Sodium iodoacetate-induced OA rat model. After the induction of OA with intra-articular injection of sodium iodoacetate, the patellar surface, lateral and medial condyles, and tibial plateau were observed on days 7, 10, and 14. Macroscopic analysis revealed that the normal articular cartilage surface was smooth and bright, whereas the sodium iodoacetate-injected cartilage was damaged, concave, and inflamed on day 14 (Fig. 1A). A thick layer of the cartilage was observed in the normal articular cartilage samples on histological analysis, whereas the sodium iodoacetate-injected cartilages were uneven, thin, and infiltrated with hyperchromatic cells on day 14 (Fig. 1B). Plasma IL-1β levels increased after OA induction (Fig. 1C). IL-1β is a pro-inflammatory cytokine produced by joint tissues in patients or animals with OA1,17. These results indicated that the OA rat model was well established on day 14 after administration of sodium iodoacetate injection.
Macroscopic view of knee articular cartilage after treatment. The sodium iodoacetate-induced OA rats were treated with NS, SVF, or ADSC intra-articular injection. Figure 2 indicates that on day 7 after the treatments, the cartilages of the patellar surface, lateral and medial condyles, and tibial plateau of the NS control group were severely damaged, concave, and inflamed. However, the cartilages of the patellar surface presented no signs of OA in all rats, whereas the cartilages of the condyles and the tibial plateau were slightly damaged and inflamed in the SVF and ADSC treatment groups (Fig. 2). On day 14 after the treatments, the damage and inflammation were worse than those on day 7 in the NS group, wherein the articular cartilages of the patellar surface, lateral and medial condyles, and tibial plateau were even more dilapidated. Importantly, no obvious appearance of OA was observed through the cartilages of the patellar surface, lateral and medial condyles, and tibial plateau in the SVF and ADSC treatment groups, which recovered similar to the normal articular cartilage (Fig. 2). These results suggested that SVF and ADSC treatments may contribute to cartilage repair and regeneration in OA.
Histological observations of articular cartilage after SVF/ADSC treatment. H&E staining revealed that the surfaces of condyle and tibial plateau were rough, the cartilage layer was thin, and more hyperchromatic cells were observed in OA-induced tissues (Fig. 3). On days 7 and 14 after SVF/ADSC treatment, a thick layer of cartilage without irregular surface was observed, which was recovered similar to that of the normal cartilage (Fig. 3). These results suggested that both SVF and ADSC treatments may contribute to cartilage regeneration in OA.
Safranin O staining was also used to observe the cartilages in this study. The results indicated that the amount of articular cartilage in NS group was less than that in ADSC treatment group both at the joint and cement lines (Fig. 4A, 4C, 4D, 4F). The amount of articular cartilage in SVF group was also less than that in ADSC treatment group at the joint but approximately the same at the cement line (Fig. 4A, 4B, 4D, 4E). The SVF group had more calcified cartilage at the joint compared with the other two groups and also had the densest bone marrow of all the groups (Fig. 4).
Blood sample analysis of OA rat model after treatment. Blood samples (1 mL) were collected on days 7 and 14 after the treatments. WBC counts in the blood samples and inflammatory cytokine IL-1β levels were measured. The WBC counts were as follows: on day 14 after OA induction, 10.83 ± 0.75 × 109/L; on day 14 after the NS treatment, 8.82 ± 1.57 × 109/L; on day 14 after the SVF treatment, 11.3 ± 1.64 × 109/L; and on day 14 after the ADSC treatment, 12.32 ± 1.18 × 109/L (Fig. 5A). The average plasma IL-1β level on day 14 after the induction of OA was 793.33 pg/mL. However, the plasma IL-1β levels on day 7 after the treatments (Fig. 5B) were as follows: the SVF group, 87.55 pg/mL; the ADSC group, 79.67 pg/mL; and the NS group, 714.88 pg/mL. Notably, the plasma IL-1β levels on day 14 after the SVF and ADSC treatments reduced to 75.42 pg/mL and 40.2 pg/mL, respectively (Fig. 5B). These results suggested that SVF and ADSC treatments can cause remission of the inflammatory response.
IHC analysis. In this study, type I collagen (COL-1) and type II collagen (COL-2) were stained using IHC. The IHC results indicated that the NS group had the highest percentage of COL-1 and COL-2 positive cells both at the joint area and cement line, and the positive cell percentages were approximately 8% and 18.72% for COL-1 and 41.8% and 36.26% for COL-2, respectively (Fig. 6C, 6F, 6I, 6L). The percentages of the SVF group were 8.84% and 8.49% for COL-2 positive cells, respectively, (Fig. 6H and 6K), which were lower than those in the ADSC group (12.76% and 10.75% for COL-2 positive cells, respectively) (Fig. 6G, 6J). The differences in COL-1 positive cell percentages between the SVF group and ADSC group were minuscule (within 1%; 5.53% versus 4.1% and 2.26% versus 2.98%, respectively; Fig. 6A, 6B, 6D, 6E).