Micro-CT Evaluation of Bone Changes in Osteoarthritic Sheep Treated With Gene Therapy via TIMP-3

Osteoarthritis is commonly recognized by the development of bone spurs, inflammation, and joint degradation. Current treatments for osteoarthritis (OA) commonly include arthroscopy, pain medications, and physical therapy. Gene therapy may offer a possible curative route. The current study included fifteen ewes surgically manipulated to induce OA divided into two treatment groups. Eight ewes underwent crucial cranial ligament desmotomy (CCLD) surgery, and seven ewes underwent an ovariectomy (removal of their ovaries), comparable to cutting of the anterior cruciate ligament (ACL) in humans. These treatments induced osteoarthritis in the ewes. Three ewes from each group received a gene therapy injection of a Tissue Inhibitor of Metalloproteinase-3 transgene viral vector (rAAV-TIMP-3) in the left stifle joint (knee). TIMP-3 was used for its potential to decrease aggrecan breakdown. Aggrecan is a crucial component of healthy cartilage and connective tissue. The breakdown of aggrecan serves as an indicator of the hallmark signs of OA development in joints. We hypothesize that up-regulation of TIMP-3 would slow detectable OA progression in trabecular bone by inhibiting the action of cartilage degrading enzymes and help restore remodeling balance to the joint After treatment, ewes were routinely exercised on a treadmill at an oblique angle to hasten the onset of OA. Initial findings using the TIMP-3 transgene gene therapy included decreased joint widening (painful joint growth), decreased stance time (less time limping), and decreased osteophytosis scores (bone spurs) in surgically destabilized sheep. Femoral and tibial width was increased at the end of the study in untreated control sheep, but not in TIMP-3-treated sheep. The stifles were analyzed at Utah State University using a Nikon XT H 225 ST 2x micro-CT scanner. The software used was VGSTUDIO MAX 3, which allows micro-CT scan analysis and quantitative data to be collected. Based on the previous radiograph analysis, TIMP-3 gene therapy slowed the progression of OA in some groups. The collected measurements quantitatively confirmed effective modeling of OA symptoms. Although no statistically significant data was seen, biologically significant differences between CCLD and OVX groups were noted. Biological differences were also noted between the stifle compartments. Measurement fluctuations in the tibial compartments occurred more frequently compared to the femoral compartments. BV/TV demonstrated that joints injected with TIMP-3 were protected from the surgically induced OA progression in both CCLD and OVX stifles. Perhaps primarily using lateral compartments compounded with oblique angle exercise may save time and expense in future diagnosis of OA progression. Future work must include larger numbers of sheep to add statistical power to the experiments.