Role of Antimicrobial Peptides in Immunity of Parasitic Leeches

The review summarizes the current state of knowledge about leech immunity, with emphasis on the special role of antimicrobial peptides (AMPs), and highlights the wide variety of primary AMP structures, which seem to correlate with a variety of life strategies and the ecology of ectoparasites. Antimicrobial proteins and AMPs are a diverse class of natural molecules that are produced in all living organisms in response to an attack by a pathogen and are essential components of the immune system. AMPs can have a wide range of antibiotic activities against foreign and opportunistic bacteria, fungi, and viruses. AMPs play an important role in selection of colonizing bacterial symbionts, thus helping multicellular organisms to cope with certain environmental problems. AMPs are especially important for invertebrates, which lack an adaptive immune system. Although many AMPs are similar in physicochemical properties (a total length from 10 to 100 amino acids, a positive total charge, or a high cysteine content), their immunomodulatory activities are specific for each AMP type.

Analysis of a gene family for PDF-like peptides from Arabidopsis

Plant defensins are small, basic peptides that have a characteristic three-dimensional folding pattern which is stabilized by four disulfide bridges. We show here that Arabidopsis contains in addition to the proper plant defensins a group of 9 plant defensin-like (PdfL) genes. They are all expressed at low levels while GUS fusions of the promoters showed expression in most tissues with only minor differences. We produced two of the encoded peptides in E. coli and tested the antimicrobial activity in vitro. Both were highly active against fungi but had lower activity against bacteria. At higher concentrations hyperbranching and swollen tips, which are indicative of antimicrobial activity, were induced in Fusarium graminearum by both peptides. Overexpression lines for most PdfL genes were produced using the 35S CaMV promoter to study their possible in planta function. With the exception of PdfL4.1 these lines had enhanced resistance against F. oxysporum. All PDFL peptides were also transiently expressed in Nicotiana benthamiana leaves with agroinfiltration using the pPZP3425 vector. In case of PDFL1.4 this resulted in complete death of the infiltrated tissues after 7 days. All other PDFLs resulted only in various degrees of small necrotic lesions. In conclusion, our results show that at least some of the PdfL genes could function in plant resistance.

Potential role of a series of lysine-/leucine-rich antimicrobial peptide in inhibiting lipopolysaccharide-induced inflammation

Antimicrobial peptides have broad-spectrum killing activities against bacteria, enveloped viruses, fungi and several parasites via cell membrane permeation and exhibit primarily immunomodulatory and anti-infective functions in their interactions with host cells. However, the mechanism underlying their anti-inflammatory activity remains to be elucidated. L-K6, an analog of temporin-1CEb isolated from the skin secretion of Rana chensinensis, has demonstrated a wide range of antimicrobial activities against gram-negative and gram-positive bacteria. In this study, the potent anti-inflammatory mechanism of L-K6 and its analogs in lipopolysaccharide (LPS)-stimulated human macrophage U937 cells were evaluated. We found that L-K6 suppressed the expression of inflammatory factors by two downstream signaling components in the MyD88-dependent pathway, including the mitogen-activated protein kinases (MAPKs) and the NF (nuclear factor)-κB signaling pathway, but its analog L-K5, which had the same amino acid sequence as L-K6 but no Lys residue at the –COOH terminal, only inhibited the phosphorylation of I-κB and NF-κB. Importantly, L-K6 and L-K5 were actively taken up by U937 cells through an independent cell membrane disruption mechanism and were eventually localized to the perinuclear region. The L-K6 uptake process was mediated by endocytosis, but L-K5 was specifically taken up by U937 cells via TLR4 endocytosis. Our results demonstrated that L-K6 can neutralize LPS and diassociate LPS micelles to inhibit LPS from triggering the proinflammatory signaling pathway, and by partially inhibiting inflammatory responses by the intracellular target. However, L-K5 may mainly inhibit proinflammatory responses by intracellular reporters to modulate the NF-κB signaling pathway.

Anti-inflammatory and anti-endotoxin properties of peptides derived from the carboxy-terminal region of a defensin from the tick Ornithodoros savignyi

Antimicrobial peptides are small cationic peptides that possess a large spectrum of bioactivities, including antimicrobial, anti-inflammatory and antioxidant activities. Several antimicrobial peptides are known to inhibit lipopolysaccharide (LPS)-induced inflammation in vitro and to protect animals from sepsis. In this study, the cellular anti-inflammatory and anti-endotoxin activities of Os and Os-C, peptides derived from the carboxy-terminal of a tick defensin, were investigated. Both Os and Os-C were found to bind LPS in vitro, albeit to a lesser extent than polymyxin B and melittin, known endotoxin-binding peptides. Binding to LPS was found to reduce the bactericidal activity of Os and Os-C against Escherichia coli confirming the affinity of both peptides for LPS. At a concentration of 25 µM, the nitric oxide (NO) scavenging activity of Os was higher than glutathione, a known NO scavenger. In contrast, Os-C showed no scavenging activity. Os and Os-C inhibited LPS/IFN-γ induced NO and TNF-α production in RAW 264.7 cells in a concentration-dependent manner, with no cellular toxicity even at a concentration of 100 µM. Although inhibition of NO and TNF-α secretion was more pronounced for melittin and polymyxin B, significant cytotoxicity was observed at concentrations of 1.56 µM and 25 µM for melittin and polymyxin B, respectively. In addition, Os, Os-C and glutathione protected RAW 264.7 cells from oxidative damage at concentrations as low as 25 µM. This study identified that besides previously reported antibacterial activity of Os and Os-C, both peptides have in addition anti-inflammatory and anti-endotoxin properties.

Petrolatum: Barrier repair and antimicrobial responses underlying this "inert" moisturizer

BACKGROUND

Petrolatum is a common moisturizer often used in the prevention of skin infections after ambulatory surgeries and as a maintenance therapy of atopic dermatitis (AD). However, the molecular responses induced by petrolatum in the skin have never been assessed.

OBJECTIVE

We sought to define the cutaneous molecular and structural effects induced by petrolatum.

METHODS

Thirty-six healthy subjects and 13 patients with moderate AD (mean SCORAD score, 39) were studied by using RT-PCR, gene arrays, immunohistochemistry, and immunofluorescence performed on control skin, petrolatum-occluded skin, and skin occluded with a Finn chamber only.

RESULTS

Significant upregulations of antimicrobial peptides (S100A8/fold change [FCH], 13.04; S100A9/FCH, 11.28; CCL20/FCH, 8.36; PI3 [elafin]/FCH, 15.40; lipocalin 2/FCH, 6.94, human β-defensin 2 [DEFB4A]/FCH, 4.96; P < .001 for all) and innate immune genes (IL6, IL8, and IL1B; P < .01) were observed in petrolatum-occluded skin compared with expression in both control and occluded-only skin. Application of petrolatum also induced expression of key barrier differentiation markers (filaggrin and loricrin), increased stratum corneum thickness, and significantly reduced T-cell infiltrates in the setting of "normal-appearing" or nonlesional AD skin, which is known to harbor barrier and immune defects.

CONCLUSIONS

Petrolatum robustly modulates antimicrobials and epidermal differentiation barrier measures. These data shed light on the beneficial molecular responses of petrolatum in barrier-defective states, such as AD and postoperative wound care.

β-Boomerang Antimicrobial and Antiendotoxic Peptides: Lipidation and Disulfide Bond Effects on Activity and Structure

Drug-resistant Gram-negative bacterial pathogens and endotoxin- or lipopolysaccharide (LPS)-mediated inflammations are among some of the most  prominent health issues globally. Antimicrobial peptides (AMPs) are eminent molecules that can kill drug-resistant strains and neutralize LPS toxicity. LPS, the outer layer of the outer membrane of Gram-negative bacteria safeguards cell integrity against hydrophobic compounds, including antibiotics and AMPs. Apart from maintaining structural integrity, LPS, when released into the blood stream, also induces inflammatory pathways leading to septic shock. In previous works, we have reported the de novo design of a set of 12-amino acid long cationic/hydrophobic peptides for LPS binding and activity. These peptides adopt β-boomerang like conformations in complex with LPS. Structure-activity studies demonstrated some critical features of the β-boomerang scaffold that may be utilized for the further development of potent analogs. In this work, β-boomerang lipopeptides were designed and structure-activity correlation studies were carried out. These lipopeptides were homo-dimerized through a disulfide bridge to stabilize conformations and for improved activity. The designed peptides exhibited potent antibacterial activity and efficiently neutralized LPS toxicity under in vitro assays. NMR structure of C4YI13C in aqueous solution demonstrated the conserved folding of the lipopeptide with a boomerang aromatic lock stabilized with disulfide bond at the C-terminus and acylation at the N-terminus. These lipo-peptides displaying bacterial sterilization and low hemolytic activity may be useful for future applications as antimicrobial and antiendotoxin molecules.

Avian antimicrobial host defense peptides: from biology to therapeutic applications

Host defense peptides (HDPs) are an important first line of defense with antimicrobial and immunomoduatory properties. Because they act on the microbial membranes or host immune cells, HDPs pose a low risk of triggering microbial resistance and therefore, are being actively investigated as a novel class of antimicrobials and vaccine adjuvants. Cathelicidins and β-defensins are two major families of HDPs in avian species. More than a dozen HDPs exist in birds, with the genes in each HDP family clustered in a single chromosomal segment, apparently as a result of gene duplication and diversification. In contrast to their mammalian counterparts that adopt various spatial conformations, mature avian cathelicidins are mostly α-helical. Avian β-defensins, on the other hand, adopt triple-stranded β-sheet structures similar to their mammalian relatives. Besides classical β-defensins, a group of avian-specific β-defensin-related peptides, namely ovodefensins, exist with a different six-cysteine motif. Like their mammalian counterparts, avian cathelicidins and defensins are derived from either myeloid or epithelial origin expressed in a majority of tissues with broad-spectrum antibacterial and immune regulatory activities. Structure-function relationship studies with several avian HDPs have led to identification of the peptide analogs with potential for use as antimicrobials and vaccine adjuvants. Dietary modulation of endogenous HDP synthesis has also emerged as a promising alternative approach to disease control and prevention in chickens.

Characterization of antimicrobial, cytotoxic, and antiendotoxin properties of short peptides with different hydrophobic amino acids at "a" and "d" positions of a heptad repeat sequence

To understand the influence of different hydrophobic amino acids at "a" and "d" positions of a heptad repeat sequence on antimicrobial, cytotoxic, and antiendotoxin properties, four 15-residue peptides with leucine (LRP), phenylalanine (FRP), valine (VRP), and alanine (ARP) residues at these positions were designed, synthesized, and characterized. Although valine is similarly hydrophobic to leucine and phenylalanine, VRP showed significantly lesser cytotoxicity than LRP and FRP; further, the replacement of leucines with valines at "a" and "d" positions of melittin-heptads drastically reduced its cytotoxicity. However, all four peptides exhibited significant antimicrobial activities that correlate well with their interactions with mammalian and bacterial cell membranes and the corresponding lipid vesicles. LRP most efficiently neutralized the LPS-induced pro-inflammatory mediators like NO, TNF-α, and IL-6 in macrophages followed by FRP, VRP, and ARP. The results could be useful for designing short antimicrobial and antiendotoxin peptides with understanding the basis of their activity.

Synthesis and properties of cyclic gomesin and analogues

Gomesin (Gm) was the first antimicrobial peptide (AMP) isolated from the hemocytes of a spider, the Brazilian mygalomorph Acanthoscurria gomesiana. We have been studying the properties of this interesting AMP, which also displays anticancer, antimalarial, anticryptococcal and anti-Leishmania activities. In the present study, the total syntheses of backbone-cyclized analogues of Gm (two disulfide bonds), [Cys(Acm)(2,15)]-Gm (one disulfide bond) and [Thr(2,6,11,15),(D)-Pro(9)]-Gm (no disulfide bonds) were accomplished, and the impact of cyclization on their properties was examined. The consequence of simultaneous deletion of pGlu(1) and Arg(16) -Glu-Arg(18) -NH(2) on Gm antimicrobial activity and structure was also analyzed. The results obtained showed that the synthetic route that includes peptide backbone cyclization on resin was advantageous and that a combination of 20% DMSO/NMP, EDC/HOBt, 60 °C and conventional heating appears to be particularly suitable for backbone cyclization of bioactive peptides. The biological properties of the Gm analogues clearly revealed that the N-terminal amino acid pGlu(1) and the amidated C-terminal tripeptide Arg(16) -Glu-Arg(18) -NH(2) play a major role in the interaction of Gm with the target membranes. Moreover, backbone cyclization practically did not affect the stability of the peptides in human serum; it also did not affect or enhanced hemolytic activity, but induced selectivity and, in some cases, discrete enhancements of antimicrobial activity and salt tolerance. Because of its high therapeutic index, easy synthesis and lower cost, the [Thr(2,6,11,15),(D)-Pro(9)]-Gm analogue remains the best active Gm-derived AMP developed so far; nevertheless, its elevated instability in human serum may limit its therapeutic potential.

Peptide-based treatment of sepsis

Sepsis (blood poisoning) is a severe infectious disease with high mortality, and no effective therapy is actually known. In the case of Gram-negative bacteria, endotoxins (lipopolysaccharides) are known to be responsible for the strong inflammation reaction leading to the systemic infection. Peptides based on endotoxin-binding domains of human or animal proteins represent a promising approach in sepsis research. Although so far no medicament is available, the progress in recent years might lead to a breakthrough in this field. In this review, recent investigations are summarised, which may lead to an understanding of the mechanisms of action of peptides to suppress the inflammation reaction in vitro and in vivo (animal models) and thus may allow the development of effective anti-septic drugs.

Antimicrobial peptides of an anti-lipopolysaccharide factor, epinecidin-1, and hepcidin reduce the lethality of Riemerella anatipestifer sepsis in ducks

Antimicrobial peptides (AMPs) are effective against a wide range of microbes, but still no research results have reported their use in duck disease therapy. Riemerella anatipestifer (RA) is a Gram-negative bacterium which infects ducks and causes very significant economic losses. The minimum inhibitory concentrations (MICs) of epinecidin-1 for the tested RA strains ranged 6.25-50microg/ml, those of the SALF55-76 cyclic peptide ranged 12.5-25microg/ml, those of the SALF55-76 linear peptide ranged 6.25-25microg/ml, those of hepcidin TH1-5 ranged 25-400microg/ml, and those of hepcidin TH2-3 ranged 100-400microg/ml. The antimicrobial activities of these peptides were confirmed by transmission electron microscopy which showed that RA disruption of the outer membrane brought about cell death. In addition, pretreatment, co-treatment, and post-treatment with peptides were all effective in promoting a significant decrease in duck mortality and decreasing the number of infectious bacteria. A quantitative RT-PCR was performed to survey levels of gene expressions of Mn superoxide dismutase in the brain, lipoprotein lipase in the liver, and H5 histone in the spleen induced in response to bacterial infection and an injection of the AMPs in experiments with the duck, Cairina moschata. Our results indicated that the rescue of ducks by the peptides and the behavior of the peptides, which was like an enhancer in immunology, may involve regulation of the expressions of these genes. Collectively, these peptides reduced the mortality in ducks during bacterial challenge, suggesting that AMPs have the potential to serve as therapeutic drugs for use against bacterial infectious diseases in ducks.

Therapeutic potential of HDPs as immunomodulatory agents

One of the most significant advances in medical history is the discovery and development of antibiotics, which in the middle of last century was flourishing and appeared to be the ultimate solution to the treatment of life-threatening human bacterial diseases. However, lately there has been a huge decline in the rate of discovery of new antimicrobial intervention strategies in parallel with an increasing incidence of multidrug-resistant pathogens; if these circumstances do not change we will continue to approach the end of the antibiotic era. Facing this dark future, scientists are considering new strategies for intervention tailored around the appropriate (selective) stimulation of the host's immune system, and particularly rapid acting innate immunity, as an alternative to direct targeting of microbial pathogens. One recent player in such an immunomodulatory strategy is the naturally occurring host defence peptides (HDP) and their synthetic innate defence regulator (IDR) analogues. In this chapter, we will discuss the potential therapeutic use of HDPs and IDRs as immunomodulatory agents.

Host defense peptides as effector molecules of the innate immune response: a sledgehammer for drug resistance?

Host defense peptides can modulate the innate immune response and boost infection-resolving immunity, while dampening potentially harmful pro-inflammatory (septic) responses. Both antimicrobial and/or immunomodulatory activities are an integral part of the process of innate immunity, which itself has many of the hallmarks of successful anti-infective therapies, namely rapid action and broad-spectrum antimicrobial activities. This gives these peptides the potential to become an entirely new therapeutic approach against bacterial infections. This review details the role and activities of these peptides, and examines their applicability as development candidates for use against bacterial infections.

Intracellular receptor for human host defense peptide LL-37 in monocytes

The human cationic host defense peptide LL-37 has a broad range of immunomodulatory, anti-infective functions. A synthetic innate defense regulator peptide, innate defense regulator 1 (IDR-1), based conceptually on LL-37, was recently shown to selectively modulate innate immunity to protect against a wide range of bacterial infections. Using advanced proteomic techniques, ELISA, and Western blotting procedures, GAPDH was identified as a direct binding partner for LL-37 in monocytes. Enzyme kinetics and mobility shift studies also indicated LL-37 and IDR-1 binding to GAPDH. The functional relevance of GAPDH in peptide-induced responses was demonstrated by using gene silencing of GAPDH with small interfering RNA (siRNA). Previous studies have established that the induction of chemokines and the anti-inflammatory cytokine IL-10 are critical immunomodulatory functions in the anti-infective properties of LL-37 and IDR-1, and these functions are modulated by the MAPK p38 pathway. Consistent with that, this study demonstrated the importance of the GAPDH interactions with these peptides since gene silencing of GAPDH resulted in impaired p38 MAPK signaling, downstream chemokine and cytokine transcriptional responses induced by LL-37 and IDR-1, and LL-37-induced cytokine production. Bioinformatic analysis, using InnateDB, of the major interacting partners of GAPDH indicated the likelihood that this protein can impact on innate immune pathways including p38 MAPK. Thus, this study has demonstrated a novel function for GAPDH as a mononuclear cell receptor for human cathelicidin LL-37 and immunomodulatory IDR-1 and conclusively demonstrated its relevance in the functioning of cationic host defense peptides.

Pharmacodynamic activity of the lantibiotic MU1140

This study evaluated the pharmacodynamics of the lantibiotic MU1140 and the ability of selected organisms to develop resistance to this antibiotic. MU1140 demonstrated activity against all Gram-positive organisms tested, including oxacillin- and vancomycin-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus faecalis (VREF). No activity was observed against Gram-negative bacteria or yeast. Time-kill studies revealed that MU1140 was rapidly bactericidal against Streptococcus pneumoniae and multidrug-resistant S. aureus, whilst it was bacteriostatic against VREF. In vitro resistance development to MU1140, tested by sequential subculturing in subinhibitory concentrations of MU1140, revealed a stable threefold increase in the minimum inhibitory concentration (MIC) for S. aureus and S. pneumoniae. Subsequent subculturing of the strains with elevated MICs in antibiotic-free media for 7 days did not result in a reduction of their MIC values for MU1140. Collectively, our findings illustrate the therapeutic potential of MU1140 for management of Gram-positive infections.

Role of host defense peptides of the innate immune response in sepsis

Innate immune response and its effector molecules have received growing attention in research. Host defense peptides are known to be antimicrobially active. Recently, the peptides have been recognized as potent signaling molecules for cellular effectors of both innate and adaptive immunity. Mammalian peptides in particular revealed immunomodulatory functions, including endotoxin-binding and -neutralizing capacity, chemotactic activities, induction of cytokines and chemokines, promotion of wound healing, and angiogenesis. In sepsis, they present a family of natural substances that can be used in combination with antibiotics to complete a broad-spectrum antimicrobial regimen with endotoxin-neutralizing properties. Although there are side effects, host defense peptides have the potential to be significant reinforcements to the currently available therapeutic options in the future. In this review, we analyze the role of host defense peptides in infection and immune response, and discuss recent efforts to establish host defense peptides as potent novel therapeutic agents for the treatment of sepsis.

Inducible resistance of fish bacterial pathogens to the antimicrobial peptide cecropin B

Cecropin B is a cationic antimicrobial peptide originally isolated from the diapausing pupae of the giant silk moth, Hylphora cecropia. Cecropin B elicits its antimicrobial effects through disruption of the anionic cell membranes of gram-negative bacteria. Previous work by our laboratory demonstrated that a constitutively expressed cecropin B transgene conferred enhanced resistance to bacterial infection in medaka. The development of antibiotic resistance by pathogenic bacteria is a growing problem. The potential for fish bacterial pathogens to develop resistance to cecropin B was addressed in this study. Four fish bacterial pathogens were selected for the study based on their importance in aquaculture. Vibrio anguillarum, Vibrio vulnificus, and Yersinia ruckeri all exhibited inducible resistance to cecropin B. The inducible resistance of these three pathogens was correlated with reversible changes in their ultrastructures, as observed by scanning electron microscopy. V. anguillarum was demonstrated to become more adhesive to a CHSE-214 cell monolayer and to cause increased cumulative mortality in medaka following exposure to cecropin B. This work demonstrates that the resistance of fish bacterial pathogens to cecropin B is inducible and suggests that resistance to other cationic antimicrobial peptides may occur through similar means. The observed changes in ultrastructure and infectivity suggest that resistance to antimicrobial peptides is an integral part of the pathogenesis of fish gram-negative bacterial pathogens.

Cathelicidins and functional analogues as antisepsis molecules

The emergence of antibiotic-resistant bacteria together with the limited success of sepsis therapeutics has lead to an urgent need for the development of alternative strategies for the treatment of systemic inflammatory response syndrome and related disorders. Immunomodulatory compounds that do not target the pathogen directly (therefore limiting the development of pathogen resistance), and target multiple inflammatory mediators, are attractive candidates as novel therapeutics. Cationic host defence peptides such as cathelicidins have been demonstrated to be selectively immunomodulatory in that they can confer anti-infective immunity and modulate the inflammatory cascade through multiple points of intervention. The human cathelicidin LL-37, for example, has modest direct antimicrobial activity under physiological conditions, but has been demonstrated to have potent antiendotoxin activity in animal models, as well as the ability to resolve certain bacterial infections. A novel synthetic immunomodulatory peptide, IDR-1, built on this same theme has no direct antimicrobial activity, but is effective in restricting many types of infection, while limiting pro-inflammatory responses. The ability of these peptides to selectively suppress harmful pro-inflammatory responses, while maintaining beneficial infection-fighting components of host innate defences makes them a good model for antisepsis therapies that merit further investigation.

In vivo secretome sampling technology for proteomics

Secretome is a critical mediator for cell-cell and microbe-cell interaction. Identification of secretome will endow researchers with important biomarkers and therapeutic targets as well as reinforce the current methods used in the systems biology research of cell-cell interactions. Here, we introduce an in vivo sampling technique using capillary ultrafiltration (CUF) probes that are capable of continuously collecting pure in vivo secretome from tissue microenvironments. Great benefits of CUF probes when compared with other current sampling techniques have been acknowledged. CUF probes can be designed to fit various in vivo models and they are easily adapted to different protein-detection systems including mass spectrometers. The future challenges and clinical advantages of CUF probe sampling are also highlighted in this review. Many prospective properties such as simple manipulation, dynamic sampling, pathogen clearance, online mass spectrometric coupling, and disease treatment and monitoring have made CUF probes attractive for clinical uses in the near future.

Lipopolysaccharide-induced down-regulation of uteroglobin in the human nose

CONCLUSION

Lipopolysaccharide (LPS) challenge of the human nose has the capacity to reduce the amount of natural anti-inflammatory proteins, such as uteroglobin.

OBJECTIVES

Nasal challenge with LPS, an activator of innate immunity, has been shown to increase the amount of pro-inflammatory mediators in nasal lavage fluid. Uteroglobin is a newly described anti-inflammatory mediator that is secreted in the nose. This study examined the effect of nasal LPS application on the level of uteroglobin in nasal lavage fluid as well as on the expression of uteroglobin in nasal mucosa.

MATERIALS AND METHODS

Thirty-eight volunteers were challenged nasally with either 50 microg LPS or vehicle; 6 h later, nasal lavage fluid was collected and a nasal biopsy was obtained. Levels of uteroglobin, albumin and the pro-inflammatory mediators interleukin (IL)-6 and IL-8 were analysed in the lavage fluids using enzyme-linked immunosorbent assays (ELISAs). Biopsies were used for either quantification of uteroglobin mRNA by real-time PCR or for localization of the corresponding protein with immunohistochemistry.

RESULTS

The uteroglobin level decreased in nasal lavage fluid following LPS challenge, whereas the levels of IL-6 and albumin increased. Uteroglobin was mainly seen in the respiratory epithelium and its mRNA expression decreased as a consequence of the LPS challenge.

Sequence requirements and an optimization strategy for short antimicrobial peptides

Short antimicrobial host-defense peptides represent a possible alternative as lead structures to fight antibiotic resistant bacterial infections. Bac2A is a 12-mer linear variant of the naturally occurring bovine host defense peptide, bactenecin, and demonstrates moderate, broad-spectrum antimicrobial activity against Gram-positive and Gram-negative bacteria as well as against the yeast Candida albicans. With the assistance of a method involving peptide synthesis on a cellulose support, the primary sequence requirements for antimicrobial activity against the human pathogen Pseudomonas aeruginosa of 277 Bac2A variants were investigated by using a luciferase-based assay. Sequence scrambling of Bac2A led to activities ranging from superior or equivalent to Bac2A to inactive, indicating that good activity was not solely dependent on the composition of amino acids or the overall charge or hydrophobicity, but rather required particular linear sequence patterns. A QSAR computational analysis was applied to analyze the data resulting in a model that supported this sequence pattern hypothesis. The activity of selected peptides was confirmed by conventional minimal inhibitory concentration (MIC) analyses with a panel of human pathogen bacteria and fungi. Circular-dichroism (CD) spectroscopy with selected peptides in liposomes and membrane depolarization assays were consistent with a relationship between structure and activity. An additional optimization process was performed involving systematic amino acid substitutions of one of the optimal scrambled peptide variants, resulting in superior active peptide variants. This process provides a cost and time effective enrichment of new candidates for drug development, increasing the chances of finding pharmacologically relevant peptides.

Increased colorectal permeability in patients with severe sepsis and septic shock

OBJECTIVE

To develop a method for the assessment of colorectal permeability in septic patients.

DESIGN AND SETTING

Observational study in ICUs at two university hospitals.

PARTICIPANTS

Nine patients with septic shock and abdominal focus of infection, 7 with severe sepsis and pulmonary focus and 8 healthy subjects.

MEASUREMENTS AND RESULTS

Colorectal permeability was assessed as the initial appearance rate of (99m)Tc-DTPA in plasma after instillation into the rectal lumen and as the cumulative systemic recovery at 1h. To calculate the latter, volume of distribution and renal clearance of (99m)Tc-DTPA was estimated by an i.v. bolus of (51)Cr-EDTA. The initial rate of permeability was increased in patients with septic shock and severe sepsis compared with controls [29.0 (3.7-83.3), 20.6 (3.6-65.5) and 6.0 (2.2-9.6)cpm ml(-1)min(-1), respectively, p<0.05)] with a positive linear trend (r (2)=0.27, p=0.01) and correlated to L-lactate concentrations in the rectal lumen (r (2)=0.39, p<0.05). The cumulative permeability was also increased in patients with septic shock and severe sepsis compared with controls [2.07 (0.05-15.7), 0.32 (0.01-1.2) and 0.03 (0.01-0.06) per thousand, respectively, p<0.01] and correlated to the initial permeability rate (r (2)=0.26, p=0.01).

CONCLUSIONS

In septic patients, the systemic recovery of a luminally applied marker of paracellular permeability was increased and related to the luminal concentrations of L-lactate and possibly to disease severity. This suggests that the assessment of colorectal permeability by systemic recovery of (99m)Tc-DTPA is valid and that metabolic dysfunction of the mucosa contributes to increased permeability of the large bowel in patients with severe sepsis and septic shock.

Peptide antimicrobial agents

Antimicrobial host defense peptides are produced by all complex organisms as well as some microbes and have diverse and complex antimicrobial activities. Collectively these peptides demonstrate a broad range of antiviral and antibacterial activities and modes of action, and it is important to distinguish between direct microbicidal and indirect activities against such pathogens. The structural requirements of peptides for antiviral and antibacterial activities are evaluated in light of the diverse set of primary and secondary structures described for host defense peptides. Peptides with antifungal and antiparasitic activities are discussed in less detail, although the broad-spectrum activities of such peptides indicate that they are important host defense molecules. Knowledge regarding the relationship between peptide structure and function as well as their mechanism of action is being applied in the design of antimicrobial peptide variants as potential novel therapeutic agents.

The antimicrobial/elastase inhibitor elafin regulates lung dendritic cells and adaptive immunity

Infections with bacteria and viruses such as adenovirus are a feature of chronic lung diseases such as chronic obstructive pulmonary diseases (COPD), and may be instrumental in the generation of disease exacerbations. We have previously shown in acute models that elafin (a lung natural chemotactic molecule for macrophages and neutrophils, with potent antimicrobial and neutrophil elastase inhibitor activity) is upregulated in infection and modulates innate immunity. Here we present data using two independent systems of elafin overexpression in vivo (recombinant adenovirus [Ad-elafin] and an elafin transgenic mouse line) to examine the function of elafin in adaptive immunity. We show that elafin increases the number (immunofluorescence) and activation status (flow cytometric measurement) of CD11c+/MHCII+ lung dendritic cells in vivo. Analysis of cytokines produced by spleen and lung cells, and of antibodies measured in serum and bronchoalveolar lavage fluid, shows that the immunity induced is biased toward a type 1 response (production of IL-12, IFN-gamma, and IgG2a). Furthermore, elafin overexpression protected mice against further challenge with Ad-LacZ, as assessed by antibody levels and neutralization titer, as well as LacZ expression in lung tissue. Thus, the pleiotropic molecule elafin has significant potential in modulating antigen-presenting cell numbers and activity, and could be beneficial in mucosal protective strategies.