The honeybee antimicrobial peptide apidaecin differentially immunomodulates human macrophages, monocytes and dendritic cells

Combating Antimicrobial Resistance by Employing Antimicrobial Peptides: Immunomodulators and Therapeutic Agents against Infectious Diseases

The rising prevalence of multiple-drug-resistant pathogens poses a formidable challenge to conventional antimicrobial treatments. The inability of potent antibiotics to combat these "superbugs" underscores the pressing need for alternative therapeutic agents. Antimicrobial peptides (AMPs) represent an alternative class of antibiotics. AMPs are essential immunomodulatory molecules that are found in various organisms. They play a pivotal role in managing microbial ecosystems and bolstering innate immunity by targeting and eliminating invading microorganisms. AMPs also have applications in the agriculture sector by combating animal as well as plant pathogens. AMPs can be exploited for the targeted therapy of various diseases and can also be used in drug-delivery systems. They can be used in synergy with current treatments like antibiotics and can potentially lead to a lower required dosage. AMPs also have huge potential in wound healing and regenerative medicine. Developing AMP-based strategies with improved safety, specificity, and efficacy is crucial in the battle against alarming global microbial resistance. This review will explore AMPs' increasing applicability, their mode of antimicrobial activity, and various delivery systems enhancing their stability and efficacy.

In Vitro Properties and Pharmacokinetics of Temporarily PEGylated Onc72 Prodrugs

The favorable properties of antimicrobial peptides (AMPs) to rapidly kill pathogens are often limited by unfavorable pharmacokinetics due to fast degradation and renal clearance rates. Here, a prodrug strategy linking proline-rich AMP Onc72 to polyethylene glycol (PEGs) with average molecular weights of 5 and 20 kDa via a peptide linker containing a protease cleavage site is tested for the first time in vivo. Onc72 is released from these 5k- and 20k-prodrugs in mouse serum with half-life times (t1/2 ) of 8 and 14 h, respectively. Importantly, PEGylation protects Onc72 from proteolytic degradation providing a prolonged release of Onc72, balancing the degradation of free Onc72, and leading to relatively stable Onc72 concentrations and high antibacterial activities. The prodrugs are not hemolytic on human erythrocytes and show only slight cytotoxic effects on human cell lines indicating promising safety margins. When administered subcutaneously to female CD-1 mice, the prodrugs elimination t1/2 are 66 min and ≈5.5 h, respectively, compared to 43 min of free Onc72. The maximal Onc72 plasma levels are obtained ≈1 and ≈8 h postadministration, respectively. In conclusion, the prodrugs provide extended elimination t1/2 and a constant release of Onc72 in mice, potentially limiting adverse effects and increasing efficacy.

Biological and Inflammatory Effects of Antigen 5 from Polybia paulista (Hymenoptera, Vespidae) Venom in Mouse Intraperitoneal Macrophages

The social wasp Polybia paulista (Hymenoptera, Vespidae) is highly aggressive, being responsible for many medical occurrences. One of the most allergenic components of this venom is Antigen 5 (Poly p 5). The possible modulation of the in vitro immune response induced by antigen 5 from P. paulista venom, expressed recombinantly (rPoly p 5), on BALB/c mice peritoneal macrophages, activated or not with LPS, was assessed. Here, we analyzed cell viability changes, expression of the phosphorylated form of p65 NF-κB subunit, nitric oxide (NO), proinflammatory cytokines production, and co-stimulatory molecules (CD80, CD86). The results suggest that rPoly p 5 does not affect NO production nor the expression of co-stimulatory molecules in mouse peritoneal macrophages. On the other hand, rPoly p 5 induced an increase in IL-1β production in non-activated macrophages and a reduction in the production of TNF-α and MCP-1 cytokines in activated macrophages. rPoly p 5 decreased the in vitro production of the phosphorylated p65 NF-κB subunit in non-activated macrophages. These findings suggest an essential role of this allergen in the polarization of functional M2 macrophage phenotypes, when analyzed in previously activated macrophages. Further investigations, mainly in in vivo studies, should be conducted to elucidate Polybia paulista Ag5 biological role in the macrophage functional profile modulation.

Clostridioides difficile toxin A-mediated Caco-2 cell barrier damage was attenuated by insect-derived fractions and corresponded to increased gene transcription of cell junctional and proliferation proteins

Pathogenesis of C. difficile in the intestine is associated with the secretion of toxins which can damage the intestinal epithelial layer and result in diseases such as diarrhoea. Treatment for C. difficile infections consists of antibiotics which, however, have non-specific microbiocidal effects and may cause intestinal dysbiosis which results in subsequent health issues. Therefore, alternative treatments to C. difficile infections are required. We investigated whether different black soldier fly- and mealworm-derived fractions, after applying the INFOGEST digestion protocol, could counteract C. difficile toxin A-mediated barrier damage of small intestinal Caco-2 cells. Treatment and pre-treatment with insect-derived fractions significantly (p < 0.05) mitigated the decrease of the transepithelial electrical resistance (TEER) of Caco-2 cells induced by C. difficile toxin A. In relation to these effects, RNA sequencing data showed an increased transcription of cell junctional and proliferation protein genes in Caco-2 cells. Furthermore, the transcription of genes regulating immune signalling was also increased. To identify whether this resulted in immune activation we used a Caco-2/THP-1 co-culture model where the cells were only separated by a permeable membrane. However, the insect-derived fractions did not change the basolateral secreted IL-8 levels in this model. To conclude, our findings suggest that black soldier fly- and mealworm-derived fractions can attenuate C. difficile induced intestinal barrier disruption and they might be promising tools to reduce the symptoms of C. difficile infections.

Proline-rich antimicrobial peptides show a long-lasting post-antibiotic effect on Enterobacteriaceae and Pseudomonas aeruginosa

Background

Proline-rich antimicrobial peptides (PrAMPs) represent a promising class of potential therapeutics to treat multiresistant infections. They inhibit bacterial protein translation at the 70S ribosome by either blocking the peptide-exit tunnel (oncocin type) or trapping release factors (apidaecin type).

Objectives

Besides direct concentration-dependent antibacterial effects, the post-antibiotic effect (PAE) is the second most important criterion of antimicrobial pharmacodynamics to be determined in vitro. Here, PAEs of 10 PrAMPs and three antibiotics against three Escherichia coli strains, Klebsiella pneumoniae ATCC 10031 and Pseudomonas aeruginosa ATCC 27853 were studied after 1 h of exposure.

Methods

A robust high-throughput screening to determine PAEs was established, i.e. liquid handling by a 96-channel pipetting system and continuous incubation and absorbance measurement in a microplate reader.

Results

Prolonged PAEs (≥4 h) were detected for all peptides at their MIC values against all strains; PAEs were even >10 h for Api88, Api137, Bac7(1-60) and A3-APO. The PAEs increased further at 4 × MIC. Aminoglycosides gentamicin and kanamycin usually showed lower PAEs (≤4 h) at MIC, but PAEs increased to > 10 h at 4 × MIC. Bacteriostatic chloramphenicol exhibited the shortest PAEs (<4 h).

Conclusions

The PAEs of PrAMPs studied against Enterobacteriaceae and P. aeruginosa for the first time were typically 4-fold stronger than for conventional antibiotics. Together with their fast and irreversible uptake by bacteria, the observed prolonged PAE of PrAMPs helps to explain their high in vivo efficacy despite unfavourable pharmacokinetics.

ANTIMICROBIAL PEPTIDES — A POTENTIAL REPLACEMENT FOR TRADITIONAL ANTIBIOTICS

Antimicrobial peptides are a heterogeneous group of molecules involved in the innate and acquired immune response of various organisms, ranging from prokaryotes to mammals, including humans. They consist of 12–50 amino acid residues; have different physico-chemical and biological properties. The most common feature is their ability to destroy the prokaryotic cell membrane, which causes cell death. In the action, the molecules of antimicrobial peptides are embedded in the target bacteriological cells and change their conformation, forming structures in some cases resembling channels. Some other molecules of antimicrobial peptides can cover the surface of a bacteriological cell and form a carpet, when they reach a critical mass they act like detergents. In addition, being positively charged molecules of such peptides, penetrating through the membranes of parasitic and bacteriological cells, bind to polyanionic RNA and DNA molecules. Among the benefits of antimicrobial peptides is their high metabolic activity, low probability of occurrence of addictions and side effects. In addition, bacteriological pathogens that previously did not have resistance to any antimicrobial peptide are difficult to develop a strategy to control them. In this connection, these peptides are the most promising moleculessubstitutes for traditional antibiotics. The article discusses the approaches and strategies of therapeutic use, the studies of antimicrobial peptides identified in recent years; The most frequently encountered mechanisms of interaction of antimicrobial peptides and a bacteriological membrane are described, the physicochemical properties of peptide molecules are described; the results of studies on the detection of resistance of some strains of bacteria to antimicrobial peptides and antibiotics in general are summarized.

P17, an Original Host Defense Peptide from Ant Venom, Promotes Antifungal Activities of Macrophages through the Induction of C-Type Lectin Receptors Dependent on LTB4-Mediated PPARγ Activation

Despite the growing knowledge with regard to the immunomodulatory properties of host defense peptides, their impact on macrophage differentiation and on its associated microbicidal functions is still poorly understood. Here, we demonstrated that the P17, a new cationic antimicrobial peptide from ant venom, induces an alternative phenotype of human monocyte-derived macrophages (h-MDMs). This phenotype is characterized by a C-type lectin receptors (CLRs) signature composed of mannose receptor (MR) and Dectin-1 expression. Concomitantly, this activation is associated to an inflammatory profile characterized by reactive oxygen species (ROS), interleukin (IL)-1β, and TNF-α release. P17-activated h-MDMs exhibit an improved capacity to recognize and to engulf Candida albicans through the overexpression both of MR and Dectin-1. This upregulation requires arachidonic acid (AA) mobilization and the activation of peroxisome proliferator-activated receptor gamma (PPARγ) nuclear receptor through the leukotriene B4 (LTB4) production. AA/LTB4/PPARγ/Dectin-1-MR signaling pathway is crucial for P17-mediated anti-fungal activity of h-MDMs, as indicated by the fact that the activation of this axis by P17 triggered ROS production and inflammasome-dependent IL-1β release. Moreover, we showed that the increased anti-fungal immune response of h-MDMs by P17 was dependent on intracellular calcium mobilization triggered by the interaction of P17 with pertussis toxin-sensitive G-protein-coupled receptors on h-MDMs. Finally, we also demonstrated that P17-treated mice infected with C. albicans develop less severe gastrointestinal infection related to a higher efficiency of their macrophages to engulf Candida, to produce ROS and IL-1β and to kill the yeasts. Altogether, these results identify P17 as an original activator of the fungicidal response of macrophages that acts upstream PPARγ/CLRs axis and offer new immunomodulatory therapeutic perspectives in the field of infectious diseases.

Comparing naturally occurring glycosylated forms of proline rich antibacterial peptide, Drosocin

Antimicrobial peptides (AMPs) are key players of innate immunity. Amongst various classes of AMPs, proline rich AMPs from insects enjoy special attention with few members of this class bearing O-glycosylation as post-translational modification. Drosocin, a 19 amino acid glycosylated AMP is a member of proline rich class, synthesized in the haemolymph of Drosophila melanogaster upon bacterial challenge. We report herein the chemical synthesis of drosocin carrying disaccharide (β-Gal(1 → 3)α-GalNAc) and comparison of its structural and functional properties with another naturally occurring monoglycosylated form of drosocin i.e. α-GalNAc-drosocin as well as with non-glycosylated drosocin. The disaccharide containing drosocin exhibited lower potency compared to monoglycosylated drosocin against all the tested Gram negative bacteria, suggesting the role of the distal sugar or increase in the sugar chain length on the activity. Circular dichroism studies failed to demonstrate the differential effect of sugars on the overall peptide conformation. Haemolytic and cytotoxic properties of drosocin were not altered due to an increase in the sugar chain length. In addition, we have also evaluated the effect of differentially glycosylated drosocins on two pro-inflammatory cytokines secreted by murine macrophages or LPS stimulated macrophages. All the drosocin forms tested, neither could stimulate the secretion of TNF-α and IL-6 nor could modulate LPS-induced levels of TNF-α and IL-6 in murine macrophages. This study provides insights about naturally occurring two different glycosylated forms of drosocin.

In vivo Efficacy and Pharmacokinetics of Optimized Apidaecin Analogs

Proline-rich antimicrobial peptides (PrAMPs) represent promising alternative therapeutic options for the treatment of multidrug-resistant bacterial infections. PrAMPs are predominantly active against Gram-negative bacteria by inhibiting protein expression via at least two different modes of action, i.e., blocking the ribosomal exit tunnel of 70S ribosomes (oncocin-type binding) or inhibiting the assembly of the 50S ribosomal subunit (apidaecin-type binding). The in vivo efficacy and favorable biodistribution of oncocins confirmed the therapeutic potential of short PrAMPs for the first time, whereas the in vivo evaluation of apidaecins is still limited despite the promising efficacy of apidaecin-analog Api88 in an intraperitoneal murine infection model. Here, the in vivo efficacy of apidaecin-analog Api137 was studied, which rescued all NMRI mice from a lethal intraperitoneal infection with E. coli ATCC 25922 when administered three times intraperitoneal at doses of 0.6 mg/kg starting 1 h after infection. When Api88 and Api137 were administered intravenous or intraperitoneal at doses of 5 and 20 mg/kg, their plasma levels were similarly low (<3 μg/mL) and four-fold lower than for oncocin-analog Onc72. This contradicted earlier expectation based on the very low serum stability of Api88 with a half-life time of only ~5 min compared to ~6 and ~3 h for Api137 and Onc72, respectively. Pharmacokinetic data relying on a sensitive mass spectrometry method utilizing multiple reaction monitoring and isotope-labeled peptides revealed that Api88 and Api137 were present in blood, urine, and kidney, and liver homogenates at similar levels accompanied by the same major metabolites comprising residues 1-16 and 1-17. The pretended discrepancy was solved, when all peptides were incubated in peritoneal lavage. Api137 was rapidly degraded at the C-terminus, while Api88 was rather stable despite releasing the same degradation products. Onc72 was very stable explaining its higher plasma levels compared to Api88 and Api137 after intraperitoneal administration illuminating its good in vivo efficacy. The data indicate that the degradation of therapeutic peptides should be studied in serum and further body fluids. Moreover, the high efficacy in murine infection models and the fast clearance of Api88 and Api137 within ~60 min after intravenous and ~90 min after intraperitoneal injections indicate that their in vivo efficacy relates to the maximal peptide concentration achieved in blood.

Oncocin Onc72 is efficacious against antibiotic-susceptible Klebsiella pneumoniae ATCC 43816 in a murine thigh infection model

Oncocins and apidaecins are short proline-rich antimicrobial peptides (PrAMPs) representing novel antibiotic drug lead compounds that kill bacteria after internalization and inhibition of intracellular targets (e.g. 70S ribosome and DnaK). Oncocin Onc72 is highly active against Gram-negative bacteria in vitro and in vivo protecting mice in systemic infection models with Escherichia coli and KPC-producing Klebsiella pneumoniae. Here we studied its efficacy in a murine thigh infection model using meropenem as antibiotic comparator that had a 44-fold higher molar in vitro activity than Onc72. Male CD1 mice were rendered neutropenic using cyclophosphamide for four days before intramuscular infection with K. pneumoniae ATCC 43816. After 75 min oncocin Onc72 or the antibiotic comparator meropenem were administered subcutaneously with 100 mg (43 µmol) and 25 mg (65 µmol) per kg of body weight, respectively, six times every 75 min. Onc72 and meropenem administered subcutaneously reduced the thigh tissue burden of K. pneumoniae ATCC 43816 in neutropenic mice significantly by 4.14 and 4.65 a log10 cfu/g, respectively. The bacterial counts were ∼0.5 and ∼1 log10 below the pre-treatment burden, respectively, indicating bactericidal effects for both compounds. Thus, Onc72 was as efficacious as meropenem in vivo despite its much lower in vitro activity determined according to CLSI standard antimicrobial activity tests.

Immunomodulatory effects of anti-microbial peptides

Anti-microbial peptides (AMPs) were originally thought to exert protecting actions against bacterial infection by disintegrating bacterial membranes. Upon identification of internal bacterial targets, the view changed and moved toward inhibition of prokaryote-specific biochemical processes. However, the level of none of these activities can explain the robust efficacy of some of these peptides in animal models of systemic and cutaneous infections. A rapidly growing panel of reports suggests that AMPs, now called host-defense peptides (HDPs), act through activating the immune system of the host. This includes recruitment and activation of macrophages and mast cells, inducing chemokine production and altering NF-κB signaling processes. As a result, both pro- and anti-inflammatory responses are elevated together with activation of innate and adaptive immunity mechanisms, wound healing, and apoptosis. HDPs sterilize the systemic circulation and local injury sites significantly more efficiently than pure single-endpoint in vitro microbiological or biochemical data would suggest and actively aid recovering from tissue damage after or even without bacterial infections. However, the multiple and, often opposing, immunomodulatory functions of HDPs require exceptional care in therapeutic considerations.

Immunogenicity and pharmacokinetics of short, proline-rich antimicrobial peptides

Aim: The potential of proline-rich antimicrobial peptides (PrAMPs) to treat multidrug-resistant Gram-negative pathogens has been intensively investigated. They are efficacious at low doses in infection models and well tolerated in healthy mice at high doses. Methods & results: PrAMPs Onc72 and Api88 were nonimmunogenic in mice unless conjugated to a carrier protein. Monoclonal IgG1/IgG2b antibodies produced by hybridoma cells were mapped to different Onc72 regions and combined in a sandwich-ELISA in a pharmacokinetic study. Onc72 was detected at concentrations up to 32 µg/ml in murine blood after administering 20 mg/kg and reached several organs within 10 min. Conclusion: Both PrAMPs were not immunogenic and Onc72 concentrations in blood were well above the minimal inhibitory concentrations for Enterobacteriaceae further confirming their potential as novel antibiotics.

On the Functional Overlap between Complement and Anti-Microbial Peptides

Intriguingly, activated complement and anti-microbial peptides share certain functionalities; lytic, phagocytic, and chemo-attractant activities and each may, in addition, exert cell instructive roles. Each has been shown to have distinct LPS detoxifying activity and may play a role in the development of endotoxin tolerance. In search of the origin of complement, a functional homolog of complement C3 involved in opsonization has been identified in horseshoe crabs. Horseshoe crabs possess anti-microbial peptides able to bind to acyl chains or phosphate groups/saccharides of endotoxin, LPS. Complement activity as a whole is detectable in marine invertebrates. These are also a source of anti-microbial peptides with potential pharmaceutical applicability. Investigating the locality for the production of complement pathway proteins and their role in modulating cellular immune responses are emerging fields. The significance of local synthesis of complement components is becoming clearer from in vivo studies of parenchymatous disease involving specifically generated, complement-deficient mouse lines. Complement C3 is a central component of complement activation. Its provision by cells of the myeloid lineage varies. Their effector functions in turn are increased in the presence of anti-microbial peptides. This may point to a potentiating range of activities, which should serve the maintenance of health but may also cause disease. Because of the therapeutic implications, this review will consider closely studies dealing with complement activation and anti-microbial peptide activity in acute inflammation (e.g., dialysis-related peritonitis, appendicitis, and ischemia).

Synthesis, characterization, and photoinduced antibacterial activity of porphyrin-type photosensitizers conjugated to the antimicrobial peptide apidaecin 1b

Antimicrobial photodynamic therapy (aPDT) is an emerging treatment for bacterial infections that is becoming increasingly more attractive because of its effectiveness against multi-antibiotic-resistant strains and unlikelihood of inducing bacterial resistance. Among the strategies to enhance the efficacy of PDT against Gram-negative bacteria, the binding to a cationic antimicrobial peptide offers the attractive prospect for improving both the water solubilty and the localization of the photoactive drug in bacteria. In this work we have compared a number of free and apidaecin-conjugated photosensitizers (PSs) differing in structure and charge. Our results indicate that the conjugation of per se ineffective highly hydrophobic PSs to a cationic peptide produces a photosensitizing agent effective against Gram-negative bacteria. Apidaecin cannot improve the phototoxic activity of cationic PSs, which mainly depends on a very high yield of singlet oxygen production in the surroundings of the bacterial outer membrane. Apidaecin-PS conjugates appear most promising for treatment protocols requiring repeated washing after sensitizer delivery.

Effect of antimicrobial peptides from Apis mellifera hemolymph and its optimized version Api88 on biological activities of human monocytes and mast cells

Apidaecin peptides are produced by the honeybee Apis mellifera as a major part of its non-specific defense system against infections. Having verified that the peptides apidaecin 1b and Api88-a designer peptide based on the native apidaecin 1b sequence-are highly active against Gram-negative bacteria, we studied their ability to modulate biological activities of human monocytes and mast cells (MC), two important cell types of the human innate immune system. We could show that both peptides are nontoxic and fairly resistant to degradation in cell culture medium containing 10% FBS. Among the peptides tested we found Api88 to inhibit LPS-induced TNF-α production in a concentration-dependent manner. Resting monocytes did not respond to Api88. Whilst Api88 neither induced migration nor affected the phagocytic activity of monocytes it partially inhibited the generation of reactive oxygen intermediates produced in response to LPS. In human MC, however, Api88 triggered degranulation and the mobilization of intracellular Ca(2+)-ions. Taken together these data clearly indicate that Api88 is a multifunctional molecule that can modulate biological responses of human monocytes and MC in addition to its antimicrobial activity.

Api88 is a novel antibacterial designer peptide to treat systemic infections with multidrug-resistant Gram-negative pathogens

The emergence of multiple-drug-resistant (MDR) bacterial pathogens in hospitals (nosocomial infections) presents a global threat of growing importance, especially for Gram-negative bacteria with extended spectrum β-lactamase (ESBL) or the novel New Delhi metallo-β-lactamase 1 (NDM-1) resistance. Starting from the antibacterial peptide apidaecin 1b, we have optimized the sequence to treat systemic infections with the most threatening human pathogens, such as Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, and Acinetobacter baumannii. The lead compound Api88 enters bacteria without lytic effects at the membrane and inhibits chaperone DnaK at the substrate binding domain with a K(D) of 5 μmol/L. The Api88-DnaK crystal structure revealed that Api88 binds with a seven residue long sequence (PVYIPRP), in two different modes. Mice did not show any sign of toxicity when Api88 was injected four times intraperitoneally at a dose of 40 mg/kg body weight (BW) within 24 h, whereas three injections of 1.25 mg/kg BW and 5 mg/kg BW were sufficient to rescue all animals in lethal sepsis models using pathogenic E. coli strains ATCC 25922 and Neumann, respectively. Radioactive labeling showed that Api88 enters all organs investigated including the brain and is cleared through both the liver and kidneys at similar rates. In conclusion, Api88 is a novel, highly promising, 18-residue peptide lead compound with favorable in vitro and in vivo properties including a promising safety margin.

Oncocin derivative Onc72 is highly active against Escherichia coli in a systemic septicaemia infection mouse model

OBJECTIVES

The antimicrobial oncocin derivative Onc72 is highly active against a number of Gram-negative bacteria, including resistant strains. Here we study its toxicity and efficacy in a lethal mouse infection model.

METHODS

In an acute toxicity study, purified Onc72 was administered to NMRI mice in four consecutive injections within a period of 24 h as an intraperitoneal bolus. The animals' behaviour was monitored for 5 days, before several organs were examined by histopathology. A lethal Escherichia coli infection model was established and the efficacy of Onc72 was evaluated for different peptide doses considering the survival rates of each dose group and the bacterial counts in blood, lavage and organs.

RESULTS

Intraperitoneal bolus injections with single doses of 20 or 40 mg of Onc72 per kg of body weight did not result in any abnormal animal behaviour. No mouse became moribund or died within the studied period. Histopathological examinations revealed no toxic effects. When infected with E. coli at a lethal dose, none of the untreated animals survived the next 24 h, whereas all animals treated three times with Onc72 at doses of ≥5 mg/kg survived the observation period of 5 days. No bacteria were detected in the blood of treated animals after day 5 post-infection. The effective dose (ED(50)) was ∼2 mg/kg.

CONCLUSIONS

No toxic effects were observed for Onc72 within the studied dose range up to 40 mg/kg, indicating a safety margin of >20.