Mark A. Birrell

Differential Effects of Ebselen on Neutrophil Recruitment, Chemokine, and Inflammatory Mediator Expression in a Rat Model of Lipopolysaccharide-Induced Pulmonary Inflammation

We postulated that the seleno-organic compound ebselen would attenuate neutrophil recruitment and activation after aerosolized challenge with endotoxin (LPS) through its effect as an antioxidant and inhibitor of gene activation. Rats were given ebselen (1–100 mg/kg i.p.) followed by aerosolized LPS exposure (0.3 mg/ml for 30 min). Airway inflammatory indices were measured 4 h postchallenge. Bronchoalveolar lavage (BAL) fluid cellularity and myeloperoxidase activity were used as a measure of neutrophil recruitment and activation. RT-PCR analysis was performed in lung tissue to assess gene expression of TNF-α, cytokine-induced neutrophil chemoattractant-1 (CINC-1), macrophage-inflammatory protein-2 (MIP-2), ICAM-1, IL-10, and inducible NO synthase. Protein levels in lung and BAL were also determined by ELISA. Ebselen pretreatment inhibited neutrophil influx and activation as assessed by BAL fluid cellularity and myeloperoxidase activity in cell-free BAL and BAL cell homogenates. This protective effect was accompanied by a significant reduction in lung and BAL fluid TNF-α and IL-1β protein and/or mRNA levels. Ebselen pretreatment also prevented lung ICAM-1 mRNA up-regulation in response to airway challenge with LPS. This was not a global effect of ebselen on LPS-induced gene expression, because the rise in lung and BAL CINC-1 and MIP-2 protein levels were unaffected as were lung mRNA expressions for CINC-1, MIP-2, IL-10, and inducible NO synthase. These data suggest that the anti-inflammatory properties of ebselen are achieved through an inhibition of lung ICAM-1 expression possibly through an inhibition of TNF-α and IL-1β, which are potent neutrophil recruiting mediators and effective inducers of ICAM-1 expression.

Effect of the p38 kinase inhibitor, SB 203580, on allergic airway inflammation in the rat.

Tumour necrosis factor‐α (TNF‐α) and interleukin 1β (IL‐1β) have been implicated in the pathogenesis of asthma. The p38 kinase inhibitor, SB 203580 inhibits TNF‐α and IL‐1β production in vitro and in vivo. In this study the effect of SB 203580 on allergen‐induced airway TNF‐α production and inflammatory cell recruitment was investigated in sensitized Brown Norway rats. The allergen‐induced increase in bronchoalveolar lavage (BAL) TNF‐α was inhibited by SB 203580 at every dose tested (10–100 mg kg−1, p.o.). In contrast, neither ovalbumin‐induced eosinophilia or neutrophilia were inhibited by SB 203580 (10–100 mg kg−1, p.o.). In conclusion, SB 203580 inhibits BAL TNF‐α production by 95% without inhibiting either antigen‐induced airway eosinophilia or neutrophilia. This data suggests that either the residual TNF‐α is sufficent to drive allergen‐induced inflammatory cell recruitment into the lung or that TNF‐α is not involved in allergen‐induced inflammatory cell recruitment.

Utility of exhaled nitric oxide as a noninvasive biomarker of lung inflammation in a disease model

There is a great deal of interest in developing less invasive markers for monitoring airway inflammation and the effect of possible novel anti-inflammatory therapies that may take time to impact on disease pathology. Exhaled nitric oxide (eNO) has been shown to be a reproducible, noninvasive indicator of the inflammatory status of the airway in the clinic. The aim of the present study was to determine the usefulness of measuring eNO as a marker of the anti-inflammatory impact of glucocorticoid and an inhibitor of κB kinase-2 (IKK-2) inhibitor 2-[(aminocarbonyl)amino]-5-(4-fluorophenyl)-3-thiophenecarboxamide (TPCA-1), in a pre-clinical model of airway inflammation. Rats were given vehicle, budesonide or TPCA-1 prior to exposure to lipopolysaccharide, previously shown to induce an increase in eNO and airway neutrophilia/eosinophilia. Comparison of the effect of the two compounds on inflammatory components demonstrated a significant correlation between the impact on eNO and inflammatory cell burden in the airway. The current study demonstrates the usefulness of profiling potential disease-modifying therapies on exhaled nitric oxide levels and the way in which an effect on this noninvasive biomarker relates to effects on pathological parameters such as lung cellularity. Information from studies such as the current one would suggest that the measurement of exhaled nitric oxide has potential for monitoring inflammatory status in lung tissue.

Effect of the p38 kinase inhibitor, SB 203580, on sephadex induced airway inflammation in the rat

SB 203580 is a pyridinyl imidazole compound which inhibits the release of pro-inflammatory cytokines, such as tumour necrosis factor-alpha (TNF-alpha) and interleukin-1beta (IL-1beta), in vitro and in vivo by inhibiting p38 mitogen-activated protein kinase (MAPK). The present study investigated the effects of SB 203580 in a model of airway inflammation induced by the topical administration of Sephadex into the rat airways. This inflammatory response is characterized by the development of lung oedema, airway tissue inflammatory cell recruitment and an increase in lung TNF-alpha and IL-1beta levels. Sephadex-induced lung oedema was accompanied by a significant increase in lung tissue TNF-alpha but not IL-1beta levels. There was also a significant increase in lung tissue macrophages and an increase in eosinophils which did not reach significance. SB 203580 administration significantly inhibited lung oedema (ED50=18 mg x kg(-1)) in a dose-related manner but was without significant effect on lung tissue cell recruitment or cytokine levels. These data suggest that the increase in tumour necrosis factor-alpha and lung oedema are separate processes which both contribute to Sephadex pathology. Furthermore, the inhibitory effect of SB 203580 on Sephadex-induced lung oedema suggests that p38 kinase inhibitors may be of use in pulmonary pathologies in which lung oedema is a feature.

Characterization of the effects of cannabinoids on guinea-pig tracheal smooth muscle tone: role in the modulation of acetylcholine release from parasympathetic nerves

We investigated the ability of the cannabinoid agonists CP55,940 (CB1/CB2) and anandamide (endogenous cannabinoid) to modulate electrical field stimulation (EFS)‐induced acetylcholine (ACh) release from parasympathetic nerve terminals innervating guinea‐pig trachea. We assessed whether modulation of transmitter release translated to an impact on functional responses by investigating the effect of these agents on contractile responses evoked by EFS and ACh. Furthermore, we evaluated the ability of these compounds to elicit bronchodilation in pre‐contracted guinea‐pig tracheal strips. CP55,940 and anandamide significantly inhibited EFS‐evoked ACh release (maximal inhibition of 35.1±2.9% and 33.4±6.4% at 1 μM, P<0.05, respectively). The CB1 receptor antagonist SR 141716A (1 μM), had no effect on ACh release and failed to reverse the inhibitory effect of CP55,940 (1 μM). Paradoxically, CP55,940 had no significant effect on EFS‐evoked cholinergic contractile responses. Furthermore, CP55,940 did not relax pre‐contracted tracheal strips or affect contractile responses to exogenous ACh. This lack of activity on smooth muscle tone is consistent with the fact that no detectable specific binding of [3H] CP55,940 was found in tracheal homogenates. These data suggest that cannabinoid agonists inhibit ACh release from cholinergic nerve terminals via activation of CB2 receptors but that this inhibitory action does not impact on functional responses such as cholinergic contraction.

Tobacco Smoke Induced Cough: Mechanisms Driving Acute and Chronic Cough Pathology

Cough is an important protective mechanism that clears foreign material from the airway and aids in immune defence. However, chronic excessive cough of various aetiologies is a common presentation to specialist respiratory clinics, and is reported as a troublesome symptom by a significant proportion of the population (Ford et al., 2006). In extreme situations chronic cough can persist for several years, and is not only socially embarrassing, but can be painful and debilitating. Chronic cough is often associated with an underlying respiratory disease, several of which can be caused or exacerbated by exposure to tobacco smoke or environmental pollution, for example chronic obstructive pulmonary disease (COPD), emphysema, bronchitis, lung cancer and asthma. In addition, chronic cough can be of unknown cause (idiopathic) (Morice et al., 2007). Recently, the label chronic ‘cough hypersensitivity syndrome’ (CCHS) was proposed as a means of focussing the cough community and general practitioners on the symptomology of cough and understanding of the mechanisms behind cough sensation, with the ultimate goal of developing effective antitussive treatments (Millqvist et al., 1998; Chung, 2011). At present, little is known about the mechanisms that drive the cough reflex, and even less about how these mechanisms are altered to lead to chronic cough. Numerous environmental irritants are known to induce coughing such as air pollution, tobacco smoke, smoke from burning vegetation, and vehicle exhaust. This chapter focuses on tobacco smoke (TS), which is one of the most common inhaled irritants (both as an active smoker, and as a secondary environmental pollutant), and is known to contain thousands of noxious chemicals (U.S. Department of Health and Human Services, 2010). Exposure to acute TS readily evokes coughing in both animals and human non-smokers (Andre et al., 2009; Lee et al., 1993; Lee et al., 2007), and prolonged exposure to TS can lead to an altered sensitivity to a range of tussive stimuli (Karlsson et al., 1991; Doherty et al., 2000; Bergren, 2001; Dicpinigaitis, 2003; Lewis et al., 2007). It is believed that if the mechanisms behind acute or chronic cough associated with TS exposure can be revealed it would lead to the development of truly effective cough therapies. The aim of this chapter is to discuss the current understanding of how exposure to TS can cause/alter the cough response and we will consider some of the most promising new therapeutic targets for the treatment of cough.