Serum and bronchoalveolar lavage fluid concentration of osteopontin and fibronectin in West Highland white terriers either affected with canine idiopathic pulmonary fibrosis or healthy and other terriers non predisposed to the disease.

Overexpression of osteopontin (SPP1) and fibronectin (FN1), two molecules associated with pulmonary fibrosis in humans and mice, was recently identified in pro-fibrotic bronchoalveolar lavage fluid (BALF) macrophage populations in West Highland white terriers (WHWTs) affected with canine idiopathic pulmonary fibrosis (CIPF) compared to healthy WHWTs. The aims of the present study were to confirm the overexpression of SPP1 and FN1 genes at the protein level and to assess the potential utility of those proteins as serum and BALF biomarkers of CIPF severity.

Serum and BALF concentrations of SPP1 and FN1 were measured using commercially available canine ELISA kits in CIPF WHWTs at diagnosis (n=24), healthy aged-matched WHWTs (n=13) and healthy terriers from other breeds (n=15). Values obtained were compared between groups using Kruskal-Wallis test. Correlations between SPP1 and FN1 concentrations and markers of disease severity (arterial partial pressure in oxygen (PaO2) and 6-minute walked distance (6MWD)) were performed using Spearman test.

SPP1 serum concentrations were higher in CIPF WHWTs (median [interquartile range]: 2.15 ng/mL [0.87-5.13]) compared with healthy WHWTs (0.63 ng/mL [0.41-1.63]; P=0.013) and healthy terriers (0.31 ng/mL [0.19-0.51]; P<0.0001), and higher in healthy WHWTs compared with healthy terriers (P=0.002). Higher SPP1 BALF concentrations were found in CIPF (0.34 ng/mL [0.15-0.52]) and healthy WHWTs (0.25 ng/mL [0.14-0.40]) compared with heathy terriers (0.02 ng/mL [0.01-0.08]; P<0.0001 and P=0.002, respectively), while no difference was shown between CIPF and healthy WHWTs (P=0.962). SPP1 serum concentrations negatively correlated with PaO2 (r=-0.502; P=0.007), but not with 6MWD. FN1 serum concentrations were lower in WHWTs either affected with CIPF or healthy (0.81 ng/mL [0.36-1.47] and 0.61 ng/mL [0.24-0.65]) compared with healthy terriers (2.72 ng/mL [2.15-5.21]; P<0.0001 and P=0.001, respectively). No difference was found between groups in BALF FN1 concentrations (P=0.077). No correlation was identified between serum and BALF FN1 concentrations and parameters of CIPF severity.

Results of the present study did not confirm the FN1 overexpression found in BALF pro-fibrotic macrophages neither in serum nor in BALF. Serum and BALF FN1 concentrations were not associated with CIPF severity parameters. SPP1 gene overexpression was confirmed at the protein level in serum but not in BALF in CIPF compared with healthy WHWTs. Moreover, SPP1 serum concentration could serve as a biomarker of disease severity as it correlates with PaO2. Finally, the higher serum and BALF SPP1 concentrations found in the WHWT breed compared to other terriers could be linked to their predisposition to CIPF.