The role of oxidative stress in an equine model of human asthma

Validation of a commercially available photometric analytical system for assessment of plasma oxidative status in healthy horses

Reactive oxygen species (ROS) are the end-products of physiologic functions in health. Oxidative stress occurs when endogenous antioxidants are insufficient to neutralize ROS in the system. As a result, ROS can damage DNA, RNA, proteins, lipids, and cell organelles. To obtain accurate measurements of plasma oxidative stress, levels of both oxidants and antioxidants must be measured. This study validates a commercially available, semi-quantitative, photometric analytical system that measures systemic determinants of reactive oxygen metabolites (dROM) and plasma antioxidant capacity (PAC) in stored equine plasma. The objectives of this work were: 1) to validate a photometric analytical system to quantify dROM and PAC in equine plasma; and 2) to determine expected results for these tests in healthy adult horses. We hypothesized that this system would reliably and reproducibly assess dROM and PAC in equine plasma. We observed expected, dose-dependent increases in dROM generated by adding increasing concentrations of H2O2 or ascorbic acid to equine plasma to provide samples containing a known quantity of oxidants or antioxidants respectively. Mean dROM value in healthy horses was 103.3 ±20.7 U. Carr and mean PAC was 2881.0 ± 313.9 U. Cor. This system reliably and reproducibly quantified dROM and PAC in equine plasma samples.

Influence of Dietary Selenium on the Oxidative Stress in Horses

The objective of this review was to analyze the effect of dietary selenium on oxidative stress in horses by considering past and recent bibliographic sources. Some research was done on oxidative stress, related pathologies and how selenium regulates oxidative stress. Oxidizing molecules are molecules that can accept electrons from the substances with which they react. Oxidizing These molecules, of oxidizing, are found naturally in any organism, and there are antioxidant mechanisms that regulate its activity. However, when the body is stressed, oxidizing molecules outperform the antioxidants, causing an imbalance known as oxidative stress. Among antioxidant molecules, selenium can act as an important antioxidant in the body. The antioxidant activity is based on an enzyme called glutathione peroxidase, which depends on selenium and controls the activity of oxidizing molecules.

Effect of the Administration of a Nutraceutical Supplement in Racehorses with Lower Airway Inflammation

Mild−moderate equine asthma (MEA) is a chronic inflammatory disorder of the lower airways of the horse, characterized by tracheal mucus accumulation, cough and poor performance. The therapeutic approach is based on pharmacological treatment and environmental management. Moreover, the efficacy of the administration of antioxidant molecules has been reported. The aim of the present study was to evaluate the effect of the administration of a commercial nutraceutical supplement, composed of several herbal extracts, on lower airway inflammation in racehorses. Twelve Thoroughbreds affected by MEA were selected. All horses underwent a clinical examination with assignment of a clinical score, airway endoscopy and cytological examination of bronchoalveolar lavage fluid. In seven horses, the supplement was administered for 21 days in association with environmental changes, while in five horses only environmental changes were performed. All procedures were repeated at the end of the study. Data concerning the clinical score, the endoscopic scores and the cytology at the beginning and at the end of the study were statistically compared. Data showed a significant reduction (p < 0.0156) of the clinical score and a significant reduction (p < 0.0156) of the tracheal mucus score. The results showed the beneficial effect of the supplement on mild−moderate lower airway inflammation, probably due to its antioxidant activity.

Studies of molecular pathways associated with blood neutrophil corticosteroid insensitivity in equine asthma

Severe equine asthma is characterized by airway hyperresponsiveness, neutrophilic inflammation and structural alterations of the lower airways. In asthmatic horses with neutrophilic inflammation, there is insensitivity to corticosteroids characterized by the persistence of neutrophils within the airways with therapy. We hypothesized that hypoxia or oxidative stress in the microenvironment of the lung contributes to this insensitivity of neutrophils to corticosteroids in asthmatic horses. Blood neutrophils isolated from horses with severe asthma (N = 8) and from healthy controls (N = 8) were incubated under different cell culture conditions simulating hypoxia and oxidative stress and, in the presence, or absence of dexamethasone. The pro-inflammatory gene and protein expression of neutrophils were studied. In both groups, pyocyanin-induced oxidative stress increased the mRNA expression of IL-8, IL-1β, and TNF-α. While IL-1β and TNF-α were downregulated by dexamethasone under these conditions, IL-8 was not. Simulated hypoxic conditions did not enhance pro-inflammatory gene expression in neutrophils from either group of horses. In conclusion, oxidative stress but not hypoxia may contribute to corticosteroid insensitivity via a selective gene regulation pathway. Equine neutrophil responses were similar in both heathy and asthmatic horses, indicating that it is not specific to asthmatic inflammation.

Expression of xenobiotic metabolising enzymes in lungs of horses with or without histological evidence of lower airway inflammation

Mild, moderate and severe equine asthma is a problem for equine welfare. The aetiology of the disease is not known in detail but is likely multi‐factorial. One important factor may be inhaled dust which carries harmful substances which may be bioactivated and thus can lead to local inflammation in the airways. The aim of this study was to investigate gene expression and protein localisation of cytochrome P450 (CYP) enzymes, superoxide dismutase and glutathione‐S‐transferases (GST) involved in bioactivation and detoxification of harmful substances in lungs of horses with or without histological evidence of lower airway inflammation. Significantly lower gene expression of CYP2A13 and GSTM1 was observed in lungs from horses with histological evidence of lower airway inflammation compared with horses without. A higher expression, although not significant, was found for CYP1A1 in horses with histological evidence of lower airway inflammation. There were no differences in gene expression of GSTP1 and SOD3. The proteins were localised in the respiratory epithelium which is of relevance as a defence to local exposure of inhaled harmful substances. In conclusion, our study reports differential gene expression of enzymes involved in bioactivation and detoxification of foreign substances in the lungs of horses with histological evidence of lower airway inflammation compared with horses without.

Effects of a propriety oiled mixed hay feeding system on lung function, neutrophilic airway inflammation and oxidative stress in severe asthmatic horses

BACKGROUND

Hay feeding is considered the main triggering factor for airway obstruction and inflammation in severe equine asthma (SEA). Finding alternate strategies allowing hay feeding while controlling clinical signs of SEA is of importance. The Nutri-Foin Système is believed to decrease inhaled dust by incorporating soybean oil to mechanically processed hay.

OBJECTIVES

We compared airflow obstruction and airway inflammation in horses with SEA fed oiled hay or alfalfa pellet regimen.

STUDY DESIGN

Controlled trial in asthmatic research horses.

METHODS

Twelve horses in exacerbation of SEA from a research herd were studied. Horses were fed either oiled treated hay (n = 6) or alfalfa pelleted hay (n = 6) for 3 months while being stabled. Lung function, bronchoalveolar lavage fluid cytology and serum antioxidant enzyme kinetics were sequentially evaluated.

RESULTS

Pelleted hay and the hay treated with the Nutri-Foin Système similarly improved lung function, airway neutrophilia and serum antioxidant enzyme kinetics over time.

MAIN LIMITATIONS

The small number of horses in each group.

CONCLUSIONS

We conclude from this study that Nutri-Foin Système is an appropriate alternative to pelleted hay for the control of the airway obstruction in horses with SEA.

Metabolomics of tracheal wash samples and exhaled breath condensates in healthy horses and horses affected by equine asthma

The present work characterized the metabolomic profile of tracheal wash (TW) and exhaled breath condensate (EBC) in healthy horses and horses with respiratory disease. Six asthma-affected horses (group A) and six healthy controls (group H) underwent clinical, endoscopic and cytologic examinations of upper airways to confirm the active phase of asthma. TW and EBC samples were collected from each animal and investigated by proton nuclear magnetic resonance (¹H-NMR) metabolomic analysis. A total of ten out of 38 metabolites found in the TW were significantly different between the groups (p < 0.05). Higher concentrations of histamine and oxidant agents, such as glutamate, valine, leucine and isoleucine, as well as lower levels of ascorbate, methylamine, dimethylamine and O-phosphocholine, were found in group A compared to group H. Eight metabolites were found in equine EBC, namely methanol, ethanol, formate, trimethylamine, acetone, acetate, lactate and butanone, previously observed also in human EBC. Despite the fact that this was a pilot study, the results showed that the metabolomic analysis of TW and EBC has the potentiality to serve as a basis for diagnostic tools in horses with asthma.

The Contribution of Oxidative Stress and Inflamm-Aging in Human and Equine Asthma

Aging is associated with a dysregulation of the immune system, leading to a general pro-inflammatory state of the organism, a process that has been named inflamm-aging. Oxidative stress has an important role in aging and in the regulation of immune responses, probably playing a role in the development of age-related diseases. The respiratory system function physiologically declines with the advancement of age. In elderly asthmatic patients, this may contribute to disease expression. In this review, we will focus on age-related changes affecting the immune system and in respiratory structure and function that could contribute to asthma occurrence, and/or clinical presentation in the elderly. Also, naturally occurring equine asthma will be discussed as a possible model for studying the importance of oxidative stress and immun-aging/inflamm-aging in humans.

Pulmonary Remodeling in Equine Asthma: What Do We Know about Mediators of Inflammation in the Horse?

Equine inflammatory airway disease (IAD) and recurrent airway obstruction (RAO) represent a spectrum of chronic inflammatory disease of the airways in horses resembling human asthma in many aspects. Therefore, both are now described as severity grades of equine asthma. Increasing evidence in horses and humans suggests that local pulmonary inflammation is influenced by systemic inflammatory processes and the other way around. Inflammation, coagulation, and fibrinolysis as well as extracellular remodeling show close interactions. Cytology of bronchoalveolar lavage fluid and tracheal wash is commonly used to evaluate the severity of local inflammation in the lung. Other mediators of inflammation, like interleukins involved in the chemotaxis of neutrophils, have been studied. Chronic obstructive pneumopathies lead to remodeling of bronchial walls and lung parenchyma, ultimately causing fibrosis. Matrix metalloproteinases (MMPs) are discussed as the most important proteolytic enzymes during remodeling in human medicine and increasing evidence exists for the horse as well. A systemic involvement has been shown for severe equine asthma by increased acute phase proteins like serum amyloid A and haptoglobin in peripheral blood during exacerbation. Studies focusing on these and further possible inflammatory markers for chronic respiratory disease in the horse are discussed in this review of the literature.

Effect of inhaled hydrosoluble curcumin on inflammatory markers in broncho-alveolar lavage fluid of horses with LPS-induced lung neutrophilia

Background

Horses commonly suffer from chronic respiratory disease and are also used in large animal models of spontaneous or induced airway inflammation. The anti-inflammatory properties of curcumin are largely described but its low bioavailability precludes its clinical use. NDS27, a lysin salt of curcumin incorporated in beta-cyclodextrine, has high bioavailability and can be administered by inhalation. The aim of this study was to investigate the effects of inhaled NDS27 on inflammatory cytokines and proteins in the broncho-alveolar lavage fluid using a model of neutrophilic airway inflammation.

Methods

Airway neutrophilia was induced in eight horses by inhalation of lipopolysaccharides (LPS). Horses were treated with either inhalation of NDS27 or with placebo in a randomized cross-over design. Broncho-alveolar lavages were performed 6 hours after stimulation with LPS. Percentage of neutrophils, concentrations of IL-1β, TNF-α, IL-6, Club cell secretory protein, myeloperoxidase (MPO) and elastase (ELT) concentrations were determined.

Results

LPS stimulation induced significant increases in neutrophil counts and concentrations of IL-6 (70.2 ± 66.0 pg/ml), TNF-α (43.9 ± 31.2 pg/ml), MPO (580.9 ± 327.0 ng/ml) and ELT (27.6 ± 16.7 ng/ml). Treatment with NDS27 significantly prevented the increase in active and total MPO (216.4 ± 118.1 ng/ml) and ELT (5.9 ± 3.2 ng/ml) while there was a trend towards reduced IL-6 concentration.

Conclusions

Results show that, although not reducing neutrophil recruitment, NDS27 largely abolishes LPS-induced neutrophil degranulation. Reduced levels of ELT and MPO, as well as reduced MPO activity may have beneficial effects via a reduced production of reactive oxygen species implicated in chronic inflammation and airway remodeling.

A review of the equine age-related changes in the immune system: comparisons between human and equine aging, with focus on lung-specific immune-aging

The equine aging process involves many changes to the immune system that may be related to genetics, the level of nutrition, the environment and/or an underlying subclinical disease. Geriatric horses defined as horses above the age of 20, exhibit a decline in body condition, muscle tone and general well-being. It is not known whether these changes contribute to decreased immune function or are the result of declining immune function. Geriatric years are characterized by increased susceptibility to infections and a reduced antibody response to vaccination as a result of changes in the immune system. Humans and horses share many of these age-related changes, with only a few differences. Thus, inflamm-aging and immunosenescence are well-described phenomena in both human and equine research, particularly in relation to the peripheral blood and especially the T-cell compartment. However, the lung is faced with unique challenges because of its constant interaction with the external environment and thus may not share similarities to peripheral blood when considering age-related changes in immune function. Indeed, recent studies have shown discrepancies in cytokine mRNA and protein expression between the peripheral blood and bronchoalveolar lavage immune cells. These results provide important evidence that age-related immune changes or 'dys-functions' are organ-specific.

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.

Recurrent airway obstruction: a review

Recurrent airway obstruction is a widely recognised airway disorder, characterised by hypersensitivity-mediated neutrophilic airway inflammation and lower airway obstruction in a subpopulation of horses when exposed to suboptimal environments high in airborne organic dust. Over the past decade, numerous studies have further advanced our understanding of different aspects of the disease. These include clarification of the important inhaled airborne agents responsible for disease induction, improving our understanding of the underlying genetic basis of disease susceptibility and unveiling the fundamental immunological mechanisms leading to establishment of the classic disease phenotype. This review, as well as giving a clinical overview of recurrent airway obstruction, summarises much of the work in these areas that have culminated in a more thorough understanding of this debilitating disease.

Effect of potential therapeutic agents in reducing oxidative stress in pulmonary tissues of recurrent airway obstruction-affected and clinically healthy horses

REASONS FOR PERFORMING STUDY

To determine and compare the reactive oxygen and nitrogen species (ROS and RNS) in pulmonary tissues of horses affected with recurrent airway obstruction (RAO) and clinically healthy horses, and to evaluate the effectiveness of potential therapeutic agents in reducing ROS and RNS in the tissues of these horses.

OBJECTIVES

We hypothesised that RAO-affected horses would have high levels of reactive species and that the test agents would reduce them. The objectives were as follows: 1) to determine the level of ROS and RNS in pulmonary tissues (bronchial and arterial rings) of RAO-affected and clinically healthy horses; and 2) to determine the ability of pentoxifylline, pyrrolidine-dithiocarbamate and a combined use of endothelin A and B receptor antagonists (BQ123 and BQ788, respectively) in reducing reactive species.

METHODS

Arterial and bronchial rings were collected from the diaphragmatic lung lobe of each horse immediately after euthanasia. The levels of ROS and RNS were measured in control tissues and those incubated with test agents, using an electron paramagnetic resonance instrument.

RESULTS

The levels of ROS and RNS were significantly greater in arterial and bronchial tissues of RAO-affected than of clinically healthy horses. Pentoxifylline and endothelin antagonists reduced both ROS and RNS in tissues from RAO-affected horses. Basal levels of reactive species in clinically healthy horses were not affected by these agents. No difference in the level of reactive species was observed between arterial and bronchial tissues.

CONCLUSIONS

Horses affected by RAO had higher ROS and RNS than clinically healthy horses. Pentoxifylline and endothelin antagonists effectively reduced ROS and RNS in pulmonary tissues of RAO-affected horses.

POTENTIAL RELEVANCE

The study suggested a potential use for pentoxifylline and endothelin antagonists in treating RAO-affected horses. As endothelin is involved in physiological functions, therapeutic use of its antagonists is cautioned.

Harnessing opportunities in non-animal asthma research for a 21st-century science

The incidence of asthma is on the increase and calls for research are growing, yet asthma is a disease that scientists are still trying to come to grips with. Asthma research has relied heavily on animal use; however, in light of increasingly robust in vitro and computational models and the need to more fully incorporate the 'Three Rs' principles of Replacement, Reduction and Refinement, is it time to reassess the asthma research paradigm? Progress in non-animal research techniques is reaching a level where commitment and integration are necessary. Many scientists believe that progress in this field rests on linking disciplines to make research directly translatable from the bench to the clinic; a '21st-century' scientific approach to address age-old questions.

The oxidant/antioxidant equilibrium in horses

Since "free radical research" started in 1954, understanding the role of oxidants and antioxidants in physiological and pathological conditions has increased continuously. Oxidants are essentially generated by metabolic enzymes, inflammatory cells and mitochondrial electron leakage; they are indispensable for the cellular redox regulation and may, under certain conditions, have a pro-inflammatory stimulatory role. Endogenous and exogenous antioxidants counterbalance the oxidative processes and so maintain the oxidant/antioxidant equilibrium. Excessive oxidant generation or antioxidant insufficiency can lead to oxidative stress. The aims of this review are: (1) to provide an insight into the concept of the oxidant/antioxidant equilibrium by briefly introducing the oxidant and the antioxidant systems; (2) to describe how the oxidant/antioxidant equilibrium or oxidative stress can be evaluated in horses, and (3) to summarise current knowledge about oxidative stress in equine medicine and equine exercise physiology.

The relationship between polymorphisms in the glutamate cysteine ligase gene and asthma susceptibility

The present study was designed to investigate an association of common -588C/T and -23G/T polymorphisms within glutamate cysteine ligase modifier subunit gene with susceptibility to bronchial asthma. A total of 435 ethnically Russian subjects were recruited in this study, including 221 patients with asthma and 214 sex and age matched healthy subjects. As previously reported, the -588C/T and -23G/T polymorphisms were completely linked. The -588TT/-23TT genotype was found to be associated with decreased risk of allergic asthma after adjustment for age, gender and smoking status using multivariate logistic regression analysis (OR=0.33 95% CI 0.15-0.70, p=0.036). However, the -588CT/-23GT genotype was associated with increased risk of non-allergic asthma (OR=2.03 95% CI 1.05-3.90, p=0.06). This is a first study reporting the association between genetic variations in the glutamate cysteine ligase gene and susceptibility to bronchial asthma.

Oxidants and antioxidants in disease: oxidative stress in farm animals

Important infectious diseases in farm animals, such as pneumonia and enteritis, are thought to be associated with the so-called oxidative stress, i.e. a chemical phenomenon involving an imbalance in the redox status of the individual animal. The specifics of oxidative stress and how it may result in disease or be prevented are complex questions with no simple answers. However, the considerable literature on the subject suggests that many researchers consider oxidative stress-related mechanisms to be important early events in disease development. A particularly intriguing aspect is that, at least theoretically, oxidative stress should be easily prevented with antioxidants yet the use of antioxidants as therapy remains controversial. The present knowledge on oxidative stress in farm animals is the topic of this review.