gms | German Medical Science

Objectives: Osteoarthritis (OA) is a joint disease involving progressive and degenerative changes to articular cartilage that greatly affects the adult population. Autologous chondrocyte implantation (ACI) has been used to treat focal early OA defects, although there are negative long-term outcomes due to poor graft integration and the presence of inflammatory factors Bone marrow derived mesenchymal stem cells (MSCs) are an alternative cell type for cell-based treatments due to their chondrogenic capacity. However, MSC chondrogenesis leads to bone formation upon in vivo implantation. In vivo, chondrocytes reside under an oxygen tension between 2-7% oxygen or physioxia. Previous studies have demonstrated that physioxia enhances MSC chondrogenesis with reduced hypertrophic marker (collagen X and MMP13) expression compared to hyperoxia (20% oxygen). The present investigation sought to observe whether implantation of physioxic preconditioned MSCs improves cartilage repair in an early OA defect model compared to hyperoxic MSCs.

Methods: Bone marrow extracted from New Zealand white rabbits (male: 5-6 months old; n = 6) was split equally for expansion under 2% (physioxia) or 20% (hyperoxia) oxygen. Chondrogenic pellets (2 x 10⁶ cells) were formed at passage 1 and cultured in the presence of TGF- β1 under their expansion conditions. Pellet wet weight and GAG content was measured after 21 days culture. During bone marrow extraction, a dental drill (2.5mm diameter) was applied to medial femoral condyle on both knees to create an early OA defect and left untreated for 6 weeks. Following this period, physioxia and hyperoxia preconditioned MSCs were seeded into a hyaluronic acid (TETEC) hydrogel. Repair tissue was scrapped and MSC-hydrogel was injected into the right (hyperoxic MSCs) and left (physioxic MSCs) knee. Additional rabbits with described defect had tissue scrapped and left empty (n = 3 at 6 and 12 weeks). Rabbits were sacrificed at 6 (n = 3) and 12 (n = 3) weeks post-treatment, condyles harvested, decalcified in 10% EDTA and sectioned using a cryostat. Upon identification of region of interest, sections were stained with Safranin-O/Fast green and evaluated for cartilage regeneration using the Sellers scoring system by three blinded observers.

Results and conclusion: Rabbits MSCs showed significantly shorter doubling time and greater cell numbers upon culture under physioxia compared to hyperoxia(*p < 0.05). Furthermore, physioxia enhanced MSC chondrogenesis, as demonstrated by significant increases in pellet wet weight and GAG content (*p < 0.05). Implantation of physioxic preconditioned MSCs showed significantly improved cartilage regeneration (Mean Sellers score = 4 + 2; *p < 0.05) compared to hyperoxic MSCs (Sellers score = 12 + 3) and empty defects (Sellers score = 17 + 3). Physioxia enhances in vitro rabbit MSC chondrogenesis. Subsequent in vivo implantation of physioxia preconditioned MSCs improves cartilage regeneration in an early OA defect model compared to hyperoxic MSCs.