Kinetics of the inhibition of neutrophil proteinases by recombinant elafin and pre-elafin (trappin-2) expressed in Pichia pastoris

Elafin and its precursor trappin-2: What is their therapeutic potential for intestinal diseases?

Elafin and its precursor trappin-2 are known for their contribution to the physiological mucosal shield against luminal microbes. Such a contribution seems to be particularly relevant in the gut, where the exposure of host tissues to heavy loads of microbes is constant and contributes to mucosa-associated pathologies. The expression of trappin-2/elafin has been shown to be differentially regulated in diseases associated with gut inflammation. Accumulating evidence has demonstrated the protective effects of trappin-2/elafin in gut intestinal disorders associated with acute or chronic inflammation, or with gluten sensitization disorders. The protective effects of trappin-2/elafin in the gut are discussed in terms of their pleiotropic modes of action: acting as protease inhibitors, transglutaminase substrates, antimicrobial peptides or as a regulator of pro-inflammatory transcription factors. Further, the question of the therapeutic potential of trappin-2/elafin delivery at the intestinal mucosa surface is raised. Whether trappin-2/elafin mucosal delivery should be considered to ensure intestinal tissue repair is also discussed.

The emerging role of proteases in α1-antitrypsin deficiency and beyond

α1-Antitrypsin deficiency (AATD) has been historically under-recognised and under-diagnosed; recently it has begun to receive greater interest in terms of attempts at deeper elucidation of pathology and treatment options. However, the concept of disease phenotypes within AATD (emphysema, chronic bronchitis, bronchiectasis or a combination of phenotypes) has not been proposed or studied. Of the three neutrophil serine proteases, neutrophil elastase was historically believed to be the sole contributor to disease pathology in AATD. Recently, Proteinase-3 has been increasingly studied as an equal, if not greater, contributor to the disease process. Cathepsin G, however, has not been extensively evaluated in this area. Matrix metalloproteinases have also been mentioned in the pathogenesis of AATD but have not been widely explored. This article considers the available evidence for differential protease activity in patients with AATD, including the contribution to distinct phenotypes of the disease. Owing to limited literature in this area, extrapolations from studies of other chronic lung diseases with similar phenotypes, including COPD and bronchiectasis, have been made. We consider a new framework of understanding defined by protease-driven endotypes of disease which may lead to new opportunities for precision medicine.

Proteinase 3; a potential target in chronic obstructive pulmonary disease and other chronic inflammatory diseases

Chronic Obstructive Pulmonary Disease (COPD) is a common, multifactorial lung disease which results in significant impairment of patients' health and a large impact on society and health care burden. It is believed to be the result of prolonged, destructive neutrophilic inflammation which results in progressive damage to lung structures. During this process, large quantities of neutrophil serine proteinases (NSPs) are released which initiate the damage and contribute towards driving a persistent inflammatory state.Neutrophil elastase has long been considered the key NSP involved in the pathophysiology of COPD. However, in recent years, a significant role for Proteinase 3 (PR3) in disease development has emerged, both in COPD and other chronic inflammatory conditions. Therefore, there is a need to investigate the importance of PR3 in disease development and hence its potential as a therapeutic target. Research into PR3 has largely been confined to its role as an autoantigen, but PR3 is involved in triggering inflammatory pathways, disrupting cellular signalling, degrading key structural proteins, and pathogen response.This review summarises what is presently known about PR3, explores its involvement particularly in the development of COPD, and indicates areas requiring further investigation.

Synthesis, biological evaluation, and molecular modelling studies of potent human neutrophil elastase (HNE) inhibitors

We report the synthesis and biological evaluation of a new series of 3- or 4-(substituted)phenylisoxazolones as HNE inhibitors. Due to tautomerism of the isoxazolone nucleus, two isomers were obtained as final compounds (2-NCO and 5-OCO) and the 2-NCO derivatives were the most potent with IC₅₀ values in the nanomolar range (20–70 nM). Kinetic experiments indicated that 2-NCO 7d and 5-OCO 8d are both competitive HNE inhibitors. Molecular modelling on 7d and 8d suggests for the latter a more crowded region about the site of the nucleophilic attack, which could explain its lowered activity. In addition molecular dynamics (MD) simulations showed that the isomer 8d appears more prone to form H-bond interactions which, however, keep the reactive sites quite distant for the attack by Ser195. By contrast the amide 7d appears more mobile within the active pocket, since it makes single H-bond interactions affording a favourable orientation for the nucleophilic attack.

Evidence for multiple modes of neutrophil serine protease recognition by the EAP family of Staphylococcal innate immune evasion proteins

Neutrophils contain high levels of chymotrypsin-like serine proteases (NSPs) within their azurophilic granules that have a multitude of functions within the immune system. In response, the pathogen Staphylococcus aureus has evolved three potent inhibitors (Eap, EapH1, and EapH2) that protect the bacterium as well as several of its secreted virulence factors from the degradative action of NSPs. We previously showed that these so-called EAP domain proteins represent a novel class of NSP inhibitors characterized by a non-covalent inhibitory mechanism and a distinct target specificity profile. Based upon high levels of structural homology amongst the EAP proteins and the NSPs, as well as supporting biochemical data, we predicted that the inhibited complex would be similar for all EAP/NSP pairs. However, we present here evidence that EapH1 and EapH2 bind the canonical NSP, Neutrophil Elastase (NE), in distinct orientations. We discovered that alteration of EapH1 residues at the EapH1/NE interface caused a dramatic loss of affinity and inhibition of NE, while mutation of equivalent positions in EapH2 had no effect on NE binding or inhibition. Surprisingly, mutation of residues in an altogether different region of EapH2 severely impacted both the NE binding and inhibitory properties of EapH2. Even though EapH1 and EapH2 bind and inhibit NE and a second NSP, Cathepsin G, equally well, neither of these proteins interacts with the structurally related, but non-proteolytic granule protein, azurocidin. These studies expand our understanding of EAP/NSP interactions and suggest that members of this immune evasion protein family are capable of diverse target recognition modes.

Pseudomonas aeruginosa proteolytically alters the interleukin 22-dependent lung mucosal defense

The IL-22 signaling pathway is critical for regulating mucosal defense and limiting bacterial dissemination. IL-22 is unusual among interleukins because it does not directly regulate the function of conventional immune cells, but instead targets cells at outer body barriers, such as respiratory epithelial cells. Consequently, IL-22 signaling participates in the maintenance of the lung mucosal barrier by controlling cell proliferation and tissue repair, and enhancing the production of specific chemokines and anti-microbial peptides. Pseudomonas aeruginosa is a major pathogen of ventilator-associated pneumonia and causes considerable lung tissue damage. A feature underlying the pathogenicity of this bacterium is its capacity to persist and develop in the host, particularly in the clinical context of nosocomial lung infections. We aimed to investigate the ability of P. auruginosa to disrupt immune-epithelial cells cross-talk. We found that P. aeruginosa escapes the host mucosal defenses by degrading IL-22, leading to severe inhibition of IL-22-mediated immune responses. We demonstrated in vitro that, protease IV, a type 2 secretion system-dependent serine protease, is responsible for the degradation of IL-22 by P. aeruginosa. Moreover, the major anti-proteases molecules present in the lungs were unable to inhibit protease IV enzymatic activity. In addition, tracheal aspirates of patients infected by P. aeruginosa contain protease IV activity which further results in IL-22 degradation. This so far undescribed cleavage of IL-22 by a bacterial protease is likely to be an immune-evasion strategy that contributes to P. aeruginosa-triggered respiratory infections.

Inhibitors and Antibody Fragments as Potential Anti-Inflammatory Therapeutics Targeting Neutrophil Proteinase 3 in Human Disease

Proteinase 3 (PR3) has received great scientific attention after its identification as the essential antigenic target of antineutrophil cytoplasm antibodies in Wegener's granulomatosis (now called granulomatosis with polyangiitis). Despite many structural and functional similarities between neutrophil elastase (NE) and PR3 during biosynthesis, storage, and extracellular release, unique properties and pathobiological functions have emerged from detailed studies in recent years. The development of highly sensitive substrates and inhibitors of human PR3 and the creation of PR3-selective single knockout mice led to the identification of nonredundant roles of PR3 in cell death induction via procaspase-3 activation in cell cultures and in mouse models. According to a study in knockout mice, PR3 shortens the lifespan of infiltrating neutrophils in tissues and accelerates the clearance of aged neutrophils in mice. Membrane exposure of active human PR3 on apoptotic neutrophils reprograms the response of macrophages to phagocytosed neutrophils, triggers secretion of proinflammatory cytokines, and undermines immune silencing and tissue regeneration. PR3-induced disruption of the anti-inflammatory effect of efferocytosis may be relevant for not only granulomatosis with polyangiitis but also for other autoimmune diseases with high neutrophil turnover. Inhibition of membrane-bound PR3 by endogenous inhibitors such as the α-1-protease inhibitor is comparatively weaker than that of NE, suggesting that the adverse effects of unopposed PR3 activity resurface earlier than those of NE in individuals with α-1-protease inhibitor deficiency. Effective coverage of PR3 by anti-inflammatory tools and simultaneous inhibition of both PR3 and NE should be most promising in the future.

Siropins, novel serine protease inhibitors from gut microbiota acting on human proteases involved in inflammatory bowel diseases

Background

In eukaryotes, the serpins constitute a wide family of protease inhibitors regulating many physiological pathways. Many reports stressed the key role of serpins in several human physiopathologies including mainly the inflammatory bowel diseases. In this context, eukaryotic serpins were largely studied and their use to limit inflammation was reported. In comparison to that, bacterial serpins and mainly those from human gut microbiota remain poorly studied.

Results

The two genes encoding for putative serpins from the human gut bacterium Eubacterium sireaum, display low sequence identities. These genes were overexpressed and the encoded proteins, named Siropins, were purified. Activity studies demonstrated that both purified proteins inhibited serine proteases but surprisingly they preferentially inhibited two human serine proteases (Human Neutrophil Elastase and Proteinase3). The biochemical characterization of these Siropins revealed that Siropin 1 was the most active and stable at low pH values while Siropin 2 was more thermoactive and thermostable. Kinetic analysis allowed the determination of the stoichiometry of inhibition (SI) which was around 1 and of the association rate constants of 7.7 × 10⁴ for the Human Neutrophil Elastase and 2.6 × 10⁵ for the Proteinase3. Moreover, both Siropins displayed the ability to inhibit proteases usually present in fecal waters. Altogether our data indicate the high efficiency of Siropins and their probable involvement in the control of the overall intestine protease activity.

Conclusions

Here we report the purification and the biochemical characterization of two novel serpins originated from Eubacterium sireaum, a human gastro-intestinal tract commensal bacteria. These proteins that we called Siropins, efficiently inhibited two human proteases reported to be associated with inflammatory bowel diseases. The determination of the biochemical properties of these enzymes revealed different temperature and pH behaviours that may reflect adaptation of this human commensal bacterium to different ecological environments. To the best of our knowledge, it is the first bacterial serpins showing an attractive inhibition of fecal proteases recovered from a mice group with chemically induced inflammation. Altogether our data highlight the interesting potential of Siropins, and serpins from the human gut microbiota in general, to be used as new alternative to face inflammatory diseases.

Electronic supplementary material

The online version of this article (doi:10.1186/s12934-016-0596-2) contains supplementary material, which is available to authorized users.

Effects of the neutrophil elastase inhibitor EL-17 in rat adjuvant-induced arthritis

OBJECTIVES

Neutrophil elastase (NE), a granule-associated enzyme, participates in connective tissue breakdown and promotes cytokine release and specific receptor activation during various inflammatory diseases like RA. NE is increased in the SF and cartilage of RA patients and represents a target for the development of new therapeutic possibilities. The present research aimed to evaluate the preclinical pharmacological profile of the N-benzoylpyrazole derivative EL-17, a potent and selective NE inhibitor, in a rat model of RA.

METHODS

Complete Freund's Adjuvant (CFA) was injected in the tibiotarsal joint and the effect of acute or repeated treatments with EL-17 (1-30 mg/kg by mouth) were evaluated.

RESULTS

On day 14 after CFA injection, a single administration of EL-17 significantly reduced CFA-dependent hypersensitivity to mechanical noxious stimuli and the postural unbalance related to spontaneous pain. To evaluate the preventive efficacy, EL-17 was administered daily starting from the day of CFA treatment. Behavioural measurements performed on days 7 and 14 showed a progressive efficacy of EL-17 against hypersensitivity to mechanical noxious and non-noxious stimuli, as well as a decrease of hind limb weight-bearing alterations. Histological evaluation of the tibiotarsal joint (day 14) demonstrated significant prevention of articular derangement after EL-17 (30 mg/kg) treatment. The protective effects of EL-17 directly correlated with a complete reversion of the plasma NE activity increase induced by CFA.

CONCLUSIONS

The NE inhibitor EL-17 relieved articular pain after acute administration. Furthermore, repeated treatment reduced the development of hypersensitivity and protected joint tissue, revealing a disease-modifying profile.

Complete 1H, 15N and 13C assignment of trappin-2 and 1H assignment of its two domains, elafin and cementoin

Trappin-2 is a serine protease inhibitor with a very narrow inhibitory spectrum and has significant anti-microbial activities. It is a 10 kDa cationic protein composed of two distinct domains. The N-terminal domain (38 residues) named cementoin is known to be intrinsically disordered when it is not linked to the elafin. The C-terminal domain (57 residues), corresponding to elafin, is a cysteine-rich domain stabilized by four disulfide bridges and is characterized by a flat core and a flexible N-terminal part. To our knowledge, there is no structural data available on trappin-2. We report here the complete (1)H, (15)N and (13)C resonance assignment of the recombinant trappin-2 and the (1)H assignments of cementoin and elafin, under the same experimental conditions. This is the first step towards the 3D structure determination of the trappin-2.

Biodistribution and pharmacokinetics of the (99m)Tc labeled human elastase inhibitor, elafin, in rats

Elafin is a potent reversible inhibitor of the pro-inflammatory proteases leukocyte elastase and protease 3. It is currently in clinical development for the use in postoperative inflammatory diseases. We investigated the pharmacokinetics of (99m)Tc-labeled elafin ((99m)Tc-Elafin) in blood and individual organs in rat after bolus intravenous injection using the single photon emission tomography (SPECT). (99m)Tc-Elafin predominantly accumulated in the kidney reaching a maximum of 8.5% ± 0.1% of the injected dose per gram (ID/g) at 5 min post injection (p.i) and decreased only slowly during 24 h. In contrast, the initially high radio activity recorded in the other organs rapidly decreased parallel to the radioactivity detected in blood. The blood kinetics fits to a two compartment kinetics model. The radio activity in the dissected kidney was 4.98 ± 1.24%ID/g 24 h p.i, while in other organs, including the brain, no accumulation of (99m)Tc-Elafin was detected. At this time point 30% of the detected radioactivity in the kidney was identified to be not metabolized (99m)Tc-Elafin. In conclusion, the blood and organ-specific kinetic data provide a basis for planning of adequate dosing regimens and the high accumulation of intact elafin in the kidney favors clinical developments targeting inflammatory kidney diseases, such as chronic allograft nephropathy after kidney transplantation.

Respiratory protease/antiprotease balance determines susceptibility to viral infection and can be modified by nutritional antioxidants

The respiratory epithelium functions as a central orchestrator to initiate and organize responses to inhaled stimuli. Proteases and antiproteases are secreted from the respiratory epithelium and are involved in respiratory homeostasis. Modifications to the protease/antiprotease balance can lead to the development of lung diseases such as emphysema or chronic obstructive pulmonary disease. Furthermore, altered protease/antiprotease balance, in favor for increased protease activity, is associated with increased susceptibility to respiratory viral infections such as influenza virus. However, nutritional antioxidants induce antiprotease expression/secretion and decrease protease expression/activity, to protect against viral infection. As such, this review will elucidate the impact of this balance in the context of respiratory viral infection and lung disease, to further highlight the role epithelial cell-derived proteases and antiproteases contribute to respiratory immune function. Furthermore, this review will offer the use of nutritional antioxidants as possible therapeutics to boost respiratory mucosal responses and/or protect against infection.

Three-dimensional Structure of a Kunitz-type Inhibitor in Complex with an Elastase-like Enzyme

Elastase-like enzymes are involved in important diseases such as acute pancreatitis, chronic inflammatory lung diseases, and cancer. Structural insights into their interaction with specific inhibitors will contribute to the development of novel anti-elastase compounds that resist rapid oxidation and proteolysis. Proteinaceous Kunitz-type inhibitors homologous to the bovine pancreatic trypsin inhibitor (BPTI) provide a suitable scaffold, but the structural aspects of their interaction with elastase-like enzymes have not been elucidated. Here, we increased the selectivity of ShPI-1, a versatile serine protease inhibitor from the sea anemone Stichodactyla helianthus with high biomedical and biotechnological potential, toward elastase-like enzymes by substitution of the P1 residue (Lys(13)) with leucine. The variant (rShPI-1/K13L) exhibits a novel anti-porcine pancreatic elastase (PPE) activity together with a significantly improved inhibition of human neuthrophil elastase and chymotrypsin. The crystal structure of the PPE·rShPI-1/K13L complex determined at 2.0 Å resolution provided the first details of the canonical interaction between a BPTI-Kunitz-type domain and elastase-like enzymes. In addition to the essential impact of the variant P1 residue for complex stability, the interface is improved by increased contributions of the primary and secondary binding loop as compared with similar trypsin and chymotrypsin complexes. A comparison of the interaction network with elastase complexes of canonical inhibitors from the chelonian in family supports a key role of the P3 site in ShPI-1 in directing its selectivity against pancreatic and neutrophil elastases. Our results provide the structural basis for site-specific mutagenesis to further improve the binding affinity and/or direct the selectivity of BPTI-Kunitz-type inhibitors toward elastase-like enzymes.

A functional variant of elafin with improved anti-inflammatory activity for pulmonary inflammation

Elafin is a serine protease inhibitor produced by epithelial and immune cells with anti-inflammatory properties. Research has shown that dysregulated protease activity may elicit proteolytic cleavage of elafin, thereby impairing the innate immune function of the protein. The aim of this study was to generate variants of elafin (GG- and QQ-elafin) that exhibit increased protease resistance while retaining the biological properties of wild-type (WT) elafin. Similar to WT-elafin, GG- and QQ-elafin variants retained antiprotease activity and susceptibility to transglutaminase-mediated fibronectin cross-linking. However, in contrast to WT-elafin, GG- and QQ-elafin displayed significantly enhanced resistance to degradation when incubated with bronchoalveolar lavage fluid from patients with cystic fibrosis. Intriguingly, both variants, particularly GG-elafin, demonstrated improved lipopolysaccharide (LPS) neutralization properties in vitro. In addition, GG-elafin showed improved anti-inflammatory activity in a mouse model of LPS-induced acute lung inflammation. Inflammatory cell infiltration into the lung was reduced in lungs of mice treated with GG-elafin, predominantly neutrophilic infiltration. A reduction in MCP-1 levels in GG-elafin treated mice compared to the LPS alone treatment group was also demonstrated. GG-elafin showed increased functionality when compared to WT-elafin and may be of future therapeutic relevance in the treatment of lung diseases characterized by a protease burden.

Different responses to mechanical injury in neonatal and adult ovine articular cartilage

Background

Articular cartilage injury remains a major challenge in orthopedic surgery. This study aimed to identify differences in gene expression and molecular responses between neonatal and adult articular cartilage during the healing of an injury.

Methods

An established in vitro model was used to compare the transcriptional response to cartilage injury in neonatal and adult sheep by microarray analysis of gene expression. Total RNA was isolated from tissue samples, linearly amplified, and 15,208 ovine probes were applied to cDNA microarray. Validation for selected genes was obtained by real-time quantitative polymerase chain reaction (RT-qPCR).

Results

We found 1,075 (11.6%) differentially expressed probe sets in adult injured cartilage relative to normal cartilage. A total of 1,016 (11.0%) probe sets were differentially expressed in neonatal injured cartilage relative to normal cartilage. A total of 1,492 (16.1%) probe sets were differentially expressed in adult normal cartilage relative to neonatal normal cartilage. A total of 1,411 (15.3%) probe sets were differentially expressed in adult injured cartilage relative to neonatal injured cartilage. Significant functional clusters included genes associated with wound healing, articular protection, inflammation, and energy metabolism. Selected genes (PPARG, LDH, TOM, HIF1A, SMAD7, and NF-κB) were also found and validated by RT-qPCR.

Conclusions

There are significant differences in gene expression between neonatal and adult ovine articular cartilage following acute injury. They are partly due to intrinsic differences in the process of development, and partly to different biological responses to mechanical trauma between neonatal and adult articular cartilage.

Elafin, an inhibitor of elastase, is a prognostic indicator in breast cancer

Introduction

Elafin is an elastase-specific inhibitor with increased transcription in normal mammary epithelial cells compared to mammary carcinoma cells. In this report, we test the hypothesis that inhibition of elastase, through induction of elafin, leads to inhibition of human breast cancer cell viability and, therefore, predicts survival in breast cancer patients.

Methods

Panels of normal and immortalized breast epithelial cells, along with breast carcinoma cells, were used to examine the impact of adenoviral-mediated elafin expression or shRNA-mediated inhibition of elastase on the growth of cells and xenografts in nude mice. To determine the prognostic significance of decreased elafin in patients with invasive breast cancer, previously published gene array datasets were interrogated.

Results

Elafin expression had no effect on non-tumorigenic cells but resulted in marked inhibition of cell growth in breast cancer cell lines. Control-treated xenografts generated a tumor burden that necessitated sacrifice within one month of initial treatment, whereas xenograft-bearing mice treated with Ad-Elafin were alive at eight months with marked reduction in tumor growth. Elastase inhibition mimicked these results, showing decreased tumor cell growth in vitro and in vivo. Low expression of elafin gene correlated with significantly reduced time to relapse, and when combined with high expression of elastase gene was associated with decreased survival in breast cancer patients.

Conclusion

Our data suggest that elafin plays a direct role in the suppression of tumors through inhibition of elastase and thus serves as a prognostic indicator for breast cancer patients.

SLPI and trappin-2 as therapeutic agents to target airway serine proteases in inflammatory lung diseases: current and future directions

It is now clear that NSPs (neutrophil serine proteases), including elastase, Pr3 (proteinase 3) and CatG (cathepsin G) are major pathogenic determinants in chronic inflammatory disorders of the lungs. Two unglycosylated natural protease inhibitors, SLPI (secretory leucocyte protease inhibitor) and elafin, and its precursor trappin-2 that are found in the lungs, have therapeutic potential for reducing the protease-induced inflammatory response. This review examines the multifaceted roles of SLPI and elafin/trappin-2 in the context of their possible use as inhaled drugs for treating chronic lung diseases such as CF (cystic fibrosis) and COPD (chronic obstructive pulmonary disease).

War and peace between WAP and HIV: role of SLPI, trappin-2, elafin and ps20 in susceptibility to HIV infection

Despite tremendous advances in our understanding of HIV/AIDS since the first cases were reported 30 years ago, we are still a long way from understanding critical steps of HIV acquisition, pathogenesis and correlates of protection. Our new understanding of the importance of the mucosa as a target for HIV infection, as well as our recent observations showing that altered expression and responses of innate pattern recognition receptors are significantly associated with pathogenesis and resistance to HIV infection, indicate that correlates of immunity to HIV are more likely to be associated with mucosal and innate responses. Most of the heterosexual encounters do not result in productive HIV infection, suggesting that the female genital tract is protected against HIV by innate defence molecules, such as antiproteases, secreted mucosally. The present review highlights the role and significance of the serine protease inhibitors SLPI (secretory leucocyte protease inhibitor), trappin-2, elafin and ps20 (prostate stromal protein 20 kDa) in HIV susceptibility and infection. Interestingly, in contrast with SLPI, trappin-2 and elafin, ps20 has been shown to enhance HIV infectivity. Thus understanding the balance and interaction of these factors in mucosal fluids may significantly influence HIV infection.

Periodontal pathogens affect the level of protease inhibitors in gingival crevicular fluid

In periodontitis, an effective host-response is primarily related to neutrophils loaded with serine proteases, including elastase (NE) and protease 3 (PR3), the extracellular activity of which is tightly controlled by endogenous inhibitors. In vitro these inhibitors are degraded by gingipains, cysteine proteases produced by Porphyromonas gingivalis. The purpose of this study was to determine the level of selected protease inhibitors in gingival crevicular fluid (GCF) in relation to periodontal infection. The GCF collected from 31 subjects (nine healthy controls, seven with gingivitis, five with aggressive periodontitis and 10 with chronic periodontitis) was analyzed for the levels of elafin and secretory leukocyte protease inhibitor (SLPI), two main tissue-derived inhibitors of neutrophil serine proteases. In parallel, activity of NE, PR3 and arginine-specific gingipains (Rgps) in GCF was measured. Finally loads of P. gingivalis, Aggregatibacter actinomycetemcomitans, Tannerella forsythia and Treponema denticola were determined. The highest values of elafin were found in aggressive periodontitis and the lowest in controls. The quantity of elafin correlated positively with the load of P. gingivalis, Ta. forsythia and Tr. denticola, as well as with Rgps activity. In addition, NE activity was positively associated with the counts of those bacterial species, but not with the amount of elafin. In contrast, the highest concentrations of SLPI were found in periodontally healthy subjects whereas amounts of this inhibitor were significantly decreased in patients infected with P. gingivalis. Periodontopathogenic bacteria stimulate the release of NE and PR3, which activities escape the control through degradation of locally produced inhibitors (SLPI and elafin) by host-derived and bacteria-derived proteases.

Secretory leukocyte protease inhibitor (SLPI) is, like its homologue trappin-2 (pre-elafin), a transglutaminase substrate

Human lungs contain secretory leukocyte protease inhibitor (SLPI), elafin and its biologically active precursor trappin-2 (pre-elafin). These important low-molecular weight inhibitors are involved in controlling the potentially deleterious proteolytic activities of neutrophil serine proteases including elastase, proteinase 3 and cathepsin G. We have shown previously that trappin-2, and to a lesser extent, elafin can be linked covalently to various extracellular matrix proteins by tissue transglutaminases and remain potent protease inhibitors. SLPI is composed of two distinct domains, each of which is about 40% identical to elafin, but it lacks consensus transglutaminase sequence(s), unlike trappin-2 and elafin. We investigated the actions of type 2 tissue transglutaminase and plasma transglutaminase activated factor XIII on SLPI. It was readily covalently bound to fibronectin or elastin by both transglutaminases but did not compete with trappin-2 cross-linking. Cross-linked SLPI still inhibited its target proteases, elastase and cathepsin G. We have also identified the transglutamination sites within SLPI, elafin and trappin-2 by mass spectrometry analysis of tryptic digests of inhibitors cross-linked to mono-dansyl cadaverin or to a fibronectin-derived glutamine-rich peptide. Most of the reactive lysine and glutamine residues in SLPI are located in its first N-terminal elafin-like domain, while in trappin-2, they are located in both the N-terminal cementoin domain and the elafin moiety. We have also demonstrated that the transglutamination substrate status of the cementoin domain of trappin-2 can be transferred from one protein to another, suggesting that it may provide transglutaminase-dependent attachment properties for engineered proteins. We have thus added to the corpus of knowledge on the biology of these potential therapeutic inhibitors of airway proteases.

Neutrophil elastase, proteinase 3, and cathepsin G as therapeutic targets in human diseases

Polymorphonuclear neutrophils are the first cells recruited to inflammatory sites and form the earliest line of defense against invading microorganisms. Neutrophil elastase, proteinase 3, and cathepsin G are three hematopoietic serine proteases stored in large quantities in neutrophil cytoplasmic azurophilic granules. They act in combination with reactive oxygen species to help degrade engulfed microorganisms inside phagolysosomes. These proteases are also externalized in an active form during neutrophil activation at inflammatory sites, thus contributing to the regulation of inflammatory and immune responses. As multifunctional proteases, they also play a regulatory role in noninfectious inflammatory diseases. Mutations in the ELA2/ELANE gene, encoding neutrophil elastase, are the cause of human congenital neutropenia. Neutrophil membrane-bound proteinase 3 serves as an autoantigen in Wegener granulomatosis, a systemic autoimmune vasculitis. All three proteases are affected by mutations of the gene (CTSC) encoding dipeptidyl peptidase I, a protease required for activation of their proform before storage in cytoplasmic granules. Mutations of CTSC cause Papillon-Lefèvre syndrome. Because of their roles in host defense and disease, elastase, proteinase 3, and cathepsin G are of interest as potential therapeutic targets. In this review, we describe the physicochemical functions of these proteases, toward a goal of better delineating their role in human diseases and identifying new therapeutic strategies based on the modulation of their bioavailability and activity. We also describe how nonhuman primate experimental models could assist with testing the efficacy of proposed therapeutic strategies.

Functional study of elafin cleaved by Pseudomonas aeruginosa metalloproteinases

Elafin is a 6-kDa innate immune protein present at several epithelial surfaces including the pulmonary epithelium. It is a canonical protease inhibitor of two neutrophil serine proteases [neutrophil elastase (NE) and proteinase 3] with the capacity to covalently bind extracellular matrix proteins by transglutamination. In addition to these properties, elafin also possesses antimicrobial and immunomodulatory activities. The aim of the present study was to investigate the effect of Pseudomonas aeruginosa proteases on elafin function. We found that P. aeruginosa PAO1-conditioned medium and two purified Pseudomonas metalloproteases, pseudolysin (elastase) and aeruginolysin (alkaline protease), are able to cleave recombinant elafin. Pseudolysin was shown to inactivate the anti-NE activity of elafin by cleaving its protease-binding loop. Interestingly, antibacterial properties of elafin against PAO1 were found to be unaffected after pseudolysin treatment. In contrast to pseudolysin, aeruginolysin failed to inactivate the inhibitory properties of elafin against NE. Aeruginolysin cleaves elafin at the amino-terminal Lys6-Gly7 peptide bond, resulting in a decreased ability to covalently bind purified fibronectin following transglutaminase activity. In conclusion, this study provides evidence that elafin is susceptible to proteolytic cleavage at alternative sites by P. aeruginosa metalloproteinases, which can affect different biological functions of elafin.

Peptidase inhibitors in the MEROPS database

The MEROPS website (http://merops.sanger.ac.uk) includes information on peptidase inhibitors as well as on peptidases and their substrates. Displays have been put in place to link peptidases and inhibitors together. The classification of protein peptidase inhibitors is continually being revised, and currently inhibitors are grouped into 67 families based on comparisons of protein sequences. These families can be further grouped into 38 clans based on comparisons of tertiary structure. Small molecule inhibitors are important reagents for peptidase characterization and, with the increasing importance of peptidases as drug targets, they are also important to the pharmaceutical industry. Small molecule inhibitors are now included in MEROPS and over 160 summaries have been written.

Proteases and antiproteases in chronic neutrophilic lung disease - relevance to drug discovery

Chronic inflammatory lung diseases such as cystic fibrosis and emphysema are characterized by higher-than-normal levels of pulmonary proteases. While these enzymes play important roles such as bacterial killing, their dysregulated expression or activity can adversely impact on the inflammatory process. The existence of efficient endogenous control mechanisms that can dampen or halt this overexuberant protease activity in vivo is essential for the effective resolution of inflammatory lung disease. The function of pulmonary antiproteases is to fulfil this role. Interestingly, in addition to their antiprotease activity, protease inhibitors in the lung also often possess other intrinsic properties that contribute to microbial killing or termination of the inflammatory process. This review will outline important features of chronic inflammation that are regulated by pulmonary proteases and will describe the various mechanisms by which antiproteases attempt to counterbalance exaggerated protease-mediated inflammatory events. These proteases, antiproteases and their modifiers represent interesting targets for therapeutic intervention.

Protease inhibitors derived from elafin and SLPI and engineered to have enhanced specificity towards neutrophil serine proteases

The secretory leukocyte protease inhibitor (SLPI), elafin, and its biologically active precursor trappin-2 are endogeneous low-molecular weight inhibitors of the chelonianin family that control the enzymatic activity of neutrophil serine proteases (NSPs) like elastase, proteinase 3, and cathepsin G. These inhibitors may be of therapeutic value, since unregulated NSP activities are linked to inflammatory lung diseases. However SLPI inhibits elastase and cathepsin G but not proteinase 3, while elafin targets elastase and proteinase 3 but not cathepsin G. We have used two strategies to design polyvalent inhibitors of NSPs that target all three NSPs and may be used in the aerosol-based treatment of inflammatory lung diseases. First, we fused the elafin domain with the second inhibitory domain of SLPI to produce recombinant chimeras that had the inhibitory properties of both parent molecules. Second, we generated the trappin-2 variant, trappin-2 A62L, in which the P1 residue Ala is replaced by Leu, as in the corresponding position in SLPI domain 2. The chimera inhibitors and trappin-2 A62L are tight-binding inhibitors of all three NSPs with subnanomolar K(i)s, similar to those of the parent molecules for their respective target proteases. We have also shown that these molecules inhibit the neutrophil membrane-bound forms of all three NSPs. The trappin-2 A62L and elafin-SLPI chimeras, like wild-type elafin and trappin-2, can be covalently cross-linked to fibronectin or elastin by a tissue transglutaminase, while retaining their polypotent inhibition of NSPs. Therefore, the inhibitors described herein have the appropriate properties to be further evaluated as therapeutic anti-inflammatory agents.

Elafin, an elastase-specific inhibitor, is cleaved by its cognate enzyme neutrophil elastase in sputum from individuals with cystic fibrosis

Elafin is a neutrophil serine protease inhibitor expressed in lung and displaying anti-inflammatory and anti-bacterial properties. Previous studies demonstrated that some innate host defense molecules of the cystic fibrosis (CF) and chronic obstructive pulmonary disease airways are impaired due to increased proteolytic degradation observed during lung inflammation. In light of these findings, we thus focused on the status of elafin in CF lung. We showed in the present study that elafin is cleaved in sputum from individuals with CF. Pseudomonas aeruginosa-positive CF sputum, which was found to contain lower elafin levels and higher neutrophil elastase (NE) activity compared with P. aeruginosa-negative samples, was particularly effective in cleaving recombinant elafin. NE plays a pivotal role in the process as only NE inhibitors are able to inhibit elafin degradation. Further in vitro studies demonstrated that incubation of recombinant elafin with excess of NE leads to the rapid cleavage of the inhibitor. Two cleavage sites were identified at the N-terminal extremity of elafin (Val-5-Lys-6 and Val-9-Ser-10). Interestingly, purified fragments of the inhibitor (Lys-6-Gln-57 and Ser-10-Gln-57) were shown to still be active for inhibiting NE. However, NE in excess was shown to strongly diminish the ability of elafin to bind lipopolysaccharide (LPS) and its capacity to be immobilized by transglutamination. In conclusion, this study provides evidence that elafin is cleaved by its cognate enzyme NE present at excessive concentration in CF sputum and that P. aeruginosa infection promotes this effect. Such cleavage may have repercussions on the innate immune function of elafin.

The antibacterial and antifungal properties of trappin-2 (pre-elafin) do not depend on its protease inhibitory function

Trappin-2 (also known as pre-elafin) is an endogenous inhibitor of neutrophil serine proteases and is involved in the control of excess proteolysis, especially in inflammatory events, along with the structurally related secretory leucocyte proteinase inhibitor. Secretory leucocyte proteinase inhibitor has been shown to have antibacterial and antifungal properties, whereas recent data indicate that trappin-2 has antimicrobial activity against Pseudomonas aeruginosa and Staphylococcus aureus. In the present study, we tested the antibacterial properties of trappin-2 towards other respiratory pathogens. We found that trappin-2, at concentrations of 5-20 microm, has significant activity against Klebsiella pneumoniae, Haemophilus influenzae, Streptococcus pneumoniae, Branhamella catarrhalis and the pathogenic fungi Aspergillus fumigatus and Candida albicans, in addition to P. aeruginosa and S. aureus. A similar antimicrobial activity was observed with trappin-2 A62D/M63L, a trappin-2 variant that has lost its antiprotease properties, indicating that trappin-2 exerts its antibacterial effects through mechanisms independent from its intrinsic antiprotease capacity. Furthermore, the antibacterial and antifungal activities of trappin-2 were sensitive to NaCl and heparin, demonstrating that its mechanism of action is most probably dependent on its cationic nature. This enables trappin-2 to interact with the membranes of target organisms and disrupt them, as shown by our scanning electron microscopy analyses. Thus, trappin-2 not only provides an antiprotease shield, but also may play an important role in the innate defense of the human lungs and mucosae against pathogenic microorganisms.

Whey acidic protein (WAP) regulates the proliferation of mammary epithelial cells by preventing serine protease from degrading laminin

Whey acidic protein (WAP) is a major whey protein in milk that has structural similarity to the family of serine protease inhibitors with WAP motif domains characterized by a four-disulfide core. We previously reported that enforced expression of the mouse WAP transgene in mammary epithelial cells inhibits their proliferation in vitro and in vivo by means of suppressing cyclin D1 expression (Nukumi et al., 2004, Dev Biol 274: 31-44). This study was conducted in order to clarify the molecular mechanism of the inhibitory function of WAP in HC11 cells, a mammary epithelial cell line. The assembly of laminin, a component in the extracellular matrix, was much more prominent around WAP-clonal HC11 cells that stably expressed the WAP transgene than around mock-clonal HC11 cells, and the proliferation of WAP-clonal HC11 cells was particularly inhibited in the presence of laminin. A laminin degradation assay demonstrated that WAP inhibited the activity of the pancreatic elastase-mediated cleavage of laminin B1 and the phosphorylation of ERK1/2. ERK1/2 phosphorylation was blocked by an inhibitor of the epidermal growth factor (EGF) receptor AG1478. Treatment with pancreatic elastase was found to enhance the proliferation of mock-clonal HC11 cells, but had no effect on that of WAP-clonal HC11 cells. The proliferation of WAP-clonal HC11 cells was recovered by the addition of exogenous EGF. We concluded that WAP plays some role in regulating the proliferation of mammary epithelial cells by preventing elastase-type serine protease from carrying out laminin degradation and thereby suppressing the MAP kinase signal pathway.

Neutrophil elastase, proteinase 3 and cathepsin G: physicochemical properties, activity and physiopathological functions

Polymorphonuclear neutrophils form a primary line of defense against bacterial infections using complementary oxidative and non-oxidative pathways to destroy phagocytized pathogens. The three serine proteases elastase, proteinase 3 and cathepsin G, are major components of the neutrophil primary granules that participate in the non-oxidative pathway of intracellular pathogen destruction. Neutrophil activation and degranulation results in the release of these proteases into the extracellular medium as proteolytically active enzymes, part of them remaining exposed at the cell surface. Extracellular neutrophil serine proteases also help kill bacteria and are involved in the degradation of extracellular matrix components during acute and chronic inflammation. But they are also important as specific regulators of the immune response, controlling cellular signaling through the processing of chemokines, modulating the cytokine network, and activating specific cell surface receptors. Neutrophil serine proteases are also involved in the pathogenicity of a variety of human diseases. This review focuses on the structural and functional properties of these proteases that may explain their specific biological roles, and facilitate their use as molecular targets for new therapeutic strategies.

Multifaceted roles of human elafin and secretory leukocyte proteinase inhibitor (SLPI), two serine protease inhibitors of the chelonianin family

Elafin and SLPI are low-molecular weight proteins that were first identified as protease inhibitors in mucous fluids including lung secretions, where they help control excessive proteolysis due to neutrophil serine proteases (elastase, proteinase 3 and cathepsin G). Elafin and SLPI are structurally related in that both have a fold with a four-disulfide core or whey acidic protein (WAP) domain responsible for inhibiting proteases. Elafin is derived from a precursor, trappin-2 or pre-elafin, by proteolysis. Trappin-2, which is itself a protease inhibitor, has a unique N-terminal domain that enables it to become cross-linked to extracellular matrix proteins by transglutaminase(s). SLPI and elafin/trappin-2 are attractive candidates as therapeutic molecules for inhibiting neutrophil serine proteases in inflammatory lung diseases. Hence, they have become the WAP proteins most studied over the last decade. This review focuses on recent findings revealing that SLPI and elafin/trappin-2 have many biological functions as diverse as anti-bacterial, anti-fungal, anti-viral, anti-inflammatory and immuno-modulatory functions, in addition to their well-recognized role as protease inhibitors.

Characterization of human pre-elafin mutants: full antipeptidase activity is essential to preserve lung tissue integrity in experimental emphysema

Pre-elafin is a tight-binding inhibitor of neutrophil elastase and myeloblastin; two enzymes thought to contribute to tissue damage in lung emphysema. Previous studies have established that pre-elafin is also an effective anti-inflammatory molecule. However, it is not clear whether both functions are linked to the antipeptidase activity of pre-elafin. As a first step toward elucidating the structure/function relationship of this protein, we describe here the construction and characterization of pre-elafin variants with attenuated antipeptidase potential. In these mutants, the P1' methionine residue of the inhibitory loop is replaced by either a lysine (pre-elafinM25K) or a glycine (pre-elafinM25G) residue. Both mutated variants are stable and display biochemical properties undistinguishable from WT (wild-type) pre-elafin. However, compared with WT pre-elafin, their inhibitory constants are increased by one to four orders of magnitude toward neutrophil elastase, myeloblastin and pancreatic elastase, depending on the variants and enzymes tested. As suggested by molecular modelling, this attenuated inhibitory potential correlates with decreased van der Waals interactions between the variants and the enzymes S1' subsite. In elastase-induced experimental emphysema in mice, only WT pre-elafin protected against tissue destruction, as assessed by the relative airspace enlargement measured using lung histopathological sections. Pre-elafin and both mutants prevented transient neutrophil alveolitis. However, even the modestly affected pre-elafinM25K mutant, as assayed in vitro with small synthetic substrates, was a poor inhibitor of the neutrophil elastase and myeloblastin elastolytic activity measured with insoluble elastin. We therefore conclude that full antipeptidase activity of pre-elafin is essential to protect against lung tissue lesions in this experimental model.

EPI-hNE4, a proteolysis-resistant inhibitor of human neutrophil elastase and potential anti-inflammatory drug for treating cystic fibrosis

EPI-hNE4 (depelstat) is a potent inhibitor of human neutrophil elastase derived from human inter-alpha-trypsin inhibitor and designed to control the excess proteolytic activity in the sputum of cystic fibrosis patients. We analyzed its resistance to the proteolysis it is likely to encounter at inflammatory sites in vivo. EPI-hNE4 resisted hydrolysis by neutrophil matrix metalloproteases (MMPs) and serine proteases that are released from activated neutrophils in inflammatory lung secretions, including MMP-8 and MMP-9, and the elastase-related protease 3 and cathepsin G. It also resisted degradation by epithelial lung cell MMP-7 but was broken down by the Pseudomonas aeruginosa metalloelastase pseudolysin, when used in a purified system, but not when this protease competed with equimolar amounts of neutrophil elastase. We also investigated the inhibitory properties of EPI-hNE4 at the surface of purified blood neutrophils and in the sputum of cystic fibrosis patients where neutrophil elastase is in both a soluble and a gel phase. The elastase at the neutrophil surface was fully inhibited by EPI-hNE4 and formed soluble complexes. The elastase in cystic fibrosis sputum supernatants was inhibited by stoichiometric amounts of EPI-hNE4, allowing titration of the protease. But the percentage of inhibition in whole sputum homogenates varied from 50 to 100%, depending on the sample tested. EPI-hNE4 was rapidly cleaved by the digestive protease pepsin in vitro. Therefore, EPI-hNE4 seems to be an elastase inhibitor suitable for use in aerosols to treat patients with cystic fibrosis.

Proteins with whey-acidic-protein motifs and cancer

The importance of early diagnosis to reduce the morbidity and mortality from cancer has led to a search for new sensitive and specific tumour markers. Molecular techniques developed over the past few years allow simultaneous screening of thousands of genes, and have been applied to different cancers to identify many genes that are modulated in various cancers. Of these, attention has focused on genes coding for a family of proteins with whey-acidic-protein (WAP) motifs. Most notably, the genes coding for elafin, antileukoproteinase 1 (previously called secretory leucocyte proteinase inhibitor, SLPI), WAP four disulphide core domain protein 1 (previously called prostate stromal protein 20 kDa, PS20), and WAP four disulphide core domain protein 2 (previously called major human epididymis-specific protein E4, HE4), have been identified as candidate molecular markers for several cancers. In this review, we assess data for an association between cancer and human WAP proteins, and discuss their potential role in tumour progression. We also propose a new mechanism by which WAP proteins might have a role in carcinogenesis.

Safety and efficacy of recombinant alpha(1)-antitrypsin therapy in cystic fibrosis

Neutrophil elastase (NE) is thought to be the most important protease which damages the cystic fibrosis (CF) lung. Attempts have been made to suppress this activity using the plasma-derived inhibitor, alpha(1)-antitrypsin (AAT). In this pilot study, the safety and efficacy of inhaled recombinant human AAT (rAAT) as a treatment for CF were investigated. Thirty-nine patients participated in a prospective, double-blinded, randomized, placebo-controlled phase II trial to examine the effect of rAAT (500, 250, and 125 mg) on sputum NE activity. Sputum myeloperoxidase (MPO), interleukin-8, tumor necrosis factor receptors, sputum and plasma NE/AAT complexes, and safety parameters were also measured. Subjects were randomized to receive nebulized treatment once a day for 4 weeks, followed by 2-4 weeks with no study treatment, and then a 2-week rechallenge phase. Trends toward a reduction in NE activity were observed in patients treated with 500 mg and 250 mg of rAAT compared to placebo. Sputum NE/AAT complex and MPO levels were lower on rAAT compared to placebo. No major adverse events and, in particular, no allergic reactions to rAAT were observed. Although significant differences between rAAT and placebo for sputum NE activity were not observed, some improvements were found for secondary efficacy variables. This study demonstrated that nebulized rAAT is safe and well-tolerated, but has a limited effect on NE activity and other markers of inflammation.

Oxidized elafin and trappin poorly inhibit the elastolytic activity of neutrophil elastase and proteinase 3

Neutrophil proteinase-mediated lung tissue destruction is prevented by inhibitors, including elafin and its precursor, trappin. We wanted to establish whether neutrophil-derived oxidants might impair the inhibitory function of these molecules. Myeloperoxidase/H(2)O(2) and N-chlorosuccinimide oxidation of the inhibitors was checked by mass spectrometry and enzymatic methods. Oxidation significantly lowers the affinities of the two inhibitors for neutrophil elastase (NE) and proteinase 3 (Pr3). This decrease in affinity is essentially caused by an increase in the rate of inhibitory complex dissociation. Oxidized elafin and trappin have, however, reasonable affinities for NE (K(i) = 4.0-9.2 x 10(-9) M) and for Pr3 (K(i) = 2.5-5.0 x 10(-8) M). These affinities are theoretically sufficient to allow the oxidized inhibitors to form tight binding complexes with NE and Pr3 in lung secretions where their physiological concentrations are in the micromolar range. Yet, they are unable to efficiently inhibit the elastolytic activity of the two enzymes. At their physiological concentration, fully oxidized elafin and trappin do not inhibit more than 30% of an equimolar concentration of NE or Pr3. We conclude that in vivo oxidation of elafin and trappin strongly impairs their activity. Inhibitor-based therapy of inflammatory lung diseases must be carried out using oxidation-resistant variants of these molecules.

Proteolytic susceptibility of the serine protease inhibitor trappin-2 (pre-elafin): evidence for tryptase-mediated generation of elafin

A number of serine, cysteine, metallo- and acid proteases were evaluated for their ability to proteolytically cleave the serine protease inhibitor trappin-2, also known as pre-elafin, and to release elafin from its precursor. None of the metalloproteases or acid proteases examined cleaved trappin-2, while serine and cysteine proteases preferentially cleaved trappin-2 within its non-inhibitory N-terminal moiety. Cathepsin L, cathepsin K, plasmin, trypsin and tryptase were able to release elafin by cleaving the Lys 38 -Ala 39 peptide bond in trappin-2. However, purified tryptase appeared to be efficient at releasing elafin. Incubation of trappin-2 with purified mast cells first challenged with anti-immunoglobulin E or calcium ionophore A23187 resulted in the rapid generation of elafin. This proteolytic release of elafin from trappin-2 was inhibited in the presence of a tryptase inhibitor, suggesting that this mast cell enzyme was involved in the process. Finally, ex vivo incubation of trappin-2 with sputum from cystic fibrosis patients indicated the production of a proteolytic immunoreactive fragment with the same mass as that of native elafin. This cleavage did not occur when preincubating the sputum with polyclonal antibodies directed against tryptase. Taken together, these findings indicate that tryptase could likely be involved in the maturation of trappin-2 into elafin under physiological conditions.