Variation in proteoglycan metabolism by articular chondrocytes in different joint regions is determined by post-natal mechanical loading

The Response of Hip Joint Cartilage to Exercise in Children: An MRI Study Using T2-Mapping

OBJECTIVE

The aim of this study was to determine the effects of activity and cam morphology on cartilage composition during adolescence and investigate the development of cartilage composition with age.

DESIGN

Cross-sectional observational cohort study of individuals from football club academies and an age-matched control population, aged 9 to 18 years. Assessments included questionnaires and T2-mapping of hips. Primary imaging outcome measures were T2 relaxation time of acetabular and femoral cartilage, average alpha angle, and lateral epiphyseal extension.

RESULTS

The cohort consisted of 109 elite male footballers, 49 male controls, and 51 female controls. Elite male footballers had an acetabular cartilage T2 value 4.85 ms greater than male controls (P < 0.001). A significant positive correlation existed between Physical Activity Questionnaire Score and acetabular cartilage T2 value (coefficient 1.07, P < 0.001) and femoral cartilage T2 value (coefficient 0.66, P = 0.032). Individuals with a closed physis had an acetabular cartilage T2 value 7.86 ms less than individuals with an open physis. Acetabular cartilage T2 values decreased with age in elite footballers. No correlation existed between alpha angle and anterosuperior acetabular cartilage T2 value and no difference in T2 value existed between individuals with and without cam morphology.

CONCLUSIONS

This study demonstrates that high activity levels may significantly affect acetabular cartilage composition during adolescence, but cam morphology may not detrimentally affect cartilage composition until after adolescence.

Quality control methods in musculoskeletal tissue engineering: from imaging to biosensors

Tissue engineering is rapidly progressing toward clinical application. In the musculoskeletal field, there has been an increasing necessity for bone and cartilage replacement. Despite the promising translational potential of tissue engineering approaches, careful attention should be given to the quality of developed constructs to increase the real applicability to patients. After a general introduction to musculoskeletal tissue engineering, this narrative review aims to offer an overview of methods, starting from classical techniques, such as gene expression analysis and histology, to less common methods, such as Raman spectroscopy, microcomputed tomography, and biosensors, that can be employed to assess the quality of constructs in terms of viability, morphology, or matrix deposition. A particular emphasis is given to standards and good practices (GXP), which can be applicable in different sectors. Moreover, a classification of the methods into destructive, noninvasive, or conservative based on the possible further development of a preimplant quality monitoring system is proposed. Biosensors in musculoskeletal tissue engineering have not yet been used but have been proposed as a novel technology that can be exploited with numerous advantages, including minimal invasiveness, making them suitable for the development of preimplant quality control systems.

Effect of a Moderate-Intensity Aerobic Training on Joint Biomarkers and Functional Adaptations in Rats Subjected to Induced Knee Osteoarthritis

Background

Knee osteoarthritis (_kOA) is a common chronic disease that induces changes in redox status and inflammatory biomarkers, cell death, and motor impairment. Aerobic training can be a non-pharmacological alternative to prevent the progression of the disease.

Objective

To evaluate the effects of an 8 weeks moderate-intensity treadmill aerobic training program on redox status and inflammatory biomarkers and motor performance in _kOA-like changes induced by monosodium iodoacetate (MIA) in rats.

Methods

Twenty-seven rats were randomly divided into three groups: SHAM; induced _kOA (OA); and induced _kOA + aerobic training (OAE). Motor performance was evaluated by the number of falls on rotarod test, the total time of displacement and the number of failures on a 100 cm footbridge. Data for cytokines and histology were investigated locally, whereas plasma was used for redox status biomarkers.

Results

The OA group, compared to the SHAM group, increased 1.13 times the total time of displacement, 6.05 times the number of failures, 2.40 times the number of falls. There was also an increase in cytokine and in thiobarbituric acid reactive substances (TBARS) (IL1β: 5.55-fold, TNF: 2.84-fold, IL10: 1.27-fold, IL6: 1.50-fold, TBARS: 1.14-fold), and a reduction of 6.83% in the total antioxidant capacity (FRAP), and of 35% in the number of chondrocytes. The aerobic training improved the motor performance in all joint function tests matching to SHAM scores. Also, it reduced inflammatory biomarkers and TBARS level at values close to those of the SHAM group, with no change in FRAP level. The number of falls was explained by IL1β and TNF (58%), and the number of failures and the total time of displacement were also explained by TNF (29 and 21%, respectively).

Conclusion

All findings indicate the efficacy of moderate-intensity aerobic training to regulate inflammatory biomarkers associated with improved motor performance in induced _kOA-like changes, thus preventing the loss of chondrocytes.

Non-Destructive Spectroscopic Assessment of High and Low Weight Bearing Articular Cartilage Correlates with Mechanical Properties

OBJECTIVE

Autologous articular cartilage (AC) harvested for repair procedures of high weight bearing (HWB) regions of the femoral condyles is typically obtained from low weight bearing (LWB) regions, in part due to the lack of non-destructive techniques for cartilage composition assessment. Here, we demonstrate that infrared fiber optic spectroscopy can be used to non-destructively evaluate variations in compositional and mechanical properties of AC across LWB and HWB regions.

DESIGN

AC plugs (N = 72) were harvested from the patellofemoral groove of juvenile bovine stifle joints, a LWB region, and femoral condyles, a HWB region. Near-infrared (NIR) and mid-infrared (MIR) fiber optic spectra were collected from plugs, and indentation tests were performed to determine the short-term and equilibrium moduli, followed by gravimetric water and biochemical analysis.

RESULTS

LWB tissues had a significantly greater amount of water determined by NIR and gravimetric assay. The moduli generally increased in tissues from the patellofemoral groove to the condyles, with HWB condyle cartilage having significantly higher moduli. A greater amount of proteoglycan content was also found in HWB tissues, but no differences in collagen content. In addition, NIR-determined water correlated with short-term modulus and proteoglycan content (R = -0.40 and -0.31, respectively), and a multivariate model with NIR data was able to predict short-term modulus within 15% error.

CONCLUSIONS

The properties of tissues from LWB regions differ from HWB tissues and can be determined non-destructively by infrared fiber optic spectroscopy. Clinicians may be able to use this modality to assess AC prior to harvesting osteochondral grafts for focal defect repair.

Topographical Variation of Human Femoral Articular Cartilage Thickness, T1rho and T2 Relaxation Times Is Related to Local Loading during Walking

OBJECTIVE

Early detection of degenerative changes in the cartilage matrix composition is essential for evaluating early interventions that slow down osteoarthritis (OA) initiation. T1rho and T2 relaxation times were found to be effective for detecting early changes in proteoglycan and collagen content. To use these magnetic resonance imaging (MRI) methods, it is important to document the topographical variation in cartilage thickness, T1rho and T2 relaxation times in a healthy population. As OA is partially mechanically driven, the relation between these MRI-based parameters and localized mechanical loading during walking was investigated.

DESIGN

MR images were acquired in 14 healthy adults and cartilage thickness and T1rho and T2 relaxation times were determined. Experimental gait data was collected and processed using musculoskeletal modeling to identify weight-bearing zones and estimate the contact force impulse during gait. Variation of the cartilage properties (i.e., thickness, T1rho, and T2) over the femoral cartilage was analyzed and compared between the weight-bearing and non-weight-bearing zone of the medial and lateral condyle as well as the trochlea.

RESULTS

Medial condyle cartilage thickness was correlated to the contact force impulse ( r = 0.78). Lower T1rho, indicating increased proteoglycan content, was found in the medial weight-bearing zone. T2 was higher in all weight-bearing zones compared with the non-weight-bearing zones, indicating lower relative collagen content.

CONCLUSIONS

The current results suggest that medial condyle cartilage is adapted as a long-term protective response to localized loading during a frequently performed task and that the weight-bearing zone of the medial condyle has superior weight bearing capacities compared with the non-weight-bearing zones.

Structure-function relationships of fetal ovine articular cartilage

It is crucial that the properties of engineered neocartilage match healthy native cartilage to promote the functional restoration of damaged cartilage. To accurately assess the quality of neocartilage and the degree of biomimicry achieved, its properties must be evaluated against native cartilage and tissue from which the cells for neocartilage formation were sourced. Fetal ovine cartilage is a promising and translationally relevant cell source with which to engineer neocartilage, yet, it is largely non-characterized. The influence of biomechanics during cartilage development, as well as their potential impact on structure-function relationships in utero motivates additional study of fetal cartilage. Toward providing tissue engineering design criteria and elucidating structure-function relationships, 11 locations across four regions of the fetal ovine stifle were characterized. Locational and regional differences were found to exist. Although differences in GAG content were observed, compressive stiffness did not vary or correlate with any biochemical component. Patellar cartilage tensile stiffness and strength were significantly greater than those of the medial condyle. Tensile modulus and UTS significantly correlated with pyridinoline content. More advanced zonal organization, more intense collagen II staining, and greater collagen and pyridinoline contents in the trochlear groove and patella suggest these regions exhibit a more advanced maturational state than others. Regional differences in functional properties and their correlations suggest that structure-function relationships emerge in utero. These data address the dearth of information of the fetal ovine stifle, may serve as a repository of information for cartilage engineering strategies, and may help elucidate functional adaptation in fetal articular cartilage. STATEMENT OF SIGNIFICANCE: Engineered neocartilage must be evaluated against healthy native cartilage and cell source tissue to determine its quality and degree of biomimicry. While fetal ovine cartilage has emerged as a promising and translationally relevant cell source with which to engineer neocartilage, it is largely non-characterized. Therefore, 11 locations across four regions (medial condyle, lateral condyle, trochlear groove, and patella) of the fetal ovine stifle were characterized. Importantly, locational and regional differences in functional properties were observed, and significant correlations of tensile properties to collagen and crosslink contents were detected, suggesting that functional adaptation begins in utero. This study provides a repository of quantitative information, clarifies the developmental order of cartilage functional properties, and informs future cartilage engineering efforts.

The knee joint loose body as a source of viable autologous human chondrocytes

Loose bodies are fragments of cartilage or bone present in the synovial fluid. In the present study we assessed if loose bodies could be used as a source of autologous human chondrocytes for experimental purposes. Histochemical examination of loose bodies and differential enzymatic digestions were undertaken, the isolated cells were cultured in alginate bead microspheres and immunolocalisations were undertaken for chondrogenic markers such as aggrecan, and type II collagen. Isolated loose body cells had high viability (≥90% viable), expressed chondrogenic markers (aggrecan, type II collagen) but no type I collagen. Loose bodies may be a useful source of autologous chondrocytes of high viability.

Acute Osteochondral Fractures in the Lower Extremities - Approach to Identification and Treatment

Chondral and osteochondral fractures of the lower extremities are important injuries because they can cause pain and dysfunction and often lead to osteoarthritis. These injuries can be misdiagnosed initially which may impact on the healing potential and result in poor long-term outcome. This comprehensive review focuses on current pitfalls in diagnosing acute osteochondral lesions, potential investigative techniques to minimize diagnostic errors as well as surgical treatment options. Acute osteochondral fractures are frequently missed and can be identified more accurately with specific imaging techniques. A number of different methods can be used to fix these fractures but attention to early diagnosis is required to limit progression to osteoarthritis. These fractures are common with joint injuries and early diagnosis and treatment should lead to improved long term outcomes.

Effects of cyclic tensile strain on chondrocyte metabolism: a systematic review

Chondrocytes reorganize the extracellular matrix of articular cartilage in response to externally applied loads. Thereby, different loading characteristics lead to different biological responses. Despite of active research in this area, it is still unclear which parts of the extracellular matrix adapt in what ways, and how specific loading characteristics affect matrix changes. This review focuses on the influence of cyclic tensile strain on chondrocyte metabolism in vitro. It also aimed to identify anabolic or catabolic chondrocyte responses to different loading protocols. The key findings show that loading cells up to 3% strain, 0.17 Hz, and 2 h, resulted in weak or no biological responses. Loading between 3–10% strain, 0.17–0.5 Hz, and 2–12 h led to anabolic responses; and above 10% strain, 0.5 Hz, and 12 h catabolic events predominated. However, this review also discusses that various other factors are involved in the remodeling of the extracellular matrix in response to loading, and that parameters like an inflammatory environment might influence the biological response.

The regional sensitivity of chondrocyte gene expression to coactive mechanical load and exogenous TNF-α stimuli

Both mechanical load and elevated levels of proinflammatory cytokines have been associated with the risk for developing osteoarthritis (OA), yet the potential interaction of these mechanical and biological factors is not well understood. The purpose of this study was to evaluate the response of chondrocytes to the effects of dynamic unconfined compression, TNF-α, and the simultaneous effects of dynamic unconfined compression and TNF-α. The response to these three treatments was markedly different and, taken together, the response in the gene expression of chondrocytes to the different treatment conditions suggest a complex interaction between structure, biology, and mechanical loading.

The effect of compressive loading magnitude on in situ chondrocyte calcium signaling

Chondrocyte metabolism is stimulated by deformation and is associated with structural changes in the cartilage extracellular matrix (ECM), suggesting that these cells are involved in maintaining tissue health and integrity. Calcium signaling is an initial step in chondrocyte mechanotransduction that has been linked to many cellular processes. Previous studies using isolated chondrocytes proposed loading magnitude as an important factor regulating this response. However, calcium signaling in the intact cartilage differs compared to isolated cells. The purpose of this study was to investigate the effect of loading magnitude on chondrocyte calcium signaling in intact cartilage. We hypothesized that the percentage of cells exhibiting at least one calcium signal increases with increasing load. Fully intact rabbit femoral condyle and patellar bone/cartilage samples were incubated in calcium-sensitive dyes and imaged continuously under compressive loads of 10-40 % strain. Calcium signaling was primarily associated with the dynamic loading phase and greatly increased beyond a threshold deformation of about 10 % nominal tissue strain. There was a trend toward more cells exhibiting calcium signaling as loading magnitude increased (p = 0.133). These results provide novel information toward identifying mechanisms underlying calcium-dependent signaling pathways related to cartilage homeostasis and possibly the onset and progression of osteoarthritis.

Immature articular cartilage and subchondral bone covered by menisci are potentially susceptive to mechanical load

Background

The differences of mechanical and histological properties between cartilage covered by menisci and uncovered by menisci may contribute to the osteoarthritis after meniscectomy and these differences are not fully understood. The purpose of this study is to investigate potential differences in the mechanical and histological properties, and in particular the collagen architecture, of the superficial cartilage layer and subchondral bone between regions covered and uncovered by menisci using immature knee.

Methods

Osteochondral plugs were obtained from porcine tibial cartilage that was either covered or uncovered by menisci. Investigation of the thickness, mechanical properties, histology, and water content of the cartilage as well as micro-computed tomography analysis of the subchondral bone was performed to compare these regions. Collagen architecture was also assessed by using scanning electron microscopy.

Results

Compared to the cartilage uncovered by menisci, that covered by menisci was thinner and showed a higher deformity to compression loading and higher water content. In the superficial layer of cartilage in the uncovered regions, collagen fibers showed high density, whereas they showed low density in covered regions. Furthermore, subchondral bone architecture varied between the 2 regions, and showed low bone density in covered regions.

Conclusions

Cartilage covered by menisci differed from that uncovered in both its mechanical and histological properties, especially with regards to the density of the superficial collagen layer. These regional differences may be related to local mechanical environment in normal condition and indicate that cartilage covered by menisci is tightly guarded by menisci from extreme mechanical loading. Our results indicate that immature cartilage degeneration and subchondral microfracture may occur easily to extreme direct mechanical loading in covered region after meniscectomy.

Modulation of endochondral ossification by MEK inhibitors PD0325901 and AZD6244 (Selumetinib)

MEK inhibitors (MEKi) PD0325901 and AZD6244 (Selumetinib) are drugs currently under clinical investigation for cancer treatment, however the Ras-MAPK pathway is also an important mediator of normal bone cell differentiation and function. In this study we examined the effects of these compounds on endochondral processes using both in vitro and in vivo models. Treatment with PD0325901 or AZD6244 significantly increased Runx2 and Alkaline phosphate gene expression in calvarial osteoblasts and decreased TRAP+ cells in induced osteoclast cultures. To test the effects of these drugs on bone healing, C57/Bl6 mice underwent a closed tibial fracture and were treated with PD0325901 or AZD6244 at 10mg/kg/day. Animals were culled at day 10 and at day 21 post-fracture for analysis of the fracture callus and the femoral growth plate in the contralateral leg. MEKi treatment markedly increased cartilage volume in the soft callus at day 10 post-fracture (+60% PD0325901, +20% AZD6244) and continued treatment led to a delay in cartilage remodeling. At the growth plate, we observed an increase in the height of the hypertrophic zone relative to the proliferative zone of +78% in PD0325901 treated mice. Osteoclast surface was significantly decreased both at the terminal end of the growth plate and within the fracture calluses of MEKi treated animals. The mechanistic effects of MEKi on genes encoding cartilage matrix proteins and catabolic enzymes were examined in articular chondrocyte cultures. PD0325901 or AZD6244 led to increased matrix protein expression (Col2a1 and Acan) and decreased expression of catabolic factors (Mmp13 and Adamts-5). Taken together, these data support the hypothesis that MEKi treatment can impact chondrocyte hypertrophy, matrix resorption, and fracture healing. These compounds can also affect bone architecture by expanding the hypertrophic zone of the growth plate and reducing osteoclast surface systemically.

Improved repair of chondral and osteochondral defects in the ovine trochlea compared with the medial condyle

Associations between topographic location and articular cartilage repair in preclinical animal models are unknown. Based on clinical investigations, we hypothesized that lesions in the ovine femoral condyle repair better than in the trochlea. Full-thickness chondral and osteochondral defects were simultaneously established in the weightbearing area of the medial femoral condyle and the lateral trochlear facet in sheep, with chondral defects subjected to subchondral drilling. After 6 months in vivo, cartilage repair and osteoarthritis development was evaluated by macroscopic, histological, immunohistochemical, and biochemical analyses. Macroscopic and histological articular cartilage repair and type-II collagen immunoreactivity were better in the femoral trochlea, regardless of the defect type. Location-independently, osteochondral defects induced more osteoarthritic degeneration of the adjacent cartilage than drilled chondral lesions. DNA and proteoglycan contents of chondral defects were higher in the condyle, reflecting physiological topographical differences. The results indicate that topographic location dictates the structural patterns and biochemical composition of the repair tissue in sheep. These findings suggest that repair of cartilage defects at different anatomical sites of the ovine stifle joint needs to be assessed independently and that the sheep trochlea exhibits cartilage repair patterns reflective of the human medial femoral condyle.

The influence of dietary restriction before and after 10 weeks of age on osteochondrosis in growing gilts

Osteochondrosis (OC) is one of the main causes of leg weakness causing premature culling in breeding sows and develops in a short time frame in young growing gilts. Dietary restriction may have different effects on OC prevalence depending on the age of the gilts. The aim of this study is to investigate age-dependent effects of dietary restriction, ad libitum vs. restricted (80% of ad libitum), on the occurrence of OC in gilts at slaughter (26 wk of age). At weaning (4 wk of age), 211 gilts were subjected to one of 4 treatments of a feeding regime. Gilts were administered either ad libitum feeding from weaning until slaughter (AA); restricted feeding from weaning until slaughter (RR); ad libitum feeding from weaning until 10 wk of age, after which gilts were switched to restricted feeding (AR); or restricted feeding from weaning until 10 wk of age, after which gilts were switched to ad libitum feeding (RA). At slaughter, the elbow, hock, and knee joints were harvested. Joints were scored macroscopically for articular surface deformations indicative of OC. Gilts in the RA treatment had significantly higher odds of being affected by OC than gilts in the RR and AR treatments in the hock joint (OR=3.3, P=0.04 and OR=8.5, P=0.002, respectively) and at animal level (OR=2.5, P=0.001 and OR=1.9, P=0.01, respectively). Gilts in the AA treatment had higher odds of being affected by OC than gilts in the AR treatment in the hock joint (OR=5.3, P=0.01). The results indicate a possible pathway to reduce the prevalence of OC in breeding gilts that will have to last several parities. Switching from restricted feeding to ad libitum feeding after 10 wk of age increases OC prevalence as opposed to restricted feeding after 10 wk of age.

Long-term repetitive mechanical loading of the knee joint by in vivo muscle stimulation accelerates cartilage degeneration and increases chondrocyte death in a rabbit model

BACKGROUND

Excessive chronic loading is thought to be one factor responsible for the onset of osteoarthritis. For example, studies using treadmill running have shown an increased risk for osteoarthritis, thereby suggesting that muscle-induced joint loading may play a role in osteoarthritis onset and progression. However, in these studies, muscle-induced loading was not carefully quantified. Here, we present a model of controlled muscular loading which allows for the accurate quantification of joint loading. The aim of this study was to evaluate the effects of long-term, cyclic, isometric and dynamic, muscle-induced joint loading of physiologic magnitude but excessive intensity on cartilage integrity and cell viability in the rabbit knee.

METHODS

24 rabbits were divided into an (i) eccentric, (ii) concentric, or (iii) isometric knee extensor contraction group (50 min of cyclic, submaximal stimulation 3 times/week for four weeks=19,500 cycles) controlled by the stimulation of a femoral nerve cuff electrode on the right hind limb. The contralateral knee was used as a non-loaded control. The knee articular cartilages were analysed by confocal microscopy for chondrocyte death, and histologically for Mankin Score, cartilage thickness and cell density.

FINDINGS

All loaded knees had significantly increased cell death rates and Mankin Scores compared to the non-loaded joints. Cartilage thicknesses did not systematically differ between loaded and control joints.

INTERPRETATION

Chondrocyte death and Mankin Scores were significantly increased in the loaded joints, thereby linking muscular exercise of physiologic magnitude but excessive intensity to cartilage degeneration and cell death in the rabbit knee.

A low morbidity surgical approach to the sheep femoral trochlea

BACKGROUND

The ovine stifle joint is an important location for investigations on the repair of articular cartilage defects in preclinical large animals. The classical medial parapatellar approach to the femoral trochlea is hazardous because of the high risk of postoperative patellar luxation. Here, we describe a low morbidity surgical exposure of the ovine trochlea without the necessity for intraoperative patellar luxation.

METHODS

Bilateral surgical exposure of the femoral trochlea of the sheep stifle joint was performed using the classical medial parapatellar approach with intraoperative lateral patellar luxation and transection of the medial patellar retinaculum in 28 ovine stifle joints. A low morbidity approach was performed bilaterally in 116 joints through a mini-arthrotomy without the need to transect the medial patellar retinaculum or the oblique medial vastus muscle nor surgical patellar luxation. Postoperatively, all 72 animals were monitored to exclude patellar luxations and deep wound infections.

RESULTS

The novel approach could be performed easily in all joints and safely exposed the distal two-thirds of the medial and lateral trochlear facet. No postoperative patellar luxations were observed compared to a postoperative patellar luxation rate of 25% experienced with the classical medial parapatellar approach and a re-luxation rate of 80% following revision surgery. No signs of lameness, wound infections, or empyema were observed for both approaches.

CONCLUSIONS

The mini-arthrotomy presented here yields good exposure of the distal ovine femoral trochlea with a lower postoperative morbidity than the classical medial parapatellar approach. It is therefore suitable to create articular cartilage defects on the femoral trochlea without the risk of postoperative patellar luxation.

In vitro growth factor-induced bio engineering of mature articular cartilage

Articular cartilage maturation is the postnatal development process that adapts joint surfaces to their site-specific biomechanical demands. Maturation involves gross morphological changes that occur through a process of synchronised growth and resorption of cartilage and generally ends at sexual maturity. The inability to induce maturation in biomaterial constructs designed for cartilage repair has been cited as a major cause for their failure in producing persistent cell-based repair of joint lesions. The combination of growth factors FGF2 and TGFβ1 induces accelerated articular cartilage maturation in vitro such that many molecular and morphological characteristics of tissue maturation are observable. We hypothesised that experimental growth factor-induced maturation of immature cartilage would result in a biophysical and biochemical composition consistent with a mature phenotype. Using native immature and mature cartilage as reference, we observed that growth factor-treated immature cartilages displayed increased nano-compressive stiffness, decreased surface adhesion, decreased water content, increased collagen content and smoother surfaces, correlating with a convergence to the mature cartilage phenotype. Furthermore, increased gene expression of surface structural protein collagen type I in growth factor-treated explants compared to reference cartilages demonstrates that they are still in the dynamic phase of the postnatal developmental transition. These data provide a basis for understanding the regulation of postnatal maturation of articular cartilage and the application of growth factor-induced maturation in vitro and in vivo in order to repair and regenerate cartilage defects.

Chondrocyte deformation under extreme tissue strain in two regions of the rabbit knee joint

Articular cartilage and its native cells-chondrocytes-are exposed to a wide range of mechanical loading. Chondrocytes are responsible for maintaining the cartilage matrix, yet relatively little is known regarding their behavior under a complete range of mechanical loads or how cell mechanics are affected by region within the joint. The purpose of this study was to investigate chondrocyte deformations in situ under tissue loads ranging from physiological to extreme (0-80% nominal strain) in two regions of the rabbit knee joint (femoral condyles and patellae). Local matrix strains and cell compressive strains increased with increasing loads. At low loads the extracellular matrix (ECM) strains in the superficial zone were greater than the applied tissue strains, while at extreme loads, the local ECM strains were smaller than the applied strains. Cell compressive strains were always smaller than the applied tissue strains and, in our intact, in situ preparation, were substantially smaller than those previously found in hemi-cylindrical explants. This resulted in markedly different steady-state cell volume changes in the current study compared to those working with cartilage explants. Additionally, cells from different regions in the knee exhibited striking differences in deformation behavior under load. The current results suggest: (i) that the local extracellular and pericellular matrix environment is intimately linked to chondrocyte mechanobiology, protecting chondrocytes from potentially damaging strains at high tissue loads; and (ii) that cell mechanics are a function of applied load and local cartilage tissue structure.

Minor influence of lifelong voluntary exercise on composition, structure, and incidence of osteoarthritis in tibial articular cartilage of mice compared with major effects caused by growth, maturation, and aging

We investigated the effects of lifelong voluntary exercise on articular cartilage of mice. At the age of 4 weeks C57BL mice (n = 152) were divided into two groups, with one group serving as a sedentary control whereas the other was allowed free access to a running wheel from the age of 1 month onward. Mice were euthanized at four different time points (1, 2, 6, and 18 months of age). Articular cartilage samples were gathered from the load-bearing area of the tibial medial plateaus, and osteoarthritis was graded. Additionally, the proteoglycan content distribution was assessed using digital densitometry, collagen fibril orientation, and parallelism with polarized light microscopy, and collagen content using Fourier transform infrared imaging spectroscopy. The incidence of osteoarthritis increased with aging, but exercise had no effect on this trend. Furthermore, the structure and composition revealed significant growth, maturation, and age-dependent properties. Exercise exerted a minor effect on collagen fibril orientation in the superficial zone. Fibril orientation at 2 months of age was more perpendicular to surface (p < 0.05) in controls compared with runners, whereas the situation was reversed at the age of 18 months (p < 0.05). The collagen content of the superficial zone was higher (p < 0.01) at the age of 18 months in controls compared with runners but the proteoglycan content did not display any exercise-dependent changes. In conclusion, growth, maturation, and aging exerted a clear effect on integrity, structure, and composition of medial tibial plateau articular cartilage in mice, whereas lifelong voluntary exercise had only a minor effect on collagen architecture and content.

Onset of preclinical osteoarthritis: the angular spatial organization permits early diagnosis

OBJECTIVE

Superficial articular chondrocytes display distinct spatial remodeling processes in response to the onset of distant osteoarthritis (OA). Such processes may be used to diagnose early events before manifest OA results in tissue destruction and clinical symptoms. Using a novel method of spatial quantification by calculating the angles between a chondrocyte and its surrounding neighbors, we compared maturational and degenerative changes of the cellular organizations in rat and human cartilage specimens.

METHODS

The nuclei of superficial chondrocytes obtained from intact rat cartilage and from human knee cartilage, as well as from cartilage with focal and severe OA, were digitally recorded in top-down views. Their Cartesian coordinates were used to determine the nearest neighbor for each chondrocyte and the angle between these 2 cells and a reference. These angles, cellularity, nearest neighbor distances, and aggregation were analyzed as a function of location and OA severity.

RESULTS

Neighboring rat chondrocytes exhibited intricate angular patterns with 4 dominant angles that were maintained during maturation and during the onset and progression of OA. Within intact cartilage, human chondrocytes demonstrated 1 dominant angle and, thus, a significantly different angular organization. With early OA onset, human chondrocytes that were located within intact cartilage displayed an increased occurrence of 4 angles; the resulting angular patterns were indistinguishable from those observed in rats. The angular remodeling was associated with location- and OA severity-dependent changes in cellularity and aggregation.

CONCLUSION

This study is the first to identify the presence of angular characteristics of spatial chondrocyte organization and species-specific remodeling processes correlating with OA onset. The appearance of distinct angular and spatial patterns between neighboring chondrocytes can identify the onset of distant OA prior to microscopically visible tissue damage and possibly before clinical onset. With further development, this novel concept may become suitable for the diagnosis and followup of patients susceptible to OA.

Comparative anatomical measurements of osseous structures in the ovine and human knee

The ovine stifle has been increasingly used as a large animal model for the human knee. Still, comparative anatomical measurements of the knee in sheep and humans are missing. Thus, the purpose of this study was to describe and measure the osseous anatomy of the ovine stifle in comparison to the human knee. Twenty-four stifles of skeletal-mature merino-sheep and 24 human cadaver knees were obtained and distances between selected anatomical structures of the distal femur, the proximal tibia, and the patella were measured digitally and documented. Based on these, intercondylar ratio, tibial aspect ratio, patella aspect ratio and the cortical index were calculated. Regarding epicondylar width, lateral condylar width, medial condylar width and the tibial dimensions, the ovine stifle can be considered as a human knee scaled down by one third. However, sheep have a smaller trochlear width and a narrower femoral intercondylar notch than humans resulting in lower relative values for intercondylar width and intercondylar height. The distal femur's cortical index is the same in both species. In contrast, sheep have a massive bone stock below their tibial plateau and a proximal tibial shaft with remarkably thick cortical bone. The ovine stifle can be regarded as a useful model for the human knee. However, future studies should consider the differences in the femoral intercondylar notch width, the patellofemoral joint's biomechanics and the proximal tibia's cortical bone stock.

The OARSI histopathology initiative - recommendations for histological assessments of osteoarthritis in sheep and goats

OBJECTIVE

Sheep and goats are commonly used large animal species for studying pathogenesis and treatment of osteoarthritis (OA). This review focuses on the macroscopic and microscopic criteria for assessing OA in sheep and goats and recommends particular assessment criteria to assist standardization in the conduct and reporting of preclinical trials of OA.

METHODS

A review was conducted of all published OA studies using sheep and goats and the most common macroscopic, microscopic, or ultrastructural scoring systems were summarised. General recommendations regarding methods of OA assessment in the sheep and goat have been made and a preliminary study of their reliability and utility was undertaken.

RESULTS

The modified Mankin scoring system is recommended for semiquantitative histological assessment of OA due to its already widespread adoption, ease of use, similarity to scoring systems used for OA in humans, and its achievable inter-rater reliability. Specific recommendations are also provided for histological scoring of synovitis and scoring of macroscopic lesions of OA.

CONCLUSIONS

The proposed system for assessment of sheep and goat articular tissues appears to provide a useful versatile method to quantify OA change. It is hoped that by adopting more standardised quantitative outcome measures, better comparison between different studies and arthritis models will be possible. The suggested scoring systems can be modified in the future as our knowledge of disease pathophysiology advances.

Standardized cartilage biopsies from the intercondylar notch for autologous chondrocyte implantation (ACI)

Autologous chondrocyte implantation (ACI) is an established therapy for the treatment of cartilage defects across the knee joint. Even though different techniques for initial biopsy have been described, the exact location, depth, and volume of the biopsy are chosen individually by the treating surgeon. This study evaluated 252 consecutive cartilage biopsies taken from the intercondylar notch with a standardized hollow cylinder system for the isolation and in vitro cultivation of human chondrocytes assigned to ACI. All biopsies were assessed for weight of total cartilage obtained, cartilage biopsy weight per cylinder, biopsy cylinder quality, and initial cell count after digestive cellular isolation as well as cell vitality. Parameters were correlated with individual patient parameters. Mean patient age was 35.1 years (median 35.9; range 14.7-56.4). Adequate amounts of cartilage assigned to chondrocyte in vitro cultivation could be harvested in all cases. The mean overall biopsy weight averaged 75.5 mg (SD +/- 44.9) and could be identified as main factor for initial cell number (mean 1.05E+05; SD +/- 7.44E+04). No correlation was found between the initial cell count and patient age (correlation coefficient r = 0.005) or grade of joint degeneration (r = 0.040). Concerning cell viability, a total of 4.4% (SD + 3.0) of the chondrocytes harvested were apoptotic. Cartilage biopsies from the intercondylar notch using a standardized hollow cylinder system provides a reliable, safe, and successful method to obtain articular cartilage for further in vitro cultivation of articular chondrocytes to achieve autologous chondrocyte transplantation.

Metabolic activity of osteoarthritic knees correlates with BMI

Osteoarthritis of the knee has consistently been linked to obesity, defined as a body mass index (BMI) >30kg/m(2). It has been hypothesized that obesity may lead to osteoarthritis through increased joint pressure, accumulated microtrauma, and disruption of normal chondrocyte metabolism. These changes in chondrocyte metabolism have not been thoroughly investigated, and it is the purpose of this study to identify a relationship between BMI and altered chondrocyte metabolism in osteoarthritic tissue. Articular cartilage was harvested from the femoral condyles of patients after total knee arthroplasty, and analyzed in explant and alginate models. Glycosaminoglycan (GAG) content was measured using a dimethylmethylene blue assay and normalized to DNA content using a PicoGreen(R) assay. Studies have reported GAGs to be a reliable measurement of chondrocyte metabolism and osteoarthritis progression. Our results show a significant linear relationship of increasing BMI and increasing GAG content in both alginate and explant models (p<0.001 and p=0.001). Obese (BMI>/=30kg/m(2)) and non-obese (BMI<30kg/m(2)) comparisons also demonstrated significant differences with higher GAG/DNA content in obese individuals compared to non-obese (p=0.001 and p=0.015). The study results reveal significant relationships between GAG content and BMI in this population of osteoarthritic patients. The significant difference in GAG content between the obese and non-obese patients supports the connection between osteoarthritis and obesity previously reported. Higher patient BMI (>30kg/m(2)) may be similar to dynamic compression injuries which cause increased GAG synthesis in response to cartilage damage.

Influence of exercise and joint topography on depth-related spatial distribution of proteoglycan and collagen content in immature equine articular cartilage

REASONS FOR PERFORMING STUDY

There is ample evidence on topographical heterogeneity of the principal biochemical components of articular cartilage over the surface of the joint and the influence of loading thereon, but no information on depth-related zonal variation in horses.

OBJECTIVES

To study depth-related zonal variation in proteoglycan (PG) and collagen content in equine articular cartilage.

METHODS

Two techniques (safranin-O densitometry and Fourier transform infrared spectroscopy) were applied to sections of articular cartilage from the proximal phalangeal bone of the metacarpophalangeal joint of 18-month-old Thoroughbreds that had been raised at pasture from age 0-18 months without (PASTEX) and with (CONDEX) additional exercise. Two sites were investigated: site 1 at the joint margin that is unloaded at rest or at slow gaits, but subjected to high-intensity loading during athletic activity; and site 2, a continuously, but less intensively, loaded site in the centre of the joint.

RESULTS

Proteoglycan values increased from the surface to the deep layers of the cartilage, collagen content showed a reverse pattern. PG content was significantly higher at site 2 in both PASTEX and CONDEX animals without an effect of exercise. In the PASTEX animals collagen content was significantly higher at site 1, but in the CONDEX group the situation was reversed, due to a significant exercise effect on site 1, leading to a reduced collagen content.

CONCLUSIONS

Collagen and PG content gradients agree with findings in other species. The observations on PG levels suggest that the exercise level was not strenuous. The collagen results in the PASTEX group confirmed earlier findings, the lower levels at site 1 in the CONDEX group being possibly due to an advancement of the physiological maturation process of collagen remodelling.

POTENTIAL RELEVANCE

This study confirms earlier observations that even moderate variations in exercise level in early age may have significant effects on the collagen network of articular cartilage.

Ultrastructural immunolocalization of cartilage oligomeric matrix protein (COMP) in the articular cartilage on the equine third carpal bone in trained and untrained horses

The present study was designed to delineate the presence of COMP at the ultrastructural level comparing concentrations between two areas of articular cartilage from the equine third carpal bone, subjected to different loading, from trained and untrained horses. We also analyzed the fibril thickness of collagen type II in the same compartments and zones. Samples were collected from high load-bearing areas of the dorsal radial facet (intermittent high load) and an area of the palmar condyle (low constant load) in five non-trained and three trained young racehorses. The data show that COMP is much less abundant in the matrix in intermittent high loaded areas of articular cartilage from trained horses as compared to the untrained horses (p=0.036). On the other hand, the untrained horses often displayed a higher immunolabeling in loaded areas compared to unloaded areas, indicating that an adequate dynamic load promotes COMP synthesis and/or retention, while an excessive load may have an opposite effect. The collagen fibril diameter showed marked variation between individuals. The present study indicates that dynamic in vivo compression at high load and frequency lowers matrix content of COMP in the articular cartilage of the third carpal bone. It also indicates that the collagen network is influenced by mechanical load following by strenuous exercise.

Changes in collagen fibril network organization and proteoglycan distribution in equine articular cartilage during maturation and growth

The aim of this study was to record growth-related changes in collagen network organization and proteoglycan distribution in intermittently peak-loaded and continuously lower-level-loaded articular cartilage. Cartilage from the proximal phalangeal bone of the equine metacarpophalangeal joint at birth, at 5, 11 and 18 months, and at 6-10 years of age was collected from two sites. Site 1, at the joint margin, is unloaded at slow gaits but is subjected to high-intensity loading during athletic activity; site 2 is a continuously but less intensively loaded site in the centre of the joint. The degree of collagen parallelism was determined with quantitative polarized light microscopy and the parallelism index for collagen fibrils was computed from the cartilage surface to the osteochondral junction. Concurrent changes in the proteoglycan distribution were quantified with digital densitometry. We found that the parallelism index increased significantly with age (up to 90%). At birth, site 2 exhibited a more organized collagen network than site 1. In adult horses this situation was reversed. The superficial and intermediate zones exhibited the greatest reorganization of collagen. Site 1 had a higher proteoglycan content than site 2 at birth but here too the situation was reversed in adult horses. We conclude that large changes in joint loading during growth and maturation in the period from birth to adulthood profoundly affect the architecture of the collagen network in equine cartilage. In addition, the distribution and content of proteoglycans are modified significantly by altered joint use. Intermittent peak-loading with shear seems to induce higher collagen parallelism and a lower proteoglycan content in cartilage than more constant weight-bearing. Therefore, we hypothesize that the formation of mature articular cartilage with a highly parallel collagen network and relatively low proteoglycan content in the peak-loaded area of a joint is needed to withstand intermittent stress and shear, whereas a constantly weight-bearing joint area benefits from lower collagen parallelism and a higher proteoglycan content.

Central and peripheral region tibial plateau chondrocytes respond differently to in vitro dynamic compression

OBJECTIVE

The objective of this study was to test the hypotheses that chondrocytes from distinct regions of the porcine tibial plateau: (1) display region-specific baseline gene expression, and (2) respond differently to in vitro mechanical loading.

METHODS

Articular cartilage explants were obtained from central (not covered by meniscus) and peripheral (covered by meniscus) regions of porcine tibial plateaus. For baseline gene expression analysis, samples were snap frozen. To determine the effect of mechanical loading, central and peripheral region explants were exposed to equivalent dynamic compression (0-100 kPa) and compared to site-matched free-swelling controls (FSCs). mRNA levels for type II collagen (CII), aggrecan (AGGR), matrix metalloproteinase 1 (MMP-1), MMP-3, MMP-13, A disintegrin and metalloproteinase with thrombospondin motifs 4 (ADAM-TS4), ADAM-TS5, tissue inhibitor of metalloproteinases 1 (TIMP-1), TIMP-2, and tumor necrosis factor alpha (TNFalpha) were quantified using real time polymerase chain reaction (RT-PCR).

RESULTS

At baseline, mRNA levels for the structural proteins CII and AGGR were approximately twofold greater in the central region compared with peripheral region explants. In vitro dynamic compression strongly affected expression levels for CII, AGGR, MMP-3, and TIMP-2 relative to FSCs. Response differed significantly by region, with greater upregulation of CII, AGGR, and MMP-3 in central region explants.

CONCLUSIONS

Chondrocytes from different regions of the porcine tibial plateau express mRNA for structural proteins at different levels and respond to equivalent in vitro mechanical loading with distinctive changes in gene expression. These regional biological variations appear to be related to the local mechanical environment in the normal joint, and thus may indicate a sensitivity of the joint to conditions that alter joint loading such as anterior cruciate ligament (ACL) injury, meniscectomy, or joint instability.

Osteoarthritis of the ankle: bridging concepts in basic science with clinical care

Trends in science are beginning to suggest that cartilage degeneration may be related to a chronic imbalance in extracellular matrix metabolism. In cartilage, a combination of biomechanical, biochemical, and matrix-related signaling pathways regulates the equilibrium between cartilage anabolism and catabolism. A potential limitation of many current treatments of osteoarthritis is that they may not comprehensively restore regulation of a balance between cartilage anabolism and catabolism.

Gait mechanics influence healthy cartilage morphology and osteoarthritis of the knee

The response of healthy and diseased cartilage of the knee to the mechanics of walking is examined, with the goal of providing insight into the relationship between the kinematics and kinetics of the knee during walking and the maintenance of cartilage health. The combination of information from three-dimensional thickness models of cartilage derived from magnetic resonance imaging and the analysis of the interaction between load at the knee and kinematic changes during walking associated with loss of the anterior cruciate ligament demonstrated the importance of considering walking mechanics as an important factor in the initiation and progression of osteoarthritis. In particular, this material suggests that knee cartilage becomes conditioned to loading and to the large number of repetitive cycles of loading that occur during walking and that healthy cartilage homeostasis is maintained as long as there are no changes to the normal patterns of locomotion, the structure of the knee joint, or cartilage biology. Thus, there is the potential for a degenerative pathway to be initiated when a condition such as anterior cruciate ligament injury causes the repetitive loading during walking to shift to a new location. The sensitivity of cartilage to the kinematic changes is illustrated with the anterior cruciate ligament-deficient knee and the regional variations in cartilage morphology. The material presented here supports the conclusion that individual variations in the range of loading and kinematics at the knee during walking can have a profound influence on the initiation and progression of osteoarthritis of the knee.

Cells and biomaterials in cartilage tissue engineering

Cartilage defects are notoriously difficult to repair and owing to the long-term prognosis of osteoarthritis, and a rapidly aging population, a need for new therapies is pressing. Cell-based therapies for cartilage regeneration were introduced into patients in the early 1990s. Since that time the technology has developed from a simple cell suspension to more complex 3D structures. Cells, both chondrocytes and stem cells, have been incorporated into scaffold material with the aim to better recreate the natural environment of the cell, while providing more structural support to withstand the large forces applied on the de novo tissue. This review aims to provide an overview of potential cell sources and different scaffold materials, which are in development for cartilage tissue engineering.

Differing in vitro biology of equine, ovine, porcine and human articular chondrocytes derived from the knee joint: an immunomorphological study

For lack of sufficient human cartilage donors, chondrocytes isolated from various animal species are used for cartilage tissue engineering. The present study was undertaken to compare key features of cultured large animal and human articular chondrocytes of the knee joint. Primary chondrocytes were isolated from human, porcine, ovine and equine full thickness knee joint cartilage and investigated flow cytometrically for their proliferation rate. Synthesis of extracellular matrix proteins collagen type II, cartilage proteoglycans, collagen type I, fibronectin and cytoskeletal organization were studied in freshly isolated or passaged chondrocytes using immunohistochemistry and western blotting. Chondrocytes morphology, proliferation, extracellular matrix synthesis and cytoskeleton assembly differed substantially between these species. Proliferation was higher in animal derived compared with human chondrocytes. All chondrocytes expressed a cartilage-specific extracellular matrix. However, after monolayer expansion, cartilage proteoglycan expression was barely detectable in equine chondrocytes whereby fibronectin and collagen type I deposition increased compared with porcine and human chondrocytes. Animal-derived chondrocytes developed more F-actin fibers during culturing than human chondrocytes. With respect to proliferation and extracellular matrix synthesis, human chondrocytes shared more similarity with porcine than with ovine or equine chondrocytes. These interspecies differences in chondrocytes in vitro biology should be considered when using animal models.

Knee kinematics, cartilage morphology, and osteoarthritis after ACL injury

This review examines a mechanism for the initiation of osteoarthritis after anterior cruciate ligament (ACL) injury by considering the relationship between reported ambulatory changes after ACL injury, cartilage adaptation to load, and the association between cartilage loads during walking and regional variations in cartilage structure and biology. Taken together, these observations suggest that cartilage degeneration after ACL injury could be caused by a kinematic gait change that shifts ambulatory loading applied to cartilage. Such a shift may cause regions of cartilage to become newly loaded, be subjected to altered levels of compression and tension, or become unloaded. The metabolic sensitivity of chondrocytes to such changes in their mechanical environment, combined with the low adaptation potential of mature cartilage, could lead to cartilage degeneration and premature osteoarthritis after ACL injury. This proposed mechanism demonstrates the value of using the ACL injury model to understand the relationship between mechanics and biology, as well as helping to explain the importance of restoring normal ambulatory kinematics after ACL injury to avoid premature osteoarthritis.

Early exercise advances the maturation of glycosaminoglycans and collagen in the extracellular matrix of articular cartilage in the horse

REASON FOR PERFORMING STUDY

Training at a very young age may influence the characteristics of the collagen network of articular cartilage extracellular matrix (ECM) in horses.

OBJECTIVES

To investigate whether increasing workload of foals results in significant changes in the biochemical composition of articular cartilage ECM.

METHODS

Thoroughbred foals (n = 33) were divided into 2 different exercise groups from age 10 days-18 months. One group (PASTEX; n = 15) was reared at pasture; the other (CONDEX; n = 18) underwent a specific additional training programme that increased workload by 30%. At mean age 18 months, 6 animals from each group were subjected to euthanasia. The proximal articular surface of the proximal phalanx of the right hindlimb was examined for the presence of damage using the cartilage degeneration index (CDI). Samples were taken from 2 sites with known different loading patterns. Slices were analysed for DNA, glycosaminoglycans (GAG), collagen and post translational modifications of collagen (formation of hydroxylysylpyridinoline [HP] and pentosidine crosslinks, and hydroxylysine [Hyl]), and exercise groups and different sites compared.

RESULTS

There were no differences in CDI between PASTEX and CONDEX animals, indicating the absence of extra joint damage due to the exercise regimen. There were site-related differences for most biochemical variables, corroborating earlier reports. All biochemical variables showed differences between PASTEX and CONDEX groups at one of the sites, and some at both. GAG and collagen levels were lower in the CONDEX group whereas Hyl, HP crosslinks and pentosidine crosslinks were higher.

CONCLUSIONS AND POTENTIAL RELEVANCE

A measurable effect of the conditioning exercise was demonstrated. The margin between too much and too little work when training foals may be narrower than intuitively presumed.

Distinct horizontal patterns in the spatial organization of superficial zone chondrocytes of human joints

A better understanding of the unique cellular and functional properties of the superficial zone of articular cartilage may aid current strategies in tissue engineering which attempts a layered design for the repair of cartilage lesions to avert or postpone the onset of osteoarthritis. However, data pertaining to the cellular organization of non-degenerated superficial zone of articular cartilage is not available for most human joints. The present study analyzed the arrangement of chondrocytes of non-degenerated human joints (shoulder, elbow, knee, and ankle) by using fluorescence microscopy of the superficial zone in a top-down view. The resulting horizontal chondrocyte arrangements were tested for randomness, homogeneity or a significant grouping via point pattern analysis and were correlated with the joint type in which they occurred. The present study demonstrated that human superficial chondrocytes occurred in four distinct patterns of strings, clusters, pairs or single chondrocytes. Those patterns represented a significant grouping (p < 0.0001) with horizontal alignment. Each articular joint surface was dominated by only one of these four patterns (p < 0.001). Specific patterns correlated with specific diarthrodial joint types (p < 0.001). Further studies need to establish whether these organizational patterns are a consequence of their surrounding environment or whether they are linked to a functional purpose.

The response of bone, articular cartilage and tendon to exercise in the horse

Horses can gallop within hours of birth, and may begin training for athletic competition while still growing. This review cites studies on the effects of exercise on bone, tendon and articular cartilage, as detected by clinical and research imaging techniques, tissue biochemical analysis and microscopy of various kinds. For bone, alterations in bone mineral content, mineral density and the morphology of the mineralized tissue are the most common end-points. Apparent bone density increases slightly after athletic training in the cortex, but substantially in the major load paths of the epiphyses and cuboidal bones, despite the lower material density of the new bone, which is deposited subperiosteally and on internal surfaces without prior osteoclastic resorption. With training of greater intensity, adaptive change is supervened by patho-anatomical change in the form of microdamage and frank lesions. In tendon, collagen fibril diameter distribution changes significantly during growth, but not after early training. The exact amount and type of protracted training that does cause reduction in mass average diameter (an early sign of progressive microdamage) have not been defined. Training is associated with an increase in the cross-sectional area of some tendons, possibly owing to slightly greater water content of non-collagenous or newly synthesized matrix. Early training may be associated with greater thickness of hyaline but not calcified articular cartilage, at least in some sites. The age at which adaptation of cartilage to biomechanical influences can occur may thus extend beyond very early life. However, cartilage appears to be the most susceptible of the three tissues to pathological alteration. The effect of training exercise on the anatomical or patho-anatomical features of connective tissue structures is affected by the timing, type and amount of natural or imposed exercise during growth and development which precedes the training.

In Vitro, Ex Vivo, andIn VivoMethodological Approaches for Studying Therapeutic Targets of Osteoporosis and Degenerative Joint Diseases: How Biomarkers Can Assist?

Although our approach to the clinical management of osteoporosis (OP) and degenerative joint diseases (DJD)-major causes of disability and morbidity in the elderly-has greatly advanced in the past decades, curative treatments that could bring ultimate solutions have yet to be found or developed. Effective and timely development of candidate drugs is a critical function of the availability of sensitive and accurate methodological arsenal enabling the recognition and quantification of pharmacodynamic effects. The established concept that both OP and DJD arise from an imbalance in processes of tissue formation and degradation draws attention to need of establishing in vitro, ex vivo, and in vivo experimental settings, which allow obtaining insights into the mechanisms driving increased bone and cartilage degradation at cellular, organ, and organism levels. When addressing changes in bone or cartilage turnover at the organ or organism level, monitoring tools adequately reflecting the outcome of tissue homeostasis become particularly critical. In this context, bioassays targeting the quantification of various degradation and formation products of bone and cartilage matrix elements represent a useful approach. In this review, a comprehensive overview of widely used and recently established in vitro, ex vivo, and in vivo set-ups is provided, which in many cases effectively take advantage of the potentials of biomarkers. In addition to describing and discussing the advantages and limitations of each assay and their methods of evaluation, we added experimental and clinical data illustrating the utility of biomarkers for these methodological approaches.

Cyclodextrin polysulphates repress IL-1 and promote the accumulation of chondrocyte extracellular matrix

OBJECTIVE

To evaluate the influence of cyclodextrin polysulphate (CDPS) on the extracellular matrix (ECM) metabolism of human articular cartilage chondrocytes.

METHODS

Isolated chondrocytes from femoral condyle cartilage of human knee joints were cultured in gelled alginate to maintain their differentiated phenotype. During 1 week of culture, the cells were exposed to different concentrations of CDPS. Synthesis of aggrecans was investigated in these cultures after using Na(2)(35)SO(4) as a radioactive precursor during the last 24h of culture. The artificial matrix was then solubilised with Na-citrate and newly synthesised aggrecan aggregates, accumulated during culture, were liberated and assayed. The isolated chondrocytes were labelled with antibodies against aggrecan and type II collagen to analyse the ECM molecules in the cell-associated matrix (CAM). Plasma membrane levels of receptors for insulin-like growth factor-1 (IGF-1RI) and for interleukin-1 (IL-1RI and IL-1RII), as well as levels of IGF-1, IL-1alpha and -beta were determined after the cells had been permeabilized and stained with the appropriate antibodies. The release of IL-6 in the culture media was used as a variable reflecting auto/paracrine IL-1 activity of the cells in different experimental conditions.

RESULTS

CDPS significantly increased total (35)S-incorporation rates in ECM aggrecan. When compared with controls, CDPS-treated chondrocytes expressed significantly higher CAM aggrecan and type II collagen levels. As plasma membrane-bound IGFR1 and intracellular IGF-1 levels remained unchanged, this increase in accumulated CAM compounds may have resulted from suppressed catabolic activities by the chondrocytes in culture. CDPS-treated cells expressed significantly lower amounts of intracellular IL-1alpha and -beta levels. Plasma membrane-bound IL-1RI and decoy IL-1RII remained unchanged. beta-cyclodextrin-treated chondrocytes released significantly less IL-6 in the supernatant culture media.

CONCLUSION

CDPS is a novel polysulfated polysaccharide showing cartilage structure modifying effects in vitro as it improves the synthesis of aggrecan and the accumulation of CAM macromolecules. This effect probably resulted in part from the downregulation of IL-1.

Functional adaptation through changes in regional biochemical characteristics during maturation of equine superficial digital flexor tendons

OBJECTIVE

To quantify and compare biochemical characteristics of the extracellular matrix (ECM) of specimens harvested from tensional and compressive regions of the superficial digital flexor tendon (SDFT) of horses in age classes that include neonates to mature horses.

SAMPLE POPULATION

Tendon specimens were collected on postmortem examination from 40 juvenile horses (0, 5, 12, and 36 months old) without macroscopically visible signs of tendonitis.

PROCEDURE

Central core specimens of the SDFT were obtained with a 4-mm-diameter biopsy punch from 2 loaded sites, the central part of the mid-metacarpal region and the central part of the mid-sesamoid region. Biochemical characteristics of the collagenous ECM content (ie, collagen, hydroxylysylpyridinoline crosslink, and pentosidine crosslink concentrations and percentage of degraded collagen) and noncollagenous ECM content (percentage of water and glycosaminoglycans, DNA, and hyaluronic acid concentrations) were measured.

RESULTS

The biochemical composition of equine SDFT was not homogeneous at birth with respect to DNA, glycosaminoglycans, and pentosidine concentrations. For most biochemical variables, the amounts present at birth were dissimilar to those found in mature horses. Fast and substantial changes in all components of the matrix occurred in the period of growth and development after birth.

CONCLUSIONS AND CLINICAL RELEVANCE

Unlike cartilage, tendon tissue is not biochemically blank (ie, homogeneous) at birth. However, a process of functional adaptation occurs during maturation that changes the composition of equine SDFT from birth to maturity. Understanding of the maturation process of the juvenile equine SDFT may be useful in developing exercise programs that minimize tendon injuries later in life that result from overuse.

Segmental variation in the in vitro cell metabolism of nucleus pulposus cells isolated from a series of bovine caudal intervertebral discs

STUDY DESIGN

This study focuses on the association between cell metabolism and molecular matrix composition of nucleus pulposus (NP) tissue with spine level in sequential bovine caudal intervertebral discs.

OBJECTIVE

To explore the hypothesis that the molecular composition of NP tissue and corresponding cell metabolism varies with caudal spine. A secondary hypothesis is tested that potential cellular differences are maintained after monolayer culture.

SUMMARY OF BACKGROUND DATA

In articular cartilage, cell metabolism and molecular matrix composition are influenced by loading history. This may also be a feature of intervertebral discs in series.

METHODS

NP cells (nonpooled or level pooled) were isolated from four sequential bovine caudal intervertebral discs (levels 3-4, 4-5, 5-6, and 6-7) and cultured in alginate beads immediately or following monolayer culture. Levels of 3H-TdR (proliferation) and 35SO4 (GAG synthesis) incorporation were determined from 14 animals. In a separate set of 6 animals, total content of water, DNA, collagen (and type), GAG (and type) were also determined.

RESULTS

The rate of 3H-TdR and 35SO4 incorporation in freshly isolated NP cells increased nonlinearly from level 3-4 to 6-7 (P < 0.05). Monolayer cultured cells retained level-specific differences for 35SO4 and 3H-TdR incorporation similar to that of freshly isolated cells. GAG content and chondroitin sulfate proportion decreased distally (P < 0.05); however, total collagen and Type I proportion increased distally (P < 0.05). No significant differences in water or DNA content could be determined.

CONCLUSIONS

The results support the hypothesis that level-specific differences in NP cell metabolism and molecular composition are dependent on spine level potentially reflecting subtle mechanical differences between levels. Retention of level-specific differences in monolayer may suggest a certain level of cell "programming." This may be important for cellular strategies to repairspecific sites of degeneration.

Cytokine induced metalloproteinase expression and activity does not correlate with focal susceptibility of articular cartilage to degeneration

OBJECTIVE

To determine whether the focal susceptibility to cartilage degeneration in joints is related to a differential response to cytokine stimulation.

METHODS

Compare aggrecan and collagen catabolism in in-vitro models of cartilage degradation induced by retinoic acid (RA), interleukin-1 (IL-1), tumor necrosis factor alpha (TNF) and IL-1 plus oncostatin M (OSM). Glycosaminoglycan (GAG) and hydroxyproline (HyPro) quantification and Western immunoblot analyses of aggrecan and collagen degradation products were undertaken in explant cultures of normal cartilage from regions of equine joints with a known high and low susceptibility to degeneration in disease. RNA isolation and semi quantitative reverse transcription-polymerase chain reaction (RT-PCR) analysis were performed to determine the expression of aggrecanases, matrix metalloproteinases (MMPs) and their inhibitors.

RESULTS

Although the rate of basal cartilage aggrecan turnover was dependent on joint region there was no difference in the response of different cartilages to cytokines. Individual animals did show a significant difference in the response of certain cartilages to cytokines, with both decreased and increased aggrecan loss in cartilage with a low susceptibility to degeneration. Aggrecan release in both short- and long-term cultures from all cartilages was associated with increased cleavage by aggrecanases rather than MMPs. There was a poor correlation between expression of aggrecanases, MMPs or their inhibitors and cytokine induced aggrecan catabolism. IL-1 alone was able to stimulate collagen breakdown in equine articular cartilage and surprisingly, significantly more collagen loss was induced in cartilage from regions less susceptible to degeneration.

CONCLUSIONS

Collectively, these studies suggest that a regional difference in response to catabolic cytokines is unlikely to be a factor in the initiation of focal cartilage degeneration in osteoarthritis (OA).

Site- and exercise-related variation in structure and function of cartilage from equine distal metacarpal condyle

OBJECTIVE

Determine (1) the site-associated response of articular cartilage of the equine distal metacarpal condyle to training at a young age as assessed by changes in indentation stiffness and alterations in cartilage structure and composition, and (2) relationships between indentation stiffness and indices of cartilage structure and composition.

METHOD

Experimental animals (n=6) were trained on a track (increasing exercise to 1km/day by 5 months); controls (n=6) were pasture-reared. Animals were euthanized at 18 months and four osteochondral samples were harvested per metacarpal condyle from dorsal-medial, dorsal-lateral, palmar-medial, and palmar-lateral aspects. Cartilage was analyzed for India ink staining (quantified as reflectance score (RS)), short-term indentation stiffness (sphere-ended, 0.4mm diameter), thickness, and biochemical composition.

RESULTS

Cartilage structural, biochemical and biomechanical properties varied markedly with site in the joint. Sites just medial and just lateral to the sagittal ridge showed signs of early degeneration, with relatively low RS, indentation stiffness, and collagen content, and relatively high water content. Effects of exercise and side (left vs right) were not detected for any measure. Overall, indentation stiffness correlated positively with RS and collagen content, and inversely with thickness and water content.

CONCLUSION

Gentle exercise-imposed mechanical stimulation did not markedly affect articular cartilage function or structure. However, the marked site-associated variation suggests that biomechanical environment can initiate degenerative changes in immature cartilage during joint growth and maturation.

Physiological levels of hydrocortisone maintain an optimal chondrocyte extracellular matrix metabolism

OBJECTIVE

To investigate the effects of physiological doses of hydrocortisone on synthesis and turnover of cell associated matrix (CAM) by human chondrocytes obtained from normal articular cartilage.

METHODS

Human articular cartilage cells were obtained from visually intact cartilage of the femoral condyles of five donors and maintained in culture for one week to reach equilibrium in accumulated CAM compounds. 0, 0.05, 0.20, and 1.0 micro g/ml hydrocortisone was added to the nutrient media during the entire culture period. Cells were liberated and levels of CAM aggrecan, type II collagen, and fibronectin, of intracellular IGF-1, IL1alpha and beta, and of their respective plasma membrane bound receptors IGFR1, IL1RI, and the decoy receptor IL1RII, were assayed by flow cytometry.

RESULTS

In comparison with controls, hydrocortisone treated chondrocytes, at all concentrations, expressed significantly higher plasma membrane bound IGFR1. Intracellular IGF-1 levels remained unchanged. Together with these changes, reflecting an increased ability to synthesise extracellular matrix (ECM) macromolecules, hydrocortisone treated cells expressed significantly higher amounts of the plasma membrane bound decoy IL1RII. Concurrently, intracellular IL1alpha and beta levels and membrane bound IL1RI were down regulated. Levels of CAM aggrecan, type II collagen, and fibronectin were significantly up regulated in the chondrocytes treated with hydrocortisone.

CONCLUSION

0.05 micro g/ml hydrocortisone treated chondrocytes had decreased catabolic signalling pathways and showed an enhanced ability to synthesise ECM macromolecules. Because IL1 activity was decreased and the expression of IL1RII decoy receptor enhanced, more of the ECM macromolecules produced remained accumulated in the CAM of the chondrocytes. The effects were obtained at doses comparable with physiological plasma levels of hydrocortisone in humans.

dGEMRIC (delayed gadolinium-enhanced MRI of cartilage) indicates adaptive capacity of human knee cartilage

Delayed gadolinium-enhanced MRI of cartilage (dGEMRIC) is a new imaging technique to estimate joint cartilage glycosaminoglycan content by T1-relaxation time measurements after penetration of the hydrophilic contrast agent Gd-DTPA(2-). This study compares dGEMRIC in age-matched healthy volunteers with different levels of physical activity: Group 1 (n = 12): nonexercising individuals; Group 2 (n = 16): individuals with physical exercise averaging twice weekly; Group 3 (n = 9): male elite runners. dGEMRIC was performed 2 hr after an intravenous injection of Gd-DTPA(2-) at 0.3 mmol/kg body weight. T1 differed significantly between the three different levels of physical exercise. T1 values (mean of medial and lateral femoral cartilage) for Groups 1, 2, and 3 were: 382 +/- 33, 424 +/- 22 and 476 +/- 36, respectively (ms, mean +/- SD) (P = 0.0004, 1 vs. 2 and 0.0002, 2 vs. 3). Irrespective of the exercise level, T1 was longer in lateral compared to medial femoral cartilage (P = 0.00005; n = 37). In conclusion, this cross-sectional study indicates that human knee cartilage adapts to exercise by increasing the glycosaminoglycan content. Furthermore, results suggest a compartmental difference within the knee with a higher glycosaminoglycan content in lateral compared to medial femoral cartilage. A higher proportion of extracellular water, i.e., larger distribution volume, may to some extent explain the high T1 in the elite runners.

Homeostasis of the extracellular matrix of normal and osteoarthritic human articular cartilage chondrocytes in vitro

OBJECTIVE

In normal articular cartilage cells, the IGFRI/insulin-like growth factor 1 (IGF-1) autocrine pathway was shown to overrule the catabolic effects of the IL-1/IL-1RI pathway by up-regulation of the IL-1RII decoy receptor. The activity of the IGF-1/IGFR1 and IL-1/IL-1R pathways, and of the IL-1RII control mechanism in the synthesis and turnover of the extracellular matrix (ECM) by chondrocytes from normal and osteoarthritic (OA) articular cartilage was compared in order to identify possible therapeutic targets of this disease.

METHODS

Phenotypically stable human articular cartilage cells were obtained from normal and OA cartilage of the same knee showing focal OA. The cells were cultured in alginate beads over 1 week to re-establish the intracellular cytokine and growth factors, to reexpress the respective plasma membrane receptors and to reach equilibrium in accumulated cell-associated matrix (CAM) compounds. Following liberation of the cells from the alginate beads, the levels of cell-associated matrix (CAM) aggrecan, type II collagen and fibronectin, of intracellular IGF-1, IL-1alpha and beta and of their respective plasma membrane-bound receptors, IGFR1, IL-1RI and the decoy receptor IL-1RII, were assayed using flow cytometry.

RESULTS

Coordinated production and accumulation of CAM aggrecan and type II collagen under the effect of the IGFR1/IGF-1 autocrine pathway-as documented for chondrocytes from healthy controls-was absent when the chondrocytes had been obtained from OA joints. When compared with cells obtained from normal tissues, chondrocytes from fibrillated OA cartilage expressed significantly higher intracellular IGF-1 levels and plasma membrane-bound IGFR1. At the same time, significantly higher intracellular IL-1alpha and beta levels and upregulated plasma membrane-bound IL-1RI were observed. Plasma membrane-bound IL-1RII decoy receptor was downregulated in OA chondrocytes. The levels of CAM aggrecan, type II collagen and fibronectin were significantly reduced in the chondrocytes obtained from pathological tissue.

CONCLUSION

Paired analysis of normal and OA chondrocytes from the same knee joint has shown an enhanced capacity of chondrocytes from OA cartilage to produce ECM macromolecules. However, the same cells have increased catabolic signalling pathways. As a consequence of this increased IL-1 activity and the reduced amounts of IL-1RII decoy receptor, less of the produced ECM macromolecules may persist in the CAM of the OA chondrocytes.

Dynamic compressive strain inhibits nitric oxide synthesis by equine chondrocytes isolated from different areas of the cartilage surface

REASONS FOR PERFORMING STUDY

Chondrocytes within articular cartilage respond to the mechanical stresses associated with normal joint loading via a series of signalling pathways. Specific biomolecules, such as nitric oxide (NO), have been implicated in these mechanotransduction processes. It has been shown that the synthesis of NO can be inhibited by dynamic compressive strain of chondrocytes in vitro which, in turn, leads to an up-regulation of specific metabolic parameters.

HYPOTHESIS

Chondrocytes isolated from different joint locations and seeded in agarose constructs respond in a distinct manner to the application of dynamic compression.

METHODS

Chondrocytes were isolated separately from the equine patella groove and the femoral condyle, representing high loaded areas (HLA) and low loaded areas (LLA), respectively, of 6 specimens of different ages. The cells were seeded in agarose constructs and cultured either in an unstrained state or strained under dynamic loading at 1 Hz for 48 h. The synthesis of nitric oxide (NO), proteoglycan synthesis and chondrocyte proliferation were assessed.

RESULTS

Equine chondrocytes were found to synthesise significant basal levels of NO, regardless of topographical origin or age of tissue. Marked differences in both proteoglycan synthesis and cell proliferation were, however, revealed between the 2 chondrocyte subpopulations. Dynamic compression inhibited NO synthesis but significant alterations in proteoglycan synthesis and cell proliferation were apparent in a minority of cases.

CONCLUSIONS AND POTENTIAL RELEVANCE

The differential response of the subpopulations of chondrocytes derived from the HLA and LLA provides a potential mechanism which enables the biomechanical demands of differing joint regions to be maintained.