Animal models have been developed to investigate specific components of asthmatic airway inflammation, hyper-responsiveness or remodelling. However, all of these aspects are rarely observed in the same animal. Heaves is a naturally occurring disease of horses that combines these features. It is characterized by stable dust-induced inflammation, bronchospasm and remodelling. The evaluation of horses during well-controlled natural antigen exposure and avoidance in experimental settings allows the study of disease mechanisms in the asymptomatic and symptomatic stages, an approach rarely feasible in humans. Also, the disease can be followed over several years to observe the cumulative effect of repeated episodes of clinical exacerbation or to evaluate long-term treatment, contrasting most murine asthma models. This model has shown complex gene and environment interactions, the involvement of both innate and adaptive responses to inflammation, and the contribution of bronchospasm and tissue remodelling to airway obstruction, all occurring in a natural setting. Similarities with the human asthmatic airways are well described and the model is currently being used to evaluate airway remodelling and its reversibility in ways that are not possible in people for ethical reasons. Tools including antibodies, recombinant proteins or gene arrays, as well as methods for sampling tissues and assessing lung function in the horse are constantly evolving to facilitate the study of this animal model. Research perspectives that can be relevant to asthma include the role of neutrophils in airway inflammation and their response to corticosteroids, systemic response to pulmonary inflammation, and maintaining athletic capacities with early intervention.
Recent studies suggest that airway smooth muscle remodeling is an early event in the course of asthma. Little is known of the effects of long-term antigen avoidance and inhaled corticosteroids on chronically established airway remodeling. We sought to measure the effects of inhaled corticosteroids and antigen avoidance on airway remodeling in the peripheral airways of horses with heaves, a naturally occurring asthma-like disease. Heaves-affected adult horses with ongoing airway inflammation and bronchoconstriction were treated with fluticasone propionate (with and without concurrent antigen avoidance) (n = 6) or with antigen avoidance alone (n = 5). Lung function and bronchoalveolar lavage were performed at multiple time points, and peripheral lung biopsies were collected before and after 6 and 12 months of treatment. Lung function improved more quickly with inhaled corticosteroids, but eventually normalized in both groups. Inflammation was better controlled with antigen avoidance. During the study period, corrected smooth muscle mass decreased from 12.1 ± 2.8 × 10(-3) and 11.3 ± 1.2 × 10(-3) to 8.3 ± 1.4 × 10(-3) and 7.9 ± 1.0 × 10(-3) in the antigen avoidance and fluticasone groups, respectively (P = 0.03). At 6 months, smooth muscle mass was significantly smaller compared with baseline only in the fluticasone-treated animals. The subepithelial collagen area was lower at 12 months than at baseline in both groups. During the study period, airway smooth muscle remodeling decreased by approximately 30% in both groups, although the decrease was faster in horses receiving inhaled corticosteroids. Inhaled corticosteroids may accelerate the reversal of smooth muscle remodeling, even if airway inflammation is better controlled with antigen avoidance.
Recent studies suggest that airway smooth muscle remodeling is an early event in asthma, but whether it remains a dynamic process late in the course of the disease is unknown. Moreover, little is known about the effects of an antigenic exposure on chronically established smooth muscle remodeling. We measured the effects of antigenic exposure on airway smooth muscle in the central and peripheral airways of horses with heaves, a naturally occurring airway disease that shares similarities with chronic asthma. Heaves-affected horses (n = 6) and age-matched control horses (n = 5) were kept on pasture before being exposed to indoor antigens for 30 days to induce airway inflammation and bronchoconstriction. Peripheral lung and endobronchial biopsies were collected before and after antigenic exposure by thoracoscopy and bronchoscopy, respectively. Immunohistochemistry and enzymatic labeling were used for morphometric analyses of airway smooth muscle mass and proliferative and apoptotic myocytes. In the peripheral airways, heaves-affected horses had twice as much smooth muscle as control horses. Remodeling was associated with smooth muscle hyperplasia and in situ proliferation, without reduced apoptosis. Further antigenic exposure had no effect on the morphometric data. In central airways, proliferating myocytes were increased compared with control horses only after antigenic exposure. Peripheral airway smooth muscle mass is stable in chronically affected animals subjected to antigenic exposure. This increased mass is maintained in a dynamic equilibrium by an elevated cellular turnover, suggesting that targeting smooth muscle proliferation could be effective at decreasing chronic remodeling.
Background: Systemic inflammation in horses with heaves is poorly characterized. Objectives: To assess acute phase proteins (APP) and inflammatory cytokine profiles in serum of healthy horses and horses with heaves.Animals: Six healthy horses and 6 heaves-affected horses belonging to the University of Montreal. Methods: Prospective, observational study. Healthy and heaves-affected control horses were exposed to a 30-day natural challenge with hay and straw to induce clinical exacerbation of heaves. Serum samples were obtained by venipuncture before (T0) as well as after 7 (T7) and 30 days (T30) of stabling. Serum APP (haptoglobin, serum amyloid A protein [SAA] and C-reactive protein [CRP]) and cytokines (IL-2, IL-4, IFN-a, IL-10, IFN-c, and CCL-2) were measured using singleplex or multiplex ELISA.Results: Serum haptoglobin concentrations were significantly higher in heaves-affected horses at all time points with no overlap with those of healthy controls. They were also significantly increased by antigen challenge in both controls (T7) and horses with heaves (T7 and T30). Serum SAA was detected more frequently in heaves-affected horses compared with healthy controls at T7. There was no difference in serum concentrations of CRP, IL-10, IFN-c, and CCL-2 between groups, whereas IL-2, IL-4, and IFN-a remained undetectable in all samples.Conclusions and Clinical Importance: In heaves, haptoglobin is a marker of both acute and chronic systemic inflammation, whereas high concentrations of SAA indicate acute inflammation.
Background: Thrombelastography (TEG) is used to evaluate the viscoelastic properties of blood during clotting and provides a global assessment of hemostasis and clot lysis. TEG analysis initiated with recombinant human tissue factor (TF) has not been evaluated in clinically healthy horses. Objectives: The purpose of this study was to determine whether TEG results are affected by the time elapsed between sampling and analysis (storage time) of equine blood samples and to establish a preliminary equine reference interval for a modified TEG assay, using recombinant human TF to initiate coagulation. Methods: Citrated blood samples were obtained from 20 clinically healthy adult horses. Thirteen samples were stored for 30, 60, and 120 minutes at room temperature before TEG analysis. Coagulation was initiated by adding 20 mL of CaCl 2 to 330 mL of blood and 10 mL of diluted recombinant TF for a final dilution of 1:3600. Reaction (R) and clotting (K) times, angle (a), and maximum amplitude (MA) were compared between time points. A preliminary reference interval (minimum-maximum values) was determined using data from all 20 horses after 30 minutes of sample storage. Results: There was a significant effect of storage time on R, K, and a but not MA. Reference intervals were: R, 3.65-6.4 minutes; K, 1.8-5.45 minutes; a, 33.4-66.21; MA, 41.2-64.1 mm; lysis at 30 minutes post-MA (LY30), o 2.75%; and lysis at 60 minutes post-MA (LY60), 1.55-9.5%. Conclusions: TEG can be performed on equine citrated blood samples using recombinant human TF to activate clot formation. TEG parameters were significantly affected by storage time, suggesting an incomplete inhibition of coagulation in citrated blood.While conventional coagulation tests evaluate the soluble or plasmatic components of coagulation, in vivo coagulation is the sum of complex interactions among coagulation factors, platelets, endothelial cells, erythrocytes, and even leukocytes.1,2 Thrombelastography (TEG) assesses the mechanical properties of the blood clot during its formation and subsequent lysis. [3][4][5] In human medicine, TEG is used to detect clinically significant coagulation disorders in patients perioperatively and in intensive care.6 TEG is commonly performed on native fresh whole blood within 5 minutes of collection.7 This constraint limits its use in clinical pathology laboratories and in many veterinary hospital facilities. More recently, the use of citrated whole blood has extended the time that may lapse between blood collection and initiation of coagulation. 7,8 TEG has been validated and used to predict the risk of bleeding and assess hypercoagulability in dogs [9][10][11][12] and has been used to monitor heparin therapy in cats.13 TEG also was used to evaluate a horse with a platelet dysfunction.14 Horses, like other species, can have congenital and acquired coagulation disorders 15 and TEG could be useful in the rapid diagnosis of coagulopathies associated with gastrointestinal disorders or neonatal sepsis. 16,17 The objectives of this study were to as...
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