Intra-articular Injection of Hyaluronic Acid and Alpha-2-Macroglobulin to Ameliorate Knee Posttraumatic Osteoarthritis: A Rat Model
Authors: Wang Zhenyu , Huangfu Chaoji , Chen Chongwei , Zhu Mengbo , Guo Yanjing , Chen Xinping , Li Yue , Ma Yuyuan , Wang Shaowei 
Published: July 2022

Background
Posttraumatic osteoarthritis (PTOA) correlates with a dramatic increase in multiple inflammatory factors after joint injury. There is a broad spectrum proteinase inhibitor known as alpha-2-macroglobulin (A2M) that plays an important role in protecting against inflammatory injury. Endogenous A2M is abundant in serum but insufficient in synovial fluid due to its large molecular weight and has a limited effect on articular cartilage inflammation. We hypothesize that intra-articular injection of A2M has a better clinical effect than the commonly used hyaluronic acid (HA) injection therapy. Furthermore, A2M could be a safer method than alternative treatments because it is a native substance in the human body.
Method
The in vivo effects of A2M and HA on cartilage degeneration were evaluated in rats with surgery-induced anterior cruciate ligament transection (ACLT) OA. One hundred rats were randomly divided into four groups (N = 25/group): (a) sham surgery + saline (Sham + S), (b) ACLT + A2M, (c) ACLT + HA, or (d) ACLT + saline (ACLT + S). Intra-articular injections of A2M were given immediately and 3 days after surgery, and then 20 µl was injected each weekly in each joint. The animals were sacrificed 12 weeks after surgery. Indian ink staining, safranin O staining and immunohistochemical staining were performed to assess cartilage damage. The extent of OA progression was graded by the Osteoarthritis Research Society International Osteoarthritis Cartilage Histopathology Assessment System (OOCHAS) (OA score = Grade × Stage; range, 0 to 24). The concentrations of matrix metalloproteinase-13 (MMP-13) and sGAG in synovial fluid lavage were measured by ELISA and spectrophotometric quantitative determination. OA-related gene expression was quantified by qPCR.
Results
Indian ink staining showed that the articular cartilage surface in rats treated with A2M was relatively intact compared with that in the animals treated with ACLT plus saline or HA injection, but there was no significant difference between the ACLT + HA group and the ACLT + S group. Histological staining indicated that early intra-articular injection of A2M attenuated OA pathogenesis in the rat ACLT model compared with that in animals treated with saline and HA. However, intra-articular injection of HA did not significantly protect cartilage against posttraumatic OA compared with saline treatment. The ELISA results showed that A2M reduced the concentration of MMP-13 in synovial fluid compared with that in the HA treatment group and other groups. RT–qPCR indicated that intra-articular A2M inhibited catabolism and enhanced anabolic metabolism, while there was no significant difference in the expression of OA-related genes between the ACLT + HA group and the ACLT + S group.
Discussion
In rat model, intra-articular injection of A2M had obvious protective effects against cartilage degeneration compared with HA treatment. The inflammatory factor MMP-13 provides strong evidence for this inhibitory effect. Moreover, we found no significant alleviation of articular cartilage pathogenesis in the HA-treated group, which suggests that the efficacy of HA is questionable and possibly transient, although it is still extensively used in clinical practice.