Post-trauma Osteoarthritis is a sort of long course disease initiated by joint injury and consequent intra-articular inflammation, and its process is irreversible [27, 28]. Thus, to delay the cartilaginous degeneration is the main purpose of non-surgical treatment for osteoarthritis. Chronic inflammation is a critical risk factor of the cartilage destruction during the process of osteoarthritis, therefore, it is believed that the reduction of the intra-articular inflammation will retard the degeneration of cartilage [28]. Accordingly, we assumed that supplemental intra-articular injection of A2M, a autogeneic broad spectrum proteinase inhibitor, could ameliorate cartilage destruction induced by inflammation.
We set four groups to compare the protective effect of A2M and HA, two experimental groups received ACLT were treated with A2M and HA injection separately. Results of India ink staining and Safranin-O/fast green staining have been consistent. All groups received ACLT showed articular cartilage defects and outcropping of subchondral bone, which all were typical pathological changes of osteoarthritis [29]. However, there was little normal cartilage remaining in HA treated group, indicate the cartilage damages in HA group and non-treated group had no significant difference, hence the protective effect of HA is weak. This phenomenon echoed the results of clinical trials and meta-analyses, proving the uncertainty of curative effect of HA [30–32].
In A2M treated group, cartilage damage occurred similarly but obviously slighter than the HA group and non-treatment group. It could be observed that A2M-treated group had relatively intact surface and more chondrocyte cloning than non-treatment group and HA-treated group. Although the cartilage was inevitable after supplemental A2M injection, the protective effect of A2M was still very evident. Worthy of note was that OARSI histologic grading system scores in A2M-treated group also showed significant decrease, suggesting mild degeneration.
The major pathological changes of PTOA is the chronic inflammation secondary to joint injury. Due to the increasingly producing of pro-inflammatory cytokine and matrix metalloproteinase, the inflammatory damage of the articular tissue outrun regulation. Thus, relatively forceful way to analyze and compare the protective effects between HA and A2M is to study whether the intervention can inhibit the destructive cytokine and enzyme.
Accordingly, we examined more biological indicator of cartilage degeneration. Immunohistochemistry was carried out to test distribution of types II collagen and MMP-13 in cartilage. Type II collagen is produced by chondrocyte, and the level of type II collagen in degenerated cartilage with lower chondrocyte cloning will reduce [33]. While MMP-13 is a kind of enzyme catalyzing destruction of cartilage. MMP-13 induces the degradation of proteoglycan and type II collagen; thus it is used as an important indicator of cartilage damage. [34–36] in A2M injection group we detected higher type II collagen level and lower MMP-13 level, hence the protective effect of supplemental A2M injection could be confirmed. Besides we examined the sGAG concentration in synovial fluid from each group. Comparing to the non-treatment group, the synovial fluid sGAG level of the A2M group was lower. Quantitatively assessing sGAG level in synovial fluid could reflect the destruction of the cartilage extracellular matrix [37]. It is probably that the protective effect of A2M lead to lower sGAG in the group treated by this novel therapy.
In qPCR result, it is obviously that the supplemental A2M injection reduced the levels of mRNA for Runx2, MMP-3, MMP-13, and type X collagen. However, levels of mRNA for all that above in rats that underwent ACLT and saline/HA treatment were much higher than other two groups. These data suggested that A2M can protect cartilage in vivo by decreasing gene expression of catabolic factors and hypertrophic markers, as well as by increasing anabolic gene expression.
It is also apparently that the HA failed to achieved desired therapeutic effect. Immunohistochemistry Staining showed that the cartilage degeneration in rat knees with HA injection were still severe, meanwhile, the MMP-13 level was extremely higher than the sham operation group and A2M group. According to the quantitative assay of MMP13 level in synovial fluid, no significant disparity was found between HA injection group and non-treatment group. Similarly, there was no diversity between the sGAG level of HA group and non-treatment group. The result of qPCR also indicated that the HA treatment failed to prevent cartilage destruction.
As a lot of research, HA cannot display the protective effect to the injured joint tissue. A commonly accepted view is that the intra articular injection of HA can work as visco-supplementation [19]. But as early as the 1980s, a study suggested that injecting HA could not raise the specific viscosities of synovial fluid in experimental damaged joint [38]. One of the important reasons is the high molecular weight HA(HMW-HA) will be hydrolyzed to low molecular weight HA(LMW-HA) in the wound healing process, and LMW-HA cannot increase the specific viscosities of synovial fluid [39]. Furthermore, many studies believe that the LWM-HA is an active pro-inflammatory stimulator, even inducing metalloproteinases production [40–42].
Besides, there is a sort of proteoglycans called aggrecan on articular cartilage which binds to HA, providing elasticity of cartilage [43]. When PTOA happens, aggrecan on joint cartilage is dissociated, leading to loss of HA and erosion of cartilage, and finally cartilage degeneration [44]. And there is no evidence that supplement of HA without aggrecan will contribute to cartilage repairment. Additionally, previous study suggest that the HA have no influence on proteoglycan concentration in PTOA [45]. And our research also came to conclusion that there was no significant difference on mRNA level of aggrecan between the HA treated group and non-treatment group.
Although, intra-articular injection of HA supplies HMW-HA, but the change is temporary. Through the HA injection therapy, synovial fluid is difficult to recover to normal standard. While any change in molecular weight and concentration of HA in synovial fluid will aggravate the articular cartilage damage. For the reasons above, the HA treatment has been no longer recommended by American Academy of Orthopaedic Surgeons (AAOS) [22].
The reason we've decided to used A2M as an alternative therapy to replace uncertain HA therapy. Not only because A2M is able to protect articular cartilage against chronic inflammation, but also A2M has high biosafety and less side effects.
There are many studies working on solve the inflammation caused cartilage destruction in osteoarthritis. In this direction, existing and examining therapies are intra-articular calcium channel blocking anesthetics, corticosteroid injection, mesenchymal stem/stromal cells, and platelet-rich plasma [46, 47]. However, some of treatments mentioned above cannot slow down the cartilage degeneration; some are not suitable for prolonged use in clinics. A2M, as a novel therapeutic drug for knee OA, has a pretty good prospect in solving the shortcomings mentioned above. Compared with other drugs above, A2M is an autologous proteinase inhibitor so that it has no autoimmune rejection. Additionally, A2M injection contains only one kind of active ingredient, but inhibits various inflammatory factors and degenerative proteinase, due to broad-spectrum anti-inflammation effect of A2M. Therefore, A2M injection eliminates above-mentioned limitations. As a result, the safety is guaranteed and risk is controllable.
New developed technologies allowed us to concentrate A2M molecule from autologous plasma of patients, then inject A2M-rich preparation into joint to compensate for the low level of A2M in synovial fluid. [48] Furthermore, the variants of A2M called CYT-108 can be synthesized according to A2M’s molecular properties. Doubtless synthetic A2M is more economic and convenient, and the inhibitory effect of CYT-108 A2M far exceeded wild-type A2M [49].