The catabolic-to-anabolic shift seen in the canine osteoarthritic cartilage treated with knee joint distraction occurs after the distraction period

Background Cartilage regenerative mechanisms initiated by knee joint distraction (KJD) remain elusive. Animal experiments that are representative for the human osteoarthritic situation and investigate the effects of KJD at consecutive time points could be helpful in this respect but are lacking. This study investigated the effects of KJD on the osteoarthritic joint of dogs on two consecutive timepoints. Methods Osteoarthritis was bilaterally induced for 10 weeks in 12 dogs using the groove model. Subsequently, KJD was applied to the right hindlimb for 8 weeks. The cartilage, subchondral bone and synovial membrane were investigated directly after KJD treatment, and after 10 weeks of follow-up after KJD treatment. Macroscopic and microscopic joint tissue alterations were investigated using the OARSI grading system. Additionally, proteoglycan content and synthesis of the cartilage were assessed biochemically. RT-qPCR analysis was used to explore involved signaling pathways. Results Directly after KJD proteoglycan and collagen type II content were reduced accompanied by decreased proteoglycan synthesis. After 10 weeks of follow-up, proteoglycan and collagen type II content were partly restored and proteoglycan synthesis increased. RT-qPCR analysis of the cartilage suggests involvement of the TGF-β and Notch signalling pathways. Additionally, increased subchondral bone remodelling was found at 10 weeks of follow-up. Conclusion While the catabolic environment in the cartilage is still present directly after KJD, at 10 weeks of follow-up a switch towards a more anabolic joint environment was observed. Further investigation of this timepoint and the pathways involved might elucidate the regenerative mechanisms behind KJD. The Translational Potential of this Article Further elucidation of the regenerative mechanisms behind KJD could improve the existing KJD treatment. Furthermore, these findings could provide input for the discovery or improvement of other joint regenerative treatment strategies

Prolonged intra-articular retention of mesenchymal stem cells by advanced microencapsulation for regenerative joint therapies

INTRODUCTION: Intra-articular injection of mesenchymal stem cells (MSCs) show therapeutic regenerative potential for patients with osteoarthritis (OA) by restoring damaged cartilage, reducing pain, and increasing motion range in clinical studies. However, clinical efficacy is still limited, which is likely caused by the rapid clearance of MSCs from the synovial cavity. We hypothesize that prolonging the intra-articular retention of MSCs increases their therapeutic potential. Therefore, we developed an advanced micro-encapsulation technique, specifically aimed at retaining MSCs in the joint, while supporting their viability and activity. The goal herein is to assess if micro-encapsulation of MSCs prolongs their intra-articular retention and increases their therapeutic potential. METHODS: MSCs were harvested from 12 week old Wistar rats, and labelled with a near infrared (NIR) label. An enzymatically crosslinkable polymer and a microfluidic droplet generator were used to encapsulate MSCs in microgels (eMSCs). Viability and metabolic activity were assessed. Microgels with near-infrared labelled MSCs were intra-articularly injected in healthy 12 week old Wistar rats (n=6). For four months, quantitation of the NIR signal was performed using whole animal NIR-imaging. After 8 and 16 weeks, microgels were retrieved and the presence of NIR signal and viability of the eMSCs was confirmed. Additionally, 12 week old Wistar rats (n=12), were fed a high fat diet and underwent a groove surgery to induce a mild OA phenotype. eMSCs were intra-articulary injected one week after the groove operation. Functional performance of OA rats was investigated using gait analysis. At the end point from both studies, histological analysis was performed to provide greater insight in the process and mechanism of action. RESULTS & DISCUSSION: Microfluidic encapsulation allowed for the formation of homogenous, monodisperse microgels (diameter 100 μm, cv <5%), which contained ~13 cells/gel. In vitro, the MSCs maintained ~60% of their initial metabolic activity and survived for at least four weeks. In vivo, MSC microencapsulation increased the intra-articular retention from four weeks (signal eMSCs vs naked MSCs: 63% vs 13%) to four months (signal eMSCs vs naked MSCs: 11% vs N.A.). Microgels retrieved from the knee joint contained viable, NIR-positive MSCs, confirming that the NIR signal came from the injected cells. Gait analysis shows an improved function of osteoarthritic rats receiving eMSCs over rats receiving naked MSCs or saline controls. Histological analysis corroborated the data. CONCLUSIONS: Our study shows that encapsulation of MSCs in microgels increases their intraarticular retention to at least four months, while protecting the MSCs against the harsh environment within the joint. Additionally, eMSCs alleviated osteoarthritic symptoms on a functional level. This approach allows for a single intra-articular injection with a significantly extended retention of therapeutic cells within the intra-articular joint cavity

Groove model of tibia-femoral osteoarthritis in the rat

Several experimental models of osteoarthritis in rats are used to study the pathophysiology of osteoarthritis. Many mechanically induced models have the limitation that permanent joint instability is induced by, for example, ligament transection or meniscal damage. This permanent instability will counteract the potential beneficial effects of therapy. The groove model of osteoarthritisuses a one-time trigger, surgically induced cartilage damage on the femoral condyles, and has been validated for the canine tibia-femoral compartment. The present study evaluates this model for the rat knee joint. The articular cartilage of the weight bearing surface of both femoral condyles and trochlea were damaged (grooved) without damaging the underlying subchondral bone. Severity of joint degeneration was histologically assessed, in addition to patella cartilage damage, and subchondral bone characteristics by means of (contrast-enhanced) micro-CT. Mild histological degeneration of the surgically untouched tibial plateau cartilage was observed in addition to damage of the femoral condyles, without clear synovial tissue inflammation. Contrast enhanced micro-CT demonstrated proteoglycan loss of the surgically untouched patella cartilage. Besides, a more sclerotic structure of the subchondral bone was observed. The tibiafemoral groove model in a rat results in mild knee joint degeneration, without permanent joint instability and joint inflammation. This makes the rat groove model a useful model to study the onset and progression of post-traumatic non-inflammatory osteoarthritis, creating a relatively sensitive model to study disease modifying osteoarthritic drugs. 2016 The Authors. Journal of Orthopaedic Research published by Wiley Periodicals, Inc. on behalf of the Orthopaedic Research Society. J Orthop Res.Biomaterials & Tissue Biomechanic