Expression microarray as a tool to identify candidate blood biomarkers in horses suffering from inflammatory airway disease

Background: Inflammatory airway disease (IAD) affects performance and well-being in horses. Diagnosis is primarily reached by bronchoalveolar lavage (BAL) cytology but this is invasive and requires sedation.
Objectives: The purpose of this study was to identify candidate blood biomarkers of IAD using species-specific expression microarrays.
Methods: Horse Gene Expression Microarrays were used to investigate global mRNA expression in circulating leukocytes from healthy and IAD-affected standardbreds and endurance horses.
Results: Nine genes were significantly differentially regulated in standardbreds and 61 in endurance horses (P < 0.001). These genes were mainly related to inflammation (eg. ALOX15B, PLA2G12B and PENK), oxidant/antioxidant balance (eg. DUOXA2 and GSTO1-1) and stress (eg. V1aR, GRLF1, Homer-2 and MAOB). DUOXA2, ALOX15B, PLA2G12B, MAOB and GRLF1 variations of expression were further validated by RT-qPCR. The deregulation of the oxidant/antioxidant balance was demonstrated at the protein level by an increase of glutathione peroxidase (GPx) activity in heparinised whole blood of IAD-affected standardbreds (P = 0.0025) and endurance horses (P = 0.0028). There was good correlation (r = 0.7354) between BAL neutrophil percentage and whole blood GPx activity in all horses.
Conclusions: There is accumulating evidence that, even when systemic clinical signs are not evident, circulating leukocyte gene expression can reflect responses of other tissues, leading to potential diagnostic applications in the future. Although not specific for IAD, whole blood GPx activity appears to reflect BAL neutrophil percentage. This finding should be further assessed by testing a larger number of horses.