Schilter et al. Respiratory Research (2015) 16:42 DOI 10.1186/s12931-015-0200-z RESEARCH Open Access Effects of an anti-inflammatory VAP-1/SSAO inhibitor, PXS-4728A, on pulmonary neutrophil migration Heidi C Schilter1*†, Adam Collison2†, Remo C Russo3,4†, Jonathan S Foot1, Tin T Yow1, Angelica T Vieira4, Livia D Tavares4, Joerg Mattes2, Mauro M Teixeira4 and Wolfgang Jarolimek1,5 Abstract Background and purpose: The persistent influx of neutrophils into the lung and subsequent tissue damage are characteristics of COPD, cystic fibrosis and acute lung inflammation. VAP-1/SSAO is an endothelial bound adhesion molecule with amine oxidase activity that is reported to be involved in neutrophil egress from the microvasculature during inflammation. This study explored the role of VAP-1/SSAO in neutrophilic lung mediated diseases and examined the therapeutic potential of the selective inhibitor PXS-4728A. Methods: Mice treated with PXS-4728A underwent intra-vital microscopy visualization of the cremaster muscle upon CXCL1/KC stimulation. LPS inflammation, Klebsiella pneumoniae infection, cecal ligation and puncture as well as rhinovirus exacerbated asthma models were also assessed using PXS-4728A. Results: Selective VAP-1/SSAO inhibition by PXS-4728A diminished leukocyte rolling and adherence induced by CXCL1/KC. Inhibition of VAP-1/SSAO also dampened the migration of neutrophils to the lungs in response to LPS, Klebsiella pneumoniae lung infection and CLP induced sepsis; whilst still allowing for normal neutrophil defense function, resulting in increased survival. The functional effects of this inhibition were demonstrated in the RV exacerbated asthma model, with a reduction in cellular infiltrate correlating with a reduction in airways hyperractivity. Conclusions and implications: This study demonstrates that the endothelial cell ligand VAP-1/SSAO contributes to the migration of neutrophils during acute lung inflammation, pulmonary infection and airway hyperractivity. These results highlight the potential of inhibiting of VAP-1/SSAO enzymatic function, by PXS-4728A, as a novel therapeutic approach in lung diseases that are characterized by neutrophilic pattern of inflammation. Keywords: Neutrophils, Adhesion molecules, VAP-1/SSAO, Lung inflammation, COPD Background coupled with inadequate removal of neutrophils (and their Several inflammatory diseases of the lung including chronic byproducts) results in the subsequent and persistent release obstructive pulmonary disease (COPD), cystic fibrosis (CF), of a number of inflammatory mediators and proteinases acute lung injury and bronchiolitis obliterans syndrome are that contribute to progressive fibrosis and destruction of predominantly characterized by neutrophilic infiltration the lung parenchyma [6-8]. [1-4]. Neutrophils are polymorphonuclear phagocytic gran- Integral to the proper functioning of neutrophils in lung ulocytes and during normal immune responses act as the defense is their ability to egress from the microvasculature first line of defense against microorganisms by finding and and migrate through tissues to the targeted site. Upon injury neutralizing bacteria and fungi [5]. Excessive neutrophilia of organs, neutrophils up-regulate expression of cell surface receptors (such as CD44 and CD11b) [9,10]; these subse- quently bind to adhesion molecules on endothelial cells * Correspondence: [email protected] † (E-selectin, P-selectin, VAP-1/SSAO, ICAM-1), enabling Equal contributors 1Drug Discovery Department, Pharmaxis Ltd, 20 Rodborough Road, Frenchs neutrophil transmigration through the endothelial cell lining Forest, Sydney, NSW 2086, Australia into the underlying parenchyma [5,11]. In the pulmonary Full list of author information is available at the end of the article © 2015 Schilter et al.; licensee BioMed Central. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Schilter et al. Respiratory Research (2015) 16:42 Page 2 of 14 microcirculation however, neutrophil migration primarily by a small molecule impairs neutrophil migration by medi- occurs from the capillaries, and so far only neutrophil rolling ating tethering and rolling onto the vascular endothelium. and deformability (not adhesion) have been implicated in Using the small molecule inhibitor PXS-4728A, a crucial this process [12-16]. role for the enzymatic function of VAP-1/SSAO was iden- Given the potential of targeting neutrophil migration via tified in the pathogenesis of neutrophil lung inflammation, their adhesion process, a number of small molecules have injury and airway hyperreactivity. This article provides now been developed against neutrophil inflammation. Tar- support that targeting VAP-1/SSAO is a potential strategy geting P-selectin glycoprotein ligand 1 (PSGL-1/CD162) to inhibit the underlying neutrophil inflammation that con- and Mac-1 (CD11b/CD18), not only inhibits pulmonary tributes to the progression of COPD and other respiratory recruitment of neutrophils but also reduces lung damage diseases. in sepsis (29, 30). Neutralization of CD44 reduced cecal ligation puncture (CLP) induced pulmonary accumulation Materials and methods of neutrophils. Studies have also shown that neutrophilic Compound chemical properties inflammation induced by lipopolysaccharides (LPS) is at- PXS-4728A (Figure 1) is a low molecular weight fluoro- tenuated in CXCR2 deficient mice and small molecule allylamine and chemically similar to the previously CXCR2 antagonists inhibit pulmonary neutrophilic inflam- described VAP-1/SSAO inhibitor PXS-4681A [24]. mation induced by inhaled LPS [17,18]. Administration of the CXCR2 antagonists SCH527123 and SB-656933 has SSAO fluorometric enzyme activity assay been shown to inhibit the increased neutrophil content in Enzymatic activity measurement was based on the produc- sputum as a result of ozone challenge in normal volun- tion of H2O2 as described previously [24]. When measur- teers, while AZD8309 also was shown to be efficacious ing activity from tissue, samples were incubated with during inhaled LPS challenge in normal volunteers [19-21]. 0.5 mM of pargyline, to inhibit any potential endogenous Another potential target for impacting neutrophil inflam- monoamine oxidase A and B. In a 384 well plate (Greiner mation is to inhibit their migration via the adhesion mol- 384 Well Black Microclear Base), 25 μlofthesampleswere ecule VAP-1/SSAO. VAP-1 is a homodimeric 170-kDa incubated for 30 min at 37°C with or without the specific sialoglycoprotein that regulates adhesion and consequently SSAO inhibitor (1 μM Mofegiline). A reaction mixture transendothelial migration of leukocytes [22]. It is unique containing amplex red (120 μM; Life Technologies, amongst the adhesion molecules as it also functions as a Australia, A12222), horseradish peroxidase (1.5 U/ml; semicarbazide-sensitive amine oxidase (SSAO), which is Sigma-Aldrich; P2088-5KU) and Benzylamine (600 μMfor part of a family of amine oxidases capable of oxidizing pri- rhSSAO; 80 μMformousetissue,30μM for rat tissue) mary amines (e.g. methylamine) to the corresponding alde- was prepared in 0.1 M sodium phosphate buffer. 25 μlof hyde (e.g. formaldehyde), releasing hydrogen peroxide and the reaction mixture were added into each well after the ammonia. It is highly expressed on the endothelium of the 30 min incubation. The relative fluorescence units (RFU) lungs and trachea, whereas absent from leukocytes and were read every 2.5 min for 30 min at 37°C, excitation epithelial cells [23]. Although the exact function of SSAO 565 nm and emission 590 (Optima, BMG labtech), and the in the lung is not well elucidated, it has been suggested that slope of the kinetic curves for each sample was calculated SSAO might be involved in the recruitment of inflamma- using MARS data analysis software (BMG labtech) as in tory cells during pulmonary inflammation [23-25]. VAP-1/SSAO overexpressing transgenic animals show higher baseline cell counts in the BALF (bronchoalveolar lavage fluid) than in non-transgenic mice, indicative of in- creased lung inflammation, due to increased VAP-1/SSAO levels [25]. The pro-inflammatory effect of VAP-1/SSAO was evident when transgenic mice were stimulated with LPS; inflammation was significantly higher in the trans- genic than in the non-transgenic mice [25]. Neutrophil migration through the endothelium was shown to be dependent on both the adhesive and the enzymatic func- tions, with mAb and small molecule enzyme inhibitors reducing the influx of neutrophils. However, these effects were not additive, indicative of a common downstream process [22,24]. The present study demonstrates for the first time in vivo, Figure 1 Structure of PXS-4728A. that inhibition of the enzymatic function of VAP-1/SSAO Schilter et al. Respiratory Research (2015) 16:42 Page 3 of 14 RFU/30 min. The difference between the signals obtained Off-target activity in the presence of the specific SSAO inhibitor (1 μM PXS-4728A, was tested at Ricerca Inc in the “lead seeker Mofegiline low signal control) and in the absence of the in- selectivity panel”, which tests over 100 different targets. hibitor (high signal control) was considered