Protease inhibitor reduces airway response and underlying inflammation in cockroach allergen-induced murine model

Airborne indoor allergen serine proteases and their contribution to sensitisation and activation of innate immunity in allergic airway disease

Common airborne allergens (pollen, animal dander and those from fungi and insects) are the main triggers of type I allergic disorder in the respiratory system and are associated with allergic rhinitis, allergic asthma, as well as immunoglobulin E (IgE)-mediated allergic bronchopulmonary aspergillosis. These allergens promote IgE crosslinking, vasodilation, infiltration of inflammatory cells, mucosal barrier dysfunction, extracellular matrix deposition and smooth muscle spasm, which collectively cause remodelling of the airways. Fungus and insect (house dust mite and cockroaches) indoor allergens are particularly rich in proteases. Indeed, more than 40 different types of aeroallergen proteases, which have both IgE-neutralising and tissue-destructive activities, have been documented in the Allergen Nomenclature database. Of all the inhaled protease allergens, 85% are classed as serine protease activities and include trypsin-like, chymotrypsin-like and collagenolytic serine proteases. In this article, we review and compare the allergenicity and proteolytic effect of allergen serine proteases as listed in the Allergen Nomenclature and MEROPS databases and highlight their contribution to allergic sensitisation, disruption of the epithelial barrier and activation of innate immunity in allergic airways disease. The utility of small-molecule inhibitors of allergen serine proteases as a potential treatment strategy for allergic airways disease will also be discussed.

German cockroach extract prevents IL-13-induced CCL26 expression in airway epithelial cells through IL-13 degradation

Inhaled aeroallergens can directly activate airway epithelial cells (AECs). Exposure to cockroach allergens is a strong risk factor for asthma. Cockroach allergens mediate some of their effects through their serine protease activity; protease activity is also a major contributor to allergenicity. The Th2 cytokine interleukin-13 (IL-13) induces upregulation of the eosinophil chemotactic factor CCL26. CCL26 induces eosinophil migration in allergic inflammation. In this work, we studied the effect of cockroach proteases on IL-13-induced effects. Immersed cultures of the human bronchial epithelial cell line BEAS-2B and air-liquid interface (ALI) cultures of primary normal human bronchial epithelial (NHBE) cells were stimulated with IL-13, Blattella Germanica cockroach extract (CE), or both. IL-13-induced genes were analyzed with qRT-PCR. IL-13 induced upregulation of CCL26, periostin, and IL-13Rα2 in bronchial epithelial cells which were decreased by CE. CE was heat-inactivated (HICE) or pre-incubated with protease inhibitors. HICE and CE preincubated with serine protease inhibitors did not prevent IL-13-induced CCL26 upregulation. CE-degraded IL-13 and specific cleavage sites were identified. CE also decreased IL-4-induced CCL26 upregulation and degraded IL-4. Other serine proteases such as bovine trypsin and house dust mite (HDM) serine proteases did not have the same effects on IL-13-induced CCL26. We conclude that CE serine proteases antagonize IL-13-induced effects in AECs, and this CE effect is mediated primarily through proteolytic cleavage of IL-13. IL-13 cleavage by cockroach serine proteases may modulate CCL26-mediated effects in allergic airway inflammation by interfering directly with the pro-inflammatory effects of IL-13 in vivo.

Effects of the serine protease inhibitor rBmTI-A in an experimental mouse model of chronic allergic pulmonary inflammation

To evaluate whether a recombinant serine protease inhibitor (rBmTI-A) modulates inflammation in an experimental model of chronic allergic lung inflammation. Balb/c mice were divided into four groups: SAL (saline), OVA (sensitized with ovalbumin), SAL + rBmTI-A (control treated with rBmTI-A) and OVA + rBmTI-A (sensitized with ovalbumin and treated with rBmTI-A). The animals received an intraperitoneal injection of saline or ovalbumin, according to the group. The groups received inhalation with saline or ovalbumin and were treated with rBmTI-A or saline by nasal instillation. After 29 days, we evaluated the respiratory mechanics; bronchoalveolar lavage fluid (BALF); cytokines; MMP-9, TIMP-1; eosinophils; collagen and elastic fibre expression in the airways; and the trypsin-like, MMP-1, and MMP-9 lung tissue proteolytic activity. Treatment with rBmTI-A reduced the trypsin-like proteolytic activity, the elastance and resistance maximum response, the polymorphonuclear cells, IL-5, IL-10, IL-13 and IL-17A in the BALF, the expression of IL-5, IL-13, IL-17, CD4+, MMP-9, TIMP-1, eosinophils, collagen and elastic fibres in the airways of the OVA + rBmTI-A group compared to the OVA group (p < 0.05). rBmTI-A attenuated bronchial hyperresponsiveness, inflammation and remodelling in this experimental model of chronic allergic pulmonary inflammation. This inhibitor may serve as a potential therapeutic tool for asthma treatment.

Aspergillus fumigatus-Secreted Alkaline Protease 1 Mediates Airways Hyperresponsiveness in Severe Asthma

The hallmark features of allergic asthma are type 2 (eosinophilic) inflammation and airways hyperresponsiveness (AHR). Although these features often comanifest in mouse lungs in vivo, we demonstrate in this study that the serine protease Alp1 from the ubiquitous mold and allergen, Aspergillus fumigatus, can induce AHR in mice unable to generate eosinophilic inflammation. Strikingly, Alp1 induced AHR in mice devoid of protease-activated receptor 2/F2 trypsin-like receptor 1 (PAR2/F2RL1), a receptor expressed in lung epithelium that is critical for allergic responses to protease-containing allergens. Instead, using precision-cut lung slices and human airway smooth muscle cells, we demonstrate that Alp1 directly increased contractile force. Taken together, these findings suggest that Alp1 induces bronchoconstriction through mechanisms that are largely independent of allergic inflammation and point to a new target for direct intervention of fungal-associated asthma.

Respiratory syncytial virus (RSV) entry is inhibited by serine protease inhibitor AEBSF when present during an early stage of infection

Background

Host proteases have been shown to play important roles in many viral activities such as entry, uncoating, viral protein production and disease induction. Therefore, these cellular proteases are putative targets for the development of antivirals that inhibit their activity. Host proteases have been described to play essential roles in Ebola, HCV, HIV and influenza, such that specific protease inhibitors are able to reduce infection. RSV utilizes a host protease in its replication cycle but its potential as antiviral target is unknown. Therefore, we evaluated the effect of protease inhibitors on RSV infection.

Methods

To measure the sensitivity of RSV infection to protease inhibitors, cells were infected with RSV and incubated for 18 h in the presence or absence of the inhibitors. Cells were fixed, stained and studied using fluorescence microscopy.

Results

Several protease inhibitors, representing different classes of proteases (AEBSF, Pepstatin A, E-64, TPCK, PMSF and aprotinin), were tested for inhibitory effects on an RSV A2 infection of HEp-2 cells. Different treatment durations, ranging from 1 h prior to inoculation and continuing for 18 h during the assay, were evaluated. Of all the inhibitors tested, AEBSF and TPCK significantly decreased RSV infection. To ascertain that the observed effect of AEBSF was not a specific feature related to HEp-2 cells, A549 and BEAS-2B cells were also used. Similar to HEp-2, an almost complete block in the number of RSV infected cells after 18 h of incubation was observed and the effect was dose-dependent. To gain insight into the mechanism of this inhibition, AEBSF treatment was applied during different phases of an infection cycle (pre-, peri- and post-inoculation treatment). The results from these experiments indicate that AEBSF is mainly active during the early entry phase of RSV. The inhibitory effect was also observed with other RSV isolates A1998/3–2 and A2000/3–4, suggesting that this is a general feature of RSV.

Conclusion

RSV infection can be inhibited by broad serine protease inhibitors, AEBSF and TPCK. We confirmed that AEBSF inhibition is independent of the cell line used or RSV strain. The time point at which treatment with the inhibitor was most potent, was found to coincide with the expected moment of entry of the virion with the host cell.

PI3K and ERK1/2 kinase inhibition potentiate protease inhibitor to attenuate allergen induced Th2 immune response in mouse

Proteases affect immune response by activating PI3K, ERK1/2 and p38 kinase. In present study, therapeutic effect of PI3K, ERK1/2 and p38 kinase inhibitor in combination with serine protease inhibitor was evaluated in cockroach extract (CE) induced airway inflammatory disease. Mice were sensitized on day 0, 7 and 14 and challenged on day 27, 28 and 29 with CE. Mice were given PI3K, ERK1/2 and the p38 kinase inhibitor (iPI3K, iERK1/2 and the ip38) alone or with serine protease inhibitor 4-(2-Aminoethyl) benzenesulfonyl fluoride hydrochloride (AEBSF), 1h before challenge. On day 30 airway resistance of mice were determined and euthanized to collect blood, BAL fluid and lung for analysis. CE immunized mice showed PI3K, ERK1/2 and p38 kinase activation, increased airway resistance, cellular infiltration, Th2 cytokines IgE and IgG1. AEBSF given to mice reduced the CE induced allergic response. AEBSF given in combination of iPI3K/iERK1/2 reduced cellular infiltration in lungs. Furthermore, iPI3K/iERK1/2 with AEBSF significantly reduced the CE induced Th2 cytokines in comparison to monotherapy of kinase inhibitor and AEBSF (P<0.05). The combination of iPI3K/iERK1/2 with AEBSF enhanced IL-12 level that could further provide a mean of Th2 reduction. Best effect in reduction of allergic response in mice was observed on administration of AEBSF with iPI3K. Conclusively, the combination of PI3K kinase inhibitor with AEBSF reduced allergen induced airway response and has therapeutic potential for add-on therapy in allergic airway disease.