Cathelicidin and PMB neutralize endotoxins by multifactorial mechanisms including LPS interaction and targeting of host cell membranes.

Antimicrobial peptides (AMPs) contribute to an effective protection against infections. The antibacterial function of AMPs depends on their interactions with microbial membranes and lipids, such as lipopolysaccharide (LPS; endotoxin). Hyperinflammation induced by endotoxin is a key factor in bacterial sepsis and many other human diseases. Here, we provide a comprehensive profile of peptide-mediated LPS neutralization by systematic analysis of the effects of a set of AMPs and the peptide antibiotic polymyxin B (PMB) on the physicochemistry of endotoxin, macrophage activation, and lethality in mice. Mechanistic studies revealed that the host defense peptide LL-32 and PMB each reduce LPS-mediated activation also via a direct interaction of the peptides with the host cell. As a biophysical basis, we demonstrate modifications of the structure of cholesterol-rich membrane domains and the association of glycosylphosphatidylinositol (GPI)-anchored proteins. Our discovery of a host cell-directed mechanism of immune control contributes an important aspect in the development and therapeutic use of AMPs.

A Comparison between SARS-CoV-2 and Gram-Negative Bacteria-Induced Hyperinflammation and Sepsis.

Sepsis is a life-threatening condition caused by the body's overwhelming response to an infection, such as pneumonia or urinary tract infection. It occurs when the immune system releases cytokines into the bloodstream, triggering widespread inflammation. If not treated, it can lead to organ failure and death. Unfortunately, sepsis has a high mortality rate, with studies reporting rates ranging from 20% to over 50%, depending on the severity and promptness of treatment. According to the World Health Organization (WHO), the annual death toll in the world is about 11 million. One of the main toxins responsible for inflammation induction are lipopolysaccharides (LPS, endotoxin) from Gram-negative bacteria, which rank among the most potent immunostimulants found in nature. Antibiotics are consistently prescribed as a part of anti-sepsis-therapy. However, antibiotic therapy (i) is increasingly ineffective due to resistance development and (ii) most antibiotics are unable to bind and neutralize LPS, a prerequisite to inhibit the interaction of endotoxin with its cellular receptor complex, namely Toll-like receptor 4 (TLR4)/MD-2, responsible for the intracellular cascade leading to pro-inflammatory cytokine secretion. The pandemic virus SARS-CoV-2 has infected hundreds of millions of humans worldwide since its emergence in 2019. The COVID-19 (Coronavirus disease-19) caused by this virus is associated with high lethality, particularly for elderly and immunocompromised people. As of August 2023, nearly 7 million deaths were reported worldwide due to this disease. According to some reported studies, upregulation of TLR4 and the subsequent inflammatory signaling detected in COVID-19 patients "mimics bacterial sepsis". Furthermore, the immune response to SARS-CoV-2 was described by others as "mirror image of sepsis". Similarly, the cytokine profile in sera from severe COVID-19 patients was very similar to those suffering from the acute respiratory distress syndrome (ARDS) and sepsis. Finally, the severe COVID-19 infection is frequently accompanied by bacterial co-infections, as well as by the presence of significant LPS concentrations. In the present review, we will analyze similarities and differences between COVID-19 and sepsis at the pathophysiological, epidemiological, and molecular levels.

Anti-Infective and Anti-Inflammatory Mode of Action of Peptide 19-2.5.

The polypeptide Pep19-2.5 (Aspidasept®) has been described to act efficiently against infection-inducing bacteria by binding and neutralizing their most potent toxins, i.e., lipopolysaccharides (LPS) and lipoproteins/peptides (LP), independent of the resistance status of the bacteria. The mode of action was described to consist of a primary Coulomb/polar interaction of the N-terminal region of Pep19-2.5 with the polar region of the toxins followed by a hydrophobic interaction of the C-terminal region of the peptide with the apolar moiety of the toxins. However, clinical development of Aspidasept as an anti-sepsis drug requires an in-depth characterization of the interaction of the peptide with the constituents of the human immune system and with other therapeutically relevant compounds such as antibiotics and non-steroidal anti-inflammatory drugs (NSAIDs). In this contribution, relevant details of primary and secondary pharmacodynamics, off-site targets, and immunogenicity are presented, proving that Pep19-2.5 may be readily applied therapeutically against the deleterious effects of a severe bacterial infection.

A synthetic peptide sensitizes multi-drug resistant Pseudomonas aeruginosa to antibiotics for more than two hours and permeabilizes its envelope for twenty hours.

BACKGROUND: Pseudomonas aeruginosa is a Gram-negative pathogen that frequently causes life-threatening infections in immunocompromised patients. We previously showed that subinhibitory concentrations of short synthetic peptides permeabilize P. aeruginosa and enhance the lethal action of co-administered antibiotics. METHODS: Long-term permeabilization caused by exposure of multidrug-resistant P. aeruginosa strains to peptide P4-9 was investigated by measuring the uptake of several antibiotics and fluorescent probes and by using confocal imaging and atomic force microscopy. RESULTS: We demonstrated that P4-9, a 13-amino acid peptide, induces a growth delay (i.e. post-antibiotic effect) of 1.3 h on a multidrug-resistant P. aeruginosa clinical isolate. Remarkably, when an independently P4-9-treated culture was allowed to grow in the absence of the peptide, cells remained sensitive to subinhibitory concentrations of antibiotics such as ceftazidime, fosfomycin and erythromycin for at least 2 h. We designated this persistent sensitization to antibiotics occurring in the absence of the sensitizing agent as Post-Antibiotic Effect associated Permeabilization (PAEP). Using atomic force microscopy, we showed that exposure to P4-9 induces profound alterations on the bacterial surface and that treated cells need at least 2 h of growth to repair those lesions. During PAEP, P. aeruginosa mutants overexpressing either the efflux pump MexAB-OprM system or the AmpC ß-lactamase were rendered sensitive to antibiotics that are known substrates of those mechanisms of resistance. Finally, we showed for the first time that the descendants of bacteria surviving exposure to a membrane disturbing peptide retain a significant level of permeability to hydrophobic compounds, including propidium iodide, even after 20 h of growth in the absence of the peptide. CONCLUSIONS: The phenomenon of long-term sensitization to antibiotics shown here may have important therapeutic implications for a combined peptide-antibiotic treatment because the peptide would not need to be present to exert its antibiotic enhancing activity as long as the target organism retains sensitization to the antibiotic.

Inactivation of Bacteria by γ-Irradiation to Investigate the Interaction with Antimicrobial Peptides.

The activity of antimicrobial peptides (AMPs) has been investigated extensively using model membranes composed of phospholipids or lipopolysaccharides in aqueous environments. However, from a biophysical perspective, there is a large scientific interest regarding the direct interaction of membrane-active peptides with whole bacteria. Working with living bacteria limits the usability of experimental setups and the interpretation of the resulting data because of safety risks and the overlap of active and passive effects induced by AMPs. We killed or inactivated metabolic-active bacteria using γ-irradiation or sodium azide, respectively. Microscopy, flow cytometry, and SYTOX green assays showed that the cell envelope remained intact to a high degree at the minimal bactericidal dose. Furthermore, the tumor-necrosis-factor-α-inducing activity of the lipopolysaccharides and the chemical lipid composition was unchanged. Determining the binding capacity of AMPs to the bacterial cell envelope by calorimetry is difficult because of an overlapping of the binding heat and metabolic activities of the bacteria-induced by the AMPs. The inactivation of all active processes helps to decipher the complex thermodynamic information. From the isothermal titration calorimetry (ITC) results, we propose that the bacterial membrane potential (Δψ) is possibly an underestimated modulator of the AMP activity. The negative surface charge of the outer leaflet of the outer membrane of Gram-negative bacteria is already neutralized by peptide concentrations below the minimal inhibitory concentration. This proves that peptide aggregation on the bacterial membrane surface plays a decisive role in the degree of antimicrobial activity. This will not only enable many biophysical approaches for the investigation between bacteria and membrane-active peptides in the future but will also make it possible to compare biophysical parameters of active and inactive bacteria. This opens up new possibilities to better understand the active and passive interaction processes between AMPs and bacteria.

AMPs as Anti-biofilm Agents for Human Therapy and Prophylaxis.

Microbial cells show a strong natural tendency to adhere to surfaces and to colonize them by forming complex communities called biofilms. In this growth mode, biofilm-forming cells encase themselves inside a dense matrix which efficiently protects them against antimicrobial agents and effectors of the immune system. Moreover, at the physiological level, biofilms contain a very heterogeneous cell population including metabolically inactive organisms and persisters, which are highly tolerant to antibiotics. The majority of human infectious diseases are caused by biofilm-forming microorganisms which are responsible for pathologies such as cystic fibrosis, infective endocarditis, pneumonia, wound infections, dental caries, infections of indwelling devices, etc. AMPs are well suited to combat biofilms because of their potent bactericidal activity of broad spectrum (including resting cells and persisters) and their ability to first penetrate and then to disorganize these structures. In addition, AMPs frequently synergize with antimicrobial compounds and were recently reported to repress the molecular pathways leading to biofilm formation. Finally, there is a very active research to develop AMP-containing coatings that can prevent biofilm formation by killing microbial cells on contact or by locally releasing their active principle. In this chapter we will describe these strategies and discuss the perspectives of the use of AMPs as anti-biofilm agents for human therapy and prophylaxis.

Synthetic Anti-lipopolysaccharide Peptides (SALPs) as Effective Inhibitors of Pathogen-Associated Molecular Patterns (PAMPs).

Antimicrobial peptides (AMPs) are in the focus of scientific research since the 1990s. In most cases, the main aim was laid on the design of AMP to kill bacteria effectively, with particular emphasis on broadband action and independency on antibiotic resistance. However, so far no approved drug on the basis of AMP has entered the market.Our approach of constructing AMP, called synthetic anti-lipopolysaccharide peptides (SALPs), on the basis of inhibiting the inflammatory action of lipopolysaccharide (LPS, endotoxin) from Gram-negative bacteria was focused on the neutralization of the decisive toxins. These are, beside LPS from Gram-negative bacteria, the lipoproteins (LP) from Gram-positive origin. Although some of the SALPs have an antibacterial action, the most important property is the high-affinity binding to LPS and LP, whether as constituent of the bacteria or in free form which prevents the damaging inflammation, that could otherwise lead to life-threatening septic shock. Most importantly, the SALP may inhibit inflammation independently of the resistance status of the bacteria, and so far the repeated use of the peptides apparently does not cause resistance of the attacking pathogens.In this chapter, an overview is given over the variety of possible applications in the field of fighting against severe bacterial infections, from the use in systemic infection/inflammation up to various topical applications such as anti-biofilm action and severe skin and soft tissue infections.

Antimicrobial activity of synthetic cationic peptides and lipopeptides derived from human lactoferricin against Pseudomonas aeruginosa planktonic cultures and biofilms.

BACKGROUND: Infections by Pseudomonas aeruginosa constitute a serious health threat because this pathogen -particularly when it forms biofilms - can acquire resistance to the majority of conventional antibiotics. This study evaluated the antimicrobial activity of synthetic peptides based on LF11, an 11-mer peptide derived from human lactoferricin against P. aeruginosa planktonic and biofilm-forming cells. We included in this analysis selected N-acylated derivatives of the peptides to analyze the effect of acylation in antimicrobial activity. To assess the efficacy of compounds against planktonic bacteria, microdilution assays to determine the minimal inhibitory concentration (MIC), minimum bactericidal concentration (MBC) and time-kill studies were conducted. The anti-biofilm activity of the agents was assessed on biofilms grown under static (on microplates) and dynamic (in a CDC-reactor) flow regimes. RESULTS: The antimicrobial activity of lipopeptides differed from that of non-acylated peptides in their killing mechanisms on planktonic and biofilm-forming cells. Thus, acylation enhanced the bactericidal activity of the parental peptides and resulted in lipopeptides that were uniformly bactericidal at their MIC. In contrast, acylation of the most potent anti-biofilm peptides resulted in compounds with lower anti-biofilm activity. Both peptides and lipopeptides displayed very rapid killing kinetics and all of them required less than 21 min to reduce 1,000 times the viability of planktonic cells when tested at 2 times their MBC. The peptides, LF11-215 (FWRIRIRR) and LF11-227 (FWRRFWRR), displayed the most potent anti-biofilm activity causing a 10,000 fold reduction in cell viability after 1 h of treatment at 10 times their MIC. At that concentration, these two compounds exhibited low citotoxicity on human cells. In addition to its bactericidal activity, LF11-227 removed more that 50 % of the biofilm mass in independent assays. Peptide LF11-215 and two of the shortest and least hydrophobic lipopeptides, DI-MB-LF11-322 (2,2-dimethylbutanoyl-PFWRIRIRR) and DI-MB-LF11-215, penetrated deep into the biofilm structure and homogenously killed biofilm-forming bacteria. CONCLUSION: We identified peptides derived from human lactoferricin with potent antimicrobial activity against P. aeruginosa growing either in planktonic or in biofilm mode. Although further structure-activity relationship analyses are necessary to optimize the anti-biofilm activity of these compounds, the results indicate that lactoferricin derived peptides are promising anti-biofilm agents.

Novel integrated and portable endotoxin detection system based on an electrochemical biosensor.

This paper describes the design, implementation and validation of a sensitive and integral technology solution for endotoxin detection. The unified and portable platform is based on the electrochemical detection of endotoxins using a synthetic peptide immobilized on a thin-film biosensor. The work covers the fabrication of an optimized sensor, the biofunctionalization protocol and the design and implementation of the measuring and signalling elements (a microfluidic chamber and a portable potentiostat-galvanostat), framed ad hoc for this specific application. The use of thin-film technologies to fabricate the biosensing device and the application of simple immobilization and detection methods enable a rapid, easy and sensitive technique for in situ and real time LPS detection.

Interspecies transmission of antimicrobial-resistant bacteria between wild birds and mammals in urban environment.

The transmission of antibiotic-resistant bacteria among wild animal species may hold significant epidemiological implications. However, this issue is seldom explored due to the perceived complexity of these systems, which discourages experimental investigation. To address this knowledge gap, we chose a configuration of birds and mammals coexisting in an urban green area as a research model: the rook Corvus frugilegus and the striped field mouse Apodemus agrarius. The indirect transmission of antimicrobial-resistant bacteria between these species is possible because rodents inhabiting rook colonies frequently come into contact with the birds' faeces and pellets. The study was conducted in two cities in eastern Poland (Central Europe) - Lublin and Chelm. Among 71 Escherichia (E.) coli isolates studied, 19.7% showed resistance to from one to six of the antibiotics tested, with much higher prevalence of antibiotic-resistant bacteria in the birds (32%) than in the rodents (7%). Whole genome sequencing was performed on 10 selected E. coli isolates representing similar resistance phenotypes. The following antimicrobial resistance genes were detected: blaTEM-1b, tet(A), tet(B), aph(6)-Id, aph(3'')-Ib, aadA1, aadA2, catA1, floR, cmlA, sul2, sul3, dfrA14, and dfrA2. Birds from the same city and also from both neighbouring cities shared E. coli bacteria with the same sequence types, whereas isolates detected in birds were not found to have been transferred to the mammalian population, despite close contact. This demonstrates that even intensive exposure to sources of these pathogens does not necessarily lead to effective transmission of antibiotic-resistant E. coli strains between birds and mammals. Further efforts should be dedicated to investigating actual transmission of antimicrobial-resistant bacteria in various ecological systems, including those that are crucial for public health, such as urban environments. This will facilitate the development of more accurate models for epidemiological threats and the formulation of well-balanced decisions regarding the coexistence of humans and urban wildlife.

Supramolecular assembly of micellar aggregates is the basis of low endotoxin recovery (LER) in a drug formulation that can be resolved by a whole blood assay.

Lipopolysaccharide (LPS, endotoxin) is ubiquitous and represents a harmful contaminant of pharmaceutical compounds, recombinant biologicals and drug products. The pyrogen can induce severe immune responses and pathology in vitro and in vivo. Health authorities require strict control of endotoxin in parenteral drugs. However, for research and pre-clinical compound analysis, endotoxin testing is not a required quality control, which may cause potential drawbacks in the translational pipeline. Endotoxin testing is usually performed by the Limulus amebocyte lysate (LAL) assay, which is hampered by the so-called low endotoxin recovery (LER) effect when certain drug formulations are tested. A comprehensive study including structural, biophysical, and biological analyses was conducted to identify LER root cause for phosphate- and polysorbate-containing parenteral drug products. LPS in water showed extended ribbon-like aggregate structures. In placebo (formulation buffer without drug) and in drug product (drug in formulation buffer), a reaggregation of LPS into a network of interlinked micelles with hidden head group charges, and a strong reduction of the negative surface potential was observed. The non-accessibility of the LPS backbone has a direct impact leading (i) to a loss of activation of the LAL-cascade, (ii) reduced activation of the TLR4/MD-2 receptor system, and (iii) increased survival in a mouse model of endotoxemia. These data provide a structure-based explanation of the LER-underlying mechanisms. A human whole blood assay is shown to resolve LER and detect the pyrogenic activity of endotoxin with high sensitivity. This may open new test options to improve quality control in drug development and drug safety.

Preclinical investigations reveal the broad-spectrum neutralizing activity of peptide Pep19-2.5 on bacterial pathogenicity factors.

Bacterial infections are known to cause severe health-threatening conditions, including sepsis. All attempts to get this disease under control failed in the past, and especially in times of increasing antibiotic resistance, this leads to one of the most urgent medical challenges of our times. We designed a peptide to bind with high affinity to endotoxins, one of the most potent pathogenicity factors involved in triggering sepsis. The peptide Pep19-2.5 reveals high endotoxin neutralization efficiency in vitro, and here, we demonstrate its antiseptic/anti-inflammatory effects in vivo in the mouse models of endotoxemia, bacteremia, and cecal ligation and puncture, as well as in an ex vivo model of human tissue. Furthermore, we show that Pep19-2.5 can bind and neutralize not only endotoxins but also other bacterial pathogenicity factors, such as those from the Gram-positive bacterium Staphylococcus aureus. This broad neutralization efficiency and the additive action of the peptide with common antibiotics makes it an exceptionally appropriate drug candidate against bacterial sepsis and also offers multiple other medication opportunities.

Repurposing the Antibacterial Agents Peptide 19-4LF and Peptide 19-2.5 for Treatment of Cutaneous Leishmaniasis.

The lack of safe and cost-effective treatments against leishmaniasis highlights the urgent need to develop improved leishmanicidal agents. Antimicrobial peptides (AMPs) are an emerging category of therapeutics exerting a wide range of biological activities such as anti-bacterial, anti-fungal, anti-parasitic and anti-tumoral. In the present study, the approach of repurposing AMPs as antileishmanial drugs was applied. The leishmanicidal activity of two synthetic anti-lipopolysaccharide peptides (SALPs), so-called 19-2.5 and 19-4LF was characterized in Leishmania major. In vitro, both peptides were highly active against intracellular Leishmania major in mouse macrophages without exerting toxicity in host cells. Then, q-PCR-based gene profiling, revealed that this activity was related to the downregulation of several genes involved in drug resistance (yip1), virulence (gp63) and parasite proliferation (Cyclin 1 and Cyclin 6). Importantly, the treatment of BALB/c mice with any of the two AMPs caused a significant reduction in L. major infective burden. This effect was associated with an increase in Th1 cytokine levels (IL-12p35, TNF-α, and iNOS) in the skin lesion and spleen of the L. major infected mice while the Th2-associated genes were downregulated (IL-4 and IL-6). Lastly, we investigated the effect of both peptides in the gene expression profile of the P2X7 purinergic receptor, which has been reported as a therapeutic target in several diseases. The results showed significant repression of P2X7R by both peptides in the skin lesion of L. major infected mice to an extent comparable to that of a common anti-leishmanial drug, Paromomycin. Our in vitro and in vivo studies suggest that the synthetic AMPs 19-2.5 and 19-4LF are promising candidates for leishmaniasis treatment and present P2X7R as a potential therapeutic target in cutaneous leishmaniasis (CL).

Biophysical mechanisms of endotoxin neutralization by cationic amphiphilic peptides.

Bacterial endotoxins (lipopolysaccharides (LPS)) are strong elicitors of the human immune system by interacting with serum and membrane proteins such as lipopolysaccharide-binding protein (LBP) and CD14 with high specificity. At LPS concentrations as low as 0.3 ng/ml, such interactions may lead to severe pathophysiological effects, including sepsis and septic shock. One approach to inhibit an uncontrolled inflammatory reaction is the use of appropriate polycationic and amphiphilic antimicrobial peptides, here called synthetic anti-LPS peptides (SALPs). We designed various SALP structures and investigated their ability to inhibit LPS-induced cytokine secretion in vitro, their protective effect in a mouse model of sepsis, and their cytotoxicity in physiological human cells. Using a variety of biophysical techniques, we investigated selected SALPs with considerable differences in their biological responses to characterize and understand the mechanism of LPS inactivation by SALPs. Our investigations show that neutralization of LPS by peptides is associated with a fluidization of the LPS acyl chains, a strong exothermic Coulomb interaction between the two compounds, and a drastic change of the LPS aggregate type from cubic into multilamellar, with an increase in the aggregate sizes, inhibiting the binding of LBP and other mammalian proteins to the endotoxin. At the same time, peptide binding to phospholipids of human origin (e.g., phosphatidylcholine) does not cause essential structural changes, such as changes in membrane fluidity and bilayer structure. The absence of cytotoxicity is explained by the high specificity of the interaction of the peptides with LPS.

Structural features governing the activity of lactoferricin-derived peptides that act in synergy with antibiotics against Pseudomonas aeruginosa in vitro and in vivo.

Pseudomonas aeruginosa is naturally resistant to many antibiotics, and infections caused by this organism are a serious threat, especially to hospitalized patients. The intrinsic low permeability of P. aeruginosa to antibiotics results from the coordinated action of several mechanisms, such as the presence of restrictive porins and the expression of multidrug efflux pump systems. Our goal was to develop antimicrobial peptides with an improved bacterial membrane-permeabilizing ability, so that they enhance the antibacterial activity of antibiotics. We carried out a structure activity relationship analysis to investigate the parameters that govern the permeabilizing activity of short (8- to 12-amino-acid) lactoferricin-derived peptides. We used a new class of constitutional and sequence-dependent descriptors called PEDES (peptide descriptors from sequence) that allowed us to predict (Spearman's ρ = 0.74; P < 0.001) the permeabilizing activity of a new peptide generation. To study if peptide-mediated permeabilization could neutralize antibiotic resistance mechanisms, the most potent peptides were combined with antibiotics, and the antimicrobial activities of the combinations were determined on P. aeruginosa strains whose mechanisms of resistance to those antibiotics had been previously characterized. A subinhibitory concentration of compound P2-15 or P2-27 sensitized P. aeruginosa to most classes of antibiotics tested and counteracted several mechanisms of antibiotic resistance, including loss of the OprD porin and overexpression of several multidrug efflux pump systems. Using a mouse model of lethal infection, we demonstrated that whereas P2-15 and erythromycin were unable to protect mice when administered separately, concomitant administration of the compounds afforded long-lasting protection to one-third of the animals.

Antimicrobial Peptides in the Battle against Orthopedic Implant-Related Infections: A Review.

Prevention of orthopedic implant-related infections is a major medical challenge, particularly due to the involvement of biofilm-encased and multidrug-resistant bacteria. Current therapies, based on antibiotic administration, have proven to be insufficient, and infection prevalence may rise due to the dissemination of antibiotic resistance. Antimicrobial peptides (AMPs) have attracted attention as promising substitutes of conventional antibiotics, owing to their broad-spectrum of activity, high efficacy at very low concentrations, and, importantly, low propensity for inducing resistance. The aim of this review is to offer an updated perspective of the development of AMPs-based preventive strategies for orthopedic and dental implant-related infections. In this regard, two major research strategies are herein addressed, namely (i) AMP-releasing systems from titanium-modified surfaces and from bone cements or beads; and (ii) AMP immobilization strategies used to graft AMPs onto titanium or other model surfaces with potential translation as coatings. In overview, releasing strategies have evolved to guarantee higher loadings, prolonged and targeted delivery periods upon infection. In addition, avant-garde self-assembling strategies or polymer brushes allowed higher immobilized peptide surface densities, overcoming bioavailability issues. Future research efforts should focus on the regulatory demands for pre-clinical and clinical validation towards clinical translation.

An antibiotic potentiator retains its activity after being immobilized on silicone and prevents growth of multidrug-resistant Pseudomonas aeruginosa biofilms.

Device-Associated Healthcare-Associated Infections (DA-HAI) are a major threat to public health worldwide since they are associated with increased hospital stays, morbidity, mortality, financial burden, and hospital overload. A strategy to combat DA-HAI involves the use of medical devices endowed with surfaces that can kill or repel pathogens and prevent biofilm formation. We aimed to develop low-toxic protease-resistant anti-biofilm surfaces that can sensitize drug-resistant bacteria to sub-inhibitory concentrations of antibiotics. To this end, we hypothesized that polymyxin B nonapeptide (PMBN) could retain its antibiotic-enhancing potential upon immobilization on a biocompatible polymer, such as silicone. The ability of PMBN-coated silicone to sensitize a multidrug-resistant clinical isolate of Pseudomonas aeruginosa (strain Ps4) to antibiotics and block biofilm formation was assessed by viable counting, confocal microscopy and safranin uptake. These assays demonstrated that covalently immobilized PMBN enhances not only antibiotics added exogenously but also those incorporated into the functionalized coating. As a result, the functionalized surface exerted a potent bactericidal activity that precluded biofilm formation. PMBN-coated silicone displayed a high level of stability and very low cytotoxicity and hemolytic activity in the presence of antibiotics. We demonstrated for the first time that an antibiotic enhancer can retain its activity when covalently attached to a solid surface. These findings may be applied to the development of medical devices resistant to biofilm formation.

Activity of Anti-Microbial Peptides (AMPs) against Leishmania and Other Parasites: An Overview.

Anti-microbial peptides (AMPs), small biologically active molecules, produced by different organisms through their innate immune system, have become a considerable subject of interest in the request of novel therapeutics. Most of these peptides are cationic-amphipathic, exhibiting two main mechanisms of action, direct lysis and by modulating the immunity. The most commonly reported activity of AMPs is their anti-bacterial effects, although other effects, such as anti-fungal, anti-viral, and anti-parasitic, as well as anti-tumor mechanisms of action have also been described. Their anti-parasitic effect against leishmaniasis has been studied. Leishmaniasis is a neglected tropical disease. Currently among parasitic diseases, it is the second most threating illness after malaria. Clinical treatments, mainly antimonial derivatives, are related to drug resistance and some undesirable effects. Therefore, the development of new therapeutic agents has become a priority, and AMPs constitute a promising alternative. In this work, we describe the principal families of AMPs (melittin, cecropin, cathelicidin, defensin, magainin, temporin, dermaseptin, eumenitin, and histatin) exhibiting a potential anti-leishmanial activity, as well as their effectiveness against other microorganisms.

An update on endotoxin neutralization strategies in Gram-negative bacterial infections.

INTRODUCTION: Gram-negative bacterial infections represent still a severe problem of human health care, regarding the increase in multi-resistance against classical antibiotics and the lack of newly developed antimicrobials. For the fight against these germs, anti-infective agents must overcome and/or bind to the Gram-negative outer membrane consisting of a lipopolysaccharide (LPS, endotoxin) outer leaflet and an inner leaflet from phospholipids, with additional peripheral or integral membrane proteins (OMP's). AREAS COVERED: The current article reviews data of existing therapeutic options and summarizes newer approaches for targeting and neutralizing endotoxins, ranging from in vitro over in vivo animal data to clinical applications by using databases such as Medline. EXPERT OPINION: Conventional antibiotic treatment of the bacteria leads to their killing, but not necessary LPS neutralization, which may be a severe problem in particular for the systemic pathway. This is the reason why there is an increasing number of therapeutic approaches, which - besides combating whole bacteria - at the same time try to neutralize endotoxin within or outside the bacterial cells mainly responsible for the high inflammation induction in Gram-negative species.

New antiseptic peptides to protect against endotoxin-mediated shock.

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