Evaluation of leukotriene biosynthetic capacity in lung tissues from horses with recurrent airway obstruction

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.

Airway collagen and elastic fiber content correlates with lung function in equine heaves

The consequences on lung function and inflammation of alterations in the extracellular matrix affecting the peripheral airway wall in asthma are largely unknown. We hypothesized that remodeling of collagen and elastic fibers in the peripheral airway wall leads to airway obstruction and contributes to neutrophilic airway inflammation. Animals used were six heaves-affected horses and five controls. Large peripheral lung biopsies were obtained from horses with heaves in clinical remission (Baseline) and during disease exacerbation and from age-matched controls. The area of collagen and elastic fiber content in the lamina propria was measured by histological staining techniques and corrected for airway size. Collagen type 1 and type 3 content was further assessed from additional horses after postmortem lung samples by immunohistochemistry. The collagen breakdown products proline-glycine-proline (PGP) and N-acetylated-PGP (N-α-PGP) were also measured in bronchoalveolar lavage fluids (BALF) by mass spectrometry. Compared with controls, heaves-affected horses had an increase in collagen (P = 0.05) and elastic fiber contents (P = 0.04) at baseline. Collagen types 1 and 3 content was also significantly increased in diseased horses (P = 0.015) when both collagen types were combined. No further change in collagen content was observed after a 30-day antigenic challenge. Airway collagen at baseline was positively correlated with pulmonary resistance in asthmatic horses (r(2) = 0.78, P = 0.03) and elastic fiber content was positively associated with pulmonary elastance in controls (r(2) = 0.95, P = 0.02). No difference between groups was appreciated in PGP and N-α-PGP peptides in BALF. Increased airway wall collagen and elastic fiber content may contribute to residual obstruction in the asthmatic airways.

PI3K and MAPKs regulate neutrophil migration toward the airways in heaves

BACKGROUND

Neutrophils accumulate in the airways of horses with heaves. They likely play an important role in the disease pathogenesis. Understanding the pathways regulating their migration may help identifying new therapeutic targets.

HYPOTHESIS

MAPK and PI3K pathways are involved in neutrophil migration toward the airway lumen in heaves.

ANIMALS

Twelve heaves-affected horses and 4 healthy horses.

METHODS

Migratory activity of bronchoalveolar lavage fluids (BALF) from horses with heaves and healthy horses was compared by means of a Boyden chamber. Involvement of MAPK and PI3K pathways in neutrophil migration was investigated by pretreating neutrophils with inhibitors of p38 MAPK, JNK, MEK1/2, and PI3K. The capacity of a p38 MAPK inhibitor at decreasing neutrophil chemotaxis toward the airways was also evaluated in vivo.

RESULTS

BALF from symptomatic heaves-affected horses induced a greater degree of chemokinesis (P = .0004) than BALF from healthy horses. Although all pathways tested were involved in neutrophil migration, inhibition of PI3K was most potent in vitro. An inhibitor of p38 MAPK administered before challenge in horses with heaves did not alter BALF chemokinetic properties. BALF neutrophil percentage and BALF migratory activity were positively correlated after 14 and 35 days of antigen challenge in healthy (P = .05; R(2) = 0.82) and heaves-affected horses (P = .03; R(2) = 0.76), respectively.

CONCLUSIONS AND CLINICAL IMPORTANCE

MAPK and PI3K pathways regulate neutrophil migration induced by BALF of horses with heaves. Inhibition of multiple pathways might be required to completely abolish BALF-induced neutrophil migratory activity and possibly inflammation in heaves.

Increased mucus accumulation in horses chronically affected with recurrent airway obstruction is not associated with up-regulation of CLCA1, EGFR, MUC5AC, Bcl-2, IL-13 and INF-gamma expression

The mechanisms leading to mucus accumulation in equine inflammatory airway disease (IAD) and recurrent airway obstruction (RAO) are unclear. In airways of human patients with asthma and/or chronic obstructive pulmonary disease as well as in animal models of these diseases, associations of mucus hyperproduction with increased calcium-activated chloride channel 1 (CLCA1), epidermal growth factor receptor (EGFR), mucin 5AC (MUC5AC), B-cell lymphoma 2 (Bcl-2), interleukin (IL)-13 and interferon (IFN)-gamma expression have been reported. We hypothesized that increased mucus accumulation in RAO and IAD are associated with alterations in inflammatory cytokine (IL-13 and IFN-gamma) and epithelial gene (CLCA1, EGFR, Bcl-2 and MUC5AC) profiles. Therefore, mRNA expression of these genes in cell pellets extracted from bronchoalveolar lavage fluid (BALF) and bronchial epithelial brushing (BEB) was compared between 11 clinically healthy (Control group), 7 IAD- and 12 RAO-affected horses by reverse transcription polymerase chain reaction. We also performed arterial blood gas analysis, endoscopic scoring of mucus accumulation in the trachea and cytology of tracheo-bronchial secretions (TBS) and of BALF. Tracheal mucus accumulation, along with TBS and BALF neutrophils were significantly increased and arterial pO(2) was decreased in RAO-affected horses compared to the Control group. IL-13 in BALF samples was significantly lower in the RAO group. None of the other genes' relative mRNA levels displayed significant differences between groups. Our findings suggest that mucus production in equine RAO is induced by pathways independent of IL-13, CLCA1, EGFR, MUC5AC and Bcl-2 up-regulation.

Optimization of assay conditions for leukotriene B4 synthesis by neutrophils or platelets isolated from peripheral blood of monogastric animals

Neutrophils are involved in inflammation through leukotriene (LT) production. The predominant proinflammatory leukotriene released from neutrophils is LTB4, which serves as a biological marker of inflammation. The purpose of this study was to optimize the conditions ex vivo for LTB4 production by neutrophils from horses and dogs, and platelets from chickens. Optimal production of LTB4 was characterized by incubation time (2.5, 5, 10, 15 or 20 min), temperature (25 or 37 degrees C), and calcium ionophore A23187 concentration (0.1, 1, 10 or 20 microM). Incubation longer than 2.5 min did not increase production of LTB4 in chickens or horses; in dogs, incubation for 2.5 and 10 min resulted in the highest concentrations of LTB4 (P<or=0.05). In all species, incubation at 37 degrees C resulted in optimal LTB4 production (P<or=0.05). Production of LTB4 was highest when neutrophils or platelets were stimulated with 20 microM calcium ionophore in all species (P<or=0.05). These results indicate that neutrophils isolated from horses and dogs, and platelets isolated from chickens, are capable of producing LTB4. Optimum conditions for LTB4 production are similar in all three species.