Antimicrobial proteins and peptides in human lung diseases: A friend and foe partnership with host proteases

Mucus Structure, Viscoelastic Properties, and Composition in Chronic Respiratory Diseases

The respiratory mucus, a viscoelastic gel, effectuates a primary line of the airway defense when operated by the mucociliary clearance. In chronic respiratory diseases (CRDs), such as asthma, chronic obstructive pulmonary disease (COPD), and cystic fibrosis (CF), the mucus is overproduced and its solid content augments, changing its structure and viscoelastic properties and determining a derangement of essential defense mechanisms against opportunistic microbial (virus and bacteria) pathogens. This ensues in damaging of the airways, leading to a vicious cycle of obstruction and infection responsible for the harsh clinical evolution of these CRDs. Here, we review the essential features of normal and pathological mucus (i.e., sputum in CF, COPD, and asthma), i.e., mucin content, structure (mesh size), micro/macro-rheology, pH, and osmotic pressure, ending with the awareness that sputum biomarkers (mucins, inflammatory proteins and peptides, and metabolites) might serve to indicate acute exacerbation and response to therapies. There are some indications that old and novel treatments may change the structure, viscoelastic properties, and biomarker content of sputum; however, a wealth of work is still needed to embrace these measures as correlates of disease severity in association with (or even as substitutes of) pulmonary functional tests.

Nanotechnology-Based Drug Delivery Systems to Control Bacterial-Biofilm-Associated Lung Infections

Airway mucus dysfunction and impaired immunological defenses are hallmarks of several lung diseases, including asthma, cystic fibrosis, and chronic obstructive pulmonary diseases, and are mostly causative factors in bacterial-biofilm-associated respiratory tract infections. Bacteria residing within the biofilm architecture pose a complex challenge in clinical settings due to their increased tolerance to currently available antibiotics and host immune responses, resulting in chronic infections with high recalcitrance and high rates of morbidity and mortality. To address these unmet clinical needs, potential anti-biofilm therapeutic strategies are being developed to effectively control bacterial biofilm. This review focuses on recent advances in the development and application of nanoparticulate drug delivery systems for the treatment of biofilm-associated respiratory tract infections, especially addressing the respiratory barriers of concern for biofilm accessibility and the various types of nanoparticles used to combat biofilms. Understanding the obstacles facing pulmonary drug delivery to bacterial biofilms and nanoparticle-based approaches to combatting biofilm may encourage researchers to explore promising treatment modalities for bacterial-biofilm-associated chronic lung infections.

Antimicrobial peptides modulate lung injury by altering the intestinal microbiota

BACKGROUND

Mammalian mucosal barriers secrete antimicrobial peptides (AMPs) as critical, host-derived regulators of the microbiota. However, mechanisms that support microbiota homeostasis in response to inflammatory stimuli, such as supraphysiologic oxygen, remain unclear.

RESULTS

We show that supraphysiologic oxygen exposure to neonatal mice, or direct exposure of intestinal organoids to supraphysiologic oxygen, suppresses the intestinal expression of AMPs and alters intestinal microbiota composition. Oral supplementation of the prototypical AMP lysozyme to hyperoxia-exposed neonatal mice reduced hyperoxia-induced alterations in their microbiota and was associated with decreased lung injury.

CONCLUSIONS

Our results identify a gut-lung axis driven by intestinal AMP expression and mediated by the intestinal microbiota that is linked to lung injury in newborns. Together, these data support that intestinal AMPs modulate lung injury and repair. Video Abstract.

Antimicrobial peptides modulate lung injury by altering the intestinal microbiota

Mammalian mucosal barriers secrete antimicrobial peptides (AMPs) as critical host-derived regulators of the microbiota. However, mechanisms that support homeostasis of the microbiota in response to inflammatory stimuli such as supraphysiologic oxygen remain unclear. Here, we show that neonatal mice breathing supraphysiologic oxygen or direct exposure of intestinal organoids to supraphysiologic oxygen suppress the intestinal expression of AMPs and alters the composition of the intestinal microbiota. Oral supplementation of the prototypical AMP lysozyme to hyperoxia exposed neonatal mice reduced hyperoxia-induced alterations in their microbiota and was associated with decreased lung injury. Our results identify a gut-lung axis driven by intestinal AMP expression and mediated by the intestinal microbiota that is linked to lung injury. Together, these data support that intestinal AMPs modulate lung injury and repair.

In Brief

Using a combination of murine models and organoids, Abdelgawad and Nicola et al. find that suppression of antimicrobial peptide release by the neonatal intestine in response to supra-physiological oxygen influences the progression of lung injury likely via modulation of the ileal microbiota.

Highlights

Supraphysiologic oxygen exposure alters intestinal antimicrobial peptides (AMPs).Intestinal AMP expression has an inverse relationship with the severity of lung injury.AMP-driven alterations in the intestinal microbiota form a gut-lung axis that modulates lung injury.AMPs may mediate a gut-lung axis that modulates lung injury.

Cleavage of Occludin by Cigarette Smoke-Elicited Cathepsin S Increases Permeability of Lung Epithelial Cells

BACKGROUND

Chronic obstructive pulmonary disease (COPD) is an irreversible disease mainly caused by smoking. COPD is characterized by emphysema and chronic bronchitis associated with enhanced epithelial permeability.

HYPOTHESIS

Lung biopsies from smokers revealed a decreased expression level of occludin, which is a protein involved in the cohesion of epithelial tight junctions. Moreover, the occludin level correlated negatively with smoking history (pack-years), COPD grades, and cathepsin S (CatS) activity. Thus, we examined whether CatS could participate in the modulation of the integrity of human lung epithelial barriers.

METHODS AND RESULTS

Cigarette smoke extract (CSE) triggered the upregulation of CatS by THP-1 macrophages through the mTOR/TFEB signaling pathway. In a co-culture model, following the exposure of macrophages to CSE, an enhanced level of permeability of lung epithelial (16HBE and NHBE) cells towards FITC-Dextran was observed, which was associated with a decrease in occludin level. Similar results were obtained using 16HBE and NHBE cells cultured at the air-liquid interface. The treatment of THP-1 macrophages by CatS siRNAs or by a pharmacological inhibitor restored the barrier function of epithelial cells, suggesting that cigarette smoke-elicited CatS induced an alteration of epithelial integrity via the proteolytic injury of occludin.

CONCLUSIONS

Alongside its noteworthy resistance to oxidative stress induced by cigarette smoke oxidants and its deleterious elastin-degrading potency, CatS may also have a detrimental effect on the barrier function of epithelial cells through the cleavage of occludin. The obtained data emphasize the emerging role of CatS in smoking-related lung diseases and strengthen the relevance of targeting CatS in the treatment of emphysema and COPD.

Cathepsin V: Molecular characteristics and significance in health and disease

Human cysteine cathepsins form a family of eleven proteases (B, C, F, H, K, L, O, S, V, W, X/Z) that play important roles in a considerable number of biological and pathophysiological processes. Among them, cathepsin V, also known as cathepsin L2, is a lysosomal enzyme, which is mainly expressed in cornea, thymus, heart, brain, and skin. Cathepsin V is a multifunctional endopeptidase that is involved in both the release of antigenic peptides and the maturation of MHC class II molecules and participates in the turnover of elastin fibrils as well in the cleavage of intra- and extra-cellular substrates. Moreover, there is increasing evidence that cathepsin V may contribute to the progression of diverse diseases, due to the dysregulation of its expression and/or its activity. For instance, increased expression of cathepsin V is closely correlated with malignancies (breast cancer, squamous cell carcinoma, or colorectal cancer) as well vascular disorders (atherosclerosis, aortic aneurysm, hypertension) being the most prominent examples. This review aims to shed light on current knowledge on molecular aspects of cathepsin V (genomic organization, protein structure, substrate specificity), its regulation by protein and non-protein inhibitors as well to summarize its expression (tissue and cellular distribution). Then the core biological and pathophysiological roles of cathepsin V will be depicted, raising the question of its interest as a valuable target that can open up pioneering therapeutic avenues.

The influenza-injured lung microenvironment promotes MRSA virulence, contributing to severe secondary bacterial pneumonia

Influenza infection is substantially worsened by the onset of secondary pneumonia caused by bacteria, such as methicillin-resistant Staphylococcus aureus (MRSA). The bidirectional interaction between the influenza-injured lung microenvironment and MRSA is poorly understood. By conditioning MRSA ex vivo in bronchoalveolar lavage fluid collected from mice at various time points of influenza infection, we found that the influenza-injured lung microenvironment dynamically induces MRSA to increase cytotoxin expression while decreasing metabolic pathways. LukAB, a SaeRS two-component system-dependent cytotoxin, is particularly important to the severity of post-influenza MRSA pneumonia. LukAB's activity is likely shaped by the post-influenza lung microenvironment, as LukAB binds to (and is activated by) heparan sulfate (HS) oligosaccharide sequences shed from the epithelial glycocalyx after influenza. Our findings indicate that post-influenza MRSA pneumonia is shaped by bidirectional host-pathogen interactions: host injury triggers changes in bacterial expression of toxins, the activity of which may be shaped by host-derived HS fragments.

Quick and wide-range taxonomical repertoire establishment of the cystic fibrosis lung microbiota by tandem mass spectrometry on sputum samples

Microorganisms proteotyping by tandem mass spectrometry has been recently shown as a powerful methodology to identify the wide-range taxonomy and biomass of microbiota. Sputum is the recommended specimen for routine microbiological monitoring of Cystic Fibrosis (CF) patients but has been rarely submitted to tandem mass spectrometry-based proteotyping. In this study, we compared the microbial components of spontaneous and induced sputum samples from three cystic fibrosis patients. Although the presence of microbial proteins is much lower than host proteins, we report that the microbiota’s components present in the samples can be identified, as well as host biomarkers and functional insights into the microbiota. No significant difference was found in microorganism abundance between paired spontaneous and induced sputum samples. Microbial proteins linked to resistance, iron uptake, and biofilm-forming ability were observed in sputa independently of the sampling method. This unbiased and enlarged view of the CF microbiome could be highly complementary to culture and relevant for the clinical management of CF patients by improving knowledge about the host-pathogen dynamics and CF pathophysiology.

Spatial localization of cathepsins: Implications in immune activation and resolution during infections

Cathepsins were first described, as endolysosomal proteolytic enzymes in reference to the organelles where they degrade the bulk of endogenous and exogenous substrates in a slightly acidic environment. These substrates include pathogens internalized via endocytosis and/or marked for destruction by autophagy. However, the role of cathepsins during infection far exceeds that of direct digestion of the pathogen. Cathepsins have been extensively investigated in the context of tumour associated immune cells and chronic inflammation. Several cathepsin-dependent immune responses develop in the endocytic pathway while others take place in the cytosol, the nucleus, or in the extracellular space. In this review we highlight the spatial localization of cathepsins and their implications in immune activation and resolution pathways during infection.

Models using native tracheobronchial mucus in the context of pulmonary drug delivery research: Composition, structure and barrier properties

Mucus covers all wet epithelia and acts as a protective barrier. In the airways of the lungs, the viscoelastic mucus meshwork entraps and clears inhaled materials and efficiently removes them by mucociliary escalation. In addition to physical and chemical interaction mechanisms, the role of macromolecular glycoproteins (mucins) and antimicrobial constituents in innate immune defense are receiving increasing attention. Collectively, mucus displays a major barrier for inhaled aerosols, also including therapeutics. This review discusses the origin and composition of tracheobronchial mucus in relation to its (barrier) function, as well as some pathophysiological changes in the context of pulmonary diseases. Mucus models that contemplate key features such as elastic-dominant rheology, composition, filtering mechanisms and microbial interactions are critically reviewed in the context of health and disease considering different collection methods of native human pulmonary mucus. Finally, the prerequisites towards a standardization of mucus models in a regulatory context and their role in drug delivery research are addressed.

Regulatory Peptides in Asthma

Numerous regulatory peptides play a critical role in the pathogenesis of airway inflammation, airflow obstruction and hyperresponsiveness, which are hallmarks of asthma. Some of them exacerbate asthma symptoms, such as neuropeptide Y and tachykinins, while others have ameliorating properties, such as nociception, neurotensin or β-defensin 2. Interacting with peptide receptors located in the lungs or on immune cells opens up new therapeutic possibilities for the treatment of asthma, especially when it is resistant to available therapies. This article provides a concise review of the most important and current findings regarding the involvement of regulatory peptides in asthma pathology.

Immunoglobulin A Mucosal Immunity and Altered Respiratory Epithelium in Cystic Fibrosis

The respiratory epithelium represents the first chemical, immune, and physical barrier against inhaled noxious materials, particularly pathogens in cystic fibrosis. Local mucus thickening, altered mucociliary clearance, and reduced pH due to CFTR protein dysfunction favor bacterial overgrowth and excessive inflammation. We aimed in this review to summarize respiratory mucosal alterations within the epithelium and current knowledge on local immunity linked to immunoglobulin A in patients with cystic fibrosis.

Therapeutic potential of targeting cathepsin S in pulmonary fibrosis

Cathepsin S (CTSS), a lysosomal protease, belongs to a family of cysteine cathepsin proteases that promote degradation of damaged proteins in the endolysosomal pathway. Aberrant CTSS expression and regulation are associated with the pathogenesis of several diseases, including lung diseases. CTSS overexpression causes a variety of pathological processes, including pulmonary fibrosis, with increased CTSS secretion and accelerated extracellular matrix remodeling. Compared to many other cysteine cathepsin family members, CTSS has unique features that it presents limited tissue expression and retains its enzymatic activity at a neutral pH, suggesting its decisive involvement in disease microenvironments. In this review, we investigated the role of CTSS in lung disease, exploring recent studies that have indicated that CTSS mediates fibrosis in unique ways, along with its structure, substrates, and distinct regulation. We also outlined examples of CTSS inhibitors in clinical and preclinical development and proposed CTSS as a potential therapeutic target for pulmonary fibrosis.

Activity of airway antimicrobial peptides against cystic fibrosis pathogens

Antimicrobial peptides are important players of the innate host defence against invading microorganisms. The aim of this study was to evaluate the activity of airway antimicrobial peptides against the common cystic fibrosis (CF) pathogen Pseudomonas aeruginosa, and to compare it to the emerging multi-drug resistant CF pathogens Achromobacter xylosoxidans and Stenotrophomonas maltophilia. Clinical bacterial isolates from CF patients were used, and the antimicrobial activity of human beta-defensin 2 and 3, LL37 and lysozyme was evaluated using radial diffusion assay and viable counts. The cell surface zeta potential was analysed to estimate the net charge at the bacterial surface. Of the bacterial species included in the study, A. xylosoxidans was the most resistant to antimicrobial peptides, whereas P. aeruginosa was the most susceptible. The net charge of the bacterial surface was significantly more negative for P. aeruginosa compared to A. xylosoxidans, which may in part explain the differences in susceptibility.

Cathepsins and Their Endogenous Inhibitors in Host Defense During Mycobacterium tuberculosis and HIV Infection

The moment a very old bacterial pathogen met a young virus from the 80's defined the beginning of a tragic syndemic for humanity. Such is the case for the causative agent of tuberculosis and the human immunodeficiency virus (HIV). Syndemic is by definition a convergence of more than one disease resulting in magnification of their burden. Both pathogens work synergistically contributing to speed up the replication of each other. Mycobacterium tuberculosis (Mtb) and HIV infections are in the 21st century among the leaders of morbidity and mortality of humankind. There is an urgent need for development of new approaches for prevention, better diagnosis, and new therapies for both infections. Moreover, these approaches should consider Mtb and HIV as a co-infection, rather than just as separate problems, to prevent further aggravation of the HIV-TB syndemic. Both pathogens manipulate the host immune responses to establish chronic infections in intracellular niches of their host cells. This includes manipulation of host relevant antimicrobial proteases such as cathepsins or their endogenous inhibitors. Here we discuss recent understanding on how Mtb and HIV interact with cathepsins and their inhibitors in their multifactorial functions during the pathogenesis of both infections. Particularly we will address the role on pathogen transmission, during establishment of intracellular chronic niches and in granuloma clinical outcome and tuberculosis diagnosis. This area of research will open new avenues for the design of innovative therapies and diagnostic interventions so urgently needed to fight this threat to humanity.

Upregulation of gut cathepsin L during Eimeria tenella infection

Coccidiosis is a disease caused by Eimeria, which represents the first parasitic disease in poultry farming. Among them, E. tenella is a virulent species which specifically colonizes the caecum. The inflammatory response to infection is associated to numerous host proteases including cysteine cathepsins that can be deleterious for tissue and innate immunity integrity. Here, germ-free and conventional chickens were used as models to find out whether the microbiota could modify the intestinal expression of host cysteine cathepsins during coccidiosis. The basal caecal peptidase activity primarily relies on host proteases rather than proteases from the commensal flora. While mRNA levels of E. tenella cathepsins B and L remained unchanged in germ-free and conventional broilers, an overall increase in endopeptidase activity of cysteine cathepsins was found in E. tenella-infected caeca in both experimental models (P < 0.005). A significant decrease in avian cystatin C transcription was also observed in infected conventional, but not in infected germ-free broilers. Despite an unchanged mRNA level of avian cathepsin L (CatL), its protein expression raised following infection, in parallel with an increased transcription of antimicrobial β-defensins (AvBD1, AvBD2, AvBD4, AvBD6, and AvBD7). Taken together, data support that host CatL is post-translationally upregulated during E. tenella infection, and thus may be involved in the alteration of the gut proteolytic balance. Furthermore, CatL may participate to inflammation occurring during coccidiosis through its known ability to proteolytically inactivates up-regulated avian β-defensins that are key molecules of innate immunity.

Endotracheal tubes coated with a broad-spectrum antibacterial ceragenin reduce bacterial biofilm in an in vitro bench top model

BACKGROUND

Ventilator-associated pneumonia is one of the most common nosocomial infections, caused mainly by bacterial/fungal biofilm. Therefore, it is necessary to develop preventive strategies to avoid biofilm formation based on new compounds.

OBJECTIVES

We performed an in vitro study to compare the efficacy of endotracheal tubes (ETTs) coated with the ceragenin CSA-131 and that of uncoated ETTs against the biofilm of clinical strains of Pseudomonas aeruginosa (PA), Escherichia coli (EC) and Staphylococcus aureus (SA).

METHODS

We applied an in vitro bench top model using coated and uncoated ETTs that were treated with three different clinical strains of PA, EC and SA for 5 days. After exposure to biofilm, ETTs were analysed for cfu count by culture of sonicate and total number of cells by confocal laser scanning microscopy.

RESULTS

The median (IQR) cfu/mL counts of PA, EC and SA in coated and uncoated ETTs were, respectively, as follows: 1.00 × 101 (0.0-3.3 × 102) versus 3.32 × 109 (6.6 × 108-3.8 × 109), P < 0.001; 0.0 (0.0-5.4 × 103) versus 1.32 × 106 (2.3 × 103-5.0 × 107), P < 0.001; and 8.1 × 105 (8.5 × 101-1.4 × 109) versus 2.7 × 108 (8.6 × 106-1.6 × 1011), P = 0.058. The median (IQR) total number of cells of PA, EC and SA in coated and non-coated ETTs were, respectively, as follows: 11.0 [5.5-not applicable (NA)] versus 87.9 (60.5-NA), P = 0.05; 9.1 (6.7-NA) versus 62.6 (42.0-NA), P = 0.05; and 97.7 (94.6-NA) versus 187.3 (43.9-NA), P = 0.827.

CONCLUSIONS

We demonstrated significantly reduced biofilm formation in coated ETTs. However, the difference for SA was not statistically significant. Future clinical studies are needed to support our findings.

Exploring effectiveness of ab-initio protein-protein docking methods on a novel antibacterial protein complex dataset

Diseases caused by bacterial infections become a critical problem in public heath. Antibiotic, the traditional treatment, gradually loses their effectiveness due to the resistance. Meanwhile, antibacterial proteins attract more attention because of broad spectrum and little harm to host cells. Therefore, exploring new effective antibacterial proteins is urgent and necessary. In this paper, we are committed to evaluating the effectiveness of ab-initio docking methods in antibacterial protein-protein docking. For this purpose, we constructed a three-dimensional (3D) structure dataset of antibacterial protein complex, called APCset, which contained $19$ protein complexes whose receptors or ligands are homologous to antibacterial peptides from Antimicrobial Peptide Database. Then we selected five representative ab-initio protein-protein docking tools including ZDOCK3.0.2, FRODOCK3.0, ATTRACT, PatchDock and Rosetta to identify these complexes' structure, whose performance differences were obtained by analyzing from five aspects, including top/best pose, first hit, success rate, average hit count and running time. Finally, according to different requirements, we assessed and recommended relatively efficient protein-protein docking tools. In terms of computational efficiency and performance, ZDOCK was more suitable as preferred computational tool, with average running time of $6.144$ minutes, average Fnat of best pose of $0.953$ and average rank of best pose of $4.158$. Meanwhile, ZDOCK still yielded better performance on Benchmark 5.0, which proved ZDOCK was effective in performing docking on large-scale dataset. Our survey can offer insights into the research on the treatment of bacterial infections by utilizing the appropriate docking methods.

Reduced Expression of Antimicrobial Protein Secretory Leukoprotease Inhibitor and Clusterin in Chronic Rhinosinusitis with Nasal Polyps

Introduction

Antimicrobial peptides and proteins (AMPs) constitute the first line of defense against pathogenic microorganisms in the airway. The association between AMPs and chronic rhinosinusitis with nasal polyps (CRSwNP) requires further investigations. This study is aimed at investigating the expression and regulation of major dysregulated AMPs in the nasal mucosa of CRSwNP.

Methods

The expression of AMPs was analyzed in nasal tissue from patients with eosinophilic (E) CRSwNP and nonECRSwNP and healthy subjects using RNA sequencing. The 10 most abundant AMPs expressed differentially in CRSwNP patients were verified by real-time PCR, and of these, the expression and regulation of secretory leukoprotease inhibitor (SLPI) and clusterin (CLU) were investigated further.

Results

The 10 most abundant AMPs expressed differentially in CRSwNP compared to healthy control, regardless of subtypes, included BPIFA1, BPIFB1, BPIFB2, CLU, LTF, LYZ, and SLPI, which were downregulated, and S100A8, S100A9, and HIST1H2BC, which were upregulated. ELISA and immunofluorescence confirmed the decreased expression of SLPI and CLU levels in CRSwNP. SLPI is expressed in both nasal epithelial cells and glandular cells, whereas CLU is mainly expressed in glandular cells. AB/PAS staining further demonstrated that both SLPI and CLU were mainly produced by mucous cells in submucosal glands. Furthermore, the numbers of submucosal glands were significantly decreased in nasal polyp tissue of CRSwNP compared to nasal tissue of controls. SLPI was downregulated by TGF-β1 and IL-4 in cultured nasal tissues in vitro, while CLU expression was inhibited by TGF-β1. Glucocorticoid treatment for 2 weeks significantly increased the expression of all downregulated AMPs, but not LYZ. Additionally, budesonide significantly increased the expression of SLPI and CLU in cultured nasal tissues.

Conclusion

The expression of major antimicrobial proteins is significantly decreased in nasal tissue of CRSwNP. The expression of SLPI and CLU is correlated with the numbers of submucosal glands and regulated by inflammatory cytokines and glucocorticoids.

Novel Anti-Inflammatory Approaches for Cystic Fibrosis Lung Disease: Identification of Molecular Targets and Design of Innovative Therapies

Cystic fibrosis (CF) is the most common genetic disorder among Caucasians, estimated to affect more than 70,000 people in the world. Severe and persistent bronchial inflammation and chronic bacterial infection, along with airway mucus obstruction, are hallmarks of CF lung disease and participate in its progression. Anti-inflammatory therapies are, therefore, of particular interest for CF lung disease. Furthermore, a better understanding of the molecular mechanisms involved in airway infection and inflammation in CF has led to the development of new therapeutic approaches that are currently under evaluation by clinical trials. These new strategies dedicated to CF inflammation are designed to treat different dysregulated aspects such as oxidative stress, cytokine secretion, and the targeting of dysregulated pathways. In this review, we summarize the current understanding of the cellular and molecular mechanisms that contribute to abnormal lung inflammation in CF, as well as the new anti-inflammatory strategies proposed to CF patients by exploring novel molecular targets and novel drug approaches.

Antimicrobial Susceptibility Testing of Antimicrobial Peptides to Better Predict Efficacy

During the development of antimicrobial peptides (AMP) as potential therapeutics, antimicrobial susceptibility testing (AST) stands as an essential part of the process in identification and optimisation of candidate AMP. Standard methods for AST, developed almost 60 years ago for testing conventional antibiotics, are not necessarily fit for purpose when it comes to determining the susceptibility of microorganisms to AMP. Without careful consideration of the parameters comprising AST there is a risk of failing to identify novel antimicrobials at a time when antimicrobial resistance (AMR) is leading the planet toward a post-antibiotic era. More physiologically/clinically relevant AST will allow better determination of the preclinical activity of drug candidates and allow the identification of lead compounds. An important consideration is the efficacy of AMP in biological matrices replicating sites of infection, e.g., blood/plasma/serum, lung bronchiolar lavage fluid/sputum, urine, biofilms, etc., as this will likely be more predictive of clinical efficacy. Additionally, specific AST for different target microorganisms may help to better predict efficacy of AMP in specific infections. In this manuscript, we describe what we believe are the key considerations for AST of AMP and hope that this information can better guide the preclinical development of AMP toward becoming a new generation of urgently needed antimicrobials.

Antifungal Activity of Antimicrobial Peptides and Proteins against Aspergillus fumigatus

Antimicrobial peptides and proteins (AMPs) provide an important line of defence against invading microorganisms. However, the activity of AMPs against the human fungal pathogen Aspergillus fumigatus remains poorly understood. Therefore, the aim of this study was to characterise the anti-Aspergillus activity of specific human AMPs, and to determine whether A. fumigatus can possess resistance to specific AMPs, as a result of in-host adaptation. AMPs were tested against a wide range of clinical isolates of various origins (including cystic fibrosis patients, as well as patients with chronic and acute aspergillosis). We also tested a series of isogenic A. fumigatus isolates obtained from a single patient over a period of 2 years. A range of environmental isolates, obtained from soil in Scotland, was also included. Firstly, the activity of specific peptides was assessed against hyphae using a measure of fungal metabolic activity. Secondly, the activity of specific peptides was assessed against germinating conidia, using imaging flow cytometry as a measure of hyphal growth. We showed that lysozyme and histones inhibited hyphal metabolic activity in all the A. fumigatus isolates tested in a dose-dependent fashion. In addition, imaging flow cytometry revealed that histones, β-defensin-1 and lactoferrin inhibited the germination of A. fumigatus conidia.

Cathepsin S: investigating an old player in lung disease pathogenesis, comorbidities, and potential therapeutics

Dysregulated expression and activity of cathepsin S (CTSS), a lysosomal protease and a member of the cysteine cathepsin protease family, is linked to the pathogenesis of multiple diseases, including a number of conditions affecting the lungs. Extracellular CTSS has potent elastase activity and by processing cytokines and host defense proteins, it also plays a role in the regulation of inflammation. CTSS has also been linked to G-coupled protein receptor activation and possesses an important intracellular role in major histocompatibility complex class II antigen presentation. Modulated CTSS activity is also associated with pulmonary disease comorbidities, such as cancer, cardiovascular disease, and diabetes. CTSS is expressed in a wide variety of immune cells and is biologically active at neutral pH. Herein, we review the significance of CTSS signaling in pulmonary diseases and associated comorbidities. We also discuss CTSS as a plausible therapeutic target and describe recent and current clinical trials examining CTSS inhibition as a means for treatment.

Oxidation of cathepsin S by major chemicals of cigarette smoke

Lung cysteine cathepsin S (CatS) that is a potent elastase plays a deleterious role in alveolar remodeling during smoke-induced emphysema. Despite the presence of a reactive nucleophilic cysteine (Cys25) within its active site, most of its elastinolytic activity is preserved after exposure to cigarette smoke extract (CSE), a major source of sulfhydryl oxidants. This result led us to decipher CatS resistance to major and representative CSE oxidants: hydrogen peroxide, formaldehyde, acrolein and peroxynitrite. CatS was inactivated by hydrogen peroxide, peroxynitrite and acrolein in a time- and dose-dependent manner, while formaldehyde was a weaker oxidant. Hydrogen peroxide, but not CSE, formaldehyde, and peroxynitrite impaired the autocatalytic maturation of pro-CatS, whereas acrolein prevented the formation of mature CatS without hindering the initial step of the two-step autocatalytic process. Far-UV CD spectra analysis supported that oxidation by CSE and hydrogen peroxide did not led to a structural alteration of CatS, despite a notable increase of protein carbonylation, a major hallmark of oxidative damage. Evaluation of the oxidation status of Cys25 by specific biotinylated redox sensing probes suggested the formation of sulfenic acid followed by a slower conversion to sulfinic acid after incubation with hydrogen peroxide. Addition of reducing reagents (dithiothreitol, glutathione and N-acetyl cysteine) led to a partial recovery of CatS activity following incubation with CSE, hydrogen peroxide and peroxynitrite. Current results provide some mechanistic evidence of CatS stability and activity in the presence of CSE, supporting its harmful contribution to the pathophysiology of emphysema.

Lung allograft donors with excessive alcohol use have increased levels of human antimicrobial peptide LL-37

The relatively low long-term survival rate of lung transplant recipients as compared to other organ recipients serves as an impetus to identify potential lung dysfunction as early as possible. There is an association between donor heavy alcohol use and acute lung injury in the lung allograft after transplant, known as primary graft dysfunction. Excessive alcohol use (EAU) can induce pulmonary immune dysregulation in response to an infection. Antimicrobial peptides (AMPs) are an important component of the innate immune response to pulmonary infections, but the impact of EAU on AMPs in the allograft lung has not been evaluated. Our hypothesis is that specific lung AMPs, LL-37, α-defensin-1,2,3, and β-defensin-2, are dysregulated in the lungs from organ donors who had EAU. In this prospective observational investigation, we measured AMPs via ELISA and inflammatory cytokines via multiplex bead array, in bronchoalveolar lavage (BAL) fluid of lung allograft donors, comparing results based on their alcohol consumption. LL-37 levels in lung donors with EAU were found to be increased compared to nondrinker (ND) donors [median 7.7 ng/mL (IQR 4.1-37.0) vs. 2.3 ng/mL (IQR 1.1-7.9), p = 0.004], whereas α-defensins-1,2,3 were decreased only in the presence of an infection in donors with EAU compared to ND donors [median 2.2 ng/mL (IQR 1.6-2.4) vs. 3.2 ng/mL (IQR 2.3-3.8), p = 0.049]. There was no difference in β-defensin-2 levels. Gene expression levels of these AMPs were not different. Elevated levels of CXCL8 were noted in bronchial washings of donors with EAU compared to ND donors, [median 4372 pg/mL (IQR 3352-13180) vs. 867.3 pg/mL (IQR 163.6-3675), p = 0.04], suggesting a potentially heightened inflammatory response. At 1 month post-transplant, LL-37 and CXCL8 levels are decreased compared to levels at time of transplant. In lung donors with EAU, LL-37 and α-defensins-1,2,3 dysregulated levels in the presence of an infection may be a harbinger of dysfunction of the lungs through the transplant process.

Cigarette smoke induces overexpression of active human cathepsin S in lungs from current smokers with or without COPD

Cigarette smoking has marked effects on lung tissue, including induction of oxidative stress, inflammatory cell recruitment, and a protease/antiprotease imbalance. These effects contribute to tissue remodeling and destruction resulting in loss of lung function in chronic obstructive pulmonary disease (COPD) patients. Cathepsin S (CatS) is a cysteine protease that is involved in the remodeling/degradation of connective tissue and basement membrane. Aberrant expression or activity of CatS has been implicated in a variety of diseases, including arthritis, cancer, cardiovascular, and lung diseases. However, little is known about the effect of cigarette smoking on both CatS expression and activity, as well as its role in smoking-related lung diseases. Here, we evaluated the expression and activity of human CatS in lung tissues from never-smokers and smokers with or without COPD. Despite the presence of an oxidizing environment, CatS expression and activity were significantly higher in current smokers (both non-COPD and COPD) compared with never-smokers, and correlated positively with smoking history. Moreover, we found that the exposure of primary human bronchial epithelial cells to cigarette smoke extract triggered the activation of P2X7 receptors, which in turns drives CatS upregulation. The present data suggest that excessive CatS expression and activity contribute, beside other proteases, to the deleterious effects of cigarette smoke on pulmonary homeostasis.

Predicting Antimicrobial Peptides by Using Increment of Diversity with Quadratic Discriminant Analysis Method

Antimicrobial peptides are crucial components of the innate host defense system of most living organisms and promising candidates for antimicrobial agents. Accurate classification of antimicrobial peptides will be helpful to the discovery of new therapeutic targets. In this work, the Increment of Diversity with Quadratic Discriminant analysis (IDQD) was presented to classify antifungal and antibacterial peptides based on primary sequence information. In the jackknife test, the proposed IDQD model yields an accuracy of 86.02 percent with the sensitivity of 74.31 percent and specificity of 92.79 percent for identifying antimicrobial peptides, which is superior to other state-of-the-art methods. This result suggests that the proposed IDQD model can be efficiently used to antimicrobial peptide classification.

Airways exudation of plasma macromolecules: Innate defense, epithelial regeneration, and asthma

This review discusses in vivo airway aspects of plasma exudation in relation to current views on epithelial permeability and epithelial regeneration in health and disease. Microvascular-epithelial exudation of bulk plasma proteins characteristically occurs in asthmatic patients, being especially pronounced in those with severe and exacerbating asthma. Healthy human and guinea pig airways challenged by noninjurious histamine-leukotriene–type autacoids also respond through prompt mucosal exudation of nonsieved plasma macromolecules. Contrary to current beliefs, epithelial permeability in the opposite direction (ie, absorption of inhaled molecules) has not been increased in patients with asthma and allergic rhinitis or in acutely exuding healthy airways. A slightly increased subepithelial hydrostatic pressure produces such unidirectional outward perviousness to macromolecules. Lack of increased absorption permeability in asthmatic patients can further be reconciled with occurrence of epithelial shedding, leaving small patches of denuded basement membrane. Counteracting escalating barrier breaks, plasma exudation promptly covers the denuded patches. Here it creates and sustains a biologically active barrier involving a neutrophil-rich, fibrin-fibronectin net. Furthermore, in the plasma-derived milieu, all epithelial cell types bordering the denuded patch dedifferentiate and migrate from all sides to cover the denuded basement membrane. However, this speedy epithelial regeneration can come at a cost. Guinea pig in vivo studies demonstrate that patches of epithelial denudation regeneration are exudation hot spots evoking asthma-like features, including recruitment/activation of granulocytes, proliferation of fibrocytes/smooth muscle cells, and basement membrane thickening. In conclusion, nonsieved plasma macromolecules can operate on the intact airway mucosa as potent components of first-line innate immunity responses. Exuded plasma also takes center stage in epithelial regeneration. When exaggerated, epithelial regeneration can contribute to the inception and development of asthma.

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.

The Microbial Endocrinology of Pseudomonas aeruginosa: Inflammatory and Immune Perspectives

Pseudomonas aeruginosa is a major pathogen responsible for both acute and chronic infection. Known as a colonising pathogen of the cystic fibrosis (CF) lung, it is implicated in other settings such as bronchiectasis. It has the ability to cause acute disseminated or localised infection particularly in the immunocompromised. Human hormones have been highlighted as potential regulators of bacterial virulence through crosstalk between analogous "quorum sensing" (QS) systems present in the bacteria that respond to mammalian hormones. Pseudomonas aeruginosa is known to utilise interconnected QS systems to coordinate its virulence and evade various aspects of the host immune system activated in response to infection. Several human hormones demonstrate an influence on P. aeruginosa growth and virulence. This inter-kingdom signalling, termed "microbial endocrinology" has important implications for host-microbe interaction during infection and, potentially opens up novel avenues for therapeutic intervention. This phenomenon, supported by the existence of sexual dichotomies in both microbial infection and chronic lung diseases such as CF is potentially explained by sex hormones and their influence on the infective process. This review summarises our current understanding of the microbial endocrinology of P. aeruginosa, including its endogenous QS systems and their intersection with human endocrinology, pathogenesis of infection and the host immune system.

Heparin-binding protein, lysozyme, and inflammatory cytokines in bronchoalveolar lavage fluid as diagnostic tools for pulmonary infection in lung transplanted patients

Pulmonary infection is a common complication after lung transplantation, and early detection is crucial for outcome. However, the condition can be clinically difficult to diagnose and to distinguish from rejection. The aim of this prospective study was to evaluate heparin-binding protein (HBP), lysozyme, and the cytokines interleukin (IL)-1β, IL-6, IL-8, IL-10 and tumor necrosis factor (TNF) in bronchoalveolar lavage fluid (BALF) as potential biomarkers for pulmonary infection in lung-transplanted patients. One hundred thirteen BALF samples from 29 lung transplant recipients were collected at routine scheduled bronchoscopies at 3 and 6 months, or on clinical indication. Samples were classified into no, possible, probable, or definite infection at the time of sampling. Rejection was defined by biopsy results. HBP, lysozyme, and cytokines were analyzed in BALF and correlated to likelihood of infection and rejection. All biomarkers were significantly increased in BALF during infection, whereas patients with rejection presented low levels that were comparable to noninfection samples. HBP, IL-1β, and IL-8 were the best diagnostic markers of infection with area under the receiver-operating characteristic curve values of 0.88, 0.91, and 0.90, respectively. In conclusion, HBP, IL-1β, and IL-8 could be useful diagnostic markers of pulmonary infection in lung-transplanted patients.

Lung epithelial cells: therapeutically inducible effectors of antimicrobial defense

Lung epithelial cells are increasingly recognized to be active effectors of microbial defense, contributing to both innate and adaptive immune function in the lower respiratory tract. As immune sentinels, lung epithelial cells detect diverse pathogens through an ample repertoire of membrane-bound, endosomal, and cytosolic pattern-recognition receptors (PRRs). The highly plastic epithelial barrier responds to detected threats via modulation of paracellular flux, intercellular communications, mucin production, and periciliary fluid composition. Epithelial PRR stimulation also induces production of cytokines that recruit and sculpt leukocyte-mediated responses, and promotes epithelial generation of antimicrobial effector molecules that are directly microbicidal. The epithelium can alternately enhance tolerance to pathogens, preventing tissue damage through PRR-induced inhibitory signals, opsonization of pathogen-associated molecular patterns, and attenuation of injurious leukocyte responses. The inducibility of these protective responses has prompted attempts to therapeutically harness epithelial defense mechanisms to protect against pneumonias. Recent reports describe successful strategies for manipulation of epithelial defenses to protect against a wide range of respiratory pathogens. The lung epithelium is capable of both significant antimicrobial responses that reduce pathogen burdens and tolerance mechanisms that attenuate immunopathology. This manuscript reviews inducible lung epithelial defense mechanisms that offer opportunities for therapeutic manipulation to protect vulnerable populations against pneumonia.

Inflammation and host-pathogen interaction: Cause and consequence in cystic fibrosis lung disease

Cystic Fibrosis (CF) lung disease is associated with dysregulation of host defence systems, which ultimately disrupts the balance between inflammation and resolution and leaves the host susceptible to repeated infection. However, the mechanisms underlying these defects are complex and continue to garner significant interest among the CF research community. This review explores emerging data on novel aspects of innate host defence with promising biomarker and therapeutic potential for CF lung disease. Improved understanding of inflammation and host defence against pathogens in patients and animal models during the progression of CF lung disease is pivotal for the discovery of new therapeutics that can limit and/or prevent damage from birth.

Allergen specific immunotherapy enhanced defense against bacteria via TGF-β1-induced CYP27B1 in asthma

Allergen specific immunotherapy (SIT) is the only specific treatment of allergic diseases at present. How SIT impacts pulmonary innate immunity against bacteria currently remains unclear. In this study, dust mite extracts (HDM)-sensitized mice were immunized with a subcutaneous injection of HDM. These mice were then challenged with an intranasal administration of HDM. After the last challenge, mice were infected with an intranasal instillation with P. aeruginosa (P.a). We measured the score of tissue inflammation, the expression of cathelicidin-related antimicrobial peptide (CRAMP) and 25-Hydroxyvitamin D-1Alpha-hydroxylase (CYP27B1) in lung. We analyzed the effect of TGF-β1 on CRAMP and CYP27B1 in airway cells (16HBE), and investigate the role of TGF-β1-induced CYP27B1 in defense against bacteria in16HBE cell. We found that SIT attenuates HDM-induced airway inflammation and airway responsiveness (AHR), which is involved in the increased levels of HDM-specific IgG2a, IL-10, TGF-β1, IFN-γ, CRAMP and CYP27B1. SIT ameliorates pulmonary infectious inflammation associated with an improving defense of HDM-challenged mice against P. aeruginosa. Meanwhile, TGF-β1 significantly increased the expression of CYP27B1 in a dose-dependent manner. TGF-β1 did not increase the levels of CRAMP in airway epithelial cells. Furthermore, 25-dihydroxyvitamin D3 (25VD₃) is required for TGF-β1-induced CRAMP in airway epithelial cells. CRAMP was significantly increased in TGF-β1/25VD₃-treated 16HBE cells. These findings illustrated that TGF-β1 is a major player against bacterial infections in SIT models via induction of CYP27B1 rather than CRAMP. Collectively, these findings highlight a role for SIT enhancing host defense against bacteria depending on TGF-β1-induced CYP27B1in asthma.

Antimicrobial Activity of Mesenchymal Stem Cells: Current Status and New Perspectives of Antimicrobial Peptide-Based Therapies

While mesenchymal stem cells (MSCs)-based therapy appears to be promising, there are concerns regarding possible side effects related to the unwanted suppression of antimicrobial immunity leading to an increased risk of infection. Conversely, recent data show that MSCs exert strong antimicrobial effects through indirect and direct mechanisms, partially mediated by the secretion of antimicrobial peptides and proteins (AMPs). In fact, MSCs have been reported to increase bacterial clearance in preclinical models of sepsis, acute respiratory distress syndrome, and cystic fibrosis-related infections. This article reviews the current evidence regarding the direct antimicrobial effector function of MSCs, focusing mainly on the role of MSCs-derived AMPs. The strategies that might modulate the expression and secretion of these AMPs, leading to enhanced antimicrobial effect, are highlighted. Furthermore, studies evaluating the presence of AMPs in the cargo of extracellular vesicles (EVs) are underlined as perspective opportunities to develop new drug delivery tools. The antimicrobial potential of MSCs-derived EVs can also be heightened through cell conditioning and/or drug loading. Finally, improving the pharmacokinetics and delivery, in addition to deciphering the multi-target drug status of AMPs, should synergistically lead to key advances against infections caused by drug-resistant strains.

Role of Proteases in Lung Disease: A Brief Overview

Proteases play an important role in health and disease of the lung. In the normal lungs, proteases maintain their homeostatic functions that regulate processes like its regeneration and repair. Dysregulation of proteases–antiproteases balance is crucial in the manifestation of different types of lung diseases. Chronic inflammatory lung pathologies are associated with a marked increase in protease activities. Thus, in addition to protease activities, inhibition of anti-proteolytic control mechanisms are also important for effective microbial infection and inflammation in the lung. Herein, we briefly summarize the role of different proteases and to some extent antiproteases in regulating a variety of lung diseases.

Engineered nanomaterial-induced lysosomal membrane permeabilization and anti-cathepsin agents

Engineered nanomaterials (ENMs), or small anthropogenic particles approximately < 100 nm in size and of various shapes and compositions, are increasingly incorporated into commercial products and used for industrial and medical purposes. There is an exposure risk to both the population at large and individuals in the workplace with inhalation exposures to ENMs being a primary concern. Further, there is increasing evidence to suggest that certain ENMs may represent a significant health risk, and many of these ENMs exhibit distinct similarities with other particles and fibers that are known to induce adverse health effects, such as asbestos, silica, and particulate matter (PM). Evidence regarding the importance of lysosomal membrane permeabilization (LMP) and release of cathepsins in ENM toxicity has been accumulating. The aim of this review was to describe our current understanding of the mechanisms leading to ENM-associated pathologies, including LMP and the role of cathepsins with a focus on inflammation. In addition, anti-cathepsin agents, some of which have been tested in clinical trials and may prove useful for ameliorating the harmful effects of ENM exposure, are examined.

Antimicrobial Activity of Mesenchymal Stem Cells: Current Status and New Perspectives of Antimicrobial Peptide-Based Therapies

While mesenchymal stem cells (MSCs)-based therapy appears to be promising, there are concerns regarding possible side effects related to the unwanted suppression of antimicrobial immunity leading to an increased risk of infection. Conversely, recent data show that MSCs exert strong antimicrobial effects through indirect and direct mechanisms, partially mediated by the secretion of antimicrobial peptides and proteins (AMPs). In fact, MSCs have been reported to increase bacterial clearance in preclinical models of sepsis, acute respiratory distress syndrome, and cystic fibrosis-related infections. This article reviews the current evidence regarding the direct antimicrobial effector function of MSCs, focusing mainly on the role of MSCs-derived AMPs. The strategies that might modulate the expression and secretion of these AMPs, leading to enhanced antimicrobial effect, are highlighted. Furthermore, studies evaluating the presence of AMPs in the cargo of extracellular vesicles (EVs) are underlined as perspective opportunities to develop new drug delivery tools. The antimicrobial potential of MSCs-derived EVs can also be heightened through cell conditioning and/or drug loading. Finally, improving the pharmacokinetics and delivery, in addition to deciphering the multi-target drug status of AMPs, should synergistically lead to key advances against infections caused by drug-resistant strains.

pH Dependent Antimicrobial Peptides and Proteins, Their Mechanisms of Action and Potential as Therapeutic Agents

Antimicrobial peptides (AMPs) are potent antibiotics of the innate immune system that have been extensively investigated as a potential solution to the global problem of infectious diseases caused by pathogenic microbes. A group of AMPs that are increasingly being reported are those that utilise pH dependent antimicrobial mechanisms, and here we review research into this area. This review shows that these antimicrobial molecules are produced by a diverse spectrum of creatures, including vertebrates and invertebrates, and are primarily cationic, although a number of anionic examples are known. Some of these molecules exhibit high pH optima for their antimicrobial activity but in most cases, these AMPs show activity against microbes that present low pH optima, which reflects the acidic pH generally found at their sites of action, particularly the skin. The modes of action used by these molecules are based on a number of major structure/function relationships, which include metal ion binding, changes to net charge and conformational plasticity, and primarily involve the protonation of histidine, aspartic acid and glutamic acid residues at low pH. The pH dependent activity of pore forming antimicrobial proteins involves mechanisms that generally differ fundamentally to those used by pH dependent AMPs, which can be described by the carpet, toroidal pore and barrel-stave pore models of membrane interaction. A number of pH dependent AMPs and antimicrobial proteins have been developed for medical purposes and have successfully completed clinical trials, including kappacins, LL-37, histatins and lactoferrin, along with a number of their derivatives. Major examples of the therapeutic application of these antimicrobial molecules include wound healing as well as the treatment of multiple cancers and infections due to viruses, bacteria and fungi. In general, these applications involve topical administration, such as the use of mouth washes, cream formulations and hydrogel delivery systems. Nonetheless, many pH dependent AMPs and antimicrobial proteins have yet to be fully characterized and these molecules, as a whole, represent an untapped source of novel biologically active agents that could aid fulfillment of the urgent need for alternatives to conventional antibiotics, helping to avert a return to the pre-antibiotic era.

Viral-bacterial interactions in the respiratory tract

In the respiratory tract, viruses and bacteria can interact on multiple levels. It is well known that respiratory viruses, particularly influenza viruses, increase the susceptibility to secondary bacterial infections. Numerous mechanisms, including compromised physical and immunological barriers, and changes in the microenvironment have hereby been shown to contribute to the development of secondary bacterial infections. In contrast, our understanding of how bacteria shape a response to subsequent viral infection is still limited. There is emerging evidence that persistent infection (or colonization) of the lower respiratory tract (LRT) with potential pathogenic bacteria, as observed in diseases like chronic obstructive pulmonary disease or cystic fibrosis, modulates subsequent viral infections by increasing viral entry receptors and modulating the inflammatory response. Moreover, recent studies suggest that even healthy lungs are not, as had long been assumed, sterile. The composition of the lung microbiome may thus modulate responses to viral infections. Here we summarize the current knowledge on the co-pathogenesis between viruses and bacteria in LRT infections.

The Unusual Resistance of Avian Defensin AvBD7 to Proteolytic Enzymes Preserves Its Antibacterial Activity

Defensins are frontline peptides of mucosal immunity in the animal kingdom, including birds. Their resistance to proteolysis and their ensuing ability to maintain antimicrobial potential remains questionable and was therefore investigated. We have shown by bottom-up mass spectrometry analysis of protein extracts that both avian beta-defensins AvBD2 and AvBD7 were ubiquitously distributed along the chicken gut. Cathepsin B was found by immunoblotting in jejunum, ileum, caecum, and caecal tonsils, while cathepsins K, L, and S were merely identified in caecal tonsils. Hydrolysis product of AvBD2 and AvBD7 incubated with a panel of proteases was analysed by RP-HPLC, mass spectrometry and antimicrobial assays. AvBD2 and AvBD7 were resistant to serine proteases and to cathepsins D and H. Conversely cysteine cathepsins B, K, L, and S degraded AvBD2 and abolished its antibacterial activity. Only cathepsin K cleaved AvBD7 and released Ile4-AvBD7, a N-terminal truncated natural peptidoform of AvBD7 that displayed antibacterial activity. Besides the 3-stranded antiparallel beta-sheet typical of beta-defensins, structural analysis of AvBD7 by two-dimensional NMR spectroscopy highlighted the restricted accessibility of the C-terminus embedded by the N-terminal region and gave a formal evidence of a salt bridge (Asp9-Arg12) that could account for proteolysis resistance. The differential susceptibility of avian defensins to proteolysis opens intriguing questions about a distinctive role in the mucosal immunity against pathogen invasion.

Purification and Characterization of a Novel Kazal-Type Trypsin Inhibitor from the Leech of Hirudinaria manillensis

Kazal-type serine proteinase inhibitors are found in a large number of living organisms and play crucial roles in various biological and physiological processes. Although some Kazal-type serine protease inhibitors have been identified in leeches, none has been reported from Hirudinaria manillensis, which is a medically important leech. In this study, a novel Kazal-type trypsin inhibitor was isolated from leech H. manillensis, purified and named as bdellin-HM based on the sequence similarity with bdellin-KL and bdellin B-3. Structural analysis revealed that bdellin-HM was a 17,432.8 Da protein and comprised of 149 amino acid residues with six cysteines forming three intra-molecular disulfide bonds. Bdellin-HM showed similarity with the Kazal-type domain and may belong to the group of “non-classical” Kazal inhibitors according to its Cys^I-Cys^II disulfide bridge position. Bdellin-HM had no inhibitory effect on elastase, chymotrypsin, kallikrein, Factor (F) XIIa, FXIa, FXa, thrombin and plasmin, but it showed a potent ability to inhibit trypsin with an inhibition constant (K_i) of (8.12 ± 0.18) × 10⁻⁹ M. These results suggest that bdellin-HM from the leech of H. manillensis plays a potent and specific inhibitory role towards trypsin.

Antimycobacterial Activity of a New Peptide Polydim-I Isolated from Neotropical Social Wasp Polybia dimorpha

Mycobacterium abscessus subsp. massiliense, a rapidly growing mycobacteria (RGM) that is becoming increasingly important among human infectious diseases, is virulent and pathogenic and presents intrinsic resistance to several antimicrobial drugs that might hamper their elimination. Therefore, the identification of new drugs to improve the current treatment or lower the risk of inducing resistance is urgently needed. Wasp venom primarily comprises peptides that are responsible for most of the biological activities in this poison. Here, a novel peptide Polydim-I, from Polybia dimorpha Neotropical wasp, was explored as an antimycobacterial agent. Polydim-I provoked cell wall disruption and exhibited non-cytotoxicity towards mammalian cells. Polydim-I treatment of macrophages infected with different M. abscessus subsp. massiliense strains reduced 40 to 50% of the bacterial load. Additionally, the Polydim-I treatment of highly susceptible mice intravenously infected with M. abscessus subsp. massiliense induced 0.8 to 1 log reduction of the bacterial load in the lungs, spleen, and liver. In conclusion, this is the first study to show the therapeutic potential of a peptide derived from wasp venom in treating mycobacteria infections. Polydim-I acts on the M. abscessus subsp. massiliense cell wall and reduce 40–90% of the bacterial load both in vitro and in vivo. The presented results encourage further studies on the use of Polydim-I as one of the components for M. abscessus subsp. massiliense treatment.