gms | German Medical Science

Objectives: Osteoarthritis (OA) is a joint disease involving progressive and degenerative changes to cartilage encompassing a variety of etiologies including post-traumatic incident or aging. It can be treated at its early stages through cell-based tissue engineering therapies using Mesenchymal Stem Cells (MSCs). In vivo models for evaluating these strategies, have described both chondral (impaction) and osteochondral (biopsy punch) defects. The aim of the investigation was to develop a compact and reproducible defect inducing post-traumatic degenerative changes mimicking early OA. Additionally, a pilot study to evaluate MSC-hydrogel treatment was also assessed.

Methods: Surgery was performed on New Zealand white rabbits (male; 5-8 months old) with defects created on medial femoral condyle. Three approaches were evaluated: a biopsy punch (n = 3 at 6 and 12 weeks), an impaction device1 (n = 3 at 6 and 12 weeks) and a dental drill model (n = 6 at 6 and 12 weeks). At stated time points, harvested condyles were decalcified in 10% EDTA, embedded in Tissue-Tek and sectioned using a cryostat. Upon identification of region of interest, sections were stained with Safranin-O/Fast green and scored using OARSI scoring system by three blinded observers. For the pilot study, autologous bone marrow was harvested from rabbits and used to isolate and expand MSCs. The dental drill model was applied to both knee condyles and left untreated for 6 weeks. At that stage, PKH26 fluorescently labelled MSCs were seeded into a hyaluronic acid hydrogel (TETEC), repair tissue removed from both condyles and MSC-hydrogel was injected into the right knee, whilst left knee remained untreated. Rabbits were sacrificed at 1 (n = 1), 6 (n = 3) and 12 (n = 3) weeks post-treatment, processed as previously described and cartilage regeneration evaluated using the Sellers score.

Results and conclusion: Impacted condyles exhibited no histological changes (mean OARSI score = 1 + 1), whereas biopsy punched and dental drilled defects demonstrated equal signs of cartilage erosion (OARSI = 3 + 1) at assessed time points. However, biopsy punched condyles developed a diffusive defect, whereas dental drilled condyles showed a more defined, compact and reproducible defect. In the pilot study, PKH-labelled MSCs were observed at 1 and 6 weeks (mean Sellers score = 15 + 1) post-implantation within the defect space where MSC-hydrogel was injected. At 12 weeks, MSC treated defects showed improved tissue regeneration with substantial subchondral bone restoration and good integration of regenerative cartilage with surrounding intact tissue (Sellers score = 10 + 2), whereas untreated defects showed a reduced regeneration (Sellers score = 17 + 3). The dental drill model was found to be the appropriate strategy for investigating early OA progression and treatment. Application of MSCs in defects showed good cartilage regeneration after 12 weeks application, indicating their promise in the treatment of early OA defects.