To explore the effects and duration of adipose-derived mesenchymal stem cells (ADSCs) on cartilage injury and inflammatory response in knee osteoarthritis (KOA) rats.

Forty-five male SD rats were divided into the blank group, model group and treatment group randomly. Fourteen days after the KOA model establishment, the rats in the treatment group were injected with 1×10⁶ ADSCs/50 μL into the articular cavity while rats in the blank group and the KOA model group were injected with the same volume of normal saline once a week for four consecutive injections. The rats were observed at 4 weeks, 8 weeks and 12 weeks (n = 5) after the first injection. Independent blank group, model group and treatment group were set up at each observation time point. The mechanical pain threshold and thermal pain threshold of rats in each group were monitored and recorded. The degree of cartilage degeneration was observed by micro CT, HE-staining, Safranine O-fast green staining and Alcian blue staining. The protein expressions of collagen Ⅱ (COL2A1) and aggrecan (ACAN) were detected by immunohistochemistry. The expression levels of inflammatory factors IL-1β and TNF-α in articular cavity lavage fluid were detected by ELISA. Two-way factorial design ANOVA was used to analyze the main effect of group and observation time for all measurement data, and Bonferroni post-test was used for pairwise comparison.

The main effects of group in mechanical pain threshold, bone volume fraction, trabecular bone separation, Mankin score, OARSI score, COL2A1 and IL-1β in each group were statistically significant (all P < 0.05), while there was no significant difference in the main effects of time (all P > 0.05); The main effects of group and time were significant in terms of thermal pain threshold, trabecular thickness, trabecular number, ACAN and TNF-α (all P < 0.05). Compared with the blank group, the mechanical pain threshold, the thermal pain threshold, bone volume fraction, trabecular thickness and trabecular number [4 weeks: (0.92 ± 0.02) vs (1.17 ± 0.05) mm^-1, 8 weeks: (0.81 ± 0.07) vs (1.17 ± 0.04) mm^-1, 12 weeks: (0.75 ± 0.03) vs (1.16 ± 0.05) mm^-1] as well as positive cell expression rate of COL2A1 and ACAN protein were significantly decreased in the model group, while the bone trabecular separation, Mankin score, OARSI score and the expression levels of IL-1β [4 weeks: (53.87 ± 2.32) vs (29.71 ± 3.26) pg/mL, 8 weeks: (56.31 ± 5.85) vs (27.70 ± 2.69) pg/mL, (58.59 ± 3.36) vs (25.34 ± 3.23) pg/mL] and TNF-α [4 weeks: (142.52 ± 14.33) vs (71.52 ± 6.68) pg/mL, 8 weeks: (153.94 ± 7.36) vs (75.45 ± 2.78) pg/mL, (160.60 ± 10.93) vs (75.67 ± 3.20) pg/mL] were significantly increased (all P < 0.05). Compared with the model group, the mechanical pain threshold, the thermal pain threshold, the bone volume fraction, trabecular thickness, and trabecular number [4 weeks: (1.09 ± 0.04) vs (0.92 ± 0.02) mm^-1, 8 weeks: (1.02 ± 0.15) vs (0.81 ± 0.07) mm^-1, 12 weeks: (1.00 ± 0.05) vs (0.75 ± 0.03) mm^-1] and positive cell expression rate in the COL2A1 and ACAN protein was significantly increased in the treatment group, while the bone trabecular separation, Mankin score, OARSI score and the expression level of IL-1β [4 weeks: (37.15 ± 7.16) vs (53.87 ± 2.32) pg/mL, 8 weeks: (41.56 ± 7.24) vs (56.31 ± 5.85) pg/mL, 12 weeks: (42.39 ± 3.41) vs (58.59 ± 3.36) pg/mL] and TNF-α [4 weeks: (84.49 ± 7.12) vs (142.52 ± 14.33) pg/mL, 8 weeks: (88.22 ± 3.25) vs (153.94 ± 7.36) pg/mL, 12 weeks: (90.31 ± 5.29) vs (160.60 ± 10.93) pg/mL] were significantly decreased (all P < 0.05). Compared with the 4-week model group, the trabecular thickness and the expression level of TNF-α in the 12-week model group were significantly increased, while the number of trabeculae and the positive cell expression rate of ACAN protein were significantly decreased (all P < 0.05).

ADSCs can relieve the pain symptoms of KOA, reduce joint inflammation, and may repair cartilage damage by promoting chondrogenesis, which has a certain timeliness, providing experimental basis for certain timeliness characteristics of clinical stem cell therapy for KOA.