional skin model using primary keratinocytes from LCE3B/C-del genotyped donors. Functional analysis revealed that LCE3 proteins, and LCE3A in particular, have defensin-like antimicrobial activity against a variety of bacterial taxa at low micromolar concentrations. No genotype-dependent effect was observed for the inside-out or outside-in physical skin barrier function. Our findings identify an unknown biological function for LCE3 proteins and suggest a role in epidermal host defense and LCE3B/C-del-mediated psoriasis risk.

Computational prediction of the optimal oligomeric state for membrane-inserted β-barrels of protegrin-1 and related mutants

Protegrin-1 is a widely studied 18-residue β-hairpin antimicrobial peptide. Evidence suggests that it acts via a β-barrel pore formation mechanism, but the exact number of peptides comprising the pore state is unknown. In this study, we performed molecular dynamics simulations of β-barrels of protegrin and three related mutants (v14v16l, v14v16a, and r4n) in NCNC parallel topology in implicit membrane pores of varying radius and curvature for oligomeric numbers 6-14. We then identified the optimal pore radius and curvature values for all constructs and determined the total effective energy and the translational and rotational entropic losses. These, along with an estimate of membrane deformation free energy from experimental line tension values, provided an estimate of the overall energetics of formation of each pore state. The results indicated that oligomeric numbers 7-13 are generally stable, allowing the possibility of a heterogeneous pore state. The optimal oligomeric state for protegrin is the nonamer, shifting to higher numbers for the mutants. Protegrin, v14v16l, and r4n are stable as membrane-inserted β-barrels, but v14v16a seems much less so because of its decreased hydrophobicity. Copyright © 2017 European Peptide Society and John Wiley & Sons, Ltd.

Guardians of the Gut: Enteric Defensins

Enteric defensins likely play a key role in the management of the human microbiome throughout development. The functional and mechanistic diversity of defensins is much greater than was initially thought. Defensin expression and overall Paneth cell physiology likely plays a key role in the development of colitis and other inflammatory or dysbiotic diseases of the gut. As our understanding of enteric defensins grows, their potential as tools of clinical intervention becomes more apparent. In this review, we focus on the function and activity of Paneth Cell defensins and highlight their role in disease.

Variations in the interaction of human defensins with Escherichia coli: Possible implications in bacterial killing

Human α and β-defensins are cationic antimicrobial peptides characterized by three disulfide bonds with a triple stranded β-sheet motif. It is presumed that interaction with the bacterial cell surface and membrane permeabilization by defensins is an important step in the killing process. In this study, we have compared interactions of three human α-defensins HNP3, HNP4, HD5 and human β-defensins HBD1-4 that are active against Escherichia coli, with its cell surface and inner membrane as well as negatively charged model membranes. We have also included the inactive α-defensin HD6 in the study. Among the α-defensins, HNP4, HD5 and HD6 were more effective in increasing the zeta potential as compared to HNP3. Among the β-defensins, HBD1 was the least effective in increasing the zeta potential. The zeta potential modulation data indicate variations in the surface charge neutralizing ability of α- and β-defensins. Comparison of E. coli inner membrane and model membrane permeabilizing abilities indicated that HD5, HD6 and HBD1 do not permeabilize membranes. Although HBD4 does not permeabilize model membranes, considerable damage to the inner membrane of E. coli is observed. Our data indicate that mammalian defensins do not kill E. coli by a simple mechanism involving membrane permeabilization though their antibacterial potencies are very similar.

Intracellular Targeting Mechanisms by Antimicrobial Peptides

Antimicrobial peptides (AMPs) are expressed in various living organisms as first-line host defenses against potential harmful encounters in their surroundings. AMPs are short polycationic peptides exhibiting various antimicrobial activities. The principal antibacterial activity is attributed to the membrane-lytic mechanism which directly interferes with the integrity of the bacterial cell membrane and cell wall. In addition, a number of AMPs form a transmembrane channel in the membrane by self-aggregation or polymerization, leading to cytoplasm leakage and cell death. However, an increasing body of evidence has demonstrated that AMPs are able to exert intracellular inhibitory activities as the primary or supportive mechanisms to achieve efficient killing. In this review, we focus on the major intracellular targeting activities reported in AMPs, which include nucleic acids and protein biosynthesis and protein-folding, protease, cell division, cell wall biosynthesis, and lipopolysaccharide inhibition. These multifunctional AMPs could serve as the potential lead peptides for the future development of novel antibacterial agents with improved therapeutic profiles.

Design of novel antimicrobial peptide dimer analogues with enhanced antimicrobial activity in vitro and in vivo by intermolecular triazole bridge strategy

Currently, antimicrobial peptides have attracted considerable attention because of their broad-sprectum activity and low prognostic to induce antibiotic resistance. In our study, for the first time, a series of side-chain hybrid dimer peptides J-AA (Anoplin-Anoplin), J-RR (RW-RW), and J-AR (Anoplin-RW) based on the wasp peptide Anoplin and the arginine- and tryptophan-rich hexapeptide RW were designed and synthesized by click chemistry, with the intent to improve the antimicrobial efficacy of peptides against bacterial pathogens. The results showed that all dimer analogues exhibited up to a 4-16 fold increase in antimicrobial activity compared to the parental peptides against bacterial strains. Furthermore, the antimicrobial activity was confirmed by time-killing kinetics assay with two strains which showed that these dimer analogues at 1, 2×MIC were rapidly bactericidal and reduced the initial inoculum significantly during the first 2-6h. Notably, dimer peptides showed synergy and additivity effects when used in combination with conventional antibiotics rifampin or penicillin respectively against the multidrug-resistant strains. In the Escherichia coli-infected mouse model, all of hybrid dimer analogues had significantly lower degree of bacterial load than the untreated control group when injected once i.p. at 5mg/kg. In addition, the infected mice by methicillin-resistant (MRSA) strain could be effectively treated with J-RR. All of dimer analogues had membrane-active action mode. And the membrane-dependent mode of action signifies that peptides functions freely and without regard to conventional resistant mechanisms. Circular dichroism analyses of all dimer analogues showed a general predominance of α-helix conformation in 50% trifluoroethanol (TFE). Additionally, the acute toxicities study indicated that J-RR or J-AR did not show the signs of toxicity when adult mice exposed to concentration up to 120mg/kg. The 50% lethal dose (LD₅₀) of J-AA was 53.6mg/kg. In conclusion, to design and synthesize side chain-hybrid dimer analogues via click chemistry may offer a new strategy for antibacterial therapeutic option.

Fluorescence and Absorbance Spectroscopy Methods to Study Membrane Perturbations by Antimicrobial Host Defense Peptides

Antimicrobial peptides (AMPs) are currently intensely studied because of their potential as new bactericidal and bacteriostatic agents. The mechanism of action of numerous AMPs involves the permeabilization of bacterial membranes. Several methods have been developed to study peptide-membrane interactions; in particular optical spectroscopy methods are widely used. The intrinsic fluorescence properties of the Trp indole ring in Trp-containing AMPs can be exploited by measuring the fluorescence blue shift and acrylamide-induced fluorescence quenching. One important aspect of such studies is the use of distinct models of the bacterial membrane, in most cases large unilamellar vesicles (LUVs) with different, yet well-defined, phospholipid compositions. Deploying LUVs that are preloaded with fluorescent dyes, such as calcein, also allows for the study of vesicle permeabilization by AMPs. In addition, experiments using genetically engineered live Escherichia coli cells can be used to distinguish between the effects of AMPs on the outer and inner membranes of gram-negative bacteria. In combination, these methods can provide a detailed insight into the mode of action of AMPs.

Bacterial Evasion of Host Antimicrobial Peptide Defenses

Antimicrobial peptides (AMPs), also known as host defense peptides, are small naturally occurring microbicidal molecules produced by the host innate immune response that function as a first line of defense to kill pathogenic microorganisms by inducing deleterious cell membrane damage. AMPs also possess signaling and chemoattractant activities and can modulate the innate immune response to enhance protective immunity or suppress inflammation. Human pathogens have evolved defense molecules and strategies to counter and survive the AMPs released by host immune cells such as neutrophils and macrophages. Here, we review the various mechanisms used by human bacterial pathogens to resist AMP-mediated killing, including surface charge modification, active efflux, alteration of membrane fluidity, inactivation by proteolytic digestion, and entrapment by surface proteins and polysaccharides. Enhanced understanding of AMP resistance at the molecular level may offer insight into the mechanisms of bacterial pathogenesis and augment the discovery of novel therapeutic targets and drug design for the treatment of recalcitrant multidrug-resistant bacterial infections.

Characterization of the antimicrobial peptide family defensins in the Tasmanian devil (Sarcophilus harrisii), koala (Phascolarctos cinereus), and tammar wallaby (Macropus eugenii)

Defensins comprise a family of cysteine-rich antimicrobial peptides with important roles in innate and adaptive immune defense in vertebrates. We characterized alpha and beta defensin genes in three Australian marsupials: the Tasmanian devil (Sarcophilus harrisii), koala (Phascolarctos cinereus), and tammar wallaby (Macropus eugenii) and identified 48, 34, and 39 defensins, respectively. One hundred and twelve have the classical antimicrobial peptides characteristics required for pathogen membrane targeting, including cationic charge (between 1+ and 15+) and a high proportion of hydrophobic residues (>30%). Phylogenetic analysis shows that gene duplication has driven unique and species-specific expansions of devil, koala, and tammar wallaby beta defensins and devil alpha defensins. Defensin genes are arranged in three genomic clusters in marsupials, whereas further duplications and translocations have occurred in eutherians resulting in four and five gene clusters in mice and humans, respectively. Marsupial defensins are generally under purifying selection, particularly residues essential for defensin structural stability. Certain hydrophobic or positively charged sites, predominantly found in the defensin loop, are positively selected, which may have functional significance in defensin-target interaction and membrane insertion.

Oestrous cycle-dependent equine uterine immune response to induced infectious endometritis

Infectious endometritis is a major cause of reduced pregnancy rates in horses. The objectives of this study were to establish a timeline of the innate immune response in the uterus of healthy horses and to investigate the oestrous cycle effect on this. Endometrial biopsies were collected from five horses before and at 3, 12, 24, 48 and 72 h after inoculation of Escherichia coli, once in oestrus and once in dioestrus. They were analysed by quantitative real-time PCR, microbiology and histology. Neutrophil numbers increased from very low levels in the absence of inflammation to severe neutrophilia 3 h after inoculation. The concentrations of mRNAs for Toll-like receptor (TLR)2, TLR4, NOD-like receptor NLRC5, tissue inhibitor of metallopeptidases 1 (TIMP1) and chemokines CCL2, CXCL9, CXCL10 and CXCL11 were all increased 3 h after inoculation of E. coli compared to levels detected prior to inoculation. Chemokine mRNA levels remained elevated for 48 h. Concentrations of mRNAs for the antimicrobial peptides equine β-defensin 1 (EBD1), lysozyme, secretory leukoprotease inhibitor (SLPI), lipocalin 2 (LCN2), lactoferrin and uteroferrin were increased between 3 and 12 h post inoculation. The gene for secreted phospholipase A₂ (sPLA₂) was expressed constitutively. P19 uterocalin mRNA levels were higher in dioestrus than in oestrus over the first 24 h of inflammation. Neutrophils and many innate immune genes responded rapidly to the introduction of E. coli into the uterus, while the oestrous cycle stage had only a relatively minor effect on the response to E. coli. This study has delineated a useful model of innate immunity in infectious endometritis of healthy animals.

Pyrazole derived ultra-short antimicrobial peptidomimetics with potent anti-biofilm activity

In this study, we report on the first chemical synthesis of ultra-short pyrazole-arginine based antimicrobial peptidomimetics derived from the newly synthesized N-alkyl/aryl pyrazole amino acids. Through the systematic tuning of hydrophobicity, charge, and peptide length, we identified the shortest peptide Py11 with the most potent antimicrobial activity. Py11 displayed greater antimicrobial activity against antibiotic-resistant bacteria, including MRSA, MDRPA, and VREF, which was approximately 2-4 times higher than that of melittin. Besides its higher selectivity (therapeutic index) toward bacterial cells than LL-37, Py11 showed highly increased proteolytic stability against trypsin digestion and maintained its antimicrobial activity in the presence of physiological salts. Interestingly, Py11 exhibited higher anti-biofilm activity against MDRPA compared to LL-37. The results from fluorescence spectroscopy and transmission electron microscopy (TEM) suggested that Py11 kills bacterial cells possibly by integrity disruption damaging the cell membrane, leading to the cytosol leakage and eventual cell lysis. Furthermore, Py11 displayed significant anti-inflammatory (endotoxin-neutralizing) activity by inhibiting LPS-induced production of nitric oxide (NO) and TNF-α. Collectively, our results suggest that Py11 may serve as a model compound for the design of antimicrobial and antisepsis agents.

Nematode Peptides with Host-Directed Anti-inflammatory Activity Rescue Caenorhabditis elegans from a Burkholderia pseudomallei Infection

Burkholderia pseudomallei, the causative agent of melioidosis, is among a growing number of bacterial pathogens that are increasingly antibiotic resistant. Antimicrobial peptides (AMPs) have been investigated as an alternative approach to treat microbial infections, as generally, there is a lower likelihood that a pathogen will develop resistance to AMPs. In this study, 36 candidate Caenorhabditis elegans genes that encode secreted peptides of <150 amino acids and previously shown to be overexpressed during infection by B. pseudomallei were identified from the expression profile of infected nematodes. RNA interference (RNAi)-based knockdown of 12/34 peptide-encoding genes resulted in enhanced nematode susceptibility to B. pseudomallei without affecting worm fitness. A microdilution test demonstrated that two peptides, NLP-31 and Y43C5A.3, exhibited anti-B. pseudomallei activity in a dose dependent manner on different pathogens. Time kill analysis proposed that these peptides were bacteriostatic against B. pseudomallei at concentrations up to 8× MIC90. The SYTOX green assay demonstrated that NLP-31 and Y43C5A.3 did not disrupt the B. pseudomallei membrane. Instead, gel retardation assays revealed that both peptides were able to bind to DNA and interfere with bacterial viability. In parallel, microscopic examination showed induction of cellular filamentation, a hallmark of DNA synthesis inhibition, of NLP-31 and Y43C5A.3 treated cells. In addition, the peptides also regulated the expression of inflammatory cytokines in B. pseudomallei infected macrophage cells. Collectively, these findings demonstrate the potential of NLP-31 and Y43C5A.3 as anti-B. pseudomallei peptides based on their function as immune modulators.

Review: Towards antibacterial strategies: studies on the mechanisms of interaction between antibacterial peptides and model membranes

Lipopolysaccharides (LPSs) play a dual role as inflammation-inducing and as membrane-forming molecules. The former role attracts significantly more attention from scientists, possibly because it is more closely related to sepsis and septic shock. This review aims to focus the reader's attention to the other role, the function of LPS as the major constituent of the outer layer of the outer membrane of Gram-negative bacteria, in particular those of enterobacterial strains. In this function, LPS is a necessary component of the cell envelope and guarantees survival of the bacterial organism. At the same time, it represents the first target for attacking molecules which may either be synthesized by the host's innate or adaptive immune system or administered to the human body. The interaction of these molecules with the outer membrane may not only directly cause the death of the bacterial organism, but may also lead to the release of LPS into the circulation. Here, we review membrane model systems and their application for the study of molecular mechanisms of interaction of peptides such as those of the human complement system, the bactericidal/permeability-increasing protein (BPI), cationic antibacterial peptide 18 kDa (CAP18) as an example of cathelicidins, defensins, and polymyxin B (PMB). Emphasis is on electrical measurements with a reconstitution system of the lipid matrix of the outer membrane which was established in the authors' laboratory as a planar asymmetric bilayer with one leaflet being composed solely of LPS and the other of the natural phospholipid mixture. The main conclusion, which can be drawn from these investigations, is that LPS and in general its negative charges are the dominant determinants for specific peptide—membrane interactions. However, the detailed mechanisms of interaction, which finally lead to bacterial killing, may involve further steps and differ for different antibacterial peptides.

Nonionic surfactants induced changes in cell characteristics and phenanthrene degradation ability of Sphingomonas sp. GY2B

Surfactant-mediated bioremediation has been widely applied in decontaminating PAH-polluted sites. However, the impacts of surfactants on the biodegradation of PAHs have been controversial in the past years. To gain a clear insight into the influencing mechanisms, three nonionic surfactants (Tween80, TritonX-100 and Brij30) were selected to systematically investigate their effects on cell surface properties (membrane permeability, functional groups and elements), cell vitality as well as subsequent phenanthrene degradation ability of Sphingomonas sp. GY2B. Results showed that biodegradation of phenanthrene was stimulated by Tween80, slightly inhibited by TritonX-100 and severely inhibited by Brij30, respectively. Positive effect of Tween80 may arise from its role as the additional carbon source for GY2B to increase bacterial growth and activity, as demonstrated by the increasing viable cells in Tween80 amended degradation systems determined by flow cytometry. Although TritonX-100 could inhibit bacterial growth and disrupt cell membrane, its adverse impacts on microbial cells were weaker than Brij30, which may result in its weaker inhibitive extent. Results from this study can provide a rational basis on selecting surfactants for enhancing bioremediation of PAHs.

Antimicrobial peptides as novel anti-tuberculosis therapeutics

Tuberculosis (TB), a disease caused by the human pathogen Mycobacterium tuberculosis, has recently joined HIV/AIDS as the world's deadliest infectious disease, affecting around 9.6 million people worldwide in 2014. Of those, about 1.2 million died from the disease. Resistance acquisition to existing antibiotics, with the subsequent emergence of Multi-Drug Resistant mycobacteria strains, together with an increasing economic burden, has urged the development of new anti-TB drugs. In this scope, antimicrobial peptides (AMPs), which are small, cationic and amphipathic peptides that make part of the innate immune system, now arise as promising candidates for TB treatment. In this review, we analyze the potential of AMPs for this application. We address the mechanisms of action, advantages and disadvantages over conventional antibiotics and how problems associated with its use may be overcome to boost their therapeutic potential. Additionally, we address the challenges of translational development from benchside to bedside, evaluate the current development pipeline and analyze the expected global impact from a socio-economic standpoint. The quest for more efficient and more compliant anti-TB drugs, associated with the great therapeutic potential of emerging AMPs and the rising peptide market, provide an optimal environment for the emergence of AMPs as promising therapies. Still, their pharmacological properties need to be enhanced and manufacturing-associated issues need to be addressed.

Design and Application of Antimicrobial Peptide Conjugates

Antimicrobial peptides (AMPs) are an interesting class of antibiotics characterized by their unique antibiotic activity and lower propensity for developing resistance compared to common antibiotics. They belong to the class of membrane-active peptides and usually act selectively against bacteria, fungi and protozoans. AMPs, but also peptide conjugates containing AMPs, have come more and more into the focus of research during the last few years. Within this article, recent work on AMP conjugates is reviewed. Different aspects will be highlighted as a combination of AMPs with antibiotics or organometallic compounds aiming to increase antibacterial activity or target selectivity, conjugation with photosensitizers for improving photodynamic therapy (PDT) or the attachment to particles, to name only a few. Owing to the enormous resonance of antimicrobial conjugates in the literature so far, this research topic seems to be very attractive to different scientific fields, like medicine, biology, biochemistry or chemistry.

Directed multistep biocatalysis using tailored permeabilized cells

: Recent developments in the field of biocatalysis using permeabilized cells are reviewed here, with a special emphasis on the newly emerging area of multistep biocatalysis using permeabilized cells. New methods of metabolic engineering using in silico network design and new methods of genetic engineering provide the opportunity to design more complex biocatalysts for the synthesis of complex biomolecules. Methods for the permeabilization of cells are thoroughly reviewed. We provide an extended review of useful available databases and bioinformatics tools, particularly for setting up genome-scale reconstructed networks. Examples described include phosphorylated carbohydrates, sugar nucleotides, and polyketides.

Antiparasitic peptides

: The most important parasitic diseases, malaria, leishmaniasis, trypanosomiasis, and schistosomiasis, are a great burden to mankind, threatening the life of millions of people worldwide and mostly affecting the poorest. Because drug resistance is increasing and vaccines are rarely available, novel chemotherapeutic compounds are necessary in order to treat these devastating diseases. Insects serve as vectors of many human parasitic diseases and have been shown to express a huge variety of antimicrobial peptides (AMPs). Therefore, research activity on insect-derived AMPs has been increasing in the last 40 years. This chapter summarizes the current state of research on the possible role of AMPs as potential chemotherapeutic compounds against human parasitic diseases. As a representative antimicrobial peptide with antiparasitic activity, the structure of insect defensin A is shown [PDB accession code: 1ICA]. The molecule is surrounded by schematic representations of the human pathogenic parasites Plasmodium, Leishmania and Trypanosoma.

Radiotherapy for oral cancer decreases the cutaneous expression of host defence peptides

INTRODUCTION

Bacterial resistance against antibiotics has become an increasing challenge in the treatment of cutaneous infections. Consequences can be severe, especially in infected wounds following previous local radiotherapy. Certain endogenous peptide antibiotics, the host defence peptides (HDPs), exhibit broad-spectrum antimicrobial activity and promote wound healing. Their use as supplements to conventional antibiotics is a current topic of discussion; however, knowledge of their quantities in healthy and compromised tissue is a prerequisite for such discussion. To date, no data concerning HDP quantities in irradiated skin are available.

METHODS

Expression profiles of the genes encoding HDPs, namely human beta-defensin-1 (DEFB1, hBD-1), beta-defensin-2 (DEFB4A, hBD-2), beta-defensin-3 (DEFB103, hBD-3) and S100A7, were assessed in samples of non-irradiated and irradiated neck.

RESULTS

A reduction in the expression of all of the examined genes was observed in irradiated skin when compared with non-irradiated skin (statistically significant in the case of S100A7, P = 0.013). Immunohistochemistry revealed differences in HDP distribution with respect to the epithelial layers.

CONCLUSION

The study demonstrates a significant reduction in HDP gene expression in neck skin as a result of radiotherapy. These findings might represent a starting point for novel treatments of cutaneous infections in irradiated patients, such as topical supplementation of synthetic HDP.

Neutrophil-derived alpha defensins control inflammation by inhibiting macrophage mRNA translation

Neutrophils are the first and most numerous cells to arrive at the site of an inflammatory insult and are among the first to die. We previously reported that alpha defensins, released from apoptotic human neutrophils, augmented the antimicrobial capacity of macrophages while also inhibiting the biosynthesis of proinflammatory cytokines. In vivo, alpha defensin administration protected mice from inflammation, induced by thioglychollate-induced peritonitis or following infection withSalmonella entericaserovar Typhimurium. We have now dissected the antiinflammatory mechanism of action of the most abundant neutrophil alpha defensin, Human Neutrophil Peptide 1 (HNP1). Herein we show that HNP1 enters macrophages and inhibits protein translation without inducing the unfolded-protein response or affecting mRNA stability. In a cell-free in vitro translation system, HNP1 powerfully inhibited both cap-dependent and cap-independent mRNA translation while maintaining mRNA polysomal association. This is, to our knowledge, the first demonstration of a peptide released from one cell type (neutrophils) directly regulating mRNA translation in another (macrophages). By preventing protein translation, HNP1 functions as a "molecular brake" on macrophage-driven inflammation, ensuring both pathogen clearance and the resolution of inflammation with minimal bystander tissue damage.

The role of galectin-4 in physiology and diseases

Galectin-4, a tandem repeat member of the β-galactoside-binding proteins, possesses two carbohydrate-recognition domains (CRD) in a single peptide chain. This lectin is mostly expressed in epithelial cells of the intestinal tract and secreted to the extracellular. The two domains have 40% similarity in amino acid sequence, but distinctly binding to various ligands. Just because the two domains bind to different ligands simultaneously, galectin-4 can be a crosslinker and crucial regulator in a large number of biological processes. Recent evidence shows that galectin-4 plays an important role in lipid raft stabilization, protein apical trafficking, cell adhesion, wound healing, intestinal inflammation, tumor progression, etc. This article reviews the physiological and pathological features of galectin-4 and its important role in such processes.

Identification of EnvC and Its Cognate Amidases as Novel Determinants of Intrinsic Resistance to Cationic Antimicrobial Peptides

Cationic antimicrobial peptides (CAMPs) are an essential part of the innate immune system. Some Gram-negative enteric pathogens, such as Salmonella enterica, show intrinsic resistance to CAMPs. However, the molecular basis of intrinsic resistance is poorly understood, largely due to a lack of information about the genes involved. In this study, using a microarray-based genomic technique, we screened the Keio collection of 3,985 Escherichia coli mutants for altered susceptibility to human neutrophil peptide 1 (HNP-1) and identified envC and zapB as novel genetic determinants of intrinsic CAMP resistance. In CAMP killing assays, an E. coli ΔenvC_Ec or ΔzapB_Ec mutant displayed a distinct profile of increased susceptibility to both LL-37 and HNP-1. Both mutants, however, displayed wild-type resistance to polymyxin B and human β-defensin 3 (HBD3), suggesting that the intrinsic resistance mediated by EnvC or ZapB is specific to certain CAMPs. A corresponding Salmonella ΔenvC_Se mutant showed similarly increased CAMP susceptibility. The envC mutants of both E. coli and S. enterica displayed increased surface negativity and hydrophobicity, which partly explained the increased CAMP susceptibility. However, the ΔenvC_Ec mutant, but not the ΔenvC_Se mutant, was defective in outer membrane permeability, excluding this defect as a common factor contributing to the increased CAMP susceptibility. Animal experiments showed that the Salmonella ΔenvC_Se mutant had attenuated virulence. Taken together, our results indicate that the role of envC in intrinsic CAMP resistance is likely conserved among Gram-negative enteric bacteria, demonstrate the importance of intrinsic CAMP resistance for full virulence of S. enterica, and provide insight into distinct mechanisms of action of CAMPs.

Reduction Impairs the Antibacterial Activity but Benefits the LPS Neutralization Ability of Human Enteric Defensin 5

Oxidized human defensin 5 (HD5_OX), a Paneth cell-secreted antibacterial peptide with three characteristic disulfide bonds, protects the host from invasion by morbigenous microbes in the small intestine. HD5_OX can be reduced by thioredoxin (Trx) in vitro, while the biochemical properties of the reduced linear peptide, HD5_RED, remain unclear. Here, we first confirm that HD5_RED does exist in vivo. Furthermore, we reveal that the recruitment of HD5_RED to the outer membrane of Gram-negative bacteria and to the anionic lipid A is lower than that of HD5_OX, and HD5_RED is less efficient in penetrating bacterial outer and inner membranes and inducing membrane depolarization, which confers an attenuated antibacterial activity to HD5_RED. However, due to its higher structural flexibility, the binding of HD5_RED to bacterial lipopolysaccharide (LPS) is markedly stronger than that of HD5_OX. Consequently, HD5_RED is more effective in suppressing the production of the pro-inflammatory cytokine TNF-α in LPS-stimulated macrophages by blocking the interaction between LPS and LPS-binding protein, thus suggesting that HD5_RED might act as a scavenger to neutralize LPS in the gut. This study provides insights into the antibacterial and immunoregulatory effects of HD5_RED and expands the known repertoire of the enteric defensins.

The association of defensin HNP-2 with negatively charged membranes: A combined fluorescence and linear dichroism study

The association of defensin HNP-2 with negatively charged membranes has been studied using a new approach that combines fluorescence and linear dichroism (LD) spectroscopies with simulated LD spectra in order to characterise the binding kinetics and bound configurations of the peptide. Binding to membranes composed of mixtures of diacylglycerophosphocholines (PC) with either diacylglycerophosphoglycerol (PG) or diacylglycerophosphoserine (PS) was conducted at lipid:peptide ratios that yielded binding, but not membrane fusion. HNP-2 association with membranes under these conditions was a 2 stage-process, with both stages exhibiting first order kinetics. The fast initial step, with a half-life of < 1 min, was followed by a slower step with a half-life of > 3 min. Conversion between the states was estimated to have an enthalpy of activation of approximately 10 kJ mol(-1) and an entropy of activation of -0.2 kJ K mol(-1). LD spectra corresponding to each of the membrane bound states were generated by non-linear regression using a standard kinetic model. These spectra are interpreted in comparison with spectra calculated using the program Dichrocalc and reveal that the peptide associates with membranes in a small number of stable configurations. All of these configurations have a significant proportion of β-sheet structure residing in the plane of the membrane. Two configurations support structures previously proposed for defensins in membranes.

Antimicrobial activity of human α-defensin 5 and its linear analogs: N-terminal fatty acylation results in enhanced antimicrobial activity of the linear analogs

Human α-defensin 5 (HD5) exhibits broad spectrum antimicrobial activity and plays an important role in mucosal immunity of the small intestine. Although there have been several studies, the structural requirements for activity and mechanism of bacterial killing is yet to be established unequivocally. In this study, we have investigated the antimicrobial activity of HD5 and linear analogs. Cysteine deletions attenuated the antibacterial activity considerably. Candidacidal activity was affected to a lesser extent. Fatty acid conjugated linear analogs showed antimicrobial activity comparable activity to HD5. Effective surface charge neutralization of bacteria was observed for HD5 as compared to the non-fatty acylated linear analogs. Our results show that HD5 and non-fatty acylated linear analogs enter the bacterial cytoplasm without causing damage to the bacterial inner membrane. Although fatty acylated peptides exhibited antimicrobial activity comparable to HD5, their mechanism of action involved permeabilization of the Escherichia coli inner membrane. HD5 and analogs had the ability to bind plasmid DNA. HD5 had greater binding affinity to plasmid DNA as compared to the analogs. The three dimensional structure of HD5 favors greater interaction with the bacterial cell surface and also with DNA. Antibacterial activity of HD5 involves entry into bacterial cytoplasm and binding to DNA which would result in shut down of the bacterial metabolism leading to cell death. We show how a moderately active linear peptide derived from the α-defensin HD5 can be engineered to enhance antimicrobial activity almost comparable to the native peptide.

Peptides and Peptidomimetics for Antimicrobial Drug Design

The purpose of this paper is to introduce and highlight a few classes of traditional antimicrobial peptides with a focus on structure-activity relationship studies. After first dissecting the important physiochemical properties that influence the antimicrobial and toxic properties of antimicrobial peptides, the contributions of individual amino acids with respect to the peptides antibacterial properties are presented. A brief discussion of the mechanisms of action of different antimicrobials as well as the development of bacterial resistance towards antimicrobial peptides follows. Finally, current efforts on novel design strategies and peptidomimetics are introduced to illustrate the importance of antimicrobial peptide research in the development of future antibiotics.

Ultrastructural study on the morphological changes in indigenous bacteria of mucous layer and chyme throughout the rat intestine

Indigenous bacteria in the alimentary tract are exposed to various bactericidal peptides and digestive enzymes, but the viability status and morphological changes of indigenous bacteria are unclear. Therefore, the present study aimed to ultrastructurally clarify the degeneration and viability status of indigenous bacteria in the rat intestine. The majority of indigenous bacteria in the ileal mucous layer possessed intact cytoplasm, but the cytoplasm of a few bacteria contained vacuoles. The vacuoles were more frequently found in bacteria of ileal chyme than in those of ileal mucous layer and were found in a large majority of bacteria in both the mucous layer and chyme throughout the large intestine. In the dividing bacteria of the mucous layer and chyme throughout the intestine, the ratio of area occupied by vacuoles was almost always less than 10%. Lysis or detachment of the cell wall in the indigenous bacteria was more frequently found in the large intestine than in the ileum, whereas bacterial remnants, such as cell walls, were distributed almost evenly throughout the intestine. In an experimental control of long-time-cultured Staphylococcus epidermidis on agar, similar vacuoles were also found, but cell-wall degeneration was never observed. From these findings, indigenous bacteria in the mucous layer were ultrastructurally confirmed to be the source of indigenous bacteria in the chyme. Furthermore, the results suggested that indigenous bacteria were more severely degenerated toward the large intestine and were probably degraded in the intestine.

Human β-defensin 4 with non-native disulfide bridges exhibit antimicrobial activity

Human defensins play multiple roles in innate immunity including direct antimicrobial killing and immunomodulatory activity. They have three disulfide bridges which contribute to the stability of three anti-parallel β-strands. The exact role of disulfide bridges and canonical β-structure in the antimicrobial action is not yet fully understood. In this study, we have explored the antimicrobial activity of human β-defensin 4 (HBD4) analogs that differ in the number and connectivity of disulfide bridges. The cysteine framework was similar to the disulfide bridges present in μ-conotoxins, an unrelated class of peptide toxins. All the analogs possessed enhanced antimicrobial potency as compared to native HBD4. Among the analogs, the single disulfide bridged peptide showed maximum potency. However, there were no marked differences in the secondary structure of the analogs. Subtle variations were observed in the localization and membrane interaction of the analogs with bacteria and Candida albicans, suggesting a role for disulfide bridges in modulating their antimicrobial action. All analogs accumulated in the cytosol where they can bind to anionic molecules such as nucleic acids which would affect several cellular processes leading to cell death. Our study strongly suggests that native disulfide bridges or the canonical β-strands in defensins have not evolved for maximal activity but they play important roles in determining their antimicrobial potency.

Visualizing attack of Escherichia coli by the antimicrobial peptide human defensin 5

Human α-defensin 5 (HD5) is a 32-residue cysteine-rich host-defense peptide that exhibits broad-spectrum antimicrobial activity and contributes to innate immunity in the human gut and other organ systems. Despite many years of investigation, its antimicrobial mechanism of action remains unclear. In this work, we report that HD5ox, the oxidized form of this peptide that exhibits three regiospecific disulfide bonds, causes distinct morphological changes to Escherichia coli and other Gram-negative microbes. These morphologies include bleb formation, cellular elongation, and clumping. The blebs are up to ∼1 μm wide and typically form at the site of cell division or cell poles. Studies with E. coli expressing cytoplasmic GFP reveal that HD5ox treatment causes GFP emission to localize in the bleb. To probe the cellular uptake of HD5ox and subsequent localization, we describe the design and characterization of a fluorophore-HD5 conjugate family. By employing these peptides, we demonstrate that fluorophore-HD5ox conjugates harboring the rhodamine and coumarin fluorophores enter the E. coli cytoplasm. On the basis of the fluorescence profiles, each of these fluorophore-HD5ox conjugates localizes to the site of cell division and cell poles. These studies support the notion that HD5ox, at least in part, exerts its antibacterial activity against E. coli and other Gram-negative microbes in the cytoplasm.

N-Terminal fatty acylation of peptides spanning the cationic C-terminal segment of bovine β-defensin-2 results in salt-resistant antibacterial activity

Peptides spanning the C-terminal segment of bovine-β-defensin-2 (BNBD-2) rich in cationic amino acids, show antimicrobial activity. However, they exhibit considerably reduced activity at physiological concentration of NaCl. In the present study, we have investigated whether N-terminal acylation (acetylation and palmitoylation) of these peptides would result in improved antimicrobial activity. N-terminal palmitoylation though increased hydrophobicity of the peptides, did not enhance antimicrobial potency. However, antibacterial activity of these peptides was not attenuated by NaCl. Biophysical studies on the palmitoylated peptides have indicated that antibacterial activity in the presence of NaCl arises due to the ability of the peptides to interact with membranes more effectively. These peptides showed hemolytic activity which was attenuated considerably in the presence of serum and lipid vesicles. In defensin related peptides, fatty acylation would be a convenient way to generate analogs that are active in the presence of salt.

New role for human α-defensin 5 in the fight against hypervirulent Clostridium difficile strains

Clostridium difficile infection (CDI), one of the most common hospital-acquired infections, is increasing in incidence and severity with the emergence and diffusion of hypervirulent strains. CDI is precipitated by antibiotic treatment that destroys the equilibrium of the gut microbiota. Human α-defensin 5 (HD5), the most abundant enteric antimicrobial peptide, is a key regulator of gut microbiota homeostasis, yet it is still unknown if C. difficile, which successfully evades killing by other host microbicidal peptides, is susceptible to HD5. We evaluated, by means of viability assay, fluorescence-activated cell sorter (FACS) analysis, and electron microscopy, the antimicrobial activities of α-defensins 1 and 5 against a panel of C. difficile strains encompassing the most prevalent epidemic and hypervirulent PCR ribotypes in Europe (012, 014/020, 106, 018, 027, and 078). Here we show that (i) concentrations of HD5 within the intestinal physiological range produced massive C. difficile cell killing; (ii) HD5 bactericidal activity was mediated by membrane depolarization and bacterial fragmentation with a pattern of damage peculiar to C. difficile bacilli, compared to commensals like Escherichia coli and Enterococcus faecalis; and (iii) unexpectedly, hypervirulent ribotypes were among the most susceptible to both defensins. These results support the notion that HD5, naturally present at very high concentrations in the mucosa of the small intestine, could indeed control the very early steps of CDI by killing C. difficile bacilli at their germination site. As a consequence, HD5 can be regarded as a good candidate for the containment of hypervirulent C. difficile strains, and it could be exploited in the therapy of CDI and relapsing C. difficile-associated disease.

Antimicrobial peptides: a new class of antimalarial drugs?

A range of antimicrobial peptides (AMP) exhibit activity on malaria parasites, Plasmodium spp., in their blood or mosquito stages, or both. These peptides include a diverse array of both natural and synthetic molecules varying greatly in size, charge, hydrophobicity, and secondary structure features. Along with an overview of relevant literature reports regarding AMP that display antiplasmodial activity, this review makes a few considerations about those molecules as a potential new class of antimalarial drugs.

Expression pattern of arenicins-the antimicrobial peptides of polychaete Arenicola marina

Immune responses of invertebrate animals are mediated through innate mechanisms, among which production of antimicrobial peptides play an important role. Although evolutionary Polychaetes represent an interesting group closely related to a putative common ancestor of other coelomates, their immune mechanisms still remain scarcely investigated. Previously our group has identified arenicins-new antimicrobial peptides of the lugworm Arenicola marina, since then these peptides were thoroughly characterized in terms of their structure and inhibitory potential. In the present study we addressed the question of the physiological functions of arenicins in the lugworm body. Using molecular and immunocytochemical methods we demonstrated that arencins are expressed in the wide range of the lugworm tissues-coelomocytes, body wall, extravasal tissue and the gut. The expression of arenicins is constitutive and does not depend on stimulation of various infectious stimuli. Most intensively arenicins are produced by mature coelomocytes where they function as killing agents inside the phagolysosome. In the gut and the body wall epithelia arenicins are released from producing cells via secretion as they are found both inside the epithelial cells and in the contents of the cuticle. Collectively our study showed that arenicins are found in different body compartments responsible for providing a first line of defense against infections, which implies their important role as key components of both epithelial and systemic branches of host defense.

A bacterial mutant library as a tool to study the attack of a defensin peptide

Defensin attack! Here we report the screening of human defensin 5 against the Keio Collection of E. coli strains. The results of this screen further our understanding of how this important hostdefense peptide kills bacteria and how bacteria protect themselves against the attack from the human host.

Proline-rich antimicrobial peptides: potential therapeutics against antibiotic-resistant bacteria

The increasing resistance of pathogens to antibiotics causes a huge clinical burden that places great demands on academic researchers and the pharmaceutical industry for resolution. Antimicrobial peptides, part of native host defense, have emerged as novel potential antibiotic alternatives. Among the different classes of antimicrobial peptides, proline-rich antimicrobial peptides, predominantly sourced from insects, have been extensively investigated to study their specific modes of action. In this review, we focus on recent developments in these peptides. They show a variety of modes of actions, including mechanism shift at high concentration, non-lytic mechanisms, as well as possessing different intracellular targets and lipopolysaccharide binding activity. Furthermore, proline-rich antimicrobial peptides display the ability to not only modulate the immune system via cytokine activity or angiogenesis but also possess properties of penetrating cell membranes and crossing the blood brain barrier suggesting a role as potential novel carriers. Ongoing studies of these peptides will likely lead to the development of more potent antimicrobial peptides that may serve as important additions to the armoury of agents against bacterial infection and drug delivery.

Relationship between pouch microbiota and pouchitis following restorative proctocolectomy for ulcerative colitis

Restorative proctocolectomy with ileal pouch-anal anastomosis (IPAA) has become the surgical treatment of choice for many patients with medically refractory ulcerative colitis (UC) and familial adenomatous polyposis (FAP). UC patients with IPAA (UC-IPAA) are, nevertheless, susceptible to inflammatory and noninflammatory sequelae such as pouchitis, which is only rarely noted in FAP patients with IPAA. Pouchitis is the most frequent long-term complication of UC-IPAA patients, with a cumulative prevalence of up to 50%. Although the aetiology of pouchitis remains unclear, accumulating evidence suggests that a dysbiosis of the pouch microbiota and an abnormal mucosal immune response are implicated in its pathogenesis. Studies using culture and molecular techniques have detected a dysbiosis of the pouch microbiota in patients with pouchitis. Risk factors, genetic associations, and serological markers suggest that interactions between the host immune response and the pouch microbiota underlie the aetiology of this idiopathic inflammatory condition. This systematic review focuses on the dysbiosis of the microbiota that inhabit the pouch in UC and FAP patients and its interaction with the mucosal immune system. A meta-analysis was not attempted due to the highly heterogeneous microbiota composition and the different detection methods used by the various studies. Although no specific bacterial species, genus, or family has as yet been identified as pathogenic, there is evidence that a dysbiosis characterized by decreased gut microbiota diversity in UC-IPAA patients may, in genetically predisposed subjects, lead to aberrant mucosal immune regulation triggering an inflammatory process.

Inferring mechanisms of copy number change from haplotype structures at the human DEFA1A3 locus

BACKGROUND

The determination of structural haplotypes at copy number variable regions can indicate the mechanisms responsible for changes in copy number, as well as explain the relationship between gene copy number and expression. However, obtaining spatial information at regions displaying extensive copy number variation, such as the DEFA1A3 locus, is complex, because of the difficulty in the phasing and assembly of these regions. The DEFA1A3 locus is intriguing in that it falls within a region of high linkage disequilibrium, despite its high variability in copy number (n = 3-16); hence, the mechanisms responsible for changes in copy number at this locus are unclear.

RESULTS

In this study, a region flanking the DEFA1A3 locus was sequenced across 120 independent haplotypes with European ancestry, identifying five common classes of DEFA1A3 haplotype. Assigning DEFA1A3 class to haplotypes within the 1000 Genomes project highlights a significant difference in DEFA1A3 class frequencies between populations with different ancestry. The features of each DEFA1A3 class, for example, the associated DEFA1A3 copy numbers, were initially assessed in a European cohort (n = 599) and replicated in the 1000 Genomes samples, showing within-class similarity, but between-class and between-population differences in the features of the DEFA1A3 locus. Emulsion haplotype fusion-PCR was used to generate 61 structural haplotypes at the DEFA1A3 locus, showing a high within-class similarity in structure.

CONCLUSIONS

Structural haplotypes across the DEFA1A3 locus indicate that intra-allelic rearrangement is the predominant mechanism responsible for changes in DEFA1A3 copy number, explaining the conservation of linkage disequilibrium across the locus. The identification of common structural haplotypes at the DEFA1A3 locus could aid studies into how DEFA1A3 copy number influences expression, which is currently unclear.

Influence of green and gold kiwifruit on indices of large bowel function in healthy rats

The effects of kiwifruit on large bowel health were investigated in healthy rats. Four-week old Sprague-Dawley rats were given diets containing 10% homogenized green kiwifruit, gold kiwifruit or 10% glucose solution (control) over 4 or 6 wk. Green kiwifruit increased the fecal output compared to control. Growth of certain bacterial species in cecum was influenced by both green and gold kiwifruit. A significant increase in cecal Lachnospiraceae in rats fed the green kiwifruit diet was observed at week 4. At week 6, green and gold kiwifruit diets assisted in improving colonic barrier function by upregulating the expression of mucin (MUC)-2, MUC3, Toll-like receptor (TLR)-4 or trefoil factor-3 genes. Gold kiwifruit consumption increased the colonic goblet cells per crypt at week 6. Significant negative correlations between E. coli and β-defensin 1 and TLR4 expression were observed. Consuming green and gold kiwifruit for 6 wk significantly altered the biomarkers of large bowel health; indicating that regularly consuming kiwifruit helps attain optimal digestive health.

Glutamine Improves Innate Immunity and Prevents Bacterial Enteroinvasion During Parenteral Nutrition

BACKGROUND

Patients receiving parenteral nutrition (PN) are at increased risk of infectious complications compared with enteral feeding, which is in part explained by impaired mucosal immune function during PN. Adding glutamine (GLN) to PN has improved outcome in some clinical patient groups. Although GLN improves acquired mucosal immunity, its effect on innate mucosal immunity (defensins, mucus, lysozymes) has not been investigated.

METHODS

Forty-eight hours following venous cannulation, male Institute of Cancer Research mice were randomized to chow (n = 10), PN (n = 12), or PN + GLN (n = 13) for 5 days. Small intestine tissue and luminal fluid were collected for mucin 2 (MUC2), lysozyme, cryptdin 4 analysis, and luminal interleukin (IL)-4, IL-10, and IL-13 level measurement. Tissue was also harvested for ex vivo intestinal segment culture to assess tissue susceptibility to enteroinvasive Escherichia coli.

RESULTS

In both luminal and tissue samples, PN reduced MUC2 and lysozyme (P < .0001, respectively) compared with chow, whereas GLN addition increased MUC2 and lysozyme (luminal, P < .05; tissue, P < .0001, respectively) compared with PN alone. PN significantly suppressed cryptdin 4 expression, while GLN supplementation significantly enhanced expression. IL-4, IL-10, and IL-13 decreased significantly with PN compared with chow, whereas GLN significantly increased these cytokines compared with PN. Functionally, bacterial invasion increased with PN compared with chow (P < .05), while GLN significantly decreased enteroinvasion to chow levels (P < .05).

CONCLUSIONS

GLN-supplemented PN improves innate immunity and resistance to bacterial mucosal invasion lost with PN alone. This work confirms a clinical rationale for providing glutamine for the protection of the intestinal mucosa.

Two interdependent mechanisms of antimicrobial activity allow for efficient killing in nylon-3-based polymeric mimics of innate immunity peptides

Novel synthetic mimics of antimicrobial peptides have been developed to exhibit structural properties and antimicrobial activity similar to those of natural antimicrobial peptides (AMPs) of the innate immune system. These molecules have a number of potential advantages over conventional antibiotics, including reduced bacterial resistance, cost-effective preparation, and customizable designs. In this study, we investigate a family of nylon-3 polymer-based antimicrobials. By combining vesicle dye leakage, bacterial permeation, and bactericidal assays with small-angle X-ray scattering (SAXS), we find that these polymers are capable of two interdependent mechanisms of action: permeation of bacterial membranes and binding to intracellular targets such as DNA, with the latter necessarily dependent on the former. We systemically examine polymer-induced membrane deformation modes across a range of lipid compositions that mimic both bacteria and mammalian cell membranes. The results show that the polymers' ability to generate negative Gaussian curvature (NGC), a topological requirement for membrane permeation and cellular entry, in model Escherichia coli membranes correlates with their ability to permeate membranes without complete membrane disruption and kill E. coli cells. Our findings suggest that these polymers operate with a concentration-dependent mechanism of action: at low concentrations permeation and DNA binding occur without membrane disruption, while at high concentrations complete disruption of the membrane occurs. This article is part of a Special Issue entitled: Interfacially Active Peptides and Proteins. Guest Editors: William C. Wimley and Kalina Hristova.

Heparin binding carboxypeptidase E protein exhibits antibacterial activity in human semen

Carboxypeptidase E (CPE) cleaves basic amino acid residues at the C-terminal end and involves in the biosynthesis of numerous peptide hormones and neurotransmitters. It was purified from human seminal plasma by ion exchange, heparin affinity and gel filtration chromatography followed by identification through SDS-PAGE and MALDI-TOF/MS analysis, which was further confirmed by western blotting. CPE was characterized as glycoprotein by Periodic Acid Schiff (PAS) staining and treating with deglycosylating enzyme N-glycosidase F. The interaction of CPE with heparin was illustrated by surface plasmon resonance (SPR) and in silico interaction analysis. The association constant (KA) and dissociation constant (KD) of CPE with heparin was determined by SPR and found to be 1.06 × 10(5)M and 9.46 × 10(-6)M, respectively. It was detected in human spermatozoa also by western blotting using mouse anti-CPE primary antibody. 20-100 μg/ml concentration of CPE was observed as highly effective in killing Escherichia coli by colony forming unit (CFU) assay. We suggest that CPE might act not only in the innate immunity of male reproductive tract but also regulate sperm fertilization process by interacting heparin.

The potential role of increasing the release of mouse β- defensin-14 in the treatment of osteomyelitis in mice: a primary study

Mammalian β-defensins are small cationic peptides that have been implicated in mediating innate immune defenses against microbial infection. Mouse β-defensin-14 (MBD-14), based on structural and functional similarities, appears to be an ortholog of human β-defensin-3 (HBD-3). Previous studies identified signaling pathway p38 mitogen-activated protein kinase (MAPK) that contributed to the expression of MBD-14 in mouse osteoblasts upon contacted with methicillin-resistance Staphylococcus aureus (MRSA) supernatant, which provided a theoretical basis as a promising therapeutic target in the treatment of intramedullary infection with MRSA in vivo. In this study, the medullary cavities of tibiae were contaminated with MRSA 10(3) colony forming units and different doses of p38 MAPK agonists anisomycin were followed as group III or IV in 30 mice. Fifteen animals that received phosphate- buffered saline served as group II and 15 mice were not contaminated with MRSA and received phosphate-buffered saline served as controls (group I). Follow-up was 7 days. In day 1, day 4 and day 7 postoperatively, infection was evaluated by blood routine, microbiological and histological analyses after sacrifice. All animals of group II developed microbiological and histological signs of infection. Histological signs of infection, white blood counts and cultures of group III and IV showed significantly reduced bacterial growth compared to cultures of group II. Simultaneously, different doses of anisomycin significantly induced the expression of osteoblast-associated genes, including alkaline phosphatase, osteocalcin and collagen type I. In addition, the expression of HBD-3 in human interfacial membranes around infected periprosthetic joint by staphylococcus contaminated was evaluated, and the expression pattern changed with significant induction of HBD-3 in infected periprosthetic joint compared with aseptic loosening under inflammatory conditions. Our primary study indicated that the potential antibacterial role of increased MBD-14 in the osteomyelitis mouse model.

Microbicidal effects of α- and θ-defensins against antibiotic-resistant Staphylococcus aureus and Pseudomonas aeruginosa

Antibiotic-resistant bacterial pathogens threaten public health. Because many antibiotics target specific bacterial enzymes or reactions, corresponding genes may mutate under selection and lead to antibiotic resistance. Accordingly, antimicrobials that selectively target overall microbial cell integrity may offer alternative approaches to therapeutic design. Naturally occurring mammalian α- and θ-defensins are potent, non-toxic microbicides that may be useful for treating infections by antibiotic-resistant pathogens because certain defensin peptides disrupt bacterial, but not mammalian, cell membranes. To test this concept, clinical isolates of methicillin-resistant Staphylococcus aureus (MRSA), including vancomycin heteroresistant strains, and ciprofloxacin-resistant Pseudomonas aeruginosa (Cip(R)-PA) were tested for sensitivity to α-defensins Crp-4, RMAD-4 and HNPs 1-3, and to RTD-1, macaque θ-defensin-1. In vitro, 3 μM Crp-4, RMAD-4 and RTD-1 reduced MRSA cell survival by 99%, regardless of vancomycin susceptibility. For PA clinical isolates that differ in fluoroquinolone resistance and virulence phenotype, peptide efficacy was independent of strain ciprofloxacin resistance, site of isolation or virulence factor expression. Thus, Crp-4, RMAD-4 and RTD-1 are effective in vitro antimicrobials against clinical isolates of MRSA and Cip(R)-PA, perhaps providing templates for development of α- and θ-defensin-based microbicides against antibiotic resistant or virulent infectious agents.