Abstract: Objective：To investigate the efficacy of single time intra-articular different concentration of allogeneic bone marrow mesenchymal stem cells (BM-MSCs) injection in the treatment of Sprague-Dawley (SD) rat model of osteoarthritis (OA). Methods: In the study, 32 SD rats were equally randomized into 4 groups: control group, high concentration group (1×10⁷/mL BM-MSCs), low concentration group (5×10⁶/mL BM-MSCs) and high vs. low concentration group. The two knees of each rat were set up to a pair. The induction of OA was performed surgically randomly at one side in model group, and bilaterally in the other groups, which were through anterior cruciate ligament transaction (ACLT) and medial meniscus excising. After the operation, the SD rats were allowed free movement. Four weeks later, different concentrations of allogeneic BM-MSCs isolated from the SD rats, expanded in vitro and suspended in phosphate buffered solution (PBS) were delivered in the articular cavity of both knees; PBS was used as the control. After injection, we excised the femoral nerve and sciatic nerve to disuse the low limb. The cartilage histological sections of knees were scored by Mankin scoring system to assess the severity of the pathology. mRNA of collagen Ⅱ was detected by real time polymerase chain reaction (RT-PCR). eGFP was detected by fluorescence microscope. Assessments were carried out 4 weeks after the operation in model group, and 3 weeks after injection in the other groups. Results:Mankin scores of the BM-MSCs side and control side were 6.60±0.40 vs. 10.00±0.32 in low concentration group (P<0.05), and 5.40±0.51 vs. 9.60±0.51 in high concentration group (P<0.05). Mankin scores of high vs. low concentration group were 6.40±0.51 vs. 7.60±0.75 (P>0.05). mRNA expression of collagen Ⅱ of the BM-MSCs side in low concentration group was 106%±1% in contrast to the control side. As in high concentration group it was 108%±1%, and 102%±1% in high vs. low concentration group. Labeled BM-MSCs were detected unexpectedly in the synovial membrane but not in cartilage tissue three weeks from injection. Conclusion: BM-MSCs could promote cartilage repair and inhibit OA progression through a trophic mechanism. There was no difference between the two concentrations.

Key words: Osteoarthritis, Mesenchymal stromal cells, Injection, intra-articular