Immune modulation by multifaceted cationic host defense (antimicrobial) peptides

Synergy Between Proline-Rich Antimicrobial Peptides and Small Molecule Antibiotics Against Selected Gram-Negative Pathogens in vitro and in vivo

As monotherapy, modified proline-rich antimicrobial peptides (PrAMPs) protect animals from experimental bacteremia in a dose-dependent manner. We evaluated the in vitro synergy of a modified PrAMP, A3-APO, a dimer, previously shown to inhibit the 70 kDa bacterial heat shock protein DnaK, with imipenem or colistin against two antibiotic-resistant pathogens; a carbapenemase-expressing Klebsiella pneumoniae strain K97/09 and Acinetobacter baumannii (ATCC BAA-1605). Combining antimicrobials resulted in synergy for PrAMP/colistin combination against both K. pneumoniae and A. baumannii (ΣFIC = 0.08 both) and additive activity for the A3-APO/imipenem combination against K. pneumoniae (ΣFIC = 0.53). Chex1-Arg20, (designated as ARV-1502 in preclinical development), the single chain PrAMP monomer of A3-APO, showed synergy with meropenem against a carbapenem-resistant uropathogenic Escherichia coli strain (ΣFIC = 0.38). In a murine bacteremia model using K97/09, A3-APO at 1 mg/kg demonstrated improved survival when co-administered with standard (10 mg/kg) or subtherapeutic (1 mg/kg) doses of colistin at 36 h (p < 0.05). Surprisingly, the survival benefit of A3-APO was augmented when the A3-APO dose was decreased by 50% to 0.5 mg/kg (p < 0.02) in conjunction with a subtherapeutic colistin dose (1 mg/kg). ARV-1502, as monotherapy demonstrated prolonged (>24 h) activity in a mouse Escherichia coli infection assay. Co-treatment with ARV-1502 and subtherapeutic doses of ceftazidime (150 mg/kg) was studied in a mouse model of melioidosis. ARV-1502 provided a 50% improvement in long-term (62 days) survival, but only at the lowest of 3 administered doses; survival advantage was demonstrated at 2.5 mg/kg but not at 5 or 10 mg/kg. The mortality benefit of combination therapies was not routinely accompanied by a parallel decline in blood or tissue bacterial counts in surviving animals, suggesting that the anti-infective activity of the host defense peptides (HDP) is broader than simply bacterial eradication. In fact, the hormetic effect observed in either animal models suggest that low dose HDP treatment may change the dominant mode of action in experimental bacteremia.

Perinatal Hypoxic-Ischemic Encephalopathy and Neuroprotective Peptide Therapies: A Case for Cationic Arginine-Rich Peptides (CARPs)

Perinatal hypoxic-ischemic encephalopathy (HIE) is the leading cause of mortality and morbidity in neonates, with survivors suffering significant neurological sequelae including cerebral palsy, epilepsy, intellectual disability and autism spectrum disorders. While hypothermia is used clinically to reduce neurological injury following HIE, it is only used for term infants (>36 weeks gestation) in tertiary hospitals and improves outcomes in only 30% of patients. For these reasons, a more effective and easily administrable pharmacological therapeutic agent, that can be used in combination with hypothermia or alone when hypothermia cannot be applied, is urgently needed to treat pre-term (≤36 weeks gestation) and term infants suffering HIE. Several recent studies have demonstrated that cationic arginine-rich peptides (CARPs), which include many cell-penetrating peptides [CPPs; e.g., transactivator of transcription (TAT) and poly-arginine-9 (R9; 9-mer of arginine)], possess intrinsic neuroprotective properties. For example, we have demonstrated that poly-arginine-18 (R18; 18-mer of arginine) and its D-enantiomer (R18D) are neuroprotective in vitro following neuronal excitotoxicity, and in vivo following perinatal hypoxia-ischemia (HI). In this paper, we review studies that have used CARPs and other peptides, including putative neuroprotective peptides fused to TAT, in animal models of perinatal HIE. We critically evaluate the evidence that supports our hypothesis that CARP neuroprotection is mediated by peptide arginine content and positive charge and that CARPs represent a novel potential therapeutic for HIE.

The potential for immunoglobulins and host defense peptides (HDPs) to reduce the use of antibiotics in animal production

Innate defense mechanisms are aimed at quickly containing and removing infectious microorganisms and involve local stromal and immune cell activation, neutrophil recruitment and activation and the induction of host defense peptides (defensins and cathelicidins), acute phase proteins and complement activation. As an alternative to antibiotics, innate immune mechanisms are highly relevant as they offer rapid general ways to, at least partially, protect against infections and enable the build-up of a sufficient adaptive immune response. This review describes two classes of promising alternatives to antibiotics based on components of the innate host defense. First we describe immunoglobulins applied to mimic the way in which they work in the newborn as locally acting broadly active defense molecules enforcing innate immunity barriers. Secondly, the potential of host defense peptides with different modes of action, used directly, induced in situ or used as vaccine adjuvants is described.

Preclinical testing of a broad-spectrum antimicrobial endotracheal tube coated with an innate immune synthetic mimic

Background

Endotracheal tubes provide an abiotic surface on which bacteria and fungi form biofilms, and the release of endotoxins and planktonic organisms can cause damaging inflammation and infections.

Objectives

Ceragenins are small molecule mimics of antimicrobial peptides with broad-spectrum antibacterial and antifungal activity, and a ceragenin may be used to provide antimicrobial protection to the abiotic surface of an endotracheal tube.

Methods

A hydrogel film, containing CSA-131, was generated on endotracheal tubes. Elution of CSA-131 was quantified in drip-flow and static systems, antifungal and antibacterial activity was measured with repeated inoculation in growth media, biofilm formation was observed through electron microscopy, safety was determined by intubation of pigs with coated and uncoated endotracheal tubes.

Results

Optimized coatings containing CSA-131 provided controlled elution of CSA-131, with concentrations released of less than 1 μg/mL. The eluting ceragenin prevented fungal and bacterial colonization of coated endotracheal tubes for extended periods, while uncoated tubes were colonized by bacteria and fungi. Coated tubes were well tolerated in intubated pigs.

Conclusions

Thin films containing CSA-131 provide protection against microbial colonization of endotracheal tubes. This protection prevents fungal and bacterial biofilm formation on the tubes and reduces endotoxin associated with tubes. This coating is well suited for decreasing the adverse effects of intubation associated with infection and inflammation.

A coarse-grained approach to studying the interactions of the antimicrobial peptides aurein 1.2 and maculatin 1.1 with POPG/POPE lipid mixtures

In the present work we investigated the differential interactions of the antimicrobial peptides (AMPs) aurein 1.2 and maculatin 1.1 with a bilayer composed of a mixture of the lipids 1-palmitoyl-2-oleoyl-sn-glycero-3-phospho-(1'-rac-glycerol) (POPG) and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine (POPE). We carried out molecular dynamics (MD) simulations using a coarse-grained approach within the MARTINI force field. The POPE/POPG mixture was used as a simple model of a bacterial (prokaryotic cell) membrane. The results were compared with our previous findings for structures of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), a representative lipid of mammalian cells. We started the simulations of the peptide-lipid system from two different initial conditions: peptides in water and peptides inside the hydrophobic core of the membrane, employing a pre-assembled lipid bilayer in both cases. Our results show similarities and differences regarding the molecular behavior of the peptides in POPE/POPG in comparison to their behavior in a POPC membrane. For instance, aurein 1.2 molecules can adopt similar pore-like structures on both POPG/POPE and POPC membranes, but the peptides are found deeper in the hydrophobic core in the former. Maculatin 1.1 molecules, in turn, achieve very similar structures in both kinds of bilayers: they have a strong tendency to form clusters and induce curvature. Therefore, the results of this study provide insight into the mechanisms of action of these two peptides in membrane leakage, which allows organisms to protect themselves against potentially harmful bacteria. Graphical Abstract Aurein pore structure (green) in a lipid bilayer composed by POPE (blue) and POPG (red) mixture. It is possible to see water beads (light blue) inside the pore.

Computer-aided prediction of antigen presenting cell modulators for designing peptide-based vaccine adjuvants

Background

Evidences in literature strongly advocate the potential of immunomodulatory peptides for use as vaccine adjuvants. All the mechanisms of vaccine adjuvants ensuing immunostimulatory effects directly or indirectly stimulate antigen presenting cells (APCs). While numerous methods have been developed in the past for predicting B cell and T-cell epitopes; no method is available for predicting the peptides that can modulate the APCs.

Methods

We named the peptides that can activate APCs as A-cell epitopes and developed methods for their prediction in this study. A dataset of experimentally validated A-cell epitopes was collected and compiled from various resources. To predict A-cell epitopes, we developed support vector machine-based machine learning models using different sequence-based features.

Results

A hybrid model developed on a combination of sequence-based features (dipeptide composition and motif occurrence), achieved the highest accuracy of 95.71% with Matthews correlation coefficient (MCC) value of 0.91 on the training dataset. We also evaluated the hybrid models on an independent dataset and achieved a comparable accuracy of 95.00% with MCC 0.90.

Conclusion

The models developed in this study were implemented in a web-based platform VaxinPAD to predict and design immunomodulatory peptides or A-cell epitopes. This web server available at http://webs.iiitd.edu.in/raghava/vaxinpad/ will facilitate researchers in designing peptide-based vaccine adjuvants.

Electronic supplementary material

The online version of this article (10.1186/s12967-018-1560-1) contains supplementary material, which is available to authorized users.

High Throughput Screening for Natural Host Defense Peptide-Inducing Compounds as Novel Alternatives to Antibiotics

A rise in antimicrobial resistance demands novel alternatives to antimicrobials for disease control and prevention. As an important component of innate immunity, host defense peptides (HDPs) are capable of killing a broad spectrum of pathogens and modulating a range of host immune responses. Enhancing the synthesis of endogenous HDPs has emerged as a novel host-directed antimicrobial therapeutic strategy. To facilitate the identification of natural products with a strong capacity to induce HDP synthesis, a stable macrophage cell line expressing a luciferase reporter gene driven by a 2-Kb avian β-defensin 9 (AvBD9) gene promoter was constructed through lentiviral transduction and puromycin selection. A high throughput screening assay was subsequently developed using the stable reporter cell line to screen a library of 584 natural products. A total of 21 compounds with a minimum Z-score of 2.0 were identified. Secondary screening in chicken HTC macrophages and jejunal explants further validated most compounds with a potent HDP-inducing activity in a dose-dependent manner. A follow-up oral administration of a lead natural compound, wortmannin, confirmed its capacity to enhance the AvBD9 gene expression in the duodenum of chickens. Besides AvBD9, most other chicken HDP genes were also induced by wortmannin. Additionally, butyrate was also found to synergize with wortmannin and several other newly-identified compounds in AvBD9 induction in HTC cells. Furthermore, wortmannin acted synergistically with butyrate in augmenting the antibacterial activity of chicken monocytes. Therefore, these natural HDP-inducing products may have the potential to be developed individually or in combinations as novel antibiotic alternatives for disease control and prevention in poultry and possibly other animal species including humans.

Lipidated α/α-AA heterogeneous peptides as antimicrobial agents

With an increase of resistance in bacteria there is an urgent need for alternative treatment methods that could complement conventional antibiotics. In the past two decades, focus has been drawn to Host Defense Peptides (HDPs) as potential antibiotic agents. Herein we reported our studies on the development of lipidated α/α-AA heterogeneous peptides as a new class of HDP mimetics. These compounds showed potent antimicrobial activity toward both Gram-positive and Gram-negative bacteria, and they also displayed excellent selectivity as they only exhibited limited hemolytic activity. The fluorescence microscopy suggested that the mechanism of action of these heterogeneous peptides is bacterial membrane disruption, which is believed to be the major reason why it is difficult for bacteria to develop resistance. The subsequent time kill studies suggested that these compounds could rapidly eradicate bacteria. Moreover, this class of compounds could also effectively clear biofilms formed by both Gram-positive and Gram-negative bacteria. These findings suggested that lipidated α/α-AA heterogeneous peptides, as a new class of peptidomimetics, are promising antibiotic agents combating antibiotic resistance.

Human Metapneumovirus Infection Inhibits Cathelicidin Antimicrobial Peptide Expression in Human Macrophages

Human cathelicidin antimicriobial peptide (CAMP) is a critical component of host innate immunity with both antimicrobial and immunomodulatory functions. Several pathogens have been shown to downregulate CAMP expression, yet it is unclear if such modulation occurs during a viral infection. In this study, we showed that infection with human metapneumovirus (hMPV), one of the leading causes of respiratory tract infections in young children, strongly suppressed basal and vitamin-D induced CAMP expression in human macrophages. hMPV-mediated suppression of CAMP did not correlate with reduced transcriptional expression of key vitamin D signaling components, such as CYP27B1 or vitamin D receptor, suggesting a vitamin D-independent mechanism. Blocking interferon-signaling pathways did not reverse hMVP-mediated suppression of CAMP, indicating that the suppressive effect is largely interferon-independent. Instead, we identified C/EBPα as the key modulator of hMPV-mediated suppression of CAMP. hMPV infection strongly repressed the expression of C/EBPα, and a knockdown study confirmed that C/EBPα is critical for CAMP expression in human macrophages. Such modulation of CAMP (and C/EBPα) could be reproduced by TLR1/2 ligand treatment in human macrophages, suggesting a common mechanism underlying pathogen-mediated downregulation of CAMP through C/EBPα. This study opens up a new understanding of altered human antimicrobial responses following infections.

Exposure to chorioamnionitis alters the monocyte transcriptional response to the neonatal pathogen Staphylococcus epidermidis

Preterm infants are uniquely susceptible to late-onset sepsis that is frequently caused by the skin commensal Staphylococcus epidermidis. Innate immune responses, particularly from monocytes, are a key protective mechanism. Impaired cytokine production by preterm infant monocytes is well described, but few studies have comprehensively assessed the corresponding monocyte transcriptional response. Innate immune responses in preterm infants may be modulated by inflammation such as prenatal exposure to histologic chorioamnionitis which complicates 40-70% of preterm pregnancies. Chorioamnionitis alters the risk of late-onset sepsis, but its effect on monocyte function is largely unknown. Here, we aimed to determine the impact of exposure to chorioamnionitis on the proportions and phenotype of cord blood monocytes using flow cytometry, as well as their transcriptional response to live S. epidermidis. RNA-seq was performed on purified cord blood monocytes from very preterm infants (<32 weeks gestation, with and without chorioamnionitis-exposure) and term infants (37-40 weeks), pre- and postchallenge with live S. epidermidis. Preterm monocytes from infants without chorioamnionitis-exposure did not exhibit an intrinsically deficient transcriptional response to S. epidermidis compared to term infants. In contrast, chorioamnionitis-exposure was associated with hypo-responsive transcriptional phenotype regarding a subset of genes involved in antigen presentation and adaptive immunity. Overall, our findings suggest that prenatal exposure to inflammation may alter the risk of sepsis in preterm infants partly by modulation of monocyte responses to pathogens.

Novel bioactive peptides from PD-L1/2, a type 1 ribosome inactivating protein from Phytolacca dioica L. Evaluation of their antimicrobial properties and anti-biofilm activities

Antimicrobial peptides, also called Host Defence Peptides (HDPs), are effectors of innate immune response found in all living organisms. In a previous report, we have identified by chemical fragmentation, and characterized the first cryptic antimicrobial peptide in PD-L4, a type 1 ribosome inactivating protein (RIP) from leaves of Phytolacca dioica L. We applied a recently developed bioinformatic approach to a further member of the differently expressed pool of type 1 RIPs from P. dioica (PD-L1/2), and identified two novel putative cryptic HDPs in its N-terminal domain. These two peptides, here named IKY31 and IKY23, exhibit antibacterial activities against planktonic bacterial cells and, interestingly, significant anti-biofilm properties against two Gram-negative strains. Here, we describe that PD-L1/2 derived peptides are able to induce a strong dose-dependent reduction in biofilm biomass, affect biofilm thickness and, in the case of IKY31, interfere with cell-to-cell adhesion, likely by affecting biofilm structural components. In addition to these findings, we found that both PD-L1/2 derived peptides are able to assume stable helical conformations in the presence of membrane mimicking agents (SDS and TFE) and intriguingly beta structures when incubated with extracellular bacterial wall components (LPS and alginate). Overall, the data collected in this work provide further evidence of the importance of cryptic peptides derived from type 1 RIPs in host/pathogen interactions, especially under pathophysiological conditions induced by biofilm forming bacteria. This suggests a new possible role of RIPs as precursors of antimicrobial and anti-biofilm agents, likely released upon defensive proteolytic processes, which may be involved in plant homeostasis.

The novel complex combination of alum, CpG ODN and HH2 as adjuvant in cancer vaccine effectively suppresses tumor growth in vivo

Single-component adjuvant is prone to eliciting a specific type of Th1 or Th2 response. So, the development of combinatorial adjuvants inducing a robust mixed Th1/Th2 response is a promising vaccination strategy against cancer. Here, we describe a novel combination of aluminum salts (alum), CpG oligodeoxynucleotide (CpG) and innate defense regulator peptide HH2 for improving anti-tumor immune responses. The CpG-HH2 complex significantly enhanced the production of IFN-γ, TNF-α and IL-1β, promoted the uptake of antigen and strengthened the activation of p38, Erk1/2 and NF-κB in vitro, compared to CpG or HH2 alone. Immunization with NY-ESO-1 antigen plus alum-CpG-HH2 combinatorial adjuvant effectively inhibited tumor growth and reduced tumor burden in prophylactic and therapeutic tumor models and even in passive serum or cellular therapy. In addition, co-administration of NY-ESO-1 with alum-CpG-HH2 combinatorial adjuvant markedly activated NK cell cytotoxicity, induced antibody-dependent cellular cytotoxicity (ADCC), dramatically elicited cytotoxic T lymphocytes (CTLs) response, and increased infiltrating lymphocytes in tumors. Moreover, in vivo depletion of CD8⁺ T cells completely and depletion of NK cells partially blocked the anti-tumor activity of NY-ESO-1-alum-CpG-HH2 immunization. Overall, our results demonstrate a novel adjuvant combination for cancer vaccine with efficient immunomodulation by stimulating innate immunity and mediating adaptive immunity.

Tryptophan-Rich and Proline-Rich Antimicrobial Peptides

Due to the increasing emergence of drug-resistant pathogenic microorganisms, there is a world-wide quest to develop new-generation antibiotics. Antimicrobial peptides (AMPs) are small peptides with a broad spectrum of antibiotic activities against bacteria, fungi, protozoa, viruses and sometimes exhibit cytotoxic activity toward cancer cells. As a part of the native host defense system, most AMPs target the membrane integrity of the microorganism, leading to cell death by lysis. These membrane lytic effects are often toxic to mammalian cells and restrict their systemic application. However, AMPs containing predominantly either tryptophan or proline can kill microorganisms by targeting intracellular pathways and are therefore a promising source of next-generation antibiotics. A minimum length of six amino acids is required for high antimicrobial activity in tryptophan-rich AMPs and the position of these residues also affects their antimicrobial activity. The aromatic side chain of tryptophan is able to rapidly form hydrogen bonds with membrane bilayer components. Proline-rich AMPs interact with the 70S ribosome and disrupt protein synthesis. In addition, they can also target the heat shock protein in target pathogens, and consequently lead to protein misfolding. In this review, we will focus on describing the structures, sources, and mechanisms of action of the aforementioned AMPs.

Antimicrobial Peptides and Their Therapeutic Potential for Bacterial Skin Infections and Wounds

Alarming data about increasing resistance to conventional antibiotics are reported, while at the same time the development of new antibiotics is stagnating. Skin and soft tissue infections (SSTIs) are mainly caused by the so called ESKAPE pathogens (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter species) which belong to the most recalcitrant bacteria and are resistant to almost all common antibiotics. S. aureus and P. aeruginosa are the most frequent pathogens isolated from chronic wounds and increasing resistance to topical antibiotics has become a major issue. Therefore, new treatment options are urgently needed. In recent years, research focused on the development of synthetic antimicrobial peptides (AMPs) with lower toxicity and improved activity compared to their endogenous counterparts. AMPs appear to be promising therapeutic options for the treatment of SSTIs and wounds as they show a broad spectrum of antimicrobial activity, low resistance rates and display pivotal immunomodulatory as well as wound healing promoting activities such as induction of cell migration and proliferation and angiogenesis. In this review, we evaluate the potential of AMPs for the treatment of bacterial SSTIs and wounds and provide an overview of the mechanisms of actions of AMPs that contribute to combat skin infections and to improve wound healing. Bacteria growing in biofilms are more resistant to conventional antibiotics than their planktonic counterparts due to limited biofilm penetration and distinct metabolic and physiological functions, and often result in chronification of infections and wounds. Thus, we further discuss the feasibility of AMPs as anti-biofilm agents. Finally, we highlight perspectives for future therapies and which issues remain to bring AMPs successfully to the market.

Mining the tree of life: Host defense peptides as antiviral therapeutics

Discovering new therapeutics for human viral diseases is important for combatting emerging infectious viruses and omnipresent circulating viruses as well as those that can become resistant to the drugs we currently have available. The innate host defense peptide (HDP) repertoire present in animals is a wealth of potential antimicrobial agents that could be mined to meet these needs. While much of the body of research regarding HDPs is in the context of bacteria, there is increasing evidence that they can be an effective source for antivirals. Peptides can be identified in a number of ways, including eco-conservation-minded approaches. Those shown to have antiviral properties can be modified to exhibit desired properties as the relationship between structure and function is elucidated and then developed into therapeutics for human use. This review looks at the discovery and therapeutic potential of HDPs for human viral infections.

Comparison of neuroprotective efficacy of poly-arginine R18 and R18D (D-enantiomer) peptides following permanent middle cerebral artery occlusion in the Wistar rat and in vitro toxicity studies

We have previously demonstrated that arginine-rich and poly-arginine peptides possess potent neuroprotective properties, with poly-arginine peptide R18 identified as being highly effective at reducing infarct volume following middle cerebral artery occlusion (MCAO) in the Sprague Dawley rat. Since peptides synthesised using D-isoform amino acids have greater stability than L-isoform peptides due to increased resistance to proteolytic degradation, they represent potentially more effective peptide therapeutics. Therefore we compared the neuroprotective efficacy of R18 and its D-enantiomer R18D following permanent MCAO in the Wistar rat. Furthermore, as increased peptide stability may also increase peptide toxicity, we examined the effects of R18 and R18D on cultured cortical neurons, astrocytes, brain endothelial cells (bEND.3), and embryonic kidney cells (HEK293) following a 10-minute or 24-hour peptide exposure duration. The in vivo studies demonstrated that R18D resulted in a greater reduction in mean infarct volume compared to R18 (33%, p = 0.004 vs 12%, p = 0.27) after intravenous administration at 300 nmol/kg 30 minutes after MCAO. Both R18D and R18 reduced cerebral hemisphere swelling to a comparable degree (27%, p = 0.03 and 30%, p = 0.02), and improved neurological assessment scores (1.5, p = 0.02 and 2, p = 0.058 vs 3 for vehicle). No abnormal histological findings specific to peptide treatments were observed in hematoxylin and eosin stained sections of kidney, liver, spleen, lung and heart. In vitro studies demonstrated that R18 and R18D were most toxic to neurons, followed by astrocytes, HEK293 and bEND.3 cells, but only at high concentrations and/or following 24-hour exposure. These findings further highlight the neuroprotective properties of poly-arginine peptides, and indicate that R18D at the dose examined is more potent than R18 in Wistar rats, and justify continued investigation of the R18 peptide as a novel neuroprotective agent for stroke.

Sodium butyrate improves porcine host defense peptide expression and relieves the inflammatory response upon Toll-like receptor 2 activation and histone deacetylase inhibition in porcine kidney cells

Host defense peptides (HDPs) are an important component of the innate immune system and possess direct antimicrobial and immunomodulatory activities. Dietary regulation of HDPs synthesis has emerged as a novel non-antibiotic approach to combat pathogen infection. There are species- and tissue-dependent characteristics of the regulation and mechanism of HDPs. In this study, we investigated whether the histone deacetylase inhibitor (HDACi) sodium butyrate (NaB) could induce HDP expression and the mechanism underlying NaB-regulated HDP expression in PK-15 cells. Our results revealed that NaB augmented HDP expression in PK-15 cells, including porcine β-defensin 3 (pBD3), epididymis protein 2 splicing variant C (pEP2C), pBD128, pBD123, and pBD115, but no inflammatory response occurred. Inhibition of HDAC activity was not sufficient to induce the expression of pBD3 and pEP2C in comparisons of NaB and another HDACi, trichostatin A (TSA). Concomitantly, NF-κB activation was involved in the induction of HDP expression by NaB. MAPK pathway inhibition also prevented pBD3 and pEP2C induction by NaB. Furthermore, NaB could still promote pBD3 and pEP2C expression and inhibit IL-6 production in the presence of the toll-like receptor 2 (TLR2) ligand peptidoglycan. Moreover, TLR2 could be activated by both NaB and peptidoglycan, and blocking TLR2 expression suppressed HDP induction. Finally, we further showed that increased pBD3 could decrease cytokine interleukin-18 (IL-18) and increase porcine claudin 15 (pCLDN15) contents, suggesting an immunoregulatory function of pBD3. In conclusion, this work paves the way for using HDACi-NaB to induce porcine kidney defense peptides while limiting the deleterious risk of an inflammatory response.

In Silico Tools and Databases for Designing Peptide-Based Vaccine and Drugs

The prolonged conventional approaches of drug screening and vaccine designing prerequisite patience, vigorous effort, outrageous cost as well as additional manpower. Screening and experimentally validating thousands of molecules for a specific therapeutic property never proved to be an easy task. Similarly, traditional way of vaccination includes administration of either whole or attenuated pathogen, which raises toxicity and safety issues. Emergence of sequencing and recombinant DNA technology led to the epitope-based advanced vaccination concept, i.e., small peptides (epitope) can stimulate specific immune response. Advent of bioinformatics proved to be an adjunct in vaccine and drug designing. Genomic study of pathogens aid to identify and analyze the protective epitope. A number of in silico tools have been developed to design immunotherapy as well as peptide-based drugs in the last two decades. These tools proved to be a catalyst in drug and vaccine designing. This review solicits therapeutic peptide databases as well as in silico tools developed for designing peptide-based vaccine and drugs.

Serum LL-37 Levels Associated With Severity of Bronchiolitis and Viral Etiology

Background

LL-37 is a host defense peptide with antimicrobial and immunomodulatory properties. We examined the relation of serum LL-37 levels to the severity of bronchiolitis and viral etiology.

Methods

We performed a 17-center prospective cohort study in infants hospitalized with bronchiolitis over 3 winters (2011-2014). Site teams collected clinical data, nasopharyngeal aspirates and serum. We used real-time polymerase chain reaction to test nasopharyngeal aspirates for 16 viruses. We tested serum for LL-37. Severity of bronchiolitis was defined by intensive care use and hospital length of stay. Viral etiology was defined as respiratory syncytial virus (RSV) or rhinovirus (RV), including coinfections with other viruses.

Results

The median age of the 1005 enrolled infants was 3 months (interquartile range, 2-6 months). After adjustment for 12 variables, LL-37 levels in the lowest quartile, compared with the highest, were associated both with intensive care use (adjusted odds ratio [aOR], 1.97; P = .01) and longer hospital stay (1.34; P < .001). In separate multivariable models, infants with LL-37 levels in the lowest 3 quartiles, compared with the highest, were more likely to have RSV (eg, aOR, 2.6 [lowest quartile]; P < .001 [all quartiles]). By contrast, infants with the lowest 3 LL-37 quartiles were less likely to have RV (eg, aOR, 0.5 [lowest quartile]; Pall quartiles ≤ .03 [all quartiles]).

Conclusions

In a large multicenter study of infants hospitalized with bronchiolitis, lower levels of serum LL-37 were associated with increased severity of illness. There was also an inverse relationship between LL-37 levels and the most common virus causing bronchiolitis, RSV. These findings highlight the role of LL-37 in the pathogenesis of bronchiolitis.

Poly-arginine R18 and R18D (D-enantiomer) peptides reduce infarct volume and improves behavioural outcomes following perinatal hypoxic-ischaemic encephalopathy in the P7 rat

We examined the neuroprotective efficacy of the poly-arginine peptide R18 and its D-enantiomer R18D in a perinatal hypoxic-ischaemic (HI) model in P7 Sprague-Dawley rats. R18 and R18D peptides were administered intraperitoneally at doses of 30, 100, 300 or 1000 nmol/kg immediately after HI (8% O₂/92%N₂ for 2.5 h). The previously characterised neuroprotective JNKI-1-TATD peptide at a dose of 1000 nmol/kg was used as a control. Infarct volume and behavioural outcomes were measured 48 h after HI. For the R18 and R18D doses examined, total infarct volume was reduced by 25.93% to 43.80% (P = 0.038 to < 0.001). By comparison, the JNKI-1-TATD reduced lesion volume by 25.27% (P = 0.073). Moreover, R18 and R18D treatment resulted in significant improvements in behavioural outcomes, while with JNKI-1-TATD there was a trend towards improvement. As an insight into the likely mechanism underlying the effects of R18, R18D and JNKI-1-TATD, the peptides were added to cortical neuronal cultures exposed to glutamic acid excitotoxicity, resulting in up to 89, 100 and 71% neuroprotection, respectively, and a dose dependent inhibition of neuronal calcium influx. The study further confirms the neuroprotective properties of poly-arginine peptides, and suggests a potential therapeutic role for R18 and R18D in the treatment of HIE.

Biogenic corrosion inhibitor on mild steel protection in concentrated HCl medium

Turbinaria ornata (TO) extract was tested as green corrosion inhibitor on mild steel (MS) coupons in conc. HCl medium with an efficiency of 100% at 25 g l-1 during 5 min exposure. Antibacterial efficacy performed against 16 S rDNA identified marine biofilming bacteria (MBB) and human pathogenic bacteria (HPB). Maximum inhibition growth was 16 mm on MBB observed in Bacillus megaterium (MBF14 - AB894827) and 20 mm on HPB in Escherichia coli (B5 - NCIM 2931). Similarly, minimum of 10 mm on MBB witnessed in Pseudomonas sp., (MBF9 - AB894829). Toxicity studies proved 50.0% LC50 at 500 μg ml-1 in 24 hrs, whereas Balanus amphitrite resulted in 100% mortality within 12 hrs. Results including weight loss, potentiodynamic polarization and electrochemical impedance spectroscopy, FT-IR and GC-MS confirm 10-Octadecaonic acid as a major corrosion inhibitor from T. ornata and is discovered as a novel antifoulant. Anticorrosion formulation will become available soon.

Dietary modulation of endogenous host defense peptide synthesis as an alternative approach to in-feed antibiotics

Traditionally, antibiotics are included in animal feed at subtherapeutic levels for growth promotion and disease prevention. However, recent links between in-feed antibiotics and a rise in antibiotic-resistant pathogens have led to a ban of all antibiotics in livestock production by the European Union in January 2006 and a removal of medically important antibiotics in animal feeds in the United States in January 2017. An urgent need arises for antibiotic alternatives capable of maintaining animal health and productivity without triggering antimicrobial resistance. Host defense peptides (HDP) are a critical component of the animal innate immune system with direct antimicrobial and immunomodulatory activities. While in-feed supplementation of recombinant or synthetic HDP appears to be effective in maintaining animal performance and alleviating clinical symptoms in the context of disease, dietary modulation of the synthesis of endogenous host defense peptides has emerged as a cost-effective, antibiotic-alternative approach to disease control and prevention. Several different classes of small-molecule compounds have been found capable of promoting HDP synthesis. Among the most efficacious compounds are butyrate and vitamin D. Moreover, butyrate and vitamin D synergize with each other in enhancing HDP synthesis. This review will focus on the regulation of HDP synthesis by butyrate and vitamin D in humans, chickens, pigs, and cattle and argue for potential application of HDP-inducing compounds in antibiotic-free livestock production.

Paralithocins, Antimicrobial Peptides with Unusual Disulfide Connectivity from the Red King Crab, Paralithodes camtschaticus

As part of an ongoing exploration of marine invertebrates as a source of new antimicrobial peptides, hemocyte extracts from the red king crab, Paralithodes camtschaticus, were studied. Three cationic cysteine (Cys)-rich peptides, named paralithocins 1-3, were isolated by bioassay-guided purification, and their amino acid sequences determined by Edman degradation and expressed sequences tag analysis. Disulfide bond mapping was performed by high-resolution tandem mass spectrometry. The peptides (38-51 amino acids in length) share a unique Cys motif composed of eight Cys, forming four disulfide bridges with a bond connectivity of (Cys relative position) Cys1-Cys8, Cys2-Cys6, Cys3-Cys5, and Cys4-Cys7, a disulfide arrangement that has not been previously reported among antimicrobial peptides. Thus, paralithocins 1-3 may be assigned to a previously unknown family of antimicrobial peptides within the group of Cys-rich antimicrobial peptides. Although none of the isolated peptides displayed antimicrobial activity against the target strains Escherichia coli, Pseudomonas aeruginosa, or Staphylococcus aureus, they inhibited the growth of several marine bacterial strains with minimal inhibitory concentrations in the 12.5-100 μM range. These findings corroborate the hypothesis that marine organisms are a valuable source for discovering bioactive peptides with new structural motifs.

Antimicrobial Peptides: Diversity, Mechanism of Action and Strategies to Improve the Activity and Biocompatibility In Vivo

Antibiotic resistance is projected as one of the greatest threats to human health in the future and hence alternatives are being explored to combat resistance. Antimicrobial peptides (AMPs) have shown great promise, because use of AMPs leads bacteria to develop no or low resistance. In this review, we discuss the diversity, history and the various mechanisms of action of AMPs. Although many AMPs have reached clinical trials, to date not many have been approved by the US Food and Drug Administration (FDA) due to issues with toxicity, protease cleavage and short half-life. Some of the recent strategies developed to improve the activity and biocompatibility of AMPs, such as chemical modifications and the use of delivery systems, are also reviewed in this article.

Novel Miniature Membrane Active Lipopeptidomimetics against Planktonic and Biofilm Embedded Methicillin-Resistant Staphylococcus aureus

Escalating multidrug resistance and highly evolved virulence mechanisms have aggravated the clinical menace of methicillin-resistant Staphylococcus aureus (MRSA) infections. Towards development of economically viable staphylocidal agents here we report eight structurally novel tryptophan-arginine template based peptidomimetics. Out of the designed molecules, three lipopeptidomimetics (S-6, S-7 and S-8) containing 12-amino dodecanoic acid exhibited cell selectivity and good to potent activity against clinically relevant pathogens MRSA, methicillin-resistant Staphylococcus epidermidis and vancomycin-resistant Enterococcus faecium (MIC: 1.4–22.7 μg/mL). Mechanistically, the active peptidomimetics dissipated membrane potential and caused massive permeabilization on MRSA concomitant with loss of viability. Against stationary phase MRSA under nutrient-depleted conditions, active peptidomimetics S-7 and S-8 achieved > 6 log reduction in viability upon 24 h incubation while both S-7 (at 226 μg/mL) and S-8 (at 28 μg/mL) also destroyed 48 h mature MRSA biofilm causing significant decrease in viability (p < 0.05). Encouragingly, most active peptidomimetic S-8 maintained efficacy against MRSA in presence of serum/plasma while exhibiting no increase in MIC over 17 serial passages at sub-MIC concentrations implying resistance development to be less likely. Therefore, we envisage that the current template warrants further optimization towards the development of cell selective peptidomimetics for the treatment of device associated MRSA infections.

The antimicrobial effect of CEN1HC-Br against Propionibacterium acnes and its therapeutic and anti-inflammatory effects on acne vulgaris

Propionibacterium acnes is a commensal bacterium, which is involved in acne inflammation. An antimicrobial peptide named CEN1HC-Br, which was isolated and characterized form the green sea urchin, has been shown to possess broad-spectrum antibacterial activity. Little is known concerning the potential effects of its antibacterial and anti-inflammatory properties against P. acnes. To examine the potency of CEN1HC-Br in acne treatment, we conducted experiments to analyze the antibacterial and anti-inflammatory activities of CEN1HC-Br both in vitro and in vivo. The antimicrobial activity of CEN1HC-Br was evaluated by minimal inhibitory concentration (MIC) assays using the broth dilution method. To elucidate the in vitro anti-inflammatory effect, HaCaT cells and human monocytes were treated with different concentration of CEN1HC-Br after stimulation by P. acnes. The expression of TLR2 and the secretion of the pro-inflammatory cytokines IL-6, IL-8, IL-1β, TNF-α, IL-12, respectively, were measured by enzyme immunoassays. An evaluation of P. acnes-induced ear edema in rat ear was conducted to compare the in vivo antibacterial and anti-inflammatory effect of CEN1HC-Br, the expression of IL-8, TNF-α, MMP-2 and TLR2 was evaluated by immunohistochemistry and real time-PCR. CEN1HC-Br showed stronger antimicrobial activity against P. acnes than clindamycin. CEN1HC-Br significantly reduced the expression of interleukin IL-12p40, IL-6, IL-1β, TNF-α and TLR2 in monocytes, but they were not influenced by clindamycin. Both CEN1HC-Br and Clindamycin attenuated P. acnes-induced ear swelling in rat along with pro-inflammatory cytokines IL-8, TNF-α, MMP-2 and TLR2. Our data demonstrates that CEN1HC-Br is bactericidal against P. acnes and that it has an anti-inflammatory effect on monocytes. The anti-inflammatory effect may partially occur through TLR2 down-regulation, triggering an innate immune response and the inhibition of pro-inflammatory cytokines.

Importance of phosphoinositide binding by human β-defensin 3 for Akt-dependent cytokine induction

Host defense peptides (HDPs) are well-characterized for their antimicrobial activities but also variously display potent immunomodulatory effects. Human β-defensin 3 (HBD-3) belongs to a well-known HDP family known as defensins and is able to induce leukocyte chemotactic recruitment, leukocyte activation/maturation, proinflammatory cytokine release, and co-stimulatory marker expression. HBD-3-stimulated cytokine induction is NF-κB-dependent and was initially suggested to act via G protein-coupled C-C chemokine receptor phospholipase C (PLC) and/or Toll-like receptor signaling. Subsequent pharmacological inhibition, however, revealed that NF-κB activation by HBD-3 is receptor-independent and instead involves the phosphoinositide 3-kinase (PI3K)-protein kinase B (Akt) pathway, the mechanism of which remains undetermined. Recently, we have shown that HBD-3 can enter mammalian cells and bind to inner membrane phosphoinositide 4,5-bisphosphate [PI(4,5)P₂], an important second lipid messenger of PLC and PI3K-Akt pathways. In this study, we report that the interaction of HBD-3 with PI(4,5)P₂ is important for PI3K-Akt-NF-κΒ-mediated induction of tumor necrosis factor and interleukin-6. These data provide insights into the mechanism of immunomodulation by HBD-3, and more generally, highlight the complex multifaceted signaling roles of HDPs in innate defense. Furthermore, it is suggested that the proposed mode of action may be conserved in other HDPs.

Protein-Based Therapeutic Killing for Cancer Therapies

The treatment of some high-incidence human diseases is based on therapeutic cell killing. In cancer this is mainly achieved by chemical drugs that are systemically administered to reach effective toxic doses. As an innovative alternative, cytotoxic proteins identified in nature can be adapted as precise therapeutic agents. For example, individual toxins and venom components, proapoptotic factors, and antimicrobial peptides from bacteria, animals, plants, and humans have been engineered as highly potent drugs. In addition to the intrinsic cytotoxic activities of these constructs, their biological fabrication by DNA recombination allows the recruitment, in single pharmacological entities, of diverse functions of clinical interest such as specific cell-surface receptor binding, self-activation, and self-assembling as nanoparticulate materials, with wide applicability in cell-targeted oncotherapy and theragnosis.

Significance and Diagnostic Role of Antimicrobial Cathelicidins (LL-37) Peptides in Oral Health

Cathelicidins are a group of oral antimicrobial peptides that play multiple vital roles in the human body, such as their antimicrobial (broad spectrum) role against oral microbes, wound healing, and angiogenesis, with recent evidences about their role in cancer regulation. Cathelicidins are present in humans and other mammals as well. By complex interactions with the microenvironment, it results in pro-inflammatory effects. Many in vitro and in vivo experiments have been conducted to ultimately conclude that these unique peptides play an essential role in innate immunity. Peptides are released in the precursor form (defensins), which after cleavage results in cathelicidins formation. Living in the era where the major focus is on non-invasive and nanotechnology, this ultimately leads to further advancements in the field of salivaomics. Based on current spotlight innovations, we have highlighted the biochemistry, mode of action, and the importance of cathelicidins in the oral cavity.

As-CATH4 and 5, two vertebrate-derived natural host defense peptides, enhance the immuno-resistance efficiency against bacterial infections in Chinese mitten crab, Eriocheir sinensis

Host defense peptides (HDPs), a class of conserved components of animal innate immune system, possess direct antimicrobial activities against invading pathogens and broadly participate in boosting and modulating host immune responses. Cathelicidins is an important family of HDPs that has been identified exclusively in vertebrates. Considering the relatively conserved innate immune system between invertebrates and vertebrates, it is speculated that HDPs from vertebrates may also possess modulating functions on invertebrate innate immune system. In the present study, two novel cathelicidins (As-CATH4 and 5), which had been identified from the Chinese alligator in our previous study, were employed to investigate their functions as novel peptide immunostimulants in Chinese mitten crab. As-CATH4 and 5 exhibited potent, broad-spectrum, and rapid antimicrobial activities against all the tested aquatic pathogenic bacteria. Unlike traditional antibiotics, they target on bacterial cell membrane, induce membrane permeabilization and cell disruption, and ultimately result in cell death. The antimicrobial effect is far more rapid than traditional antibiotics. Therefore they are unlikely to induce bacteria resistance. After the crabs were administered with As-CATH4 and 5, the activities of lysozyme, acid phosphatase and alkaline phosphatase were significantly enhanced, which indicated that the immune system of crabs could be activated by As-CATH4 and 5. In bacteria challenge test, As-CATH4 and 5 could significantly decrease the bacterial numbers in crabs, and increase the survival rates of crabs in both pre-stimulation and co-stimulation groups. All of the results above indicated the great potential of As-CATH4 and 5 as novel peptide immunostimulants in the crab aquaculture.

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.

Conformational properties, membrane interaction, and antibacterial activity of the peptaibiotic chalciporin A: Multitechnique spectroscopic and biophysical investigations on the natural compound and labeled analogs

In this work, an extensive set of spectroscopic and biophysical techniques (including FT-IR absorption, CD, 2D-NMR, fluorescence, and CW/PELDOR EPR) was used to study the conformational preferences, membrane interaction, and bioactivity properties of the naturally occurring synthetic 14-mer peptaibiotic chalciporin A, characterized by a relatively low (≈20%), uncommon proportion of the strongly helicogenic Aib residue. In addition to the unlabeled peptide, we gained in-depth information from the study of two labeled analogs, characterized by one or two residues of the helicogenic, nitroxyl radical-containing TOAC. All three compounds were prepared using the SPPS methodology, which was carefully modified in the course of the syntheses of TOAC-labeled analogs in view of the poorly reactive α-amino function of this very bulky residue and the specific requirements of its free-radical side chain. Despite its potentially high flexibility, our results point to a predominant, partly amphiphilic, α-helical conformation for this peptaibiotic. Therefore, not surprisingly, we found an effective membrane affinity and a remarkable penetration propensity. However, chalciporin A exhibits a selectivity in its antibacterial activity not in agreement with that typical of the other members of this peptide class.

D-Cateslytin, a new antimicrobial peptide with therapeutic potential

The rise of antimicrobial resistant microorganisms constitutes an increasingly serious threat to global public health. As a consequence, the efficacy of conventional antimicrobials is rapidly declining, threatening the ability of healthcare professionals to cure common infections. Over the last two decades host defense peptides have been identified as an attractive source of new antimicrobials. In the present study, we characterized the antibacterial and mechanistic properties of D-Cateslytin (D-Ctl), a new epipeptide derived from L-Cateslytin, where all L-amino acids were replaced by D-amino acids. We demonstrated that D-Ctl emerges as a potent, safe and robust peptide antimicrobial with undetectable susceptibility to resistance. Using Escherichia coli as a model, we reveal that D-Ctl targets the bacterial cell wall leading to the permeabilization of the membrane and the death of the bacteria. Overall, D-Ctl offers many assets that make it an attractive candidate for the biopharmaceutical development of new antimicrobials either as a single therapy or as a combination therapy as D-Ctl also has the remarkable property to potentiate several antimicrobials of reference such as cefotaxime, amoxicillin and methicillin.

Host Antimicrobial Peptides: The Promise of New Treatment Strategies against Tuberculosis

Tuberculosis (TB) continues to be a devastating infectious disease and remerges as a global health emergency due to an alarming rise of antimicrobial resistance to its treatment. Despite of the serious effort that has been applied to develop effective antitubercular chemotherapies, the potential of antimicrobial peptides (AMPs) remains underexploited. A large amount of literature is now accessible on the AMP mechanisms of action against a diversity of pathogens; nevertheless, research on their activity on mycobacteria is still scarce. In particular, there is an urgent need to integrate all available interdisciplinary strategies to eradicate extensively drug-resistant Mycobacterium tuberculosis strains. In this context, we should not underestimate our endogenous antimicrobial proteins and peptides as ancient players of the human host defense system. We are confident that novel antibiotics based on human AMPs displaying a rapid and multifaceted mechanism, with reduced toxicity, should significantly contribute to reverse the tide of antimycobacterial drug resistance. In this review, we have provided an up to date perspective of the current research on AMPs to be applied in the fight against TB. A better understanding on the mechanisms of action of human endogenous peptides should ensure the basis for the best guided design of novel antitubercular chemotherapeutics.

Synthetic host defense peptide IDR-1002 reduces inflammation in Pseudomonas aeruginosa lung infection

Pseudomonas aeruginosa is a frequent cause of lung infections, particularly in chronic infections in cystic fibrosis patients. However, treatment is challenging due to P. aeruginosa evasion of the host immune system and the rise of antibiotic resistant strains. Host defense peptides (HDPs) and synthetic derivatives called innate defense regulators (IDRs) have shown promise in several infection models as an alternative to antibiotic treatment. Here we tested peptide IDR-1002 against P. aeruginosa in vitro and in vivo. Treatment of bronchial epithelial cells and macrophages with IDR-1002 or in combination with live P. aeruginosa or its LPS led to the reduction of agonist-induced cytokines and chemokines and limited cell killing by live P. aeruginosa. In an in vivo model using P. aeruginosa combined with alginate to mimic a chronic model, IDR-1002 did not reduce the bacterial burden in the lungs, but IDR-1002 mice showed a significant decrease in IL-6 in the lungs and in gross pathology of infection, while histology revealed that IDR-1002 treated mice had reduced alveolar macrophage infiltration around the site of infection and reduced inflammation. Overall, these results indicate that IDR-1002 has promise for combating P. aeruginosa lung infections and their resulting inflammation.

Cathelicidin-WA polarizes E. coli K88-induced M1 macrophage to M2-like macrophage in RAW264.7 cells

Immune cells - macrophages induced by E. coli K88 will lead to a pro-inflammatory response, which is important in host defense. Cathelicidin-WA (CWA) is an efficient antimicrobial peptide (AMP) and can exert immunomodulatory properties. Many studies have demonstrated that AMP can modulate cellular subsets but whether CWA can regulate macrophage polarization by transferring E. coli K88-induced M1 macrophage towards M2 one that of anti-inflammation remains unclear. In this study, E. coli K88 increased the expression of pro-inflammatory cytokines interleukin-6, interleukin-1β, tumor necrosis factor-α and chemokine CCL3 in RAW264.7 cells with a time-dependent manner, as well as the expression of reactive oxygen species (ROS) and inducible nitric oxide synthase (iNOS). On this basis, CWA significantly decreased the pro-inflammatory molecules but increased the anti-inflammatory mediators interleukin-4, interleukin-10 and other M2-related genes in E. coli K88-induced macrophages. Western blot analysis indicated that CWA suppressed the expression of TLR-4 and the phosphorylation of STAT1 and NF-κB which modulated M1 macrophage while induced the phosphorylation of STAT6 which activated M2 macrophage. Double staining of M1-specific CD86 and M2-specific CD206 also proved the hypothesis. These results suggested that CWA might dampen the inflammation by modulating M1 phenotype to M2 phenotype in E. coli K88-induced macrophages.

Nuclease activity gives an edge to host-defense peptide piscidin 3 over piscidin 1, rendering it more effective against persisters and biofilms

Host-defense peptides (HDPs) feature evolution-tested potency against life-threatening pathogens. While piscidin 1 (p1) and piscidin 3 (p3) are homologous and potent fish HDPs, only p1 is strongly membranolytic. Here, we hypothesize that another mechanism imparts p3 strong potency. We demonstrate that the N-termini of both peptides coordinate Cu2+ and p3-Cu cleaves isolated DNA at a rate on par with free Cu2+ but significantly faster than p1-Cu. On planktonic bacteria, p1 is more antimicrobial but only p3 features copper-dependent DNA cleavage. On biofilms and persister cells, p3-Cu is more active than p1-Cu, commensurate with stronger peptide-induced DNA damage. Molecular dynamics and NMR show that more DNA-peptide interactions exist with p3 than p1, and the peptides adopt conformations simultaneously poised for metal- and DNA-binding. These results generate several important conclusions. First, homologous HDPs cannot be assumed to have identical mechanisms since p1 and p3 eradicate bacteria through distinct relative contributions of membrane and DNA-disruptive effects. Second, the nuclease and membrane activities of p1 and p3 show that naturally occurring HDPs can inflict not only physicochemical but also covalent damage. Third, strong nuclease activity is essential for biofilm and persister cell eradication, as shown by p3, the homolog more specific toward bacteria and more expressed in vascularized tissues. Fourth, p3 combines several physicochemical properties (e.g., Amino Terminal Copper and Nickel binding motif; numerous arginines; moderate hydrophobicity) that confer low membranolytic effects, robust copper-scavenging capability, strong interactions with DNA, and fast nuclease activity. This new knowledge could help design novel therapeutics active against hard-to-treat persister cells and biofilms.

Cationic peptides from peptic hydrolysates of rice endosperm protein exhibit antimicrobial, LPS-neutralizing, and angiogenic activities

In this study, we hydrolyzed rice endosperm protein (REP) with pepsin and generated 20 fractions containing multifunctional cationic peptides with varying isoelectric point (pI) values using ampholyte-free isoelectric focusing (autofocusing). Subsequently, we determined antimicrobial activities of each fraction against the pathogens Prophyromonas gingivalis, Propionibacterium acnes, Streptocossus mutans, and Candida albicans. Fractions 18, 19, and 20 had pI values greater than 12 and exhibited antimicrobial activity against P. gingivalis, P. acnes, and C. albicans, but not against S. mutans. In further experiments, we purified and identified cationic peptides from fractions 18, 19, and 20 using reversed-phase high-performance liquid chromatography and matrix-assisted laser/desorption ionization-time-of-flight mass spectroscopy. We also chemically synthesized five identified peptides (RSVSKSR, RRVIEPR, ERFQPMFRRPG, RVRQNIDNPNRADTYNPRAG, and VVRRVIEPRGLL) with pI values greater than 10.5 and evaluated antimicrobial, lipopolysaccharide (LPS)-neutralizing, and angiogenic activities. Among these synthetic peptides, only VVRRVIEPRGLL exhibited antimicrobial activity against P. gingivalis, with an IC₅₀ value of 87μM. However, all five cationic peptides exhibited LPS-neutralizing and angiogenic activities with little or no hemolytic activity against mammalian red blood cells at functional concentrations. These present data show dual or multiple functions of the five identified cationic peptides with little or no hemolytic activity. Therefore, fractions containing cationic peptides from REP hydrolysates have the potential to be used as dietary supplements and functional ingredients in food products.

Exploiting the human peptidome for novel antimicrobial and anticancer agents

Infectious diseases and cancers are leading causes of death and pose major challenges to public health. The human peptidome encompasses millions of compounds that display an enormous structural and functional diversity and represents an excellent source for the discovery of endogenous agents with antimicrobial and/or anticancer activity. Here, we discuss how to exploit the human peptidome for novel antimicrobial and anticancer agents through the generation of peptide libraries from human body fluids and tissues and stepwise purification of bioactive compounds.

Antimicrobial peptides as an alternative to anti-tuberculosis drugs

Tuberculosis (TB) presently accounts for high global mortality and morbidity rates, despite the introduction four decades ago of the affordable and efficient four-drugs (isoniazid, rifampicin, pyrazinamide and ethambutol). Thus, a strong need exists for new drugs with special structures and uncommon modes of action to effectively overcome M. tuberculosis. Within this scope, antimicrobial peptides (AMPs), which are small, cationic and amphipathic peptides that comprise a section of the innate immune system, are currently the leading potential agents for the treatment of TB. Many studies have recently illustrated the capability of anti-mycobacterial peptides to disrupt the normal mycobacterial cell wall function through various modes, thereby interacting with the intracellular targets, as well as encompassing nucleic acids, enzymes and organelles. This review presents a wide array of antimicrobial activities, alongside the associated properties of the AMPs that could be utilized as potential agents in therapeutic tactics for TB treatment.

Differential Interaction of Antimicrobial Peptides with Lipid Structures Studied by Coarse-Grained Molecular Dynamics Simulations

In this work; we investigated the differential interaction of amphiphilic antimicrobial peptides with 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) lipid structures by means of extensive molecular dynamics simulations. By using a coarse-grained (CG) model within the MARTINI force field; we simulated the peptide-lipid system from three different initial configurations: (a) peptides in water in the presence of a pre-equilibrated lipid bilayer; (b) peptides inside the hydrophobic core of the membrane; and (c) random configurations that allow self-assembled molecular structures. This last approach allowed us to sample the structural space of the systems and consider cooperative effects. The peptides used in our simulations are aurein 1.2 and maculatin 1.1; two well-known antimicrobial peptides from the Australian tree frogs; and molecules that present different membrane-perturbing behaviors. Our results showed differential behaviors for each type of peptide seen in a different organization that could guide a molecular interpretation of the experimental data. While both peptides are capable of forming membrane aggregates; the aurein 1.2 ones have a pore-like structure and exhibit a higher level of organization than those conformed by maculatin 1.1. Furthermore; maculatin 1.1 has a strong tendency to form clusters and induce curvature at low peptide-lipid ratios. The exploration of the possible lipid-peptide structures; as the one carried out here; could be a good tool for recognizing specific configurations that should be further studied with more sophisticated methodologies.

Inulin-Type Fructans Modulates Pancreatic-Gut Innate Immune Responses and Gut Barrier Integrity during Experimental Acute Pancreatitis in a Chain Length-Dependent Manner

Acute pancreatitis (AP) is a common abdominal inflammatory disorder and one of the leading causes of hospital admission for gastrointestinal disorders. No specific pharmacological or nutritional therapy is available but highly needed. Inulin-type fructans (ITFs) are capable of modifying gut immune and barrier homeostasis in a chemistry-dependent manner and hence potentially applicable for managing AP, but their efficacy in AP has not been demonstrated yet. The current study aimed to examine and compare modulatory effects of ITFs with different degrees of fermentability on pancreatic-gut immunity and barrier function during experimentally induced AP in mice. BALB/c mice were fed short (I)- or long (IV)-chain ITFs supplemented diets for up to 3 days before AP induction by caerulein. Attenuating effects on AP development were stronger with ITF IV than with ITF I. We found that long-chain ITF IV attenuated the severity of AP, as evidenced by reduced serum amylase levels, lipase levels, pancreatic myeloperoxidase activity, pancreatic edema, and histological examination demonstrating reduced pancreatic damage. Short-chain ITF I demonstrated only partial protective effects. Both ITF IV and ITF I modulated AP-associated systemic cytokine levels. ITF IV but not ITF I restored AP-associated intestinal barrier dysfunction by upregulating colonic tight junction modulatory proteins, antimicrobial peptides, and improved general colonic histology. Additionally, differential modulatory effects of ITF IV and ITF I were observed on pancreatic and gut immunity: ITF IV supplementation prevented innate immune cell infiltration in the pancreas and colon and tissue cytokine production. Similar effects were only observed in the gut with ITF I and not in the pancreas. Lastly, ITF IV but not ITF I downregulated AP-triggered upregulation of IL-1 receptor-associated kinase 4 (IRAK-4) and phosphor-c-Jun N-terminal kinase (p-JNK), and a net decrease of phosphor-nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) p65 (p-NF-κB p65) nuclear translocation and activation in the pancreas. Our findings demonstrate a clear chain length-dependent effect of inulin on AP. The attenuating effects are caused by modulating effects of long-chain inulin on the pancreatic-gut immunity via the pancreatic IRAK-4/p-JNK/p-NF-κBp65 signaling pathway and on prevention of disruption of the gut barrier.

Differential Regulation of Mas-Related G Protein-Coupled Receptor X2-Mediated Mast Cell Degranulation by Antimicrobial Host Defense Peptides and Porphyromonas gingivalis Lipopolysaccharide

Porphyromonas gingivalis is a keystone pathogen that contributes to periodontal pathogenesis by disrupting host-microbe homeostasis and promoting dysbiosis. The virulence of P. gingivalis likely reflects an alteration in the lipid A composition of its lipopolysaccharide (LPS) from the penta-acylated (PgLPS₁₆₉₀) to the tetra-acylated (PgLPS_1435/1449) form. Mast cells play an important role in periodontitis, but the mechanisms of their activation and regulation remain unknown. The expression of epithelium- and neutrophil-derived host defense peptides (HDPs) (LL-37 and human β-defensin-3), which activate mast cells via Mas-related G protein-coupled receptor X2 (MRGPRX2), is increased in periodontitis. We found that MRGPRX2-expressing mast cells are present in normal gingiva and that their numbers are elevated in patients with chronic periodontitis. Furthermore, HDPs stimulated degranulation in a human mast cell line (LAD2) and in RBL-2H3 cells stably expressing MRGPRX2 (RBL-MRGPRX2). PgLPS₁₆₉₀ caused substantial inhibition of HDP-induced mast cell degranulation, but PgLPS_1435/1449 had no effect. A fluorescently labeled HDP (FAM-LL-37) bound to RBL-MRGPRX2 cells, and PgLPS₁₆₉₀ inhibited this binding, but PgLPS_1435/1449 had no effect. These findings suggest that low-level inflammation induced by HDP/MRGPRX2-mediated mast cell degranulation contributes to gingival homeostasis but that sustained inflammation due to elevated levels of both HDPs and MRGPRX2-expressing mast cells promotes periodontal disease. Furthermore, differential regulation of HDP-induced mast cell degranulation by PgLPS₁₆₉₀ and PgLPS_1435/1449 may contribute to the modulation of disease progression.