Aims. Arthrofibrosis is a relatively common complication after joint injuries and surgery, particularly in the knee. The present study used a previously described and validated rabbit model to assess the biomechanical, histopathological, and molecular effects of the mast cell stabilizer ketotifen on surgically induced knee joint contractures in female rabbits. Methods. A group of 12 skeletally mature rabbits were randomly divided into two groups. One group received subcutaneous (SQ) saline, and a second group received SQ ketotifen injections. Biomechanical data were collected at eight, ten, 16, and 24 weeks. At the time of necropsy, posterior capsule tissue was collected for histopathological and gene expression analyses (messenger RNA (mRNA) and protein). Results. At the 24-week timepoint, there was a statistically significant increase in passive extension among rabbits treated with ketotifen compared to those treated with saline (p = 0.03). However, no difference in capsular stiffness was detected. Histopathological data failed to demonstrate a decrease in the density of fibrous tissue or a decrease in α-smooth muscle actin (α-SMA) staining with ketotifen treatment. In contrast, tryptase and α-SMA protein expression in the ketotifen group were decreased when compared to saline controls (p = 0.007 and p = 0.01, respectively). Furthermore, there was a significant decrease in α-SMA (ACTA2) gene expression in the ketotifen group compared to the control group (p < 0.001). Conclusion. Collectively, these data suggest that ketotifen mitigates the severity of contracture formation in a rabbit model of arthrofibrosis. Cite this article: Bone Joint Res 2020;9(6):302–310

Summary. Previous work in a rabbit model of post-traumatic joint contractures shows that the mast cell stabilizer ketotifen decreases contracture severity. We show here that ketotifen decreases collagen gel contraction mediated by rabbit joint capsule fibroblasts when mast cells are present. Introduction. Ketotifen was shown to decrease contracture severity and associated joint capsule fibrosis in an animal model of post-traumatic joint contractures. Ketotifen prevents the release of profibrotic growth factors from mast cells (MC). An in vitro collagen gel contraction assay is used to examine the effect of ketotifen on joint capsule fibroblasts obtained from this animal model. Methods. Six New Zealand White rabbits had a standardised procedure to induce post-traumatic joint contractures and the joint capsule was harvested 4 weeks later. The capsules were minced, placed into T75 culture flasks and incubated at 37. 0. C in a humidified atmosphere containing 5% CO. 2. The Joint Capsule fibroblasts (JC, 2.5 × 10. 5. cells/mL) were mixed with neutralised collagen solution composed of 59% neutralised PureCol collagen I, serum free DMEM/F12 with 1x serum replacement and 1x antibiotic-antimycotic. Aliquots of solution were then cast into wells of a tissue culture plate. Gelation occurred over 3h at 37°C in a humidified incubator. The collagen gel/cells were maintained with DMEM/F-12 plus 1% serum replacement and 1% antibiotic-antimycotic and incubated at 37°C for 12 h. The gels were released and gel area was calculated up to 72h post-release. Different experiments were conducted with various combinations of a human mast cell line (HMC-1, 7.5 × 10. 5. cells/mL), the neuropeptide Substance P (SP, 10. −6. M) and Ketotifen fumurate at 10. −4. , 10. −6. , 10. −8. and 10. −10. M. The various interventions were combined with the JC and collagen gel during the gelation step. Statistical comparisons used a two way ANOVA with a Posthoc Tukey test. Significance was set at p < 0.05. Results. The JC contracted the collagen gels in all conditions, with statistically significant differences between time intervals from 6 h to 72 h. When ketotifen alone was added to JC, there was no effect on collagen gel contraction in the range of doses tested. Adding MC to JC led to a significantly increased rate of gel contraction that was inhibited by ketotifen in a dose-dependent manner. The effect was maximal with a concentration of 10. −4. M while the effect was absent by the dose of 10. −10. M. There were statistically significant differences amongst different doses except for comparisons between doses closest to each other (10. −4. vs 10. −6. , 10. −6. vs 10. −8. , 10. −8. vs 10. −10. M). Including SP with MC and JC further increased the rate of gel contraction, which was also significantly inhibited by ketotifen in a similar dose-dependent fashion. Discussion/Conclusion. Fibroblasts from rabbit joint capsules contract collagen gels with the effect enhanced by the addition of mast cells. Ketotifen prevents the release of mediators by mast cells, and ketotifen modified the collagen gel assay. It appears that the inhibition of the gel contraction by the fibroblasts is via mast cell stabilization since ketotifen had no direct affect on the fibroblasts in the concentrations evaluated. Ketotifen is a medication used in the chronic treatment of asthma. It has a wide safety profile, it is already approved for human use and it is available in oral preparations

Purpose: To determine if mast cell activity is vital to the induction of joint capsule fibrosis and contracture formation in a rabbit model of posttraumatic joint contracture. Method: To reproducibly induce joint contractures, we used a model of surgical injury and immobilization of the knee in skeletally mature New Zealand white rabbits. Four animals groups were studied: a non-operative control group (CON), an operative contracture group (ORC) and two-operative groups treated with a mast cell stabilizer, Ketotifen fumarate at doses of 0.5mg/kg (KF0.5) and 1.0mg/kg (KF1.0) twice daily subcutaneously, respectively. Animals were sacrificed after 8 weeks of immobilization. Flexion contractures (biomechanics), cellular counts of myofibroblasts and mast cells within the joint capsule (immunohistochemistry) and the joint capsule protein expression of TGF-β1, collagen I and III were quantified (western blots). Biomechanical data was interpreted using a linear regression analysis of repeated measures and an ANOVA analysis of variance was used for molecular data. Significance was defined at p< 0.05 for all statistical tests. Results: Flexion contractures were most severe in the ORC group and treatment with Ketotifen (both KF0.5 and KF1.0) significantly reduced contracture severity by 52% and 42%, respectively (p< 0.03). Joint capsule myofibroblast and mast cell hyperplasia was a prominent feature of the more severely contracted ORC group and myofibroblast and mast cell numbers were dramatically reduced in both Ketotifen groups (p< 0.001). The expression of TGF-β1 and collagen I was also increased in the ORC group and significantly reduced in both Ketotifen groups (p< 0.01). Conclusion: Joint capsule fibrosis, characterized by hyperplasia of myofibroblasts and mast cells and enhanced collagen deposition, is a prominent feature of posttraumatic joint contractures in this animal model. Treatment with a mast cell stabilizer reduced the molecular markers of joint capsule fibrosis and the resultant biomechanical severity of contracture formation. These results suggest mast cell activity may be an important process in the development of posttraumatic contractures and future work is needed to determine if pharmacological inhibition of mast cell activity has a preventative or therapeutic role in humans

Aims

As has been shown in larger animal models, knee immobilization can lead to arthrofibrotic phenotypes. Our study included 168 C57BL/6J female mice, with 24 serving as controls, and 144 undergoing a knee procedure to induce a contracture without osteoarthritis (OA).

Purpose. Recent work has shown that joint contracture severity can be decreased with the mast cell stabilizer ketotifen in association with decreased numbers of myofibroblasts and mast cells in the joint capsule of a rabbit model of post-traumatic contractures. Neuropeptides such as Substance P (SP) can induce mast cells to release growth factors. Using a gel contraction assay, we test the hypothesis that joint capsule cell-mediated contraction of a collagen gel can be enhanced with SP, but the effect is magnified in the presence of mast cells. Method. Anterior elbow joint capsules were obtained at the time of surgical release from 2 men (age 34 and 54) and 1 woman (age 40) with chronic (> 1 year) post-traumatic joint contractures. The human mast cell line HMC-1 (Mayo Clinic, Rochester), SP and the NK1 receptor antagonist RP67580 (Sigma, Oakville, ON) were used. NK1 is the SP receptor. Neutralized Collagen solution composed with 58% Vitrogen 100 purified collagen mixed with HMC-1 cells only (7.5 105), human capsule cells (2.5 105), or human capsule cells (2.5 105) and 7.5 105 mast cells (1:3) were cast into 24- well tissue culture plates. In some experiments, SP (1 × 10. −5. M) +/− RP67580 (0.5 mM) were added. The gels were maintained with 0.5 ml DMEM composed with 2% BSA and incubated at 37C for 12 h for gelation to occur. The gels were then detached from the wall and the bottom of culture plate wells, and photographed at regular intervals up to 72 hours. Gel contraction studies were carried out on passage 4 and done in triplicate for each patient. The average value of each patients triplicate was combined to give a mean contraction at each time point. Statistical analysis involved an ANOVA with posthoc Bonferroni correction. P < 0.001 was significant. Results. Mast cells alone or with SP were unable to contract collagen gels. Joint capsule cells were able to contract the collagen gels and this was enhanced in the presence of SP, although not statistically significant. Joint capsule cells combined with mast cells enhanced the gel contraction more than joint capsule cells alone or with SP (p<0.001). The addition of SP accelerated the joint capsule cell-mediated gel contraction in the presence of mast cells the greatest (p<0.001 over all other conditions). The inhibitor RP67580 completely abolished the collagen gel contraction of the joint capsule cells in all conditions. Conclusion. The in vitro experiment shows that joint capsule cell function, in the form of collagen gel contraction, is modified by the presence of mast cells and neuropeptides. These findings are significant as they strengthen the hypothesis that a myofibroblast mast cell neuropeptide fibrosis axis may be contributing to the joint capsule changes underling the loss of motion in post-traumatic joint contractures. In vivo studies with the rabbit model of post-traumatic contractures will be performed using the compounds examined in the current study

Purpose: The objective of the present study was to determine whether human mast cells can modify behavior of human elbow contracture capsule cells in an in vitro collagen gel contraction assay. Method: Posterior elbow joint capsule was obtained from a 38 year old man with a chronic (> 1 year) post-traumatic joint contracture. Joint capsule cells were isolated and suspended at a density of 2.5 x 105 cells/ml, and mixed with neutralized Collagen solution composed with 58% Vitrogen 100 purified collagen. Aliquots of collagen gel without cells, with only the human mast cell line, HMC-1 (2.5× 105), human capsule cells (2.5 × 105), human capsule cells (2.5 × 105) and an equal number of mast cells (1:1), or human capsule cells (2.5× 105) and 7.5× 105 mast cells (1:3) were then cast into wells tissue culture plate. The gels were maintained with 0.5 ml DMEM composed with 2% BSA and incubated at 37°C for 12 h for gelation to occur. After 12 hr initial culture, the gels were detached from the wall and the bottom of culture plate wells, and gel area was determined at 0h, 2h, 4h, 6h, 24h, 48h, and 72h Gel contraction studies were carried out on passage 6 and done in triplicate. The blocking assay to inhibit mast cell – joint capsule cell interaction employed antibodies to Stem Cell Factor (SCF) and c-kit. SCF (0.5, 1 or 10 microg/ml) and/or c-kit (0.05, 0.1 or1 microg/ml) were added individually or in combination (SCF 10 microg/ ml and c-kit 1 microg/ml only) to cells/collagen gel mixture before gel casting. The ratio of human capsule cells and HMC-1 were kept constant at 1:3 throughout the experiment. The inhibitory effect of SCF and c-kit antibodies on collagen gel contraction induced by human capsule cells and HMC-1 was expressed in percentage of gel areas at 24h post release. Inhibition effect (%) = 100% – [(gel size – c-kit or SCF gel size)/(blank gel size – JC:M gel size)x 100%]. Statistical analysis involved an ANOVA with posthoc Bonferroni correction. P < 0.001 was significant. Data are mean ± standard deviation. Results: Joint capsule cells were able to contract collagen gels in a time-dependent manner. This contraction was significantly enhanced in the presence of the HMC-1 cells in a dose dependent fashion (p < 0.001). HMC-1 cells were unable to contract the collagen gels by themselves. Experiments with antibodies to the mast cell – fibroblast direct cell-cell communication determinants SCF or c-kit showed inhibition of the enhanced contraction at 24 hours between 43 – 72%. Combining the highest dose of SCF and c-kit led to 82% inhibition. Conclusion: This study has shown that cells isolated from human elbow joint contracture capsules respond to mast cells in a collagen gel assay in a dose dependent manner. This study is consistent with our previous work which has shown that ketotifen, a mast cell stabilizer that prevents mast cell degranulation and liberation of factors, can reduce contracture severity in a rabbit model of post-traumatic joint contractures

Objectives

Sustained intra-articular delivery of pharmacological agents is an attractive modality but requires use of a safe carrier that would not induce cartilage damage or fibrosis. Collagen scaffolds are widely available and could be used intra-articularly, but no investigation has looked at the safety of collagen scaffolds within synovial joints. The aim of this study was to determine the safety of collagen scaffold implantation in a validated in vivo animal model of knee arthrofibrosis.