Asthma is a chronic disease of airway hyper-responsiveness, airway inflammation and episodic bronchoconstriction. With asthma forecasted to increase by an additional 100 million cases by 2025, there is a critical and immediate need to address new asthma therapies. Guidelines for asthma treatment in the emergency department conditionally recommend intravenous magnesium sulfate (MgSO4). However, some investigations have failed to demonstrate beneficial effects. Ethical constraints limit evaluation of the bronchodilatory effects of MgSO4 alone in patients with acute asthma exacerbation, independent of other conventional therapeutics. To address this ethical dilemma, this study consisted of two phases: 1) quantification of the independent pulmonary effect of three doubling doses of MgSO4 in the spontaneous equine model of asthma during naturally occurring exacerbations of bronchoconstriction, and 2) evaluation of arterial blood gas parameters in response to administration of MgSO4 at a dose identified in phase 1 that yielded greatest efficacy without deleterious side effects.

Pulmonary surfactant is synthesized in the alveoli and lines the respiratory epithelium of the airways. Phospholipids, the main component of surfactant, confer it its ability to lower surface tension and to prevent alveolar collapse. Airway surfactant helps maintain smaller airway patency, improves muco-ciliary clearance, decreases bronchoconstriction, and modulates pulmonary immunity. Surfactant alterations in human asthma are therefore believed to contribute to the severity of airway obstruction. The goal of our first study was to characterize surfactant phospholipid composition and function in healthy horses, and to investigate the influence of age and bronchoalveolar lavage fluid (BALF) sample characteristics on surfactant. For that purpose, BALF was collected from 17 healthy horses and evaluated for BALF recovery percentage, cell count, and cell differential. BALF was separated into crude surfactant pellets (CSP) and supernatant and was analyzed for phospholipid content, protein content, phospholipid composition, and surface tension. Interestingly, phospholipid (surfactant) content in CSP significantly decreased with age. BALF recovery percentage, nucleated cell count, and cytological profile did not affect surfactant composition or function. The hypothesis of our second study was that surfactant alterations in RAO-affected horses are related to clinical stage of RAO. The objectives were 1) to compare surfactant phospholipid composition and function between Non-RAO and RAO horses at clinical stages and 2) to investigate relationships between surfactant alterations and variables assessing clinical stage of RAO. Seven horses with confirmed RAO and seven Non-RAO horses were evaluated in pairs (RAO/Non-RAO) at baseline, during exposure to hay, and post-exposure. Assessments included: clinical scoring, measure of maximal change in pleural pressure (ΔPplmax), airway endoscopy, and BALF cell counts and differentials. Samples were processed and analyzed as described above. Phospholipid levels in BALF were significantly lower in RAO versus Non-RAO horses, even in the absence of clinical signs. In the group of RAO horses, phospholipid content was significantly lower during exposure versus baseline. Furthermore, exposure to hay led to an increase in the protein versus phospholipid ratio in BALF from RAO horses. No significant differences were found in BALF protein content, phospholipid composition, or surface tension between or within groups of horses. Phosphatidylglycerol percentage had a tendency to be lower in RAO horses with higher clinical scores. Supernatant protein content was related to BALF neutrophilia in RAO crisis and overall ΔPplmax . In conclusion, our study demonstrated that surfactant alterations in RAO horses are present in remission and are exacerbated following exposure to hay. It is conceivable that a lower amount of surfactant in bronchioli of RAO horses may contribute to the horses' propensity to develop airway obstruction, mucous accumulation, and bronchial hyperresponsiveness. This may be exacerbated during crisis by a relatively higher protein versus phospholipid ratio. Furthermore, a progressive decrease of surfactant levels in older horses may contribute to a worsening of clinical signs in older RAO-affected horses. / Ph. D.

In healthy airways, mucus forms part of the innate immune response protecting the respiratory epithelium from damage by pathogens and environmental debris (Rose and Voynow, 2006). Conversely, in many respiratory diseases, mucus becomes part of the airway disease pathology. Mucus hypersecretion along with reduced clearance can cause blockage of the small airways, impairing gas exchange, promoting inflammation and becoming a culture medium for bacterial colonisation (Thornton et al., 2008). Recurrent airway obstruction (RAO) is a common yet poorly understood equine chronic respiratory disease where such altered mucus properties and clearance have been identified as major factors in the disease pathology (Davis and Rush, 2002; Gerber et al., 2000; Kaup et al., 1990; Robinson, 2001). The gel-forming mucins are largely responsible for the transport properties of mucus. The major equine airway gel-forming mucin in health is Muc5b and to a lesser extent Muc5ac; produced in specialised respiratory epithelial goblet cells and sub-mucosal glands (Rousseau et al., 2011b). Changes in mucin relative and net amounts and their macromolecular properties and interactions have been attributed to the altered physical properties of airway mucus in airways disease (Groneberg et al., 2002a; Jefcoat et al., 2001; Kirkham et al., 2002; Robinson et al., 2003; Sheehan et al., 1995).The project investigates the biochemical properties of mucins present in mucus from healthy horses and horses with RAO. This project identifies the anatomical presence of mucin-producing goblet cells and glands in fixed tissues from the respiratory tracts of healthy horses and subsequently examines mucin-production sites in respiratory tracts from horses with RAO. Finally the project investigates a methodology for the study of mucin production in airway cells harvested from live horses suffering from RAO.Our investigations confirmed that horses with RAO have more endotracheal mucus than healthy controls, and that Muc5b is the predominant mucin with Muc5ac also present in RAO horse mucus, both during symptomatic disease and when horses are asymptomatic. Mucins are produced in epithelial goblet cells and sub-mucosal glands dispersed throughout the length and circumference of the equine trachea and bronchi. Goblet cell hyperplasia occurs in symptomatic exposed RAO horse airways, although goblet cells are smaller than in asymptomatic RAO horse airways. Exposure to a dusty stable environment is associated with more goblet cells per length of bronchial compared to tracheal epithelium in all horses. RAO horses have larger sub-mucosal glands containing more mucin than control horses. Primary epithelial cell cultures grown at an air liquid interface are an alternative approach to study equine airway mucus, although the use of this culture system is in its early stages. We have developed novel ways to harvest equine airway epithelial cells (tracheal brushing) and shown it is possible to freeze cells collected via tracheal epithelial brushing in 20 % FBS and then culture to ALI at a later date.

Objective - evaluate horses with acute airway obstruction using three treatment regimens: tapering doses of dexamethasone (DEX), environmental modification (ENV), and a combination of both treatments (DEX + ENV) by analyzing clinical parameters, pulmonary function testing, bronchoalveolar lavage fluid (BALF) cytology and BALF cell expression of the cytokines IFN-? and IL-4 Animals - 6 horses with recurrent airway obstruction (RAO) Procedures - Clinical examination, pulmonary function test, and collection of BALF prior to treatment and during 22 day treatment period Hypothesis - Alterations in clinical parameters, pulmonary function and airway inflammation in acute equine RAO will return to remission values by treating with DEX, ENV or DEX + ENV Results - All horses demonstrated clinical disease, reduced pulmonary dynamic compliance (Cdyn) and an increased maximum change in pleural pressures (?Pplmax) when in a challenge environment. All treatments improved clinical parameters, ?Pplmax and Cdyn. BALF cytology during an RAO crisis demonstrated neutrophilic inflammation. ENV or DEX + ENV resulted in a significant decrease in airway neutrophilia that was maintained throughout the treatment period. In contrast, treatment with DEX caused a reduction in airway neutrophilia initially followed by a rebound neutrophilia as the period between administrations of dexamethasone (0.05mg/kg) was increased to 72 hours. The rebound neutrophilia was not accompanied by equivalent deterioration in clinical parameters or pulmonary function. Conclusions - Environmental modification is important in the management of RAO horses. Treatment of clinical RAO with a decreasing dosage protocol of corticosteroids in the absence of environmental modification results in the persistence of airway inflammation without recrudescence of clinical disease. / Master of Science