Validation of an in vitro single-impact load model of the initiation of osteoarthritis-like changes in articular cartilage

Loss of collagen content is localized near cartilage lesions on the day of injurious loading and intensified on day 12

Joint injury can lead to articular cartilage damage, excessive inflammation, and post-traumatic osteoarthritis (PTOA). Collagen is an essential component for cartilage function, yet current literature has limited understanding of how biochemical and biomechanical factors contribute to collagen loss in injured cartilage. Our aim was to investigate spatially dependent changes in collagen content and collagen integrity of injured cartilage, with an explant model of early-stage PTOA. We subjected calf knee cartilage explants to combinations of injurious loading (INJ), interleukin-1α-challenge (IL) and physiological cyclic loading (CL). Using Fourier transform infrared microspectroscopy, collagen content (Amide I band) and collagen integrity (Amide II/1338 cm-1 ratio) were estimated on days 0 and 12 post-injury. We found that INJ led to lower collagen content near lesions compared to intact regions on day 0 (p < 0.001). On day 12, near-lesion collagen content was lower compared to day 0 (p < 0.05). Additionally, on day 12, INJ, IL, and INJ + IL groups exhibited lower collagen content along most of tissue depth compared to free-swelling control group (p < 0.05). CL groups showed higher collagen content along most of tissue depth compared to corresponding groups without CL (p < 0.05). Immunohistochemical analysis revealed higher MMP-1 and MMP-3 staining intensities localized within cell lacunae in INJ group compared to CTRL group on day 0. Our results suggest that INJ causes rapid loss of collagen content near lesions, which is intensified on day 12. Additionally, CL could mitigate the loss of collagen content at intact regions after 12 days.

Urocortin-1 Is Chondroprotective in Response to Acute Cartilage Injury via Modulation of Piezo1

Post-traumatic OA (PTOA) is often triggered by injurious, high-impact loading events which result in rapid, excessive chondrocyte cell death and a phenotypic shift in residual cells toward a more catabolic state. As such, the identification of a disease-modifying OA drug (DMOAD) that can protect chondrocytes from death following impact injury, and thereby prevent cartilage degradation and progression to PTOA, would offer a novel intervention. We have previously shown that urocortin-1 (Ucn) is an essential endogenous pro-survival factor that protects chondrocytes from OA-associated pro-apoptotic stimuli. Here, using a drop tower PTOA-induction model, we demonstrate the extent of Ucn's chondroprotective role in cartilage explants exposed to excessive impact load. Using pathway-specific agonists and antagonists, we show that Ucn acts to block load-induced intracellular calcium accumulation through blockade of the non-selective cation channel Piezo1 rather than TRPV4. This protective effect is mediated primarily through the Ucn receptor CRF-R1 rather than CRF-R2. Crucially, we demonstrate that the chondroprotective effect of Ucn is maintained whether it is applied pre-impact or post-impact, highlighting the potential of Ucn as a novel DMOAD for the prevention of injurious impact overload-induced PTOA.

Ground reaction force patterns in knees with and without radiographic osteoarthritis and pain: descriptive analyses of a large cohort (the Multicenter Osteoarthritis Study)

OBJECTIVE

To compare ground reaction force patterns (GRF) during walking among legs defined by presence or absence of knee pain and/or radiographic knee osteoarthritis (ROA).

METHOD

Principal component analysis extracted major modes of variation (PCs) in GRF data from the Multicenter Osteoarthritis Study during self-paced walking. Legs were categorized as pain + ROA (n = 168), ROA only (n = 303), pain only (n = 476), or control (n = 1877). Relationships between group and GRF PCs were examined using Generalized Estimating Equations, adjusted for age, sex, body mass index, race, and clinic site with and without additional adjustment for gait speed.

RESULTS

With or without speed adjustment, pain + ROA had flatter vertical GRF waveforms than control (speed adjusted PC2 difference [95%CI]: -66 [-113,-20]), pain + ROA and ROA only had higher lateral GRF at impact and greater mid-stance medial GRF than control (speed adjusted PC3 difference: 9 [3,16] and 6 [2,10], respectively), and ROA only had higher early vs late medial GRF than control (speed adjusted PC2 difference: 7 [2,13]). Pain only had flatter vertical GRF waveforms and a smaller difference between anterior and posterior GRF than control only without speed adjustment.

CONCLUSION

In this large sample, sustained mid-stance loading and higher impact loads were identified in legs with ROA or ROA and pain, even when adjusting for differences in gait speed and other confounders. While it remains to be seen whether these features precede or result from ROA and pain, the presence of these patterns in the speed-adjusted models could have implications on gait interventions aimed to change joint loading.

Longitudinal T2 Mapping and Texture Feature Analysis in the Detection and Monitoring of Experimental Post-Traumatic Cartilage Degeneration

Background: Traumatic cartilage injuries predispose articulating joints to focal cartilage defects and, eventually, posttraumatic osteoarthritis. Current clinical-standard imaging modalities such as morphologic MRI fail to reliably detect cartilage trauma and to monitor associated posttraumatic degenerative changes with oftentimes severe prognostic implications. Quantitative MRI techniques such as T2 mapping are promising in detecting and monitoring such changes yet lack sufficient validation in controlled basic research contexts. Material and Methods: 35 macroscopically intact cartilage samples obtained from total joint replacements were exposed to standardized injurious impaction with low (0.49 J, n = 14) or high (0.98 J, n = 14) energy levels and imaged before and immediately, 24 h, and 72 h after impaction by T2 mapping. Contrast, homogeneity, energy, and variance were quantified as features of texture on each T2 map. Unimpacted controls (n = 7) and histologic assessment served as reference. Results: As a function of impaction energy and time, absolute T2 values, contrast, and variance were significantly increased, while homogeneity and energy were significantly decreased. Conclusion: T2 mapping and texture feature analysis are sensitive diagnostic means to detect and monitor traumatic impaction injuries of cartilage and associated posttraumatic degenerative changes and may be used to assess cartilage after trauma to identify “cartilage at risk”.

Co-culture of osteochondral explants and synovial membrane as in vitro model for osteoarthritis

The purpose of the current study was to establish an in vitro model for osteoarthritis (OA) by co-culture of osteochondral and synovial membrane explants. Osteochondral explants were cultured alone (control-1) or in co-culture with synovial membrane explants (control-2) in standard culture medium or with interleukin-1β (IL1β) and tumor necrosis factor (TNFα) added to the culture medium (OA-model-1 = osteochondral explant; OA-model-2 = osteochondroal-synovial explant). In addition, in OA-model groups a 2-mm partial-thickness defect was created in the centre of the cartilage explant. Changes in the expression of extracellular matrix (ECM) genes (collagen type-1 (Col1), Col2, Col10 and aggrecan) as well as presence and quantity of inflammatory marker genes (IL6, matrix metalloproteinase-1 (MMP1), MMP3, MMP13, a disintegrin and metalloproteinase with-thrombospondin-motif-5 (ADAMTS5) were analysed by immunohistochemistry, qPCR and ELISA. To monitor the activity of classically-activated pro-inflammatory (M1) versus alternatively-activated anti-inflammatory/repair (M2) synovial macrophages, the nitric oxide/urea ratio in the supernatant of osteochondral-synovial explant co-cultures was determined. In both OA-model groups immunohistochemistry and qPCR showed a significantly increased expression of MMPs and IL6 compared to their respective control group. ELISA results confirmed a statistically significant increase in MMP1and MMP3 production over the culturing period. In the osteochondral-synovial explant co-culture OA-model the nitric oxide/urea ratio was increased compared to the control group, indicating a shift toward M1 synovial macrophages. In summary, chemical damage (TNFα, IL1β) in combination with a partial-thickness cartilage defect elicits an inflammatory response similar to naturally occurring OA in osteochondral explants with and without osteochondral-synovial explant co-cultures and OA-model-2 showing a closer approximation of OA due to the additional shift of synovial macrophages toward the pro-inflammatory M1 phenotype.

Comparison between in vitro and in vivo cartilage overloading studies based on a systematic literature review

Methodological differences between in vitro and in vivo studies on cartilage overloading complicate the comparison of outcomes. The rationale of the current review was to (i) identify consistencies and inconsistencies between in vitro and in vivo studies on mechanically-induced structural damage in articular cartilage, such that variables worth interesting to further explore using either one of these approaches can be identified; and (ii) suggest how the methodologies of both approaches may be adjusted to facilitate easier comparison and therewith stimulate translation of results between in vivo and in vitro studies. This study is anticipated to enhance our understanding of the development of osteoarthritis, and to reduce the number of in vivo studies. Generally, results of in vitro and in vivo studies are not contradicting. Both show subchondral bone damage and intact cartilage above a threshold value of impact energy. At lower loading rates, excessive loads may cause cartilage fissuring, decreased cell viability, collagen network de-structuring, decreased GAG content, an overall damage increase over time, and low ability to recover. This encourages further improvement of in vitro systems, to replace, reduce, and/or refine in vivo studies. However, differences in experimental set up and analyses complicate comparison of results. Ways to bridge the gap include (i) bringing in vitro set-ups closer to in vivo, for example, by aligning loading protocols and overlapping experimental timeframes; (ii) synchronizing analytical methods; and (iii) using computational models to translate conclusions from in vitro results to the in vivo environment and vice versa. © 2018 The Authors. Journal of Orthopaedic Research® Published by Wiley Periodicals, Inc. J Orthop Res 9999:1-11, 2018.

The effect of irrigation time and type of irrigation fluid on cartilage surface friction

It is known that fluid irrigation used during arthroscopic procedures causes a wash-out of lubricating substances from the articular cartilage surface and leads to increased friction. It was the goal of this study to investigate whether this effect depends on the time of irrigation and type of fluid used. Rabbit hind legs were used for the tests. The knees were dissected and the friction coefficient of the femoral cartilage measured against glass in a boundary lubrication state. To determine the influence of irrigation time and fluid, groups of 12 knees received either no irrigation (control), 15, 60 or 120min of irrigation with lactated Ringer's solution or 60min of irrigation with normal saline or a sorbitol/mannitol solution. The time of irrigation had a significant effect on the static and kinetic coefficient of friction (CoF), as had the type of fluid. Longer irrigation time with Ringer's solution was associated with increased friction coefficients (relative increase of the kinetic CoF compared to the control after 15, 60 and 120min: 16%, 76% and 88% respectively). The sorbitol/mannitol solution affected the static and kinetic CoF significantly less than either Ringer's or normal saline. The washout of lubricating glycoproteins from the cartilage surface and the associated increase of friction can be effectively influenced by controlling the time of irrigation and type of fluid used. The time of exposure to the irrigation fluid should be as short as possible and monosaccharide solutions might offer a benefit compared to salt solutions in terms of the resultant friction.

Low-energy impact of human cartilage: predictors for microcracking the network of collagen

OBJECTIVE

We aimed to determine the minimum mechanical impact to cause microstructural damage in the network of collagen (microcracking) within human cartilage and hypothesized that energies below 0.1 J or 1 mJ/mm³ would suffice.

DESIGN

We completed 108 low-energy impact tests (0.05, 0.07, or 0.09 J; 0.75 or 1.0 m/s²) using healthy cartilage specimens from six male donors (30.2 ± 8.8 yrs old). Before and after impact we acquired, imaging the second harmonic generation (SHG), ten images from each specimen (50 μm depth, 5 μm step size), resulting in 2160 images. We quantified both the presence and morphology of microcracks. We then correlated test parameters (predictors) impact energy/energy dissipation density, nominal stress/stress rate, and strain/strain rate to microcracking and tested for significance. Where predictors significantly correlated with microstructural outcomes we fitted binary logistic regression plots with 95% confidence intervals (CIs).

RESULTS

No specimens presented visible damage following impact. We found that impact energy/energy dissipation density and nominal stress/stress rate were significant (P < 0.05) predictors of microcracking while both strain and strain rate were not. In our test configuration, an impact energy density of 2.93 mJ/mm³, an energy dissipation density of 1.68 mJ/mm³, a nominal stress of 4.18 MPa, and a nominal stress rate of 689 MPa/s all corresponded to a 50% probability of microcracking in the network of collagen.

CONCLUSIONS

An impact energy density of 1.0 mJ/mm³ corresponded to a ∼20% probability of microcracking. Such changes may initiate a degenerative cascade leading to post-traumatic osteoarthritis.

Therapeutic opportunities to prevent post-traumatic arthritis: Lessons from the natural history of arthritis after articular fracture

An estimated 12% of patients seeking surgical intervention for symptomatic arthritis have an etiology of post-traumatic arthritis (PTA). The onset of PTA is rapid in the setting of articular fracture (AF). The investigation began with development of a murine model of a closed AF that develops PTA. In the process of characterizing this model a technique was developed for assessing quantitative synovial fluid biomarker concentrations. The work began with observations of the natural history of PTA development in the C57BL/6 strain of mice. A species of mice (MRL/MpJ) was found that is protected from PTA after AF. Further work identified key differences between mouse strains that did and did not develop PTA. This knowledge led to an intervention based on anti-cytokine (interleukin 1 receptor antagonist, (IL-1Ra) delivery in the C57BL/6 strain of mice that successfully prevented PTA following AF. This success in preventing PTA in the murine model has elucidated several important clinical implications: 1) Pro-inflammatory cytokines play an important role in the development of PTA after joint injury, 2) Pharmacologic intervention can lessen the severity of PTA after an AF, and 3) The murine AF model of joint injury provides a novel means of studying mechanisms of PTA development.

Evaluation of Single-Impact-Induced Cartilage Degeneration by Optical Coherence Tomography

Posttraumatic osteoarthritis constitutes a major cause of disability in our increasingly elderly population. Unfortunately, current imaging modalities are too insensitive to detect early degenerative changes of this disease. Optical coherence tomography (OCT) is a promising nondestructive imaging technique that allows surface and subsurface imaging of cartilage, at near-histological resolution, and is principally applicable in vivo during arthroscopy. Thirty-four macroscopically normal human cartilage-bone samples obtained from total joint replacements were subjected to standardized single impacts in vitro (range: 0.25 J to 0.98 J). 3D OCT measurements of impact area and adjacent tissue were performed prior to impaction, directly after impaction, and 1, 4, and 8 days later. OCT images were assessed qualitatively (DJD classification) and quantitatively using established parameters (OII, Optical Irregularity Index; OHI, Optical Homogeneity Index; OAI, Optical Attenuation Index) and compared to corresponding histological sections. While OAI and OHI scores were not significantly changed in response to low- or moderate-impact energies, high-impact energies significantly increased mean DJD grades (histology and OCT) and OII scores. In conclusion, OCT-based parameterization and quantification are able to reliably detect loss of cartilage surface integrity after high-energy traumatic insults and hold potential to be used for clinical screening of early osteoarthritis.

Measuring microscale strain fields in articular cartilage during rapid impact reveals thresholds for chondrocyte death and a protective role for the superficial layer

Articular cartilage is a heterogeneous soft tissue that dissipates and distributes loads in mammalian joints. Though robust, cartilage is susceptible to damage from loading at high rates or magnitudes. Such injurious loads have been implicated in degenerative changes, including chronic osteoarthritis (OA), which remains a leading cause of disability in developed nations. Despite decades of research, mechanisms of OA initiation after trauma remain poorly understood. Indeed, although bulk cartilage mechanics are measurable during impact, current techniques cannot access microscale mechanics at those rapid time scales. We aimed to address this knowledge gap by imaging the microscale mechanics and corresponding acute biological changes of cartilage in response to rapid loading. In this study, we utilized fast-camera and confocal microscopy to achieve roughly 85 µm spatial resolution of both the cartilage deformation during a rapid (~3 ms), localized impact and the chondrocyte death following impact. Our results showed that, at these high rates, strain and chondrocyte death were highly correlated (p<0.001) with a threshold of 8% microscale strain norm before any cell death occurred. Additionally, chondrocyte death had developed by two hours after impact, suggesting a time frame for clinical therapeutics. Moreover, when the superficial layer was removed, strain - and subsequently chondrocyte death - penetrated deeper into the samples (p<0.001), suggesting a protective role for the superficial layer of articular cartilage. Combined, these results provide insight regarding the detailed biomechanics that drive early chondrocyte damage after trauma and emphasize the importance of understanding cartilage and its mechanics on the microscale.

Tissue engineering strategies to study cartilage development, degeneration and regeneration

Cartilage tissue engineering has primarily focused on the generation of grafts to repair cartilage defects due to traumatic injury and disease. However engineered cartilage tissues have also a strong scientific value as advanced 3D culture models. Here we first describe key aspects of embryonic chondrogenesis and possible cell sources/culture systems for in vitro cartilage generation. We then review how a tissue engineering approach has been and could be further exploited to investigate different aspects of cartilage development and degeneration. The generated knowledge is expected to inform new cartilage regeneration strategies, beyond a classical tissue engineering paradigm.

The effect of recombinant human fibroblast growth factor-18 on articular cartilage following single impact load

The aim of this in vitro study was to ascertain the effect of recombinant human Fibroblast Growth Factor-18 (rhFGF18) on the repair response of mechanically damaged articular cartilage. Articular cartilage discs were harvested from healthy mature horses (n = 4) and subjected to single impact load (SIL). The impacted explants, together with unimpacted controls were cultured in modified DMEM ± 200 ng/ml rhFGF18 for up to 30 days. Glycosaminoglycan (GAG) release into the media was measured using the dimethylmethylene blue (DMMB) assay. Aggrecan neopepitope CS846, collagen type II synthesis (CPII) and cleavage (C2C) were measured by ELISA. Histological analysis and TUNEL staining were used to assess repair cell number and cell death. Impacted explants treated with rhFGF18 showed significantly more GAG and CS846 release into the media (p < 0.05), there was also a significant decrease in C2C levels at Day 20. Loaded sections treated with rhFGF18 had more repair cells and significantly less cell death (p < 0.001) at Day 30 in culture. In an in vitro damage/repair model, rhFGF18 increases the proteoglycan synthesis, the repair cell number and prevents apoptosis at Day 30. This suggests that rhFGF18 may be a good candidate for enhancement of cartilage repair following mechanical damage.

Biomarkers affected by impact velocity and maximum strain of cartilage during injury

Osteoarthritis is one of the most common, debilitating, musculoskeletal diseases; 12% associated with traumatic injury resulting in post-traumatic osteoarthritis (PTOA). Our objective was to develop a single impact model with cartilage "injury level" defined in terms of controlled combinations of strain rate to a maximum strain (both independent of cartilage load resistance) to study their sensitivity to articular cartilage cell viability and potential PTOA biomarkers. A servo-hydraulic test machine was used to measure canine humeral head cartilage explant thickness under repeatable pressure, then subject it (except sham and controls) to a single impact having controlled constant velocity V=1 or 100mm/s (strain rate 1.82 or 182/s) to maximum strain ε=10%, 30%, or 50%. Thereafter, explants were cultured in media for twelve days, with media changed at day 1, 2, 3, 6, 9, 12. Explant thickness was measured at day 0 (pre-injury), 6 and 12 (post-injury). Cell viability, and tissue collagen and glycosaminoglycan (GAG) were analyzed immediately post-injury and day 12. Culture media were tested for biomarkers: GAG, collagen II, chondroitin sulfate-846, nitric oxide, and prostaglandin E2 (PGE2). Detrimental effects on cell viability, and release of GAG and PGE2 to the media were primarily strain-dependent, (PGE2 being more prolonged and sensitive at lower strains). The cartilage injury model appears to be useful (possibly superior) for investigating the relationship between impact severity of injury and the onset of PTOA, specifically for discovery of biomarkers to evaluate the risk of developing clinical PTOA, and to compare effective treatments for arthritis prevention.

Joint instability and cartilage compression in a mouse model of posttraumatic osteoarthritis

Joint instability and cartilage trauma have been previously studied and identified as key mediators in the development of posttraumatic osteoarthritis (PTOA). The purpose of this study was to use an in vivo model to compare the effect of joint instability, caused by the rupture of the anterior cruciate ligament (ACL), versus cartilage compression. In this study, mice were subjected to cyclical axial loads of twelve Newtons (N) for 240 cycles or until the ACL ruptured. One and eight weeks after this procedure, knees were sectioned coronally and evaluated for osteoarthritis by histology. Using a scoring scale established by [Pritzker K, Gay S, Jimenez S, et al. (2006): Osteoarthritis Cartilage 14:13-29], the articular cartilage across each surface was scored and combined to produce a total degeneration score. The ACL-ruptured group had a significantly greater total degeneration score than either control or compression treated joints at 1 and 8 weeks. Additionally, only sections from ACL-ruptured knees consistently showed synovitis after 1 week and osteophyte formation after 8 weeks. Thus, it appears using that ACL rupture consistently creates a severe osteoarthritis phenotype, while axial cartilage compression alone does not appear to be an appropriate method of inducing PTOA in vivo.

Key Pathways to Prevent Posttraumatic Arthritis for Future Molecule-Based Therapy

Joint injuries are common, especially among young adults aged 18 to 44 years. They are accompanied by a cascade of events that increase the risk of posttraumatic osteoarthritis (PTOA). Therefore, understanding of biological responses that predispose to PTOA should help in determining treatment modalities to delay and/or prevent the onset and progression of the disease. The vast majority of the literature pointed to chondrocyte death and apoptosis, inflammation and matrix damage/fragmentation being the earliest events that follow joint trauma. Together these events lead to the development of osteoarthritis-like focal cartilage lesions that if untreated have a tendency to expand and progress to fully developed disease. Currently, the only treatments available for joint trauma are surgical interventions. Experimental biologic approaches involve engineering of cartilage with the use of cells (stem cells or chondrocytes), juvenile or adult cartilage pieces, scaffolds, and various polymeric matrices. The major challenge for all of them is regeneration of normal functional mature hyaline cartilage that can sustain the load, resist compression, and most important, integrate with the host tissue. If the tissue is spontaneously repaired it fails to reproduce original structure and function and thus, may be more susceptible to re-injury. Thus, there is a critical need to develop novel molecular mechanism-based therapeutic approaches to biologic chondral and/or osteochondral repair. The focus of this review is on the earliest molecular and cellular manifestations of injury that can be grouped based on the following therapeutic options for PTOA: chondroprotection, anti-inflammatory, matrix protection, and matrix remodeling/matrix synthesis.

The measurement of joint mechanics and their role in osteoarthritis genesis and progression

Mechanics play a role in the initiation and progression of osteoarthritis. However, our understanding of which mechanical parameters are most important, and what their impact is on the disease, is limited by the challenge of measuring the most important mechanical quantities in living subjects. Consequently, comprehensive statements cannot be made about how mechanics should be modified to prevent, slow or arrest osteoarthritis. Our current understanding is based largely on studies of deviations from normal mechanics caused by malalignment, injury, and deformity. Some treatments for osteoarthritis focus on correcting mechanics, but there appears to be scope for more mechanically based interventions.

Development of an in vitro model of injury-induced osteoarthritis in cartilage explants from adult horses through application of single-impact compressive overload

OBJECTIVE

To develop an in vitro model of cartilage injury in full-thickness equine cartilage specimens that can be used to simulate in vivo disease and evaluate treatment efficacy.

SAMPLE

15 full-thickness cartilage explants from the trochlear ridges of the distal aspect of the femur from each of 6 adult horses that had died from reasons unrelated to the musculoskeletal system.

PROCEDURES

To simulate injury, cartilage explants were subjected to single-impact uniaxial compression to 50%, 60%, 70%, or 80% strain at a rate of 100% strain/s. Other explants were left uninjured (control specimens). All specimens underwent a culture process for 28 days and were subsequently evaluated histologically for characteristics of injury and early stages of osteoarthritis, including articular surface damage, chondrocyte cell death, focal cell loss, chondrocyte cluster formation, and loss of the extracellular matrix molecules aggrecan and types I and II collagen.

RESULTS

Compression to all degrees of strain induced some amount of pathological change typical of clinical osteoarthritis in horses; however, only compression to 60% strain induced significant changes morphologically and biochemically in the extracellular matrix.

CONCLUSIONS AND CLINICAL RELEVANCE

The threshold strain necessary to model injury in full-thickness cartilage specimens from the trochlear ridges of the distal femur of adult horses was 60% strain at a rate of 100% strain/s. This in vitro model should facilitate study of pathophysiologic changes and therapeutic interventions for osteoarthritis.

A rat model of chondrocyte death after closed intra-articular fracture

OBJECTIVE

The development of osteoarthritis after intra-articular fractures has been described for decades, although the exact mechanical and cellular changes that occur remain poorly understood. There are several animal models to study this phenomenon, but they are mechanistically different from physiologic fractures in several important ways. This article describes a novel model that recreates the kinematics present in high-energy trauma and intra-articular fractures.

METHODS

We designed a "drop tower" for the creation of intercondylar femoral fractures in rats and tested it on cadaveric rats to determine the optimal kinetic parameters. Intra-articular fractures were then created in live rats and the animals were killed at 0, 24, and 72 hours after the fracture. Cartilage samples were obtained for live/dead staining, and the relationships among fracture time, cartilage depth, and cell viability were evaluated.

RESULTS

The model reproduced intra-articular fractures very similar to those seen in high-energy trauma, although we required significantly higher energies (3600 mJ) than those reported in other fracture models (40-200 mJ). Cartilage viability decreased with time (68% immediately after the fracture and 46% at 72 hours, P = 0.02) and increased with depth from the articular surface (47% at the surface vs. 66% in the deepest layer, P = 0.001).

CONCLUSIONS

This model is a physiologically relevant reliable method for creating intra-articular fractures in rats and can produce meaningful data about the biologic changes occurring in cartilage after injury. Cell viability decreases with time postfracture and with proximity to the articular surface.

Effect of a solution of hyaluronic acid-chondroitin sulfate-N-acetyl glucosamine on the repair response of cartilage to single-impact load damage

OBJECTIVE

To investigate effects of 1% hyaluronic acid-chondroitin sulfate-N-acetyl glucosamine (HCNAG) on the damage repair response in equine articular cartilage.

SAMPLE

Articular cartilage from 9 clinically normal adult horses.

PROCEDURES

Full-thickness cartilage disks were harvested from the third metacarpal bone. Cartilage was single-impact loaded (SIL) with 0.175 J at 0.7 m/s and cultured in DMEM plus 1 % (vol/vol) HCNAG or fibroblastic growth factor (FGF)-2 (50 ng/mL). Histologic and immunohistochemical techniques were used to identify tissue architecture and apoptotic cells and to immunolocalize type I and II collagen and proliferating nuclear cell antigen (PCNA).

RESULTS

Type II collagen immunoreactivity increased in SIL cartilage, compared with control samples. At days 14 and 28 (day 0 = initiation of culture), control samples had significantly fewer repair cells than did other treatment groups. In control samples and SIL + HCNAG, there was a significant decrease in apoptotic cell number, compared with results for SIL and SIL + FGF-2 samples. At days 14 and 28, there was a significant increase in chondrocytes stained positive for PCNA in the control samples.

CONCLUSIONS AND CLINICAL RELEVANCE

1% HCNAG significantly affected apoptotic and repair cell numbers in an SIL damage-repair technique in adult equine articular cartilage. However, HCNAG had no effect on the number of PCNA-positive chondrocytes or on type II collagen immunohistochemical results. The inclusion of 1% HCNAG in lavage solutions administered after arthroscopy may be beneficial to cartilage health by increasing the number of repair cells and decreasing the number of apoptotic cells.

Early detection of biomolecular changes in disrupted porcine cartilage using polarized Raman spectroscopy

We evaluate the feasibility of applying polarized Raman spectroscopy in probing the early biochemical compositions and orientation changes in impacted porcine cartilage explants. We divide 100 fresh tibial cartilage explants into four groups: control (unimpacted) and 3 groups of single impact at 15, 20, and 25 MPa. Each group is examined for biochemical changes using Raman microscopy, cell viability changes using confocal fluorescence microscopy, and histological changes using the modified Mankin score. For the 15-MPa impact group, the modified Mankin score (p>0.05, n=15) and cell viability test (p>0.05, n=5) reveal no significant changes when compared to the control, but polarized Raman spectroscopy detects significant biochemical changes. A significant decrease in the parallel polarized intensity of the pyranose ring band at 1126 cm(-1) suggests a possible decrease in the glycoaminoglycan content in early cartilage damage (one-way analysis of variance with a post hoc Bonferonni test, p<0.05, n=10). For impacts greater than 15 MPa, cell viability and modified Mankin score are consistent with the changes in the observed polarized Raman signals. This suggests that the polarized Raman spectroscopy technique has potential for diagnosis and detection of early cartilage damage at the molecular level.

Diminished cartilage creep properties and increased trabecular bone density following a single, sub-fracture impact of the rabbit femoral condyle

Traumatic injury to articular cartilage can lead to post-traumatic arthritis. We used a custom pendulum device to deliver a single, near-fracture impact to the medial femoral condyles of rabbits. Impact was localized to a region ∼3 mm in diameter, and impact stress averaged ∼100 MPa. Animals were euthanized at 0, 1, and 6 months after impact. Cartilage mechanical properties from impacted and sham knees were evaluated by creep-indentation testing, and periarticular trabecular bone was evaluated by microCT and histomorphometry. Impact caused immediate and statistically significant loss of cartilage thickness (-40% vs. sham) and led to a greater than twofold increase in creep strain. From 0 to 6 months after impact, the ability of cartilage to recover from creep deformation became significantly impaired (percent recovery different from control at 1 and 6 months). At 1 month, there was a 33% increase in the trabecular bone volume fraction of the epiphysis beneath the site of impact compared to control, and increased bone formation was observed histologically. Taken together, these findings demonstrate that a single, high-energy impact below the fracture threshold leads to acute deleterious changes in the viscoelastic properties of articular cartilage that worsen with time, while at the same time stimulating increased bone formation beneath the impact site.

Extent and distribution of tibial osteochondral disruption during simulated landing impact with axial tibial rotation restraint

Post-traumatic knee osteochondral injuries are often coupled with anterior cruciate ligament (ACL) injury mechanisms during landing. However, it is not well understood whether restraining axial tibial rotation during landing would influence the extent and distribution of osteochondral disruption. Using ski landing as an example, this study subjected knee specimens to simulated landing impact without and with axial tibial rotation restraint, and investigated the extent and distribution of osteochondral disruption at the tibial plateau. Twenty-one porcine knee specimens were randomly divided into three test conditions, namely: (1) control, (2) impact only (I), and 3) impact with restraint (IR). Simulated landing impact was applied to the specimens based on a single 10 Hz haversine. Osteochondral explants were obtained from anterior, middle and posterior regions of medial and lateral tibial compartments. The extent of cartilage and trabecular disruption in these explants was examined based on histology, SEM and microCT. Only specimens in unrestrained condition incurred ACL failure upon impact. Restraining axial tibial rotation during simulated impact generally inflicted cartilage damage and deformation, and further caused trabecular disruption. Axial tibial rotation restraint did not necessarily restrict anterior tibial translation, as indicated by the presence of relative posterior femoral translation and osteochondral disruption at anterior-posterior tibial regions. While the results obtained in the current study may not be completely translatable to human models, there is likelihood that restraining axial tibial rotation during landing may help to prevent ACL failure, but will also induce osteochondral disruption in most tibial regions.

Diagnostic Modalities for Diseased Articular Cartilage-From Defect to Degeneration: A Review

The progression of cartilage matrix damage to generalized degeneration is associated with specific pathophysiological and clinical aspects. Reliable detection of stage-related characteristics of cartilage disease serves both a therapeutic and prognostic goal. Over the past years, several (pre)clinical diagnostic modalities for cartilage pathologies have been advocated. Each modality focuses on different aspects of the disease. Early diagnosis, before irreversible damage has occurred, opens up the possibility for better treatment and improves the patients' prognosis. This article gives an overview of the diagnostic modalities available for monitoring cartilage pathology and focuses on reliability, clinical value, current status, and possible applications.

Tibial cartilage damage and deformation at peak displacement compression during simulated landing impact

BACKGROUND

Structural changes of articular cartilage at the point of peak displacement compression during a landing impact are unknown.

HYPOTHESIS

Extent of damage and deformation is significantly different for superficial, middle, and deep cartilage zones at peak displacement compression during simulated landing impact compared with after impact.

STUDY DESIGN

Controlled laboratory study.

METHODS

Explants were extracted from porcine tibial cartilages and divided into 3 test conditions: nonimpact control, impact and release, and impact and hold. Impact compression, with peak deformation of 2 mm, was applied based on a single 10-Hz haversine to simulate landing impact. For impact and release, explants were subjected to formalin fixation on removal of load after impact. For impact and hold, explants were immediately immersed in formalin with peak deformation maintained at 2 mm. After fixation, the explants underwent histology, whereby Mankin scores and cartilage thicknesses were obtained.

RESULTS

Peak stresses of 9.8 to 28.1 MPa were noted during impact compression. For impact and release, substantial cartilage defects such as surface fraying and fissures were observed. For impact and hold, explants exhibited less severe matrix damage, such as superficial irregularities and tidemark disruption. Mankin scores were lower (indicating less damage; P <.05) in impact and hold than in impact and release condition. Superficial cartilage zone thickness was reduced (P <.05) in both impact and hold and impact and release conditions, relative to nonimpact control.

CONCLUSION

Not only does the loading phase of impact compression play a role in introducing substantial damage and deformation to cartilage, the unloading phase contributes to overall cartilage damage by exacerbating fissure propagation from surface lesions. Clinical Relevance Imaging of clinical injuries may underestimate the magnitude of cartilage compression that occurred during injury. Cartilage tissue engineering scaffolds must be designed to cope with the effects of loading and unloading phases, especially at the superficial zone, so that the repair site can function as well as does the neighboring native cartilage.

Progressive chondrocyte death after impact injury indicates a need for chondroprotective therapy

BACKGROUND

Impact injury to articular cartilage can lead to posttraumatic osteoarthritis.

HYPOTHESES

This study tests the hypotheses that (1) chondrocyte injury occurs after impact at energies insufficient to fracture the cartilage surface, and that (2) cartilage injury patterns vary with impact energy, time after injury, and cartilage thickness.

STUDY DESIGN

Controlled laboratory study.

METHODS

Fresh bovine osteochondral cores were randomly divided into 5 groups: (1) control, (2) 0.35 J, (3) 0.71 J, (4) 1.07 J, and (5) 1.43 J impact energies. Cores were subjected to computer-controlled impact loading and full-thickness sections were then prepared and incubated in Dulbecco's Modified Eagle's Medium/F12 at 37 degrees C. Adjacent sections were harvested 1 and 4 days after impact for viability staining and fluorescent imaging. The area of dead and living chondrocytes was quantified using custom image analysis software and reported as a percentage of total cartilage area.

RESULTS

The highest impact energy fractured the cartilage in all cores (1.43 J, n = 17). Seventy-three percent and 64% of the osteochondral cores remained intact after lower energy impacts of 0.71 J and 1.07 J, respectively. At lower energy levels, fractured cores were thinner (P <.01) than those remaining intact. In cores remaining intact after impact injury, chondrocyte death increased with increasing impact energy (P <.05) and with greater time after impact (P <.05). A progressive increase in dead cells near the bone/cartilage interface and at the articular surface was observed.

CONCLUSION

These data showing progressive chondrocyte death after impact injury at energies insufficient to fracture the cartilage surface demonstrate a potential need for early chondroprotective therapy.

CLINICAL RELEVANCE

These data show that efforts to reduce chondrocyte morbidity after joint injury may be a useful strategy to delay or prevent the onset of posttraumatic osteoarthritis.

Anti-apoptotic treatments prevent cartilage degradation after acute trauma to human ankle cartilage

OBJECTIVES

To investigate the effect of anti-apoptotic agents on cartilage degradation after a single impact to ankle cartilage.

DESIGN

Ten human normal tali were impacted with the impulse of 1 Ns generating peak forces in the range of 600 N using a 4 mm diameter indenter. Eight millimeter cartilage plugs containing the 4 mm diameter impacted core and a 4 mm adjacent ring were removed and cultured with or without P188 surfactant (8 mg/ml), caspase-3 (10 uM), or caspase-9 (2 uM) inhibitors for 48 h. Results were assessed in the superficial and middle-deep layers immediately after injury at day 0 and at 2, 7 and 14 days after injury by live/dead cell and Tunel assays and by histology with Safranin O/fast green staining.

RESULTS

A single impact to human articular cartilage ex vivo resulted in cell death, cartilage degeneration, and radial progression of apoptosis to the areas immediately adjacent to the impact. The P188 was more effective in preventing cell death than the inhibitors of caspases. It reduced cell death by more than 2-fold (P<0.05) in the core and by about 30% in the ring in comparison with the impacted untreated control at all time points. P188 also prevented radial expansion of apoptosis in the ring region especially in the first 7 days post-impaction (7.5% Tunel-positive cells vs 46% in the untreated control; P<0.01). Inhibitors of caspase-3 or -9 were effective in reducing cell death in the impacted core only at early time points, but were ineffective in doing so in the ring. Mankin score was significantly improved in the P188 and caspase-3 treated groups.

CONCLUSIONS

Early intervention with the P188 and caspase-3 inhibitor may have therapeutic potential in the treatment of cartilage defects immediately after injury.

Damage and degenerative changes in menisci-covered and exposed tibial osteochondral regions after simulated landing impact compression-a porcine study

The capacity of menisci-covered and exposed tibial osteochondral regions in resisting impact-induced damage and degeneration is not fully understood. This study sought to evaluate damage and degenerative changes in these regions upon a single simulated landing impact. We hypothesized that the menisci-covered regions are more susceptible to damage and degeneration than their exposed counterparts. Menisci-covered and exposed tibial osteochondral explants were extracted from fresh porcine hind legs and placed in culture up to 14 days. Impact compression, based on a single 10-Hz haversine, was performed at Day 1. Control (non-impact) and impacted explants were randomly selected for cell viability assessment, glycoaminoglycan and collagen content assays, histology, immunohistochemistry, and micro-computed tomography. When subjected to 2-mm displacement compression, exposed explants achieved a significantly higher peak impact stress (p < 0.05) than menisci-covered explants. No significant difference in cell viability, glycoaminoglycan and collagen content, and Mankin scores (p > 0.05) was observed between both explant groups. Both groups were observed with reduced proteoglycan and type II collagen staining at Day 14; the exposed group was noted with increased cartilage volume at Days 7-14. The inferior resistance of menisci-covered regions, against impact-induced damage and degeneration, is a potential factor that may contribute to the meniscectomy model of osteoarthritis.

Inhibition of anterior tibial translation or axial tibial rotation prevents anterior cruciate ligament failure during impact compression

BACKGROUND

Anterior cruciate ligament injury is prevalent in activities involving large and rapid landing impact loads.

HYPOTHESIS

Inhibition of anterior tibial translation/axial tibial rotation forestalls the ligament from failing at the range of peak compressive load that can induce ligament failure when both factors are unrestrained.

STUDY DESIGN

Controlled laboratory study.

METHODS

Sixteen porcine knee specimens were mounted onto a material testing system at 70 degrees of flexion and were divided into 4 test groups: impact compression without restraint (IC), anterior tibial translation restraint (ICA), axial tibial rotation restraint (ICR), and combination of both restraints (ICC). Compression was successively repeated with increasing actuator displacement until ligament failure or visible bone fracture was observed. During compression, rotational and translational joint data were obtained using a motion capture system.

RESULTS

The IC group underwent ligament failure via femoral avulsion; the peak compressive force during failure ranged from 1.4 to 4.0 kN. The ICA, ICR, and ICC test groups developed visible bone fracture with the ligament intact; the peak compressive force during fracture ranged from 2.2 to 6.9 kN. Posterior femoral displacement and axial tibial rotation for the ICA and ICR groups, respectively, were significantly lower relative to the IC group (P < .05). Both factors were substantially reduced in the ICC group, but peak compressive force was higher compared with the IC group (P < .05).

CONCLUSION

Substantial inhibition of these factors in an impact setup, which can induce ligament failure with the factors unrestrained, was able to prevent failure.

CLINICAL RELEVANCE

Adequate inhibition of anterior tibial translation and axial tibial rotation by knee bracing during injurious impact is necessary for effective ligament protection.

The measurement of joint mechanics and their role in osteoarthritis genesis and progression

Mechanics play a role in the initiation, progression, and successful treatment of osteoarthritis. However, we don't yet know enough about which specific mechanical parameters are most important and what their impact is on the disease process to make comprehensive statements about how mechanics should be modified to prevent, slow, or arrest the disease process. The objectives of this review are (1) to summarize methods for assessing joint mechanics and their relative merits and limitations, (2) to describe current evidence for the role of mechanics in osteoarthritis initiation and progression, and (3) to describe some current treatment approaches that focus on modifying joint mechanics.

P188 reduces cell death and IGF-I reduces GAG release following single-impact loading of articular cartilage

Prior joint injury predisposes an individual to developing post-traumatic osteoarthritis, for which there is presently no disease modifying treatment. In this condition, articular cartilage degenerates due to cell death and matrix breakdown, resulting in tissue with diminished biomechanical function. P188, a nonionic surfactant, and the growth factor IGF-I have been shown to decrease cell death. Additionally, IGF-I is known to have beneficial effects on cartilage matrix. The objective of this study was to determine the efficacy of P188, IGF-I, and their combination following articular cartilage impact injury with two energy levels, 1.1 J ("low") and 2.8 J ("high"), at 24 h and 1 week. Bovine articular cartilage with attached underlying bone was impacted at the low or high level. Impact sites were explanted and examined immediately, or cultured for 24 h or 1 week in serum-free media supplemented with P188 (8 mgml), IGF-I (100 ngml), or their combination. Gross morphology, cell viability, GAG release to the media, and tissue mechanical properties were assessed. Immediately postimpact, high level impacted tissue had significantly increased gross morphology scores, indicating tissue damage, which were maintained over 1 week. Gross scores following low impact were initially similar to nonimpacted controls, but, at 24 h and 1 week, low impact gross scores significantly increased compared to nonimpacted controls. Additionally, at 24 h, high impact resulted in increased cell death, and both low and high impacts had increased GAG release compared to nonimpacted controls. Furthermore, high impact caused decreased tissue stiffness at 24 h that appeared to worsen over 1 week, evident by the percent decrease from nonimpacted controls increasing from 16% to 26%. No treatment type studied mitigated this loss. The combination did not perform better than either individual treatment; however, following low impact at 1 week, P188 reduced cell death by 75% compared to no treatment and IGF-I decreased GAG release from the tissue by 49%. In conclusion, high impact resulted in immediate tissue changes that worsened over 1 week. Though not causing immediate changes, low impact also resulted in tissue degeneration evident by 24 h. No treatment studied was effective at 24 h, but by 1 week P188 and IGF-I ameliorated established detrimental changes occurring in articular cartilage postimpact. However, further work is needed to optimize treatment strategies to prevent and/or reverse cell death and matrix destruction in a way that maintains tissue mechanical properties, and hence its functionality.

Apoptosis and gene expression of collagenases but not gelatinases in rabbit disc fragment cultures

OBJECT

The object of this study was to characterize the biological response of isolated intervertebral disc fragments to in vitro culture conditions with respect to cell death and inflammatory and catabolic changes. The acquired data could help to gain a better understanding of the biological reaction of disc tissue when exposed to environmental changes along with altered nutritional and osmotic conditions, as are encountered in different in vitro disc models or disc diseases in vivo.

METHODS

Intervertebral disc anulus fragments were isolated from Burgundy rabbits and cultured in standard media for 3 days. The disc fragments were analyzed for their swelling properties, proteoglycan loss on histological studies, lactate dehydrogenase activity, apoptosis, gene expression of collagenases and gelatinases, and for proinflammatory (MCP-1, IL-8, and IL-6) and apoptosis-associated (TNF-alpha, Fas-L, and caspase 3) genes.

RESULTS

The results demonstrate that disc specimens were swelling, and a loss of proteoglycans with disarrangement of anulus architecture was observed. The disc cells underwent rapid apoptosis with upregulation of various proinflammatory genes. Both collagenases, matrix metalloproteinase (MMP)-1 and MMP-13, were increasingly transcribed, whereas the gelatinases MMP-2 and MMP-9 did not respond or were downregulated.

CONCLUSIONS

Cultured disc fragments swell and undergo necrotic and apoptotic cell death combined with a catabolic gene response and gene expression of proinflammatory and chemoattractant proteins. Some of these findings have been demonstrated before in various spinal disorders. In addition, disc fragments are not suitable for long-term culture if a stable disc metabolism is desired, and the described changes have to be considered when using isolated disc material for in vitro cultures.

Alterations in the vimentin cytoskeleton in response to single impact load in an in vitro model of cartilage damage in the rat

Background

Animal models have provided much information on molecular and cellular changes in joint disease, particularly OA. However there are limitations to in vivo work and single tissue in vitro studies can provide more specific information on individual events. The rat is a commonly used laboratory species but at the current time only in vivo models of rat OA are available to study. The purpose of this study was to investigate the damage that single impact load (SIL) of 0.16J causes in a rat cartilage in vitro model and assess whether this load alters the arrangement of vimentin.

Methods

Rat cartilage was single impact loaded (200 g from 8 cm) and cultured for up to 48 hours (n = 72 joints). Histological changes were measured using a semi-quantitative modified Mankin score. Immunolocalisation was used to identify changes in vimentin distribution.

Results

SIL caused damage in 32/36 cartilage samples. Damage included surface fibrillation, fissures, fragmentation, changes in cellularity and loss of proteoglycan. SIL caused a statistically significant increase in modified Mankin score and chondrocyte clusters over time. SIL caused vimentin disassembly (as evidenced by collapse of vimentin around the nucleus).

Conclusion

This study describes a model of SIL damage to rat cartilage. SIL causes changes in histological/chemical parameters which have been measured using a semi-quantitative modified Mankin score. Single impact load also causes changes in the pattern of vimentin immunoreactivity, indicating vimentin dissassembley. Using a semi-quantitative scoring system the disassembly was shown to be statistically significant in SIL damaged cartilage.

The changes described in this paper suggest that this novel single tissue rat model of joint damage is a possible candidate model to replace in vivo models.

Effects of doxycycline on articular cartilage GAG release and mechanical properties following impact

The effects of doxycycline were examined on articular cartilage glycosaminoglycan (GAG) release and biphasic mechanical properties following two levels of impact loading at 1 and 2 weeks post-injury. Further, treatment for two continuous weeks was compared to treatment for only the 1st week of a 2-week culture period. Following impact at two levels, articular cartilage explants were cultured for 1 or 2 weeks with 0, 50, or 100 microM doxycycline. Histology, GAG release to the media, and creep indentation biomechanical properties were examined. The "High" (2.8 J) impact level had gross surface damage, whereas "Low" (1.1 J) impact was indiscernible from non-impacted controls. GAG staining decreased after High impact, but doxycycline did not visibly affect staining. High impact resulted in decreased aggregate moduli at both 1 and 2 weeks and increased permeability at 2 weeks, but tissue mechanical properties were not affected by doxycycline treatment. At 1 week, High impact resulted in more GAG release compared to non-impacted controls. However, following High impact, 100 microM doxycycline reduced cumulative GAG release at 1 and 2 weeks by 30% and 38%, respectively, compared to no treatment. Interestingly, there was no difference in GAG release comparing 2 weeks continuous treatment with 1 week on, 1 week off. These results support the hypothesis that doxycycline can mitigate GAG release from articular cartilage following impact loads. However, doxycycline was unable to prevent the loss of tissue stiffness observed post-impact, presumably due to initial matrix damage resulting solely from mechanical trauma.

Anterior cruciate ligament failure and cartilage damage during knee joint compression: a preliminary study based on the porcine model

BACKGROUND

Anterior cruciate ligament (ACL) injury incurred from high-impact activities leads to an increased risk of osteoarthritis.

HYPOTHESIS

Impact forces that cause ACL failure can also inflict cartilage damage, whereby its extent and distribution may be influenced by the ligament failure mechanism.

STUDY DESIGN

Descriptive laboratory study.

METHODS

Six porcine knee specimens were mounted to a material testing system at 70 degrees of flexion. During compression, rotational and translational data of the specimens were recorded with a motion-capture system. Compression was successively repeated with increasing actuator displacement until a significant drop in compressive force response was observed; ligament failure was assessed by dissection. Osteocartilage explants were extracted from the meniscus-covered sites (anterior, exterior, and posterior) and exposed (interior) sites on both tibial compartments. The explants were sectioned, stained, and histologically scored using the modified Mankin grading system.

RESULTS

Five of the 6 specimens incurred ACL failure. On failure, a significant compressive force drop (1812.5-2659.3 N) was observed together with considerable posterior femoral translation; 2 specimens underwent external rotation, while 2 had internal rotation and 1 had no substantial rotation. Generally, the meniscus-covered sites displayed significant surface fraying and occasional deep clefts; the exposed site did not present substantial surface irregularities but indicated more tidemark disruption. Higher Mankin scores observed at certain sites illustrated a localized presence of contact and shear forces, which may be caused by pivoting and sliding of the femoral condyles during rotation.

CONCLUSION

The porcine model can be a tenable preliminary option for assessing the role of the human ACL during joint compression. Impact loads that result in ligament failure can potentially inflict considerable cartilage damage; the damage profile may be affected by the type of failure mechanism.

CLINICAL RELEVANCE

Cartilage injury arising at the time of ACL injury may lead to an accelerated risk of joint degeneration.

Temporal effects of impact on articular cartilage cell death, gene expression, matrix biochemistry, and biomechanics

Articular cartilage injury can cause post-traumatic osteoarthritis, but early processes leading to the disease are not well understood. The objective of this study was to characterize two levels of impact loading at 24 h, 1 week, and 4 weeks in terms of cell death, gene expression, extracellular matrix biochemistry, and tissue biomechanical properties. The data show cell death increased and tissue stiffness decreased by 24 h following High impact (2.8 J). These degradative changes persisted at 1 and 4 weeks, and were further accompanied by measurable changes in ECM biochemistry. Moreover, following High impact at 24 h there were specific changes in gene expression that distinguished injured tissue from adjacent tissue that was not loaded. In contrast, Low impact (1.1 J) showed little change from control specimens at 24 h or 1 week. However, at 4 weeks, a significant increase in cell death and significant decrease in tissue stiffness were present. The constellation of findings indicates Low impacted tissue exhibited a delayed biological response. The study characterizes a model system for examining the biology of articular cartilage post-impact, as well as identifies possible time points and success criteria to be used in future studies employing intervention agents.

Effect of a glucosamine derivative on impact-induced chondrocyte apoptosis in vitro. A preliminary report

Here, we report that a lipophilic derivative of glucosamine, Glu5, is able to prevent impact-induced chondrocyte death by the putative mechanism of reducing mitochondrial depolarisation following a single impact load in vitro.

Chondrocyte outgrowth into a gelatin scaffold in a single impact load model of damage/repair - effect of BMP-2

Background

Articular cartilage has little capacity for repair in vivo, however, a small number of studies have shown that, in vitro, a damage/repair response can be induced. Recent work by our group has shown that cartilage can respond to single impact load and culture by producing repair cells on the articular surface. The purpose of this study was to identify whether chondrocyte outgrowth into a 3D scaffold could be observed following single impact load and culture. The effect of bone morphogenic-2 (BMP-2) on this process was investigated.

Methods

Cartilage explants were single impact loaded, placed within a scaffold and cultured for up to 20 days +/- BMP-2. Cell numbers in the scaffold, on and extruding from the articular surface were quantified and the immunohistochemistry used to identify the cellular phenotype.

Results

Following single impact load and culture, chondrocytes were observed in a 3D gelatin scaffold under all culture conditions. Chondrocytes were also observed on the articular surface of the cartilage and extruding out of the parent cartilage and on to the cartilage surface. BMP-2 was demonstrated to quantitatively inhibit these events.

Conclusion

These studies demonstrate that articular chondrocytes can be stimulated to migrate out of parent cartilage following single impact load and culture. The addition of BMP-2 to the culture medium quantitatively reduced the repair response. It may be that the inhibitory effect of BMP-2 in this experimental model provides a clue to the apparent inability of articular cartilage to heal itself following damage in vivo.

Vertebral endplate trauma induces disc cell apoptosis and promotes organ degeneration in vitro

There is a major controversy whether spinal trauma with vertebral endplate fractures can result in post-traumatic disc degeneration. Intervertebral discs, which are adjacent to burst endplates, are frequently removed and an intercorporal spondylodesis is performed. In any case, the biological effects within the discs following endplate fractures are poorly elucidated to date. The aim of our investigations was therefore to establish a novel disc/endplate trauma culture model to reproducibly induce endplate fractures and investigate concurrent disc changes in vitro. This model is based on a full-organ disc/endplate culture system, which has been validated by the authors before. Intervertebral disc/endplate specimens were isolated from Burgundy rabbits and cultured in standard media (DMEM/F12, 10%FCS). Burst endplate fractures were induced in half of the specimens with a custom-made fracture device and subsequently cultured for 9 days. The biological effects such as necrotic or apoptotic cell death and the expression of pro-apoptotic genes and other genes involved in organ degeneration, e.g. matrix metalloproteinases (MMPs) were analyzed. Cell damage was assessed by quantification of the lactate dehydrogenase (LDH) activity in the supernatant. The expression of genes involved in the cellular apoptotic pathway (caspase 3) and the pro-apoptotic proteins FasL and TNF-alpha were monitored. The results demonstrate that LDH levels increased significantly post trauma compared to the control and remained elevated for 3 days. Furthermore, a constant up-regulation of the caspase 3 gene in both disc compartments was present. The pro-apoptotic proteins FasL and TNF-alpha were up regulated predominantly in the nucleus whereas the MMP-1 and -13 transcripts (collagenases) were increased in both disc structures. From this study we can conclude that endplate burst fractures result in both necrotic and apoptotic cell death in nucleus and annulus tissue. Moreover, FasL and TNF-alpha expression by nucleus cells may lead to continued apoptosis induced by Fas- and TNF-alpha receptor bearing cells. In addition TNF-alpha over-expression has potentially deleterious effects on disc metabolism such as over-expression of matrix proteinases. Taken together, the short term biological response of the disc following endplate fracture exhibits characteristics, which may initiate the degeneration of the organ.

Calcium signaling leads to mitochondrial depolarization in impact-induced chondrocyte death in equine articular cartilage explants

OBJECTIVE

Chondrocyte apoptosis is an important factor in the progression of osteoarthritis. This study aimed to elucidate the mechanisms involved upstream of caspase 9 activation and, in particular, calcium signaling and mitochondrial depolarization.

METHODS

Articular cartilage explants obtained from healthy horses were subjected to a single impact load (500-gm weight dropped from a height of 50 mm) and cultured in vitro for up to 48 hours. Chondrocyte death was quantified by the TUNEL method. Release of proteoglycans was determined by the dimethylmethylene blue assay. Weight change was measured, and mitochondrial depolarization was determined using JC-1 staining. To assess the role of calcium signaling in impact-induced chondrocyte death, explants were preincubated in culture medium containing various concentrations of calcium. Inhibitors were used to assess the role of individual signaling components in impact-induced chondrocyte death.

RESULTS

Calcium quenching, inhibitors of calpains, calcium/calmodulin-regulated kinase II (CaMKII), and mitochondrial depolarization reduced impact-induced chondrocyte death after 48 hours in culture. Transient mitochondrial depolarization was observed 3-6 hours following a single impact load. Mitochondrial depolarization was prevented by calcium quenching, inhibitors of calpain, CaMKII, permeability transition pore formation, ryanodine receptor, and the mitochondrial uniport transporter. Cathepsin B did not appear to be involved in impact-induced chondrocyte death. The calpain inhibitor prevented proteoglycan loss, but the percentage weight gain and proteoglycan loss were unaffected by all treatments used.

CONCLUSION

Following a single impact load, calcium is released from the endoplasmic reticulum via the ryanodine receptor and is taken up by the mitochondria via the uniport transporter, causing mitochondrial depolarization and caspase 9 activation. In addition, calpains and CaMKII play important roles in causing mitochondrial depolarization.

Inhibition of caspase-9 reduces chondrocyte apoptosis and proteoglycan loss following mechanical trauma

OBJECTIVE

Chondrocyte death, a notable feature of osteoarthritis, may play a role in the initiation of cartilage degeneration. The present study was aimed at uncovering the nature and involvement of cell death in the initiation of cartilage degeneration induced by mechanical trauma.

METHODS

Articular cartilage discs obtained from healthy skeletally mature horses were subjected to a single-impact load (500 g from 50 mm) using a simple drop-tower device and cultured in vitro for 48 h. Chondrocyte death was examined using two independent methods: transmission electron microscopy and caspase-3 activity assay. To elucidate the signalling mechanisms involved in impact-induced cell death measured by terminal deoxynucleotidyl transferase-deoxyuridine triphosphate (dUTP) nick-end labelling (TUNEL), cartilage discs were incubated with specific caspase-3, -8 and -9 inhibitors prior to impact. Additionally, weight gain and glycosaminoglycan (GAG) release, markers of cartilage degeneration were monitored.

RESULTS

After 48 h, ultrastructural evidence of apoptosis was observed. Caspase-3 was activated after 12h of culture post-impact. When quantified by TUNEL, impact trauma induced death in 52.6% of superficial chondrocytes after 48 h in culture, compared to 4.2% in unimpacted controls. Specific caspases-3 and -9 inhibitors significantly reduced impact-induced apoptosis to 24.3% and 14.7%, respectively. Caspase-8 inhibition had no effect on chondrocyte death (60.3%). Impact-induced GAG release into the medium was significantly reduced by inhibition of cell death, but weight gain remained unaffected by caspase inhibition.

CONCLUSION

These results suggest that impact trauma-induced chondrocyte death is predominantly due to caspase-9-dependent apoptosis and is linked to cartilage degeneration.