Investigation of serum circulating cell free nucleosomes as biomarker of canine idiopathic pulmonary fibrosis in West Highland white terriers

Canine idiopathic pulmonary fibrosis (CIPF) occurs in aged West Highland white terriers (WHWTs). The disease is characterized by profound fibrotic lung distortion leading to progressive respiratory impairment. Cell-free nucleosomes (cf-nucleosomes), which contain DNA and histones, contribute to gene expression regulation and are released into the circulation from any damaged cells. Accordingly, cf-nucleosomes have been shown increased in dogs with sepsis, cancer, immune-mediated haemolytic anaemia and trauma with both diagnostic and prognostic values. In human idiopathic pulmonary fibrosis (IPF), a disease similar to CIPF, a combination of circulating cf-nucleosomes with specific epigenetic features has been identified with a good diagnostic accuracy to discriminate IPF patients from healthy subjects.
In this study, we aimed to determine whether the amount of cf-nucleosomes in blood can be used as a non-invasive diagnostic biomarker for CIPF in WHWTs. Serum cf-nucleosomes were measured in 12 WHWTs affected with CIPF and compared with 10 healthy age-matched WHWTs, 9 healthy age-matched dogs from other breeds and 9 dogs affected with community acquired bacterial pneumonia (CAP). ELISA kits (NuQ®) validated for dogs were used to measure cf-nucleosomes concentrations. Kruskal Wallis test with pairwise post-hoc Conover-Iman tests and Bonferroni correction for multiple comparisons were used to compare cf-nucleosomes concentrations between groups.
Cf-nucleosomes concentration was significantly increased in dogs affected with CAP (22.06ng/mL (12.79-30.56)) in comparison with WHWTs affected with CIPF (1.53ng/mL (0.94-3.33); P<0.0001) and healthy WHWTs (3.12ng/mL (2.42-6.16); P=0.002). Cf-nucleosomes concentration was also higher in dogs affected with CAP in comparison with healthy dogs from other breeds although it was not significant because of 2 outliers (4.88ng/mL (2.98-10.41); P=0.019). There was no difference between WHWTs affected with CIPF and healthy dogs of the same breed (P=0.087) or different breeds (P=0.012).
Results of this study did not support the use of circulating cf-nucleosomes for the non-invasive diagnosis of CIPF in WHWTs. However, increased circulating cf-nucleosomes concentration was found in dogs affected with CAP, probably because of a higher rate of cell injury induced by the acute inflammation that occurs in such disease. Whether measurement of circulating cf-nucleosome can help discriminate CAP from other acute respiratory diseases and serve as monitoring tool for medical therapy requires further studies.