Circulatory CCL2 distinguishes Duchenne muscular dystrophy dogs

To establish a minimally invasive approach to studying body-wide muscle inflammation in the canine Duchenne muscular dystrophy (DMD) model, we evaluated 13 cytokines/chemokines in frozen sera from 90 affected (239 sera) and 73 normal (189 sera) dogs (0.00 to 45.2 months of age). Linear mixed-effects model analysis suggested that ten cytokines/chemokines were significantly elevated in affected dogs, including interleukin (IL)-2, IL-6, IL-7, IL-8, IL-10, IL-15, IL-18, C-C motif chemokine ligand 2 (CCL2), C-X-C motif chemokine ligand 1 (CXCL1) and granulocyte-macrophage colony-stimulating factor (GM-CSF). Further, cytokine/chemokine elevation coincided with the onset of muscle disease. Importantly, only CCL2 showed consistent changes at all ages, with the most pronounced increase occurring between 3 and 9 months. To study the effects of sample storage and type, we compared fresh versus frozen, and serum versus plasma, samples from the same dog. Similar readings were often obtained in fresh and frozen sera. Although plasma readings were significantly lower for many cytokines/chemokines, this did not compromise the robustness of CCL2 as a biomarker. Our study establishes a baseline for using circulatory cytokines/chemokines as biomarkers in canine DMD studies.