Controlled release of celecoxib from polyesteramide microparticles in a rat model of osteoarthritis

INTRODUCTION: Osteoarthritis (OA) is a common musculoskeletal disease, resulting in decreased productivity and high health costs. Oral antiinflammatory agents are effective in reducing pain and inflammation but have limited duration after oral or local administration while their prolonged used can be accompanied by systemic side effects. These limitations can be addressed by local administration of controlled release systems of anti-inflammatory drugs. The aims of the current study were to 1) confirm safety and efficacy of the intra-articular application of a local delivery system releasing celecoxib based on polyesteramide microspheres (PEAMs) in a rat model with induced knee joint OA and 2) find the optimal dose and determine possible side effects. METHODS: The animal experiment was conducted upon approval of the ethics committee of Utrecht University (protocol # 2014.III.10.086). Unilateral OA was induced by anterior cruciate ligament (ACL) transection and partial medial meniscectomy in 24 rats. After six weeks, rats were randomly divided into four groups receiving either a bolus injection of celecoxib (0.4 mg in 25 muL), unloaded PEAMs or PEAMs loaded with celecoxib (0.03 mg, 0.23 mg and 0.4 mg celecoxib in 25muL). During the 16 week follow up, pressure plate measurements were obtained weekly with an incapacitance measurement device to monitor pain and load bearing of both hind limbs. Post mortem, animals were assessed macroscopically and histopathologically to rule out systemic side effects of celecoxib. Micro-CT and histology (Mankin and OARSI score) of both treated and untreated contralateral knee joints were utilized to determine disease progression and the effects of continued exposure to celecoxib. Inflammation was visualized by scoring the amount of synovitis (Krenn score) and by immunohistochemistry of CD68, a marker for macrophages. All data were examined for normal distribution (Shapiro Wilks test). Kruskal Wallis and Mann-Whitney U tests were performed on non-normally distributed data, whereas general linear regression models based on ANOVA were used for normally distributed data. P <0.05 was considered significant after correcting for multiple testing with Benjamini & Hochberg False Discovery Rate posthoc tests. RESULTS: After surgical induction of OA, dynamic load bearing was significantly reduced in the operated limb. However, load bearing returned to normal within a month after surgery in all groups, and remained normal regardless of treatment. Systemic effects were absent upon post mortem analysis. Celecoxib-loaded microspheres, in all concentrations, reduced the formation of osteophytes (figure 1), bone cysts and loose bodies on micro-CT. Moreover, there was less subchondral sclerosis in the groups treated with PEAMs loaded with celecoxib when compared to unloaded PEAMs, although values were still higher than in healthy control joints. Histological scores were significantly higher in OA vs healthy control joints. Controlled release of celecoxib was not able to reduce the osteoarthritic changes at the histological level, regardless of the loading dose of celecoxib, in this model. CONCLUSION AND DISCUSSION: Mild to moderate OA was induced by ACL transection and partial medial meniscectomy without clear long term effects on weight bearing. Intra-articular injection of PEAMs loaded with celecoxib in the dose range of 0.03 - 0.4 mg was safe in OA joints; no adverse local or systemic effects were noted. While there was no clear effect of celecoxib on cartilage histology, celecoxib did reduce osteophyte, cyst and loose body formation in OA joints. Follow up studies in a large animal model with naturally occurring OA as a preclinical model for translation to humans is warranted to determine the efficacy of c PEAMs loaded with celecoxib in inhibiting pain and inflammation. PEAMs with celecoxib in the studied dose range does not lead to systemic or local side effects. (Figure Presented).