I. Sophie T. Bos

Arginase inhibition protects against allergen-induced airway obstruction, hyperresponsiveness, and inflammation.

RATIONALE In a guinea pig model of allergic asthma, using perfused tracheal preparations ex vivo, we demonstrated that L-arginine limitation due to increased arginase activity underlies a deficiency of bronchodilating nitric oxide (NO) and airway hyperresponsiveness (AHR) after the allergen-induced early and late asthmatic reaction. OBJECTIVES Using the same animal model, we investigated the acute effects of the specific arginase inhibitor 2(S)-amino-6-boronohexanoic acid (ABH) and of L-arginine on AHR after the early and late reaction in vivo. In addition, we investigated the protection of allergen-induced asthmatic reactions, AHR, and airway inflammation by pretreatment with the drug. METHODS Airway responsiveness to inhaled histamine was measured in permanently instrumented, freely moving guinea pigs sensitized to ovalbumin at 24 hours before allergen challenge and after the allergen-induced early and late asthmatic reactions by assessing histamine PC(100) (provocative concentration causing a 100% increase of pleural pressure) values. MEASUREMENTS AND MAIN RESULTS Inhaled ABH acutely reversed AHR to histamine after the early reaction from 4.77 +/- 0.56-fold to 2.04 +/- 0.34-fold (P < 0.001), and a tendency to inhibition was observed after the late reaction (from 1.95 +/- 0.56-fold to 1.56 +/- 0.47-fold, P < 0.10). Quantitatively similar results were obtained with inhaled l-arginine. Remarkably, after pretreatment with ABH a 33-fold higher dose of allergen was needed to induce airway obstruction (P < 0.01). Consequently, ABH inhalation 0.5 hour before and 8 hours after allergen challenge protected against the allergen-induced early and late asthmatic reactions, AHR and inflammatory cell infiltration. CONCLUSIONS Inhalation of ABH or l-arginine acutely reverses allergen-induced AHR after the early and late asthmatic reaction, presumably by attenuating arginase-induced substrate deficiency to NO synthase in the airways. Moreover, ABH considerably reduces the airway sensitivity to inhaled allergen and protects against allergen-induced bronchial obstructive reactions, AHR, and airway inflammation. This is the first in vivo study indicating that arginase inhibitors may have therapeutic potential in allergic asthma.

Arginase strongly impairs neuronal nitric oxide-mediated airway smooth muscle relaxation in allergic asthma

BackgroundUsing guinea pig tracheal preparations, we have recently shown that endogenous arginase activity attenuates inhibitory nonadrenergic noncholinergic (iNANC) nerve-mediated airway smooth muscle relaxation by reducing nitric oxide (NO) production – due to competition with neuronal NO-synthase (nNOS) for the common substrate, L-arginine. Furthermore, in a guinea pig model of allergic asthma, airway arginase activity is markedly increased after the early asthmatic reaction (EAR), leading to deficiency of agonist-induced, epithelium-derived NO and subsequent airway hyperreactivity.In this study, we investigated whether increased arginase activity after the EAR affects iNANC nerve-derived NO production and airway smooth muscle relaxation.MethodsElectrical field stimulation (EFS; 150 mA, 4 ms, 4 s, 0.5 – 16 Hz)-induced relaxation was measured in tracheal open-ring preparations precontracted to 30% with histamine in the presence of 1 μM atropine and 3 μM indomethacin. The contribution of NO to EFS-induced relaxation was assessed by the nonselective NOS inhibitor Nω-nitro-L-arginine (L-NNA, 100 μM), while the involvement of arginase activity in the regulation of EFS-induced NO production and relaxation was investigated by the effect of the specific arginase inhibitor Nω-hydroxy-nor-L-arginine (nor-NOHA, 10 μM). Furthermore, the role of substrate availability to nNOS was measured in the presence of exogenous L-arginine (5.0 mM).ResultsAt 6 h after ovalbumin-challenge (after the EAR), EFS-induced relaxation (ranging from 3.2 ± 1.1% at 0.5 Hz to 58.5 ± 2.2% at 16 Hz) was significantly decreased compared to unchallenged controls (7.1 ± 0.8% to 75.8 ± 0.7%; P < 0.05 all). In contrast to unchallenged controls, the NOS inhibitor L-NNA did not affect EFS-induced relaxation after allergen challenge, indicating that NO deficiency underlies the impaired relaxation. Remarkably, the specific arginase inhibitor nor-NOHA normalized the impaired relaxation to unchallenged control (P < 0.05 all), which effect was inhibited by L-NNA (P < 0.01 all). Moreover, the effect of nor-NOHA was mimicked by exogenous L-arginine.ConclusionThe results clearly demonstrate that increased arginase activity after the allergen-induced EAR contributes to a deficiency of iNANC nerve-derived NO and decreased airway smooth muscle relaxation, presumably via increased substrate competition with nNOS.

Noncanonical WNT-5A signaling regulates TGF-β-induced extracellular matrix production by airway smooth muscle cells

Transforming growth factor β (TGF‐β), a key mediator of fibrotic responses, is increased in asthma and drives airway remodeling by inducing expression of extracellular matrix (ECM) proteins. We investigated the molecular mechanisms underlying TGF‐β‐induced ECM expression by airway smooth muscle cells and demonstrate a novel link between TGF‐β and Wingless/integrase 1 (WNT) signaling in ECM deposition. Airway smooth muscle expresses abundant WNT ligands, with the noncanonical WNT‐5A being the most profoundly expressed. Interestingly, WNT‐5A shows ~2‐fold higher abundance in airway smooth muscle cells isolated from individuals with asthma than individuals without asthma. WNT‐5A is markedly induced in response to TGF‐β (4–16‐fold; EC50 0.3 ng/ml) and is required for collagen and fibronectin expression by airway smooth muscle. WNT‐5A engages noncanonical WNT signaling pathways, as inhibition of Ca2+ and c‐Jun N‐terminal kinase (JNK) signaling attenuated this TGF‐β response, whereas the canonical WNT antagonist Dickkopf 1 (DKK‐1) did not. Accordingly, WNT‐5A induced JNK phosphorylation and nuclear translocation of nuclear factor of activated T cells c1 (NFATc1). Furthermore, silencing of the WNT‐5A receptors Frizzled 8 (FZD8) and RYK attenuated TGF‐β‐induced ECM expression. Collectively, these findings demonstrate that noncanonical WNT‐5A signaling is activated by and necessary for TGF‐β‐induced ECM production by airway smooth muscle cells, which could have significance in asthma pathogenesis.—Kumawat, K., Menzen, M. H., Bos, I. S. T., Baarsma, H. A., Borger, P., Roth, M., Tamm, M., Halayko, A. J., Simoons, M., Prins, A., Postma, D. S., Schmidt, M., and Gosens, R. Noncanonical WNT‐5A signaling regulates TGF‐β‐induced extracellular matrix production by airway smooth muscle cells. FASEB J. 27, 1631–1643 (2013). www.fasebj.org

Allergic sensitization enhances the contribution of Rho-kinase to airway smooth muscle contraction

Repeated allergen challenge has been shown to increase the role of Rho‐kinase in airway smooth muscle (ASM) contraction. We considered the possibility that active allergic sensitization by itself, that is, without subsequent allergen exposure, could be sufficient to enhance Rho‐kinase‐mediated ASM contraction. Guinea pigs were actively IgE‐sensitized to ovalbumin (OA), using Al(OH)3 as adjuvant. Contractile responsiveness to Gq‐coupled receptor agonists (methacholine, histamine or PGF2α) was investigated in tracheal rings. No effect of sensitization was observed on basal‐ and methacholine‐induced myogenic tone. In contrast, potency of histamine and PGF2α increased, that is, EC50 decreased, after OA‐sensitization by 2.6‐ and 4.7‐fold, respectively, without effect on maximal contraction (Emax). Basal tone in preparations from both control and OA‐sensitized animals was strongly decreased in the presence of the Rho‐kinase inhibitor (+)‐(R)‐trans‐4‐(1‐aminoethyl)‐N‐(4‐pyridyl) cyclohexane carboxamide (Y‐27632) (1 μM). In control preparations, the Emax and potency of histamine were unaffected by Y‐27632, but were decreased for PGF2α (by 38.2% and 2.0‐fold, respectively). However, in preparations from OA‐sensitized animals, Y‐27632 induced a significant reduction in Emax (33.5%) and potency (2.3‐fold) of histamine and of PGF2α (48.3% and 6.6‐fold, respectively), normalizing the OA‐sensitization‐induced increase in sensitivity toward these agonists. We also investigated the contribution of Rho‐kinase in vivo by measuring airway responsiveness toward inhaled histamine in permanently instrumented, unanaesthetized control and OA‐sensitized guinea pigs. Treatment with Y‐27632 by inhalation (5 mM, nebulizer concentration) decreased airway responsiveness toward histamine both in control and OA‐sensitized animals. However, the histamine PC100 ratio pre/post Y‐27632 inhalation was significantly smaller in OA‐sensitized animals as compared to control animals, indicating an enhanced contribution of Rho‐kinase. Expression of RhoA, an upstream activator of Rho‐kinase, was significantly increased (2.6‐fold) in lung homogenates of OA‐sensitized guinea pigs compared to control animals, as determined by Western analysis. In conclusion, the results show a receptor‐dependent role of Rho‐kinase in agonist‐induced ASM contraction. The contribution of Rho‐kinase to contractile airway responsiveness, both in vivo and ex vivo, is augmented after active allergic sensitization, as a consequence of increased expression of RhoA presumably. Inhibition of the RhoA/Rho‐kinase pathway may be considered a useful pharmacotherapeutical target in allergy and asthma.

The integrin-blocking peptide RGDS inhibits airway smooth muscle remodeling in a guinea pig model of allergic asthma.

RATIONALE Airway remodeling, including increased airway smooth muscle (ASM) mass and contractility, contributes to airway hyperresponsiveness in asthma. The mechanisms driving these changes are, however, incompletely understood. Recently, an important role for extracellular matrix proteins in regulating ASM proliferation and contractility has been found, suggesting that matrix proteins and their integrins actively modulate airway remodeling. OBJECTIVES To investigate the role of RGD (Arg-Gly-Asp)-binding integrins in airway remodeling in an animal model of allergic asthma. METHODS Using a guinea pig model of allergic asthma, the effects of topical application of the integrin-blocking peptide RGDS (Arg-Gly-Asp-Ser) and its negative control GRADSP (Gly-Arg-Ala-Asp-Ser-Pro) were assessed on markers of ASM remodeling, fibrosis, and inflammation induced by repeated allergen challenge. In addition, effects of these peptides on human ASM proliferation and maturation were investigated in vitro. MEASUREMENTS AND MAIN RESULTS RGDS attenuated allergen-induced ASM hyperplasia and hypercontractility as well as increased pulmonary expression of smooth muscle myosin heavy chain and the proliferative marker proliferating cell nuclear antigen (PCNA). No effects were observed for GRADSP. The RGDS effects were ASM selective, as allergen-induced eosinophil and neutrophil infiltration as well as fibrosis were unaffected. In cultured human ASM cells, we demonstrated that proliferation induced by collagen I, fibronectin, serum, and platelet-derived growth factor requires signaling via RGD-binding integrins, particularly of the alpha(5)beta(1) subtype. In addition, RGDS inhibited smooth muscle alpha-actin accumulation in serum-deprived ASM cells. CONCLUSIONS This is the first study indicating that integrins modulate ASM remodeling in an animal model of allergic asthma, which can be inhibited by a small peptide containing the RGD motif.

The inhaled Rho kinase inhibitor Y-27632 protects against allergen-induced acute bronchoconstriction, airway hyperresponsiveness, and inflammation

Recently, we have shown that allergen-induced airway hyperresponsiveness (AHR) after the early (EAR) and late (LAR) asthmatic reaction in guinea pigs could be reversed acutely by inhalation of the Rho kinase inhibitor Y-27632. The present study addresses the effects of pretreatment with inhaled Y-27632 on the severity of the allergen-induced EAR and LAR, the development of AHR after these reactions, and airway inflammation. Using permanently instrumented and unrestrained ovalbumin (OA)-sensitized guinea pigs, single OA challenge-induced EAR and LAR, expressed as area under the lung function (pleural pressure, P(pl)) time-response curve, were measured, and histamine PC(100) (provocation concentration causing a 100% increase of P(pl)) values were assessed 24 h before, and at 6 and 24 h after, the OA challenge (after the EAR and LAR, respectively). Thirty minutes before and 8 h after OA challenge, saline or Y-27632 (5 mM) was nebulized. After the last PC(100) value, bronchoalveolar lavage (BAL) was performed, and the inflammatory cell profile was determined. It was demonstrated that inhalation of Y-27632 before allergen challenge markedly reduced the immediate allergen-induced peak rise in P(pl), without significantly reducing the overall EAR and LAR. Also, pretreatment with Y-27632 considerably protected against the development of AHR after the EAR and fully prevented AHR after the LAR. These effects could not be explained by a direct effect of Y-27632 on the histamine responsiveness, because of the short duration of the acute bronchoprotection of Y-27632 (<90 min). In addition, Y-27632 reduced the number of total inflammatory cells, eosinophils, macrophages, and neutrophils recovered from the BAL. Altogether, inhaled Y-27632 protects against acute allergen-induced bronchoconstriction, development of AHR after the EAR and LAR, and airway inflammation in an established guinea pig model of allergic asthma.

Inhalation of the Rho-kinase inhibitor Y-27632 reverses allergen-induced airway hyperresponsiveness after the early and late asthmatic reaction

BackgroundIn guinea pigs, we have previously demonstrated that the contribution of Rho-kinase to airway responsiveness in vivo and ex vivo is enhanced after active sensitization with ovalbumin (OA). Using conscious, unrestrained OA-sensitized guina pigs, we now investigated the role of Rho-kinase in the development of airway hyperresponsiveness (AHR) after the allergen-induced early (EAR) and late asthmatic reaction (LAR) in vivo.MethodsHistamine and PGF2α PC100-values (provocation concentrations causing 100% increase in pleural pressure) were assessed before OA-challenge (basal airway responsiveness) and after the OA-induced EAR (5 h after challenge) and LAR (23 h after challenge). Thirty minutes later, saline or the specific Rho-kinase inhibitor Y-27632 (5 mM, nebulizer concentration) were nebulized, after which PC100-values were reassessed.ResultsIn contrast to saline, Y-27632 inhalation significantly decreased the basal responsiveness toward histamine and PGF2α before OA-challenge, as indicated by increased PC100 -values. Both after the allergen-induced EAR and LAR, AHR to histamine and PGF2α was present, which was reversed by Y-27632 inhalation. Moreover, there was an increased effectiveness of Y-27632 to reduce airway responsiveness to histamine and PGF2α after the EAR and LAR as compared to pre-challenge conditions. Saline inhalations did not affect histamine or PGF2α PC100-values at all. Interestingly, under all conditions Y-27632 was significantly more effective in reducing airway responsiveness to PGF2α as compared to histamine. Also, there was a clear tendency (P = 0.08) to a more pronounced degree of AHR after the EAR for PGF2α than for histamine.ConclusionThe results indicate that inhalation of the Rho-kinase inhibitor Y-27632 causes a considerable bronchoprotection to both histamine and PGF2α. Moreover, the results are indicative of a differential involvement of Rho-kinase in the agonist-induced airway obstruction in vivo. Increased Rho-kinase activity contributes to the allergen-induced AHR to histamine and PGF2α after both the EAR and the LAR, which is effectively reversed by inhalation of Y-27632. Therefore, Rho-kinase can be considered as a potential pharmacotherapeutical target in allergic asthma.

Role of contractile prostaglandins and Rho-kinase in growth factor-induced airway smooth muscle contraction

BackgroundIn addition to their proliferative and differentiating effects, several growth factors are capable of inducing a sustained airway smooth muscle (ASM) contraction. These contractile effects were previously found to be dependent on Rho-kinase and have also been associated with the production of eicosanoids. However, the precise mechanisms underlying growth factor-induced contraction are still unknown. In this study we investigated the role of contractile prostaglandins and Rho-kinase in growth factor-induced ASM contraction.MethodsGrowth factor-induced contractions of guinea pig open-ring tracheal preparations were studied by isometric tension measurements. The contribution of Rho-kinase, mitogen-activated protein kinase (MAPK) and cyclooxygenase (COX) to these reponses was established, using the inhibitors Y-27632 (1 μM), U-0126 (3 μM) and indomethacin (3 μM), respectively. The Rho-kinase dependency of contractions induced by exogenously applied prostaglandin F2α (PGF2α) and prostaglandin E2 (PGE2) was also studied. In addition, the effects of the selective FP-receptor antagonist AL-8810 (10 μM) and the selective EP1-antagonist AH-6809 (10 μM) on growth factor-induced contractions were investigated, both in intact and epithelium-denuded preparations. Growth factor-induced PGF2α-and PGE2-release in the absence and presence of Y-27632, U-0126 and indomethacin, was assessed by an ELISA-assay.ResultsEpidermal growth factor (EGF)-and platelet-derived growth factor (PDGF)-induced contractions of guinea pig tracheal smooth muscle preparations were dependent on Rho-kinase, MAPK and COX. Interestingly, growth factor-induced PGF2α-and PGE2-release from tracheal rings was significantly reduced by U-0126 and indomethacin, but not by Y-27632. Also, PGF2α-and PGE2-induced ASM contractions were largely dependent on Rho-kinase, in contrast to other contractile agonists like histamine. The FP-receptor antagonist AL-8810 (10 μM) significantly reduced (approximately 50 %) and the EP1-antagonist AH-6809 (10 μM) abrogated growth factor-induced contractions, similarly in intact and epithelium-denuded preparations.ConclusionThe results indicate that growth factors induce ASM contraction through contractile prostaglandins – not derived from the epithelium – which in turn rely on Rho-kinase for their contractile effects.

A guinea pig model of acute and chronic asthma using permanently instrumented and unrestrained animals

To investigate mechanisms underlying allergen-induced asthmatic reactions, airway hyperresponsiveness and remodeling, we have developed a guinea pig model of acute and chronic asthma using unanesthetized, unrestrained animals. To measure airway function, ovalbumin (IgE)-sensitized animals are permanently instrumented with a balloon-catheter, which is implanted inside the pleural cavity and exposed at the neck of the animal. Via an external cannula, the balloon-catheter is connected to a pressure transducer, an amplifier, an A/D converter and a computer system, enabling on-line measurement of pleural pressure (Ppl)—closely correlating with airway resistance—for prolonged periods of time. Using aerosol inhalations, the method has been successfully applied to measure ovalbumin-induced early and late asthmatic reactions and airway hyperresponsiveness. Because airway function can be monitored repeatedly, intra-individual comparisons of airway responses (e.g., to study drug effects) are feasible. Moreover, this model is suitable to investigate chronic asthma and airway remodeling, which occurs after repeated allergen challenges. The protocol for establishing this model takes about 4 weeks.

Functional consequences of human airway smooth muscle phenotype plasticity

BACKGROUND AND PURPOSE Airway smooth muscle (ASM) phenotype plasticity, characterized by reversible switching between contractile and proliferative phenotypes, is considered to contribute to increased ASM mass and airway hyper‐responsiveness in asthma. Further, increased expression of collagen I has been observed within the ASM bundle of asthmatics. Previously, we showed that exposure of intact bovine tracheal smooth muscle (BTSM) to collagen I induces a switch from a contractile to a hypocontractile, proliferative phenotype. However, the functional relevance of this finding for intact human ASM has not been established.