Inflammatory Pattern of the Infrapatellar Fat Pad in Dogs with Canine Cruciate Ligament Disease

Introduction:
The infrapatellar fat pad (IFP), an intracapsular and extrasynovial adipose tissue, has become increasingly recognized as an active endocrine organ that may initiate and progress osteoarthritis. The objective of this study was to identify the canine IFP as a potential source of inflammation in CCL disease of dogs.

Material and Methods:
IFP, tight subcutaneous adipose tissue (ScAT) and synovial fluid were obtained from 36 dogs suffering from CCL disease and 23 healthy dogs. Specimens were harvested during arthroscopy and subsequently analyzed for selected inflammatory factors on the level of gene expression, protein release and cell phenotype using qRT PCR, ELISA and flow cytometry techniques, respectively.

Results:
Compared to the ScAT or healthy tissues, the IFP from dogs with CCL rupture showed an inflammatory pattern characterized by increased T-cells and macrophages, higher amounts of interleukins (IL-1b, IL-6) and matrix metalloproteinases (MMP-1, MMP-13), concurrent with an increase in its gene expression. Secretion of adipokines was modulated in the IFP of diseased dogs. While adiponectin secretion was 2-fold higher in the IFP, leptin secretion was decreased by more than 90% of that observed in the corresponding ScAT and also more than 80% of that observed in the IFP of control dogs.

Discussion/Conclusion:
In conclusion, the present study showed that a higher secretory activity and cell activation discriminated IFP from ScAT in canine CCL disease. The IFP of CCL diseased dogs may drive and control local pathological processes.