Evidence-based respiratory medicine in horses

Immunomodulatory asthma therapy in the equine animal model: A dose-response study and evaluation of a long-term effect

INTRODUCTION

Equine asthma represents a naturally occurring animal model for human allergic neutrophilic asthma. Inhalative nanoparticle-bound cytosine-phosphate-guanosine (CpG-GNP) immunotherapy, independent of specific allergens, has already shown promising clinical and immunological results in previous studies and offers the possibility to treat the underlying cause of the disease. This study analyses the relationship between dose and response, and evaluates a possible long-term effect.

METHODS

In the prospective, randomised, double-blind clinical field study, 29 horses suffering from equine asthma received 10 inhalation treatments with either 187.5 µg CpG-GNP (CpG single dose [CpGsd]; n = 11), 375 µg CpG-GNP double dose (CpG double dose [CpGdd]; n = 9) (q48h for 20 days) or 1600 µg beclomethasone (n = 9) (q24h for 10 days). Each horse was examined three times: before the treatment (I), immediately after the 10 inhalations (II), and 8 weeks after the final inhalation (III). The three groups were compared according to clinical and laboratory parameters. The study examined the sustainability of the long-term effect of the treatment after 8 weeks, as well as the tolerability of the formula as a double dose.

RESULTS

The CpGsd resulted in a significant improvement in 82% of the parameters, the CpGdd in 72%. In the long-term evaluation, the CpGsd showed a significant improvement in 100% of the parameters in comparison to the initial values, the CpGdd in 67%. On the immunological level, the bronchoalveolar lavage revealed a significant reduction of IL-4, IL-8, and interferon-γ.

CONCLUSION

Both CpG groups displayed significant improvements in clinical and laboratory parameters, especially regarding the long-term effect of CpGsd. Doubling the CpG dose did not result in any improvement in comparison to the original single dose. On the immunological level, an anti-inflammatory, as well as an immunomodulatory effect, apart from a Th2-dominated immune response, could be observed. This immunomodulatory inhalation treatment could indicate a new possibility for human allergic asthma therapy.

Corticosteroids and Immune Suppressive Therapies in Horses

Immune suppressive therapies target exaggerated and deleterious responses of the immune system. Triggered by exogenous or endogenous factors, these improper responses can lead to immune or inflammatory manifestations, such as urticaria, equine asthma, or autoimmune and immune-mediated diseases. Glucocorticoids are the most commonly used immune suppressive drugs and the only ones supported by robust evidence of clinical efficacy in equine medicine. In some conditions, combining glucocorticoids with other pharmacologic and nonpharmacologic treatments, such as azathioprine, antihistamine, bronchodilators, environmental management, or desensitization, can help to decrease dosages and associated side effects.

Oxidant-antioxidant status in the blood of horses with symptomatic recurrent airway obstruction (RAO)

Background

Systemic oxidative stress in horses with recurrent airway obstruction (RAO) is poorly characterized.

Objectives

The goal of this study was to investigate whether equine RAO is associated with systemic disturbances in the oxidant‐antioxidant equilibrium.

Animals

Seven healthy horses and 7 horses with symptomatic RAO.

Methods

A prospective study. Healthy and RAO‐affected horses were exposed to a 48‐hour challenge with moldy hay and straw to induce clinical exacerbation of RAO. Venous blood was collected and the activities of the superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), and glutathione reductase (GR) in equine erythrocyte lysates were measured. The concentration of thiobarbituric acid‐reactive substances (TBARSs) was assessed both in erythrocyte lysates and in plasma.

Results

A significant increase in the activities of GPx and SOD was detected in RAO‐affected horses compared with the control animals. There was no significant difference between groups in terms of the erythrocyte lysate activities of CAT, GR, or TBARs or the plasma concentration of TBARs.

Conclusion and Clinical Importance

Our results support the hypothesis that RAO in horses is associated with systemic oxidative stress. Future studies are needed to assess whether horses suffering from RAO can benefit from antioxidant supplementation.

Neutrophil and macrophage apoptosis in bronchoalveolar lavage fluid from healthy horses and horses with recurrent airway obstruction (RAO)

BACKGROUND

Dysregulation of apoptosis has been implicated in a range of diseases including tumors, neurodegenerative and autoimmune diseases, as well as allergic asthma and chronic obstructive pulmonary disease (COPD) in humans. Although it has a different pathophysiology, delayed apoptosis of various inflammatory cells may play a pivotal role in the development of recurrent airway obstruction (RAO) in horses. Reduction of inflammatory cell apoptosis or a dysregulation of this process could lead to chronic inflammation and tissue injury. Therefore, the aim of this study was to investigate the rate of apoptosis and necrosis of neutrophils and macrophages in bronchoalveolar lavage fluid obtained from seven horses suffering from RAO (study group) and seven control horses.

RESULTS

We demonstrated that neutrophil/macrophage apoptosis is altered in RAO-affected horses compared with the control group in the BAL fluid. We found a significant difference between the median percentage of early and late apoptosis of neutrophils between the study and control group of horses. Moreover, we found a positive correlation between the rate of apoptosis and the median percentage of macrophages in RAO-affected horses.

CONCLUSION

The findings suggest that apoptosis dysregulation may play a significant role in the pathogenesis of RAO. However, further studies are needed to clarify the role of altered apoptosis in the course of equine recurrent airway obstruction.

Anesthesia of the geriatric equine

Advancements in veterinary medicine have resulted in an increased number of geriatric horses being presented for medical or surgical procedures that require general anesthesia. Due to the physiological changes associated with aging and the likelihood of concurrent disease conditions, the geriatric equine is at an increased risk during anesthesia. The main physiological changes associated with aging, and their impact on anesthesia, are discussed in this review.

Corticosteroids and antigen avoidance decrease airway smooth muscle mass in an equine asthma model

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.

Heaves, an asthma-like disease of horses

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.