| Object: Osteoarthritis (OA) is a chronic, degenerative disorder of unknown cause characterized by gradual loss of articular cartilage. It is the most prevalent disease in our society, with a worldwide distribution. Since joint function is remarkably affected, daily living and social activities of patients with OA are restricted. OA process results in cystic degeneration of the bone surrounding the joint, with loss of cartilage and irregular, abnormal bone formation at the edges of the joint and narrowing of the joint space. The articular cartilage, which is the matured hyaline cartilage, has no vessels, and the cells for repair cannot be provided. There are limits to the division potential of the cartilage cells and their ability to be repaired. Therefore, it becomes difficult to treat OA when it progresses and the articular cartilage degenerates. At present, there are many conservative treatments for OA, but their clinical outcomes are limited. Advanced OA only be managed by artificial joint replacements, but there are problems concerning the degree of invasion, cost, and long-term prognosis. For these reasons, an effective conservative treatment to inhibit OA progression is needed. Basic fibroblast growth factor (bFGF) is regarded as one of the most potent mitogens for chondrocytes in vitro, which can accelerate cartilage metabolism or promote cartilage regeneration. The effect of bFGF cannot be maintained, even when it is locally injected, because its biologic half-life is short (3~5 minutes). Therefore, it is important to maintain the bFGF concentrations by using a sustained-release system of gelatin hydrogel microspheres. At present, many studies showed that the tissue inhibitors of metallomatrix-1 (TIMP-1) and tissue inhibitors of metallomatrix-1 (TIMP-1) could regulate the synthesis and degradation metabolism of extra-cellular matrix (ECM), and play important roles in the development the degradation of articular cartilage. So, in this experiment, bFGF was made into chitosan microspheres to maintain the bFGF local effective concentrations. To observe the inhibitory effects of bFGF in microspheres in treating OA in the rabbit knee and influence to express of TIMP-1 and MMP-13 mRNA. Our objective was to investigate the partial mechanism by intraarticular injections of bFGF in microspheres.Methods: The experiment was performed on 54 adult New Zealand white rabbits. We used intra-articular injection caroid in rabbit knee to induce osteoarthritis models. These animals were divided into a model group and four therapeutic groups (PBS-M, bFGF-S, bFGF-10-M, bFGF-100-M) at random, at the same time we made a control group. Meanwhile, we used chitosan to make microsphere with PBS or bFGF impregnated. We injected the PBS-impregnated or bFGF impregnated microsphere or bFGF-liquid into rabbit knee at week 3 and 6, and killed the animals at week 9. Cartilage pathology was scored by Indian Ink system in naked eyes. And scored by Mankin system in HE or PAS staining. The expression of cartilage TIMP-1 and MMP-13 mRNA was monitored by real-time PCR.Results:1 Shape and size of Chitosan microspheresIt can be got that chitosan microspheres made from the optimal formula have good sphericity and narrow size distribution by optical microscopy and SEM photography. The size distribution was range from 3μm to 7μm. The average diameter was 4.69±0.06μm.2 The result of Ink score in each group: Compared with control animals, the injury of model animals was dramatic (3.38±0.65 vs. 0.15±0.37, P<0.05), There were no differences between the model group and the therapeutic groups that used PBS-impregnated microsphere or bFGF-liquid at the injury of knee (3.08±0.64, 3.31±0.63 vs. 3.38±0.65, P>0.05). However, in bFGF-impregnated microsphere group the injury of cartilage decreased (1.92±0.49, 1.31±0.48 vs. 3.38±0.65, P<0.05). And compared with 10-bFGF-impregnated microsphere group, in 100-bFGF-impregnated microsphere group the injury of cartilage was notably decreased (1.31±0.48 vs. 1.92±0.49, P <0.05).3 The result of Mankin score in each group: Compared with control animals, the injury of model animals was dramatic (13.08±0.64 vs. 0.53±0.51, P<0.05), There were no differences between the model group and the therapeutic groups that used PBS-impregnated microsphere or bFGF-liquid at the injury of knee (12.15±1.07, 12.85±0.80 vs. 13.08±0.64, P>0.05). However, in bFGF-impregnated microsphere group the injury of cartilage decreased (8.08±0.49, 5.85±0.69 vs. 13.08±0.64, P<0.05). And compared with 10-bFGF-impregnated micro- sphere group, in 100-bFGF-impregnated microsphere group the injury of cartilage was notably decreased (5.85±0.69 vs. 8.08±0.49, P<0.05).4 Charges of cartilage TIMP-1,MMP-13 mRNA expression in each group: Compared with control group, the injury of model animals was dramatic, and the expression of TIMP-1 mRNA was decreased, meanwhile MMP-13 mRNA was increased (P<0.05). There were no differences between the model group and the therapeutic groups that used PBS-impregnated microsphere or bFGF-liquid at the expression of TIMP-1 and MMP-13 mRNA (P>0.05). However, in bFGF-impregnated microsphere group the expression of TIMP-1 mRNA was increased, and MMP-13 mRNA was notably decreased (P <0.05). And compared with 10-bFGF- impregnated microsphere group, in 100-bFGF-impregnated microsphere group the expression of TIMP-1 mRNA was increased, and MMP-13 mRNA was notably decreased (P <0.05).Conclusion: 1 The intra-articular injection caroid can successfully induce osteoarthritis model in the rabbit knee. bFGF-impregnated microsphere is successfully made from Chitosan.2 The bFGF can Sustained release to recovery the damage of cartilage of rabbit osteoarthritis only when it impregnated in microsphere.3 Compared with control animals, the injury of model animals was dramatic, and the expression of TIMP-1 mRNA was decreased, meanwhile MMP-13 mRNA was increased. However, the injury of knee was released in the bFGF-impregnated microsphere group, the expression of TIMP-1 mRNA was increased, and MMP-13 mRNA was notably decreased. So the pathogenesis of this role may through up-regulated TIMP-1 mRNA and down-regulated MMP-13 mRNA.
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