Tracheal Wash Metabolome in Horses with Recurrent Airways Obstruction (RAO)

Metabolomics consists of the analysis of all metabolites that are present within an organism that provide unique insights into metabolic changes associated with disease [1]. Because of the high diagnostic potential of metabolomic studies, already established in humans with respiratory disease [2], we aimed to investigate the metabolomic profile of tracheal wash (TW) in horses affected by recurrent airway obstruction (RAO). Six horses with known history of RAO (1 male, 2 geldings, 3 females), median age 18 years, BCS 2.5-3.0, represented the study group (Group S). Six healthy horses with no history of RAO (1 male, 3 geldings, 2 females), median age 13 years, BCS 3.0, represented the control group (Group C). Tracheal wash was performed as described by others [3]; 5ml aliquot of TW, collected into sterile tubes with no anticoagulant, was used for cytological evaluation immediately after collection, another 1.5ml aliquot was stored at -80°C for metabolomic analysis. Endoscopic assessment of tracheal mucus (Grade 2-3) and cytologic examination by differential count of TW smears (neutrophils>30%), confirmed the acute phase of RAO in Group S [3]. The Mann-Whitney test was applied to find significant differences in metabolites concentrations between groups. P values <0.05 were considered statistically significant. Metabolomic analysis, determined by 1H-NMR [4], showed a total of 38 molecules in TW samples and 13 out of 38 showed significant differences between groups. Mean values ± standard deviations of significant different metabolites between groups are expressed as mM/L x10-2: Histamine (Group S=2.7±0.8; Group C=1.5±0.2), Valine (Group S=1.8±1.2; Group C=0.6±0.3), Leucine (Group S=4.3±3.1; Group C=1.2±0.8), Isoleucine (Group S=2.5±1.6; Group C=0.9±0.2), Glutamate (Group S=6.3±2.1; Group C=2.6±1.1), Aspartate (Group S=10.8±3.8; Group C=7.7±2.7), Taurine (Group S=20.2±9.9; Group C=10.7±8.8), Alanine (Group S=3.8±2.2; Group C=1.6±1.0), Lactate (Group S=18.9±18.4; Group C=102.5±114.9), Methylamine (Group S=0.2±0.1; Group C=0.5±0.5), Dimethylamine (Group S=0.05±0.03; Group C=0.11±0.02), Propylene glycol (Group S=0.2±0.1; Group C=0.5±0.4), and O-phosphocholine (Group S=0.2±0.1; Group C=0.5±0.3). Changes in given metabolites might result from the inflammatory process as well as from the oxidative stress associated with lower airway disorders occurring in horses suffering from RAO [5]. On the basis of our results, metabolomic analysis of TW could represent a valuable diagnostic tool in horses with RAO.