Comparison of the bioactivity and apoptotic responses of hyaline cartilage chondrocytes and fibrocartilage chondrocytes obtained by bone marrow stimulation in rats.

OBJECTIVE: The microfracture technique is often considered the standard therapy for treating cartilage defects. The aim of the treatment is the migration of mesenchymal stem cells from the bone marrow into the defect area. However, this regeneration process often results in the formation of fibrocartilage instead of natural hyaline cartilage, due to cellular mechanisms whose causes are not well understood. Therefore, in this study, the differences in bioactivity and apoptosis of fibrocartilage tissue-derived chondrocytes (FCh) obtained by bone marrow stimulation and natural hyaline cartilage tissue-derived chondrocytes (HCh) in the knee joint of rats were compared. METHODS: A total of 24 Wistar albino rats were used in this study, and one hind leg of each animal was operated on, while the other served as a control. A 2-step surgical procedure was performed: First, a microfracture was generated at a 2 mm × 2 mm cartilage defect area in the medial condyle of the femur after a left knee arthrotomy. Second, 6 weeks later, after a double knee arthrotomy, fibrocartilage from the microfracture area of the left knee and 2 × 2 mm of hyaline cartilage from the medial femoral condyle of the right knee were harvested. Chondrocytes were isolated and grouped as HCh or FCh, and cell viability and apoptosis were determined by MTT (4,5-dimethylthiazol -2-yl)-2,5-diphenyltetrazolium bromide) and caspase-3 assays using enzyme-linked immunosorbent assay (ELISA) kits. RESULTS: Fibrocartilage tissue-derived chondrocytes showed similar bioactivity and apoptotic response as HCh under physiological conditions. However, low-dose H2O2 decreased viability (bioactivity) and increased apoptosis in FCh without affecting HCh. High-dose H2O2 reduced the bioactivity of both cell types and induced apoptosis, while the response of FCh to oxidative stress was more aggressive than that of HCh. CONCLUSION: The different response patterns in oxidative stress may provide a basis for understanding the limited survival time of bone marrow-derived fibrocartilage tissue induced by microfractures. LEVEL OF EVIDENCE: N/A.