The tryptase inhibitor APC-366 reduces the acute airway response to allergen in pigs sensitized to Ascaris suum

Novel, Self-Assembling Dimeric Inhibitors of Human β Tryptase

β-Tryptase, a homotetrameric serine protease, has four identical active sites facing a central pore, presenting an optimized setting for the rational design of bivalent inhibitors that bridge two adjacent sites. Using diol, hydroxymethyl phenols or benzoyl methyl hydroxamates, and boronic acid chemistries to reversibly join two [3-(1-acylpiperidin-4-yl)phenyl]methanamine core ligands, we have successfully produced a series of self-assembling heterodimeric inhibitors. These heterodimeric tryptase inhibitors demonstrate superior activity compared to monomeric modes of inhibition. X-ray crystallography validated the dimeric mechanism of inhibition, and compounds demonstrated high selectivity against related proteases, good target engagement, and tryptase inhibition in HMC1 xenograft models. Screening 3872 possible combinations from 44 boronic acid and 88 diol derivatives revealed several combinations that produced nanomolar inhibition, and seven unique pairs produced greater than 100-fold improvement in potency over monomeric inhibition. These heterodimeric tryptase inhibitors demonstrate the power of target-driven combinatorial chemistry to deliver bivalent drugs in a small molecule form.

The emerging role of mast cell proteases in asthma

It is now well established that mast cells (MCs) play a crucial role in asthma. This is supported by multiple lines of evidence, including both clinical studies and studies on MC-deficient mice. However, there is still only limited knowledge of the exact effector mechanism(s) by which MCs influence asthma pathology. MCs contain large amounts of secretory granules, which are filled with a variety of bioactive compounds including histamine, cytokines, lysosomal hydrolases, serglycin proteoglycans and a number of MC-restricted proteases. When MCs are activated, e.g. in response to IgE receptor cross-linking, the contents of their granules are released to the exterior and can cause a massive inflammatory reaction. The MC-restricted proteases include tryptases, chymases and carboxypeptidase A3, and these are expressed and stored at remarkably high levels. There is now emerging evidence supporting a prominent role of these enzymes in the pathology of asthma. Interestingly, however, the role of the MC-restricted proteases is multifaceted, encompassing both protective and detrimental activities. Here, the current knowledge of how the MC-restricted proteases impact on asthma is reviewed.

Mast cell tryptase - Marker and maker of cardiovascular diseases

Mast cells are tissue-resident cells, which have been proposed to participate in various inflammatory diseases, among them the cardiovascular diseases (CVDs). For mast cells to be able to contribute to an inflammatory process, they need to be activated to exocytose their cytoplasmic secretory granules. The granules contain a vast array of highly bioactive effector molecules, the neutral protease tryptase being the most abundant protein among them. The released tryptase may act locally in the inflamed cardiac or vascular tissue, so contributing directly to the pathogenesis of CVDs. Moreover, a fraction of the released tryptase reaches the systemic circulation, thereby serving as a biomarker of mast cell activation. Actually, increased levels of circulating tryptase have been found to associate with CVDs. Here we review the biological relevance of the circulating tryptase as a biomarker of mast cell activity in CVDs, with special emphasis on the relationship between activation of mast cells in their tissue microenvironments and the pathophysiological pathways of CVDs. Based on the available in vitro and in vivo studies, we highlight the potential molecular mechanisms by which tryptase may contribute to the pathogenesis of CVDs. Finally, the synthetic and natural inhibitors of tryptase are reviewed for their potential utility as therapeutic agents in CVDs.

Ascariasis as a model to study the helminth/allergy relationships

Ascariasis is the most frequent soil transmitted helminthiasis and, as well as other helminth infections, is expected to influence the clinical presentation of allergic diseases such as asthma. Indeed, several clinical and experimental works have shown an important impact either increasing or suppressing symptoms, and the same effects have been detected on the underlying immune responses. In this review we analyze the work on this field performed in Colombia, a Latin American tropical country, including aspects such as the molecular genetics of the IgE response to Ascaris; the allergenic activity of Ascaris IgE-binding molecular components and the immunological and clinical influences of ascariasis on asthma. The analysis allows us to conclude that the impact of ascariasis on the inception and evolution of allergic diseases such as asthma deserves more investigation, but advances have been made during the last years. The concurrent parasite-induced immunostimulatory and immunosuppressive effects during this helminthiasis do modify the natural history of asthma and some aspects of the practice of allergology in the tropics. Theoretically it can also influence the epidemiological trends of allergic diseases either by its absence or presence in different regions and countries.

A Novel, Nonpeptidic, Orally Active Bivalent Inhibitor of Human β-Tryptase

β-Tryptase is released from mast cells upon degranulation in response to allergic and inflammatory stimuli. Human tryptase is a homotetrameric serine protease with 4 identical active sites directed toward a central pore. These active sites present an optimized scenario for the rational design of bivalent inhibitors, which bridge 2 adjacent active sites. Using (3-[1-acylpiperidin-4-yl]phenyl)methanamine as the pharmacophoric core and a disiloxane linker to span 2 active sites we have successfully produced a novel bivalent tryptase inhibitor, compound 1a, with a comparable profile to previously described inhibitors. Pharmacological properties of compound 1a were studied in a range of in vitro enzymic and cellular screening assays, and in vivo xenograft models. This non-peptide inhibitor of tryptase demonstrated superior activity (IC50 at 100 pmol/L tryptase = 1.82 nmol/L) compared to monomeric modes of inhibition. X-ray crystallography validated the dimeric mechanism of inhibition, and 1a demonstrated good oral bioavailability and efficacy in HMC-1 xenograft models. Furthermore, compound 1a demonstrated extremely slow off rates and high selectivity against-related proteases. This highly potent, orally bioavailable and selective inhibitor of human tryptase will be an invaluable tool in future studies to explore the therapeutic potential of attenuating the activity of this elusive target.

Flavanol-Rich Cocoa Powder Interacts with Lactobacillus rhamnossus LGG to Alter the Antibody Response to Infection with the Parasitic Nematode Ascaris suum

Consumption of the probiotic bacteria LactobacillusrhamnosusLGG and flavanol-rich cocoa have purported immune modulating effects. This study compared the host response to infection with Ascaris suum in three-month-old pigs fed a standard growth diet supplemented with a vehicle control: LGG, cocoa powder (CP) or LGG + CP. Pigs were inoculated with infective A. suum eggs during Week 5 of dietary treatment and euthanized 17 days later. Lactobacillus abundance was increased in pigs fed LGG or LGG + CP. Specific anti-A. suum IgG2 antibodies were decreased (p < 0.05) in LGG + CP-fed pigs compared to pigs fed CP alone. Pigs fed LGG had significantly reduced expression (p < 0.05) of Eosinophil peroxidase (EPX), Interleukin 13 (IL-13), Eotaxin 3 (CCL26), Toll-like receptor 2 (TLR2), TLR4, and TLR9 and Interleukin-1Beta (IL1B) in the tracheal-bronchial lymph node (TBLN) independent of CP treatment. These results suggested that feeding LGG significantly reduced the localized prototypical Th2-related markers of infection with A. suum in the TBLN. Although feeding CP does not appear to affect the A. suum-induced Th2-associated cytokine response, feeding LGG + CP reduced anti-A. suum antibodies and delayed intestinal expulsion of parasitic larvae from the intestine.

Tryptase inhibitors: a patent review

INTRODUCTION

Tryptase is one of the main serine-proteinases located in the secretory granules of mast cells, and is released through degranulation, which is involved in the pathogenesis of allergic inflammatory disease, cardiovascular diseases, lung fibrosis and tumor. Therefore, inhibitors targeting tryptase may represent a new direction for the treatment of allergic inflammatory disease and other diseases. Areas covered: In this article, we discussed the history and development of tryptase inhibitors and described a variety of tryptase inhibitors via their structures and biological importance in clinical studies and drug development for tryptase-related diseases. Expert opinion: Initial tryptase inhibitors based on indole structure as the hydrophobic substituent on a benzylamine-piperidine template have low specificity and poor bioavailability. Therefore, designing new and specific inhibitors targeting tryptase should be involved in future clinical studies. Modifications toward indoles with varying N-substitution, introducing an amide bond, and growing the chain length contribute to an increase in the specific selectivity and potency of tryptase inhibitors. Tryptase has become the research hotspot to explore many related diseases. Therefore, there has been growing appreciation for the potential importance of the tryptase inhibitors as a target for treating these diseases.

Molecularly targeted therapies for asthma: Current development, challenges and potential clinical translation

Extensive research into the therapeutics of asthma has yielded numerous effective interventions over the past few decades. However, adverse effects and ineffectiveness of most of these medications especially in the management of steroid resistant severe asthma necessitate the development of better medications. Numerous drug targets with inherent airway smooth muscle tone modulatory role have been identified for asthma therapy. This article reviews the latest understanding of underlying molecular aetiology of asthma towards design and development of better antiasthma drugs. New drug candidates with their putative targets that have shown promising results in the preclinical and/or clinical trials are summarised. Examples of these interventions include restoration of Th1/Th2 balance by the use of newly developed immunomodulators such as toll-like receptor-9 activators (CYT003-QbG10 and QAX-935). Clinical trials revealed the safety and effectiveness of chemoattractant receptor-homologous molecule expressed on Th2 cells (CRTH2) antagonists such as OC0000459, BI-671800 and ARRY-502 in the restoration of Th1/Th2 balance. Regulation of cytokine activity by the use of newly developed biologics such as benralizumab, reslizumab, mepolizumab, lebrikizumab, tralokinumab, dupilumab and brodalumab are at the stage of clinical development. Transcription factors are potential targets for asthma therapy, for example SB010, a GATA-3 DNAzyme is at its early stage of clinical trial. Other candidates such as inhibitors of Rho kinases (Fasudil and Y-27632), phosphodiesterase inhibitors (GSK256066, CHF 6001, roflumilast, RPL 554) and proteinase of activated receptor-2 (ENMD-1068) are also discussed. Preclinical results of blockade of calcium sensing receptor by the use of calcilytics such as calcitriol abrogates cardinal signs of asthma. Nevertheless, successful translation of promising preclinical data into clinically viable interventions remains a major challenge to the development of novel anti-asthmatics.

Harnessing opportunities in non-animal asthma research for a 21st-century science

The incidence of asthma is on the increase and calls for research are growing, yet asthma is a disease that scientists are still trying to come to grips with. Asthma research has relied heavily on animal use; however, in light of increasingly robust in vitro and computational models and the need to more fully incorporate the 'Three Rs' principles of Replacement, Reduction and Refinement, is it time to reassess the asthma research paradigm? Progress in non-animal research techniques is reaching a level where commitment and integration are necessary. Many scientists believe that progress in this field rests on linking disciplines to make research directly translatable from the bench to the clinic; a '21st-century' scientific approach to address age-old questions.

Airway disease: the use of large animal models for drug discovery

Large animal models have contributed to our current understanding of respiratory pathophysiology and the effects of pulmonary disease modifying drugs. For drug development, the benefit of using large animals over smaller animal species is primarily due to the greater similarity between humans and equivalent sized animals in terms of gross anatomy, morphometry, structure and physiology of their respiratory systems. Thus, when appropriate lung structure and function are required for correctly assessing the efficacy of novel drugs, large animals can play an important role in the development of these drugs to combat respiratory disease. The most widely used and best characterised large animal for drug development has been the sheep model of asthma. Recently, large animal models for chronic obstructive pulmonary disease (COPD) and cystic fibrosis (CF) have been reported but thus far have not been used extensively for drug development. Some important limitations of using large animals are the large costs associated with this type of research, as well as the poorer understanding of disease mechanisms in these species relative to rodents. In this review we discuss the extent of correlations between preclinical testing performed in large animal models and the initial indication of clinical efficacy in ongoing clinical trials.

Tryptase does not alter transepithelial conductance or paracellular permeability in human airway epithelial cells

BACKGROUND

Cell tight junction proteins create a barrier between airway epithelial cells to limit paracellular transport from the apical to basolateral surface. This barrier can impede the entry of respiratory pathogens and toxins from the airway lumen into the systemic circulation. Mast cell-mediated inflammation in the human airway can cause a disruption of this barrier. Tryptase is one of the major mediators released by mast cells and has been studied extensively in diseases such as asthma, reflux, and sinusitis. We hypothesize that tryptase may play a role in airway paracellular permeability by disrupting the cell tight junction proteins.

METHODS

We tested this hypothesis by applying tryptase on the apical and basolateral surface to primary human airway epithelia grown in an air-liquid interface and measured changes in the transepithelial conductance and paracellular permeability of the membrane during short (every minute) and longer (over hours) time courses. We then immunostained the cell membranes for occludins and claudins to observe for changes in the structure of the tight junctions after tryptase application.

RESULTS

Our data show that tryptase does not alter paracellular permeability in human airway cells over minutes or hours, and that tryptase does not alter the structure of the cell junction.

CONCLUSION

Tryptase alone does not alter paracellular permeability in human airway cells. Tryptase may be altering the epithelial membrane independent of the cell tight junction pathway or other mast cell mediators may play a role in permeability.

Active monomers of human beta-tryptase have expanded substrate specificities

beta-Tryptase, a product of the TPSAB1 and TPSB2 genes, is a trypsin-like serine protease that is a major and selective component of the secretory granules of all human mast cells, accounting for as much as 25% of cell protein. Once mast cells are activated, beta-tryptase is released along with histamine and heparin proteoglycan. beta-Tryptase is a unique enzyme with a homotetrameric structure in which active sites face into the central cavity of the four monomers, stabilized by heparin-proteoglycan. This structure makes beta-tryptase resistant to most biological inhibitors of serine proteases. Without stabilization, at neutral pH beta-tryptase converts to inactive monomers. Tryptase levels are elevated in bronchoalveolar lavage (BAL) fluid obtained from atopic asthmatics and in serum during systemic anaphylactic shock. Several synthetic small molecular weight beta-tryptase inhibitors reduced Ag-induced airway hypersensitivity in animals, suggesting that beta-tryptase is involved in the pathogenesis of airway inflammation. Although the major biologic substrate(s) of beta-tryptase remain ambiguous, the protease can digest several proteins of potential biologic importance, including fibrinogen, fibronectin, pro-urokinase, pro-matrix metalloprotease-3 (proMMP-3), protease activated receptor-2 (PAR2) and complement component C3. Recently, monomers of beta-tryptase with enzymatic activity have been detected in vitro. Here we discuss how beta-tryptase monomers with enzymatic activity were identified as well as their potential role in vivo.

Mast Cell Proteases

Mast cells (MCs) are traditionally thought of as a nuisance for its host, for example, by causing many of the symptoms associated with allergic reactions. In addition, recent research has put focus on MCs for displaying harmful effects during various autoimmune disorders. On the other hand, MCs can also be beneficial for its host, for example, by contributing to the defense against insults such as bacteria, parasites, and snake venom toxins. When the MC is challenged by an external stimulus, it may respond by degranulation. In this process, a number of powerful preformed inflammatory "mediators" are released, including cytokines, histamine, serglycin proteoglycans, and several MC-specific proteases: chymases, tryptases, and carboxypeptidase A. Although the exact effector mechanism(s) by which MCs carry out their either beneficial or harmful effects in vivo are in large parts unknown, it is reasonable to assume that these mediators may contribute in profound ways. Among the various MC mediators, the exact biological function of the MC proteases has for a long time been relatively obscure. However, recent progress involving successful genetic targeting of several MC protease genes has generated powerful tools, which will enable us to unravel the role of the MC proteases both in normal physiology as well as in pathological settings. This chapter summarizes the current knowledge of the biology of the MC proteases.

Inflammatory conditions increase expression of protease-activated receptor-2 by human airway smooth muscle cells in culture

The protease-activated receptor-2 (PAR-2) has been implicated in airway inflammation and bronchial hyperresponsiveness. We wondered whether inflammatory conditions may upregulate PAR-2 expression by the human airway smooth muscle. To do so, we treated human airway smooth muscle cells (HASMC) in primary culture with interleukin-1beta (IL-1beta), a pro-inflammatory and asthma-associated cytokine. Cells were starved for 24 h and incubated with or without IL-1beta. Online fluorescent polymerase chain reaction after reverse transcription quantified PAR-2 mRNA, and Western blotting measured PAR-2 protein expression. PAR-2 was constitutively expressed by HASMC in primary culture, and IL-1beta (10 U/mL) time dependently elevated PAR-2 mRNA with a maximum of 4.7-fold after 1.5 h (P < 0.01), and PAR-2 protein expression with a maximum of 1.5-fold after 24 h (P < 0.01). The concentration dependence of the IL-1beta effect (0.1-30 U/mL) confirmed a maximal increase of PAR-2 expression at 10 U/mL. Our study clearly shows that IL-1beta upregulates PAR-2 mRNA and protein expression by HASMC in culture. This increased expression of PAR-2 in inflammatory conditions may have functional consequences in the bronchial dysfunction of asthmatic airways.

Expression and characterization of recombinant γ-tryptase

Tryptases are trypsin-like serine proteases whose expression is restricted to cells of hematopoietic origin, notably mast cells. gamma-Tryptase, a recently described member of the family also known as transmembrane tryptase (TMT), is a membrane-bound serine protease found in the secretory granules or on the surface of degranulated mast cells. The 321 amino acid protein contains an 18 amino acid propeptide linked to the catalytic domain (cd), followed by a single-span transmembrane domain. gamma-Tryptase is distinguished from other human mast cell tryptases by the presence of two unique cysteine residues, Cys(26) and Cys(145), that are predicted to form an intra-molecular disulfide bond linking the propeptide to the catalytic domain to form the mature, membrane-anchored two-chain enzyme. We expressed gamma-tryptase as either a soluble, single-chain enzyme with a C-terminal His tag (cd gamma-tryptase) or as a soluble pseudozymogen activated by enterokinase cleavage to form a two-chain protein with an N-terminal His tag (tc gamma-tryptase). Both recombinant proteins were expressed at high levels in Pichia pastoris and purified by affinity chromatography. The two forms of gamma-tryptase exhibit comparable kinetic parameters, indicating the propeptide does not contribute significantly to the substrate affinity or activity of the protease. Substrate and inhibitor library screening indicate that gamma-tryptase possesses a substrate preference and inhibitor profile distinct from that of beta-tryptase. Although the role of gamma-tryptase in mast cell function is unknown, our results suggest that it is likely to be distinct from that of beta-tryptase.

Biology of mast cell tryptase. An inflammatory mediator

In 1960, a trypsin-like activity was found in mast cells [Glenner GG & Cohen LA (1960) Nature 185, 846-847] and this activity is now commonly referred to as 'tryptase'. Over the years, much knowledge about mast cell tryptase has been gathered, and a recent (18 January 2006) PubMed search for the keywords 'tryptase + mast cell*' retrieved 1661 articles. However, still very little is known about its true biological function. For example, the true physiological substrate(s) for mast cell tryptase has not been identified, and the potential role of tryptase in mast cell-related disease is not understood. Mast cell tryptase has several unique features, with perhaps the most remarkable being its organization into a tetrameric state with all of the active sites oriented towards a narrow central pore and its consequent complete resistance towards endogenous macromolecular protease inhibitors. Much effort has been invested to elucidate these properties of tryptase. In this review we summarize the current knowledge of mast cell tryptase, including novel insights into its possible biological functions and mechanisms of regulation.

Effects of a reversible beta-tryptase and trypsin inhibitor (RWJ-58643) on nasal allergic responses

BACKGROUND

beta-Tryptase is a multifunctional mast cell serine protease released during mast cell degranulation and tryptase/trypsin inhibitors are a novel potential therapeutic approach for allergic inflammatory diseases.

OBJECTIVES

This study was performed to assess the effects of RWJ-58643 on nasal symptoms, eosinophil influx, and cytokine and chemokine release following nasal allergen challenge (NAC).

METHODS

Male patients with grass pollen allergic rhinitis (n=16) out of season received single doses of RWJ-58643 (100, 300, 600 microg) or matched placebo given 30 min before NAC in a double-blind, randomized crossover design. A single dose of 200 microg budesonide was studied in an open-label extension phase. NAC was performed with Timothy grass pollen (ALK) via a nasal device, and nasal lavage was performed at times 0 (pre-drug, pre-allergen), 0.5 (30 min post-drug, pre-NAC) 1.5, 2.5, 4.5, 6.5, 8.5, and 24 h after drug administration. Nasal lavage mediators were analysed using a sensitive multiplexed bead immunoassay system.

RESULTS

Low-dose RWJ-58643 (100 microg) and budesonide (200 microg) significantly reduced symptoms, eosinophils and levels of IL-5 following NAC. However, higher doses of RWJ-58643 (300 and 600 microg) caused a late eosinophilia and preceding increases in IL-5 compared with placebo.

CONCLUSIONS

This study suggests that combined beta-tryptase and trypsin inhibition has therapeutic potential in allergic inflammation, however, this property is dose responsive and higher doses are ineffective and may cause eosinophilia.

New anti-inflammatory therapies and targets for asthma and chronic obstructive pulmonary disease

Asthma and chronic obstructive pulmonary disease (COPD) are diseases of the airways with an underlying inflammatory component. The prevalence and healthcare burden of asthma and COPD is still rising and is predicted to continue to rise in the foreseeable future. Beta-agonists and corticosteroids form the basis of the therapies available to treat asthma. However, the treatments available for COPD, corticosteroids and anticholinergics, reduce the number and severity of exacerbations, but have a limited effect on slowing the progression of the disease. The inflammatory processes underlying the pathology of asthma have received a great deal of attention and more recently, those underlying COPD have begun to be elucidated. This has resulted in the identification of new targets that will allow the development of novel approaches by the pharmaceutical industry, which will be able to focus its efforts in an attempt to provide new and improved therapies to treat these debilitating diseases. The resultant therapies should impinge on the underlying development of these diseases rather than providing symptomatic relief or palliative treatment alone. This review will outline new targets and novel approaches currently under investigation, which may provide opportunities for novel anti-inflammatory therapeutic interventions that slow or halt disease progression in asthma and COPD.

Structural requirements and mechanism for heparin-dependent activation and tetramerization of human betaI- and betaII-tryptase

Tryptase, a tetrameric serine protease, is a main constituent of the secretory granules in human mast cells, where it is stored in complex with heparin or chondroitin sulfate proteoglycan. Human tryptase has been implicated in a variety of clinical conditions including asthma, but the mechanisms that lead to its tetramerization/activation have not been extensively investigated. Here we addressed the activation mechanisms for human betaI and betaII-tryptase, which differ in that betaI-tryptase is N-glycosylated at Asn102 whereas betaII-tryptase has a Lys residue at position 102, and consequently lacks the corresponding N-glycosylation. We found that both tryptases were dependent on heparin for activation/tetramerization, but whereas betaI-tryptase activation preferentially occurred at acidic pH, betaII-tryptase activation was less pH-dependent. Both betaI and betaII-tryptase bound strongly to heparin-Sepharose at acidic pH but with lower affinity at neutral pH. Further, while addition of heparin to betaI-tryptase predominantly resulted in formation of active tetrameric enzyme, betaII-tryptase showed a tendency to form inactive aggregates. betaI and betaII-tryptase were similar in that the minimal heparin size to induce activation was an octasaccharide and in that the interaction with heparin and structurally related polysaccharides was dependent on high anionic charge density rather than on specific structural motifs. Addition of decasaccharides to both betaI and betaII-tryptase resulted in the formation of active monomeric enzyme, whereas intact heparin promoted assembly of tetrameric enzyme. This, together with a bell-shaped dose response curve for heparin-induced activation, suggests that the mechanism for tetramerization involves bridging of individual tryptase monomers by heparin. Taken together, this study indicates a key role for heparin in the activation of human beta-tryptase.

New advances and potential therapies for the treatment of asthma

Asthma is a disease of the airways with an underlying inflammatory component. The prevalence and healthcare burden of asthma is still rising and is predicted to continue to rise in the current century. Inhaled beta(2)-adrenoceptor agonists and corticosteroids form the basis of the treatments available to alleviate the symptoms of asthma. There is a need for novel, safe treatments to tackle the underlying inflammation that characterizes asthma pathology. Furthermore, there is a requirement for new treatments to be developed as oral therapy in order to alleviate patient compliance issues, especially in children. A multitude of new approaches and new targets are being investigated, which may provide opportunities for novel therapeutic interventions in this debilitating disease. For simplicity, these approaches can be divided into two categories. The first comprises therapies directed against specific components or steps seen in allergic asthma. By 'components' we mean the key inflammatory cells (T cells [in particular T(h)2], B cells, eosinophils, mast cells, basophils and antigen presenting cells [APC]) and mediators (immunoglobulin E [IgE], cytokines, histamines, leukotrienes and prostanoids) believed to be involved in the chronic inflammation seen in asthma. By 'steps' we mean the allergic response, such as antigen processing and presentation, T(h)2-cell activation, B-cell isotype switching, mast cell involvement and airway remodeling. The other category of novel approaches to disease modification in asthma encompasses general anti-inflammatory therapies including phosphodiesterase 4 (PDE4) inhibitors, p38 mitogen-activated protein kinase (MAPK) inhibitors, peroxisome proliferator-activated receptor-gamma (PPARgamma) agonists, and lipoxins.

Inhibitors of mast cell tryptase beta as therapeutics for the treatment of asthma and inflammatory disorders

A survey of the available biological data on tryptase inhibitors suggests that there is considerable interest in tryptase as a therapeutic target particularly for the treatment of allergic asthma and inflammatory disorders. This interest was driven primarily by data from studies carried out on the cellular and in vivo actions of this serine protease over the past decade, all of which have suggested a pro-inflammatory role for tryptase. Tryptase beta is the form of interest in allergic asthma and the data from numerous studies have shown that tryptase cannot only contribute to airway bronchoconstriction and hyperresponsiveness, but may have a key role in fibrosis and ECM turnover, hallmarks of the remodeling process. Hence, inhibitors of tryptase have the potential to make an impact on fibrosis and airway wall remodelling. However, few studies, if any, have been carried out to determine the effect of tryptase inhibitors on airway remodeling and this is an area that warrants further investigation with the appropriate models because the eventual positioning of tryptase inhibitors in asthma therapy will be strengthened by data supporting an impact on airway remodeling in addition to effects on bronchial hyperresponsiveness. This review has focused on tryptase inhibitors in the pipeline and it is clear that with a few exceptions, the majority of these compounds are targeted for inhaled delivery. Finally, judging by the interest from numerous pharmaceutical companies, it appears the stage is set for tryptase inhibitors to make their mark as drugs of the future for allergic asthma and the results from clinical trials is awaited with eager anticipation.

Proteinase-activated receptor-2 mediates hyperresponsiveness in isolated guinea pig bronchi

The mast cell serine protease tryptase has been implicated as a critical mediator of airway hyperresponsiveness in vitro and in vivo. We have previously demonstrated that tryptase promotes hyperresponsiveness in isolated guinea pig bronchi. In this study, we have investigated the potential role of tryptase-mediated activation of proteinase-activated receptor-2 (PAR-2) in promoting airway hyperresponsiveness. Ex vivo exposure of guinea pig bronchi to the PAR-2 agonists H(2)N-Ser-Leu-Ile-Gly-Arg-Leu-CONH(2) (SLIGRL) and t-cinnamoyl-H(2)N-Leu-Ile-Gly-Arg-Leu-O-CONH(2) (t-c-LIGRLO) (0.1-10 microM) induced a concentration-dependent increase of contractile response to histamine. Treatment with 10 microM SLIGRL or t-c LIGRLO for 45 min increased subsequent responsiveness to histamine (0.3mM) by 54+/-3% and 69+/-5%, respectively (P<0.05 vs. control). In contrast, the PAR-1 agonist peptide H(2)N-Ser-Phe-Leu-Leu-Arg-Asn-CONH(2) (SFLLRN) did not promote significant changes in the airway. Effects of the peptides were observed following at least a 30-min preincubation with the tissue. Coincubation with indomethacin or removal of epithelial cells is required for PAR-2-mediated hyperreactivity. The inactive analogue H(2)N-Leu-Ser-Ile-Gly-Arg-Leu-CONH(2) (LISGRL; 10 microM) failed to promote hyperresponsiveness. Neuropeptide antagonists blocked the effect of the PAR-2 agonists. Selective antagonists of NK1 (L-703,606), NK2 (L-659,877), and CGRP (alphaCGRP 8-37) provided additive inhibition of PAR-2-mediated hyperreactivity. Pretreatment of bronchi with capsaicin (0.8 microM) also prevented the effects of SLIGRL. These results demonstrate the potential involvement of tryptase-mediated activation of PAR-2 in promoting airway hyperresponsiveness. These results further demonstrate that the PAR-2-mediated response involves a neurogenic mechanism involving neuropeptide release.

Polycationic peptides as inhibitors of mast cell serine proteases

When mast cells are activated, e.g. during allergic responses, they secrete the serine proteases chymase and tryptase, which both are complex-bound to heparin proteoglycan in vivo. Previous reports have demonstrated potent pro-inflammatory effects of both tryptase and chymase in different animal models, suggesting that these serine proteases may be relevant targets for therapeutic intervention. Recent investigations have shown that heparin-binding compounds can cause tryptase inhibition and it has been suggested that the inhibitory activity of such compounds is due to interference with the binding of heparin to tryptase. Here we tested various polycationic peptides for their ability to inhibit heparin-free human recombinant betaI-tryptase. We demonstrate powerful direct inhibition of tryptase (IC(50) values approximately 1-100 nM) by poly-Arg and poly-Lys of different molecular weights. Poly-Arg and poly-Lys showed predominantly competitive inhibition kinetics, although decreases in the k(cat) values for the chromogenic substrate S-2288 were also observed. Peptides built up from heparin-binding motifs were also inhibitors of tryptase, albeit of lower efficiency than poly-Arg/Lys. Tryptase inhibition was strongly dependent on the size of the polycationic peptides. The various polycationic peptides were also inhibitory for heparin-dependent activities of chymase. The tryptase inhibition caused by the polycationic peptides could be reversed by adding heparin. After heparin-induced rescue of tryptase activity, the major part of the tryptase activity was sensitive to inhibition by bovine pancreatic trypsin inhibitor, whereas tryptase before addition of polycationic peptide was completely resistant. Taken together, our findings indicate that polycationic peptides can be used as powerful agents for combined inhibition of mast cell tryptase and chymase.

Endothelin-induced vascular and bronchial effects in pig airways: role in acute allergic responses

The effects of endothelin (ET) agonists on airway mechanics and bronchial blood flow were studied as well as the effects of mixed ET-receptor antagonist bosentan on allergen-induced airway reactions in the pig. ET agonists [ET-1, ET-3, and the ET(B) receptor-selective agonist Sarafotoxin 6c (Sf6c)] were given as intravenous injections (0.4-200 pmol/kg) to eight anesthetized pigs. Bosentan (10 mg/kg iv) was then administered, and the injections were repeated. Only Sf6c caused a significant increase in airway resistance, and this response was blocked by bosentan. Sf6c and ET-1 (200 and 400 pmol/kg, respectively) were also given as aerosols to five pigs. Sf6c, but not ET-1, caused bronchoconstriction via this route. All agonists (intravenous) caused increases in bronchial vascular conductance, an effect that was blocked by an NO-synthase inhibitor (N(G)-nitro-L-arginine) but unaffected by a cyxlooxygenase inhibitor (diclofenac). Fourteen pigs were sensitized with ascaris suum antigen. Under anesthesia, eight pigs were pretreated with bosentan, and six pigs were controls. They were all challenged with allergen aerosol resulting in acute bronchoconstriction and elevation of ET-1 in bronchoalveolar lavage fluid. Bosentan did not affect the maximal acute airway obstruction but markedly increased baseline bronchial vascular conductance, suggesting a basal vascular tone regulated by ETs. In conclusion, ETs induce bronchoconstriction primarily via the ET(B) receptor in the pig. However, ETs are probably not involved in the allergen-induced acute bronchoconstriction in this model.