Synthesis of abnormal articular cartilage proteoglycans in rapidly destructive arthropathy (osteoarthritis)

Summary Articular cartilage fragments were obtained from four femoral heads and one femoral condyle, resected in five patients undergoing prosthetic surgery for rapidly destructive arthropathy (RDA) and from one normal femoral head and one normal femoral condyle resected at autopsy. The cartilage fragements were labelled in vitro with ³⁵SO₄ and newly-synthesized proteoglycans, (³⁵S-PGs) were then extracted with 4 M guanidinium hydrochloride (GuHCl) and analyzed. In three cases a much greater and in one case a significantly increased proportion of small ³⁵S-PGs enriched in dermatan sulfate (DS) was demonstrated in diseased tissues in comparison with control samples. These DS ³⁵S-PGs were completely unable to interact with hyaluronan (HA) and had longer glycosamino-glycan (GAG) side chains than large ³⁵S-PGs. Also, large ³⁵S-PGs extracted from diseased tissue interacted poorly under associative conditions with exogenous HA when this was added to the crude extract. However, they interacted much better following the addition of exogenous HA to the purified high density proteoglycans. This suggests the presence of an inhibitor of PG-HA interaction in the crude extract which is lost during PG purification. The synthesis of an abnormally large proportion of small PGs by articular chondrocytes and impaired aggregation of large PGs may account for the accelerated destruction of articular cartilage in this condition.     

Calcification of articular cartilage in human osteoarthritis

Objective

Hypertrophic chondrocyte differentiation is a key step in endochondral ossification that produces basic calcium phosphates (BCPs). Although chondrocyte hypertrophy has been associated with osteoarthritis (OA), chondrocalcinosis has been considered an irregular event and linked mainly to calcium pyrophosphate dihydrate (CPPD) deposition. The aim of this study was to determine the prevalence and composition of calcium crystals in human OA and analyze their relationship to disease severity and markers of chondrocyte hypertrophy.

Methods

One hundred twenty patients with end‐stage OA undergoing total knee replacement were prospectively evaluated. Cartilage calcification was studied by conventional x‐ray radiography, digital‐contact radiography (DCR), field‐emission scanning electron microscopy (FE‐SEM), and synovial fluid analysis. Cartilage calcification findings were correlated with scores of knee function as well as histologic changes and chondrocyte hypertrophy as analyzed in vitro.

Results

DCR revealed mineralization in all cartilage specimens. Its extent correlated significantly with the Hospital for Special Surgery knee score but not with age. FE‐SEM analysis showed that BCPs, rather than CPPD, were the prominent minerals. On histologic analysis, it was observed that mineralization correlated with the expression of type X collagen, a marker of chondrocyte hypertrophy. Moreover, there was a strong correlation between the extent of mineralization in vivo and the ability of chondrocytes to produce BCPs in vitro. The induction of hypertrophy in healthy human chondrocytes resulted in a prominent mineralization of the extracellular matrix.

Conclusion

These results indicate that mineralization of articular cartilage by BCP is an indissociable process of OA and does not characterize a specific subset of the disease, which has important consequences in the development of therapeutic strategies for patients with OA.

     

Subchondral bone sclerosis in osteoarthritis: not just an innocent bystander

Abstract

?Osteoarthritis (OA) is considered to be a complex illness in which the tissues of the joint play a significant role in the initiation and/or progression of the pathophysiology. We still do not completely understand what initiates the degradation and loss of cartilage. However, it has been suggested that increased catabolism due to elevated cytokines and growth factors in OA joints plays a significant role. Recent evidence suggests a key role for the subchondral bone tissue in the progression and/or initiation of OA. Indeed, the subchondral bone tissue produces a number of similar proinflammatory cytokines, and growth factors are involved in cartilage tissue remodeling. Interestingly, studies have shown the presence of clefts or channels in the tidemark that appears early in OA, indicating a possible way to traffic cytokines and growth factors from the subchondral compartment to the overlying cartilage. Therefore, it is possible that certain bone-derived products drive cartilage metabolism. Potential candidates include insulin-like growth factor-1 (IGF-1), transforming growth factor-β (TGF-β) interleukin 1β (IL-1β), and interleukin-6 (IL-6). Demonstrating that the subchondral bone plays a role in the initiation of OA would greatly contribute to furthering our knowledge of this pathology and provide new insights for therapeutic approaches.     

Subchondral bone sclerosis in osteoarthritis: not just an innocent bystander

 Osteoarthritis (OA) is considered to be a complex illness in which the tissues of the joint play a significant role in the initiation and/or progression of the pathophysiology. We still do not completely understand what initiates the degradation and loss of cartilage. However, it has been suggested that increased catabolism due to elevated cytokines and growth factors in OA joints plays a significant role. Recent evidence suggests a key role for the subchondral bone tissue in the progression and/or initiation of OA. Indeed, the subchondral bone tissue produces a number of similar proinflammatory cytokines, and growth factors are involved in cartilage tissue remodeling. Interestingly, studies have shown the presence of clefts or channels in the tidemark that appears early in OA, indicating a possible way to traffic cytokines and growth factors from the subchondral compartment to the overlying cartilage. Therefore, it is possible that certain bone-derived products drive cartilage metabolism. Potential candidates include insulin-like growth factor-1 (IGF-1), transforming growth factor-β (TGF-β) interleukin 1β (IL-1β), and interleukin-6 (IL-6). Demonstrating that the subchondral bone plays a role in the initiation of OA would greatly contribute to furthering our knowledge of this pathology and provide new insights for therapeutic approaches. Acknowledgments The Arthritis Society of Canada grant No. 98043 and the Fonds De la Recherche en Santé du Québec (FRSQ) “équipe Prioritaire” supported this research. Correspondence to:D. Lajeunesse     

阿仑膦酸钠对兔膝骨关节炎关节软骨及软骨下骨保护的作用

目的研究阿仑膦酸钠(ALN)对兔膝骨关节炎关节软骨及软骨下骨的保护作用。方法健康3月龄雄性日本大耳白兔30只,随机分为对照组(Sham)、盐水组(ACLT+NS)和ALN(ACLT+ALN),每组10只。盐水组和ALN行右侧膝关节前交叉韧带切断术(ACLT)造膝骨关节炎模型。术后ACLT+ALN组皮下注射ALN20μg·kg-1·2 d-1,连续6 w;ACLT+NS组则给予等剂量盐水,给药后6 w处死动物,在处死前10d和4d分别皮下注射盐酸四环素和钙黄绿素行荧光双标记。取右侧膝胫骨近端包埋制成硬组织切片,用于软骨下骨小梁形态计量学测量;取股骨远端行骨密度测量,脱钙制成切片,行HE染色和Mankin评分,免疫组化染色切片观察MMP-13表达。结果①Mankin评分:ACLT+NS组分数显著高于Sham组和ACLT+ALN组(P0.05)。②股骨远端骨密度:ACLT+ALN组均显著高于ACLT+NS组。③骨组织形态计量学结果:ACLT+ALN组骨小梁相对体积、厚度、数量等均高于ACLT+NS组(P0.05);而ACLT+ALN组骨小梁分离度低于ACLT+NS组(P0.05)。④免疫组化:ACLT+ALN组和Sham组MMP-13的表达显著低于ACLT+NS组。结论皮下注射ALN 20μg·kg-1·2d-1能够保护关节软骨,维持骨量,改善软骨下骨小梁微观结构。     

Apoptotic chondrocytes from osteoarthrotic human articular cartilage and abnormal calcification of subchondral bone

OBJECTIVE: Osteoarthrosis (OA) is accompanied by altered subchondral bone remodeling. We investigated the role of chondrocytes in the mechanism of abnormal cartilage calcification. METHODS: Knee articular cartilage samples from OA and normal tissue were studied. Macroscopic and microscopic observations, alkaline phosphatase staining for light and electron microscopy (bright and dark fields). TUNEL technique, electron diffraction, and x-ray microanalyses were performed. RESULTS: Chondrocytes from patients displayed a morphology of apoptosis and showed abundant alkaline phosphatase (ALP)-rich matrix vesicles (MV) budding from the plasma membrane with hydroxyapatite microcrystals on their surface. Farther from the cells, hydroxyapatite crystals were detected on the MV surface and increased as they approached the subchondral bone. The concentration of Ca and P and their ratio increased inside the ALP-rich MV in relation to the proximity to subchondral bone. In the OA subchondral bone the ratio Ca/P varied from 3.936 to 0.974. In normal tissue the ratio was very homogeneous (maximum 1.973, minimum 1.781). CONCLUSION: In situ, apoptotic chondrocytes correlate with factors known to be involved in the calcification of the extracellular matrix. This suggests that apoptosis is involved in the abnormal calcification of OA cartilage, and consequently in the altered remodeling of the subchondral bone.     

Subchondral bone and cartilage damage: A prospective study in older adults

Objective

There is limited longitudinal evidence relating subchondral bone changes to cartilage damage and loss. The aim of this study was to describe the association between baseline tibial bone area and tibial subchondral bone mineral density (BMD) with tibial cartilage defect development and cartilage volume loss.

Methods

A total of 341 subjects (mean age 63 years, range 52–79 years) underwent measurement at baseline and ∼2.7 years later. Tibial knee cartilage volume, cartilage defects (graded on a scale of 0–4), and bone area were determined using T1‐weighted fat suppression magnetic resonance imaging. Tibial subchondral BMD was determined using dual x‐ray absorptiometry.

Results

In multivariable analysis, baseline bone area positively predicted cartilage defect development at the medial and lateral tibial sites (odds ratio [OR] 1.6 per 1 SD increase, 95% confidence interval [95% CI] 1.0, 2.6, and OR 2.4 per 1 SD increase, 95% CI 1.4, 4.0, respectively) and cartilage volume loss at the medial tibial site (β = −34.9 per 1 SD increase, 95% CI −49.8, −20.1). In contrast, baseline subchondral BMD positively predicted cartilage defect development at the medial tibial site only (OR 1.6 per 1 SD increase, 95% CI 1.2, 2.1) and was not associated with cartilage loss.

Conclusion

The results of this study demonstrated that bone area predicted medial and lateral cartilage defect development and medial cartilage volume loss, while subchondral BMD predicted medial defect development but not cartilage loss. These associations were independent of each other, indicating there are multiple mechanisms by which subchondral bone changes may lead to cartilage damage.

     

软骨下骨与骨性关节炎病变的发生发展:从基础研究到临床治疗

骨性关节炎(OA)是软骨与骨的退行性变过程。软骨下骨是构成关节结构和功能的基本单位之一,维持软骨正常结构和功能。在复杂应力和生物学作用下,OA软骨下骨的重塑和结构改变使软骨承受更高的应力。软骨下骨内血管生成和结构病变扩大了骨软骨异常交流途径,软骨下骨产生的代谢调节因子通过异常生物学交流直接促进软骨退变。研究软骨下骨内细胞及其变化,血管生成与骨软骨间生物学交流,揭示软骨下骨重塑和结构变化特点,探寻改善骨重塑治疗方法,将有利于延缓OA病变进展,有效防治OA。     

Meniscal and articular cartilage changes in knee osteoarthritis: a cross-sectional double-contrast macroradiographic study

OBJECTIVE: In knee osteoarthritis (OA) damage to meniscal cartilage is associated with the changes in articular cartilage. Using double-contrast macroradiographs we determined whether the degree of meniscal cartilage damage was similar to or different from that at the corresponding regions of the articular cartilage on the tibia and femur. DESIGN: Double-contrast microfocal macroradiographs,x7-x9 magnification, were obtained of the tibio-femoral joint in 20 osteoarthritic knee patients with medial compartment disease (Kellgren and Lawrence grades I-III). The appearance of the meniscus and the femoral and tibial articular cartilage were graded separately using a 5-point scale. RESULTS: In the medial diseased compartment, articular cartilage damage on the tibia was similar to that of the meniscus, which had significantly greater (P<0.02) degenerative changes than the cartilage on the femur. In the lateral compartment, meniscal damage was significantly worse than in either tibial (P<0.04) or femoral articular cartilages (P<0.01), respectively; none was as severe as that in the medial osteoarthritic compartment. CONCLUSION: Although the cross-sectional nature of this study precluded definite aetiological inferences, this study showed that degenerative changes in the meniscal and articular cartilages were not totally variable. Because of its larger articular surface, changes in the medial femoral cartilage were less marked than at the meniscal and tibial cartilages in the osteoarthritic compartment. In the lateral compartment, meniscal damage precedes tibial and femoral articular cartilage changes. In knees with medial compartment OA, combined meniscal and articular cartilage damage would account for detection of radiographic joint space loss and not meniscal extrusion only.     

Biochemical markers of bone and cartilage remodeling in prediction of longterm progression of knee osteoarthritis

OBJECTIVE: To investigate the relationship between biochemical markers of bone and cartilage remodeling and severity or progression (symptoms and structure) of knee osteoarthritis (OA). METHODS: Mean and minimal joint space width (JSW) of the femorotibial joint were measured from standardized radiographs taken at baseline and at the end of a 3-year longitudinal study of patients with knee OA. Pain, stiffness, and physical function subscales of the Western Ontario and McMaster Universities Osteoarthritis (WOMAC) index were assessed at the same time points. Biochemical markers [serum keratan sulfate (KS), serum hyaluronic acid (HA), urine pyridinoline (PYD) and deoxypyridinoline (DPD), serum osteocalcin (OC), cartilage oligomeric matrix protein (COMP)] were assessed at baseline and after 1 year. RESULTS: At baseline, no significant correlations were observed between values of biochemical markers and JSW or any of the WOMAC scores. Baseline markers were not correlated with 3-year percentage changes observed in mean or minimal JSW and WOMAC scores. Changes observed after 1 year in OC and HA were significantly correlated with 3-year progression in mean JSW (r = -0.24, p = 0.04 and r = 0.27, p = 0.02, respectively) and in minimal JSW (r = -0.31, p = 0.01 and r = 0.24, p = 0.04, respectively). In patients from the lowest quartile of 1-year changes in HA (< -21.22 ng/ml), mean JSW decreased after 3 years by 0.76 (1.23) mm compared to an increase of 0.11 (0.83) mm in patients in the highest quartile (> +14.34 ng/ml) (p = 0.03). CONCLUSION: The 3-year radiological progression of knee OA could be predicted by a 1-year increase in OC or a 1-year decrease in HA levels.     

Screening of degradative enzymes from articular cartilage in experimental osteoarthritis

Summary Sixteen rabbits were killed 12 weeks after sectioning of the right knee anterior cruciate ligament. The left unoperated knee served as a control. The surface area of fibrillated cartilage from femoral condyles and tibial plateau was evaluated and expressed as a percentage of articular surfaces area. Cartilage from the femoro-patellar surfaces was homogenized for the quantification of several degradative activities, based on the release of digested products. Acid phosphatase, several glycosidases and neutral protease activity from the operated joint cartilage were significantly elevated, while collagenolytic activity was unmodified. The percentage of fibrillated cartilage correlated positively with arylsulfatase, glucosidase and neutral protease but negatively with mannosidase and fucosidase. The results may be consistent with the hypothesis of a sequential degradative process leading to cartilage destruction.     

The clinical correlates of articular cartilage defects in symptomatic knee osteoarthritis: a prospective study

OBJECTIVES: To determine whether articular cartilage defects are associated with cartilage loss and joint replacement in subjects with symptomatic knee osteoarthritis (OA). METHODS: One hundred and seventeen subjects with symptomatic knee OA underwent magnetic resonance imaging of their dominant knee at baseline and 2 yr later. Cartilage defects were identified as prevalent (defect score > or =2) in each knee compartment. Occurrence of joint replacement by 4 yr was documented. RESULTS: Cartilage defects were present in 81% of medial, 64% of lateral tibiofemoral compartments and 55% of patellar cartilages. Annual patellar cartilage loss was highest in those with defects compared with no defects (5.5% vs 3.2%, P = 0.01). Tibial cartilage loss was not associated with defects in the medial (4.6% vs 5.8%, P = 0.42) or lateral (4.7% vs 6.5%, P = 0.21) tibial cartilages. Higher total cartilage defect scores (8-15) were associated with a 6.0-fold increased risk of joint replacement over 4 yr compared with those with lower scores (2-7) (95% confidence interval 1.6, 22.3), independently of potential confounders. CONCLUSIONS: Articular cartilage defects are associated with disease severity in knee OA and predict patellar cartilage loss and knee replacement.     

Quantitative magnetic resonance imaging of articular cartilage in knee osteoarthritis

PURPOSE OF REVIEW: Attempts to evaluate knee cartilage damage and progression seem logical in osteoarthritis research. Magnetic resonance imaging allows for precise visualization of joint structures such as cartilage, bone, synovial tissues, ligaments and menisci, and their pathologic changes. RECENT FINDINGS: Recent advances in magnetic resonance technology have enabled researchers to evaluate cartilage damage and progression over the cross-sectional and longitudinal planes. Although anatomic changes can be seen, for many years the quantification of the cartilage changes has been the real challenge. Quantitative assessment of cartilage morphology using magnetic resonance imaging with fat-suppressed gradient echo sequences and digital postprocessing techniques provides high accuracy and adequate precision for cross-sectional and longitudinal studies in osteoarthritis patients. Recent data on precision, reliability, and sensitivity to change of quantitative parameters of cartilage morphology in osteoarthritis are presented in this review. Longitudinal studies currently available suggest that changes of cartilage volume, potentially as much as 5% per year, occur in osteoarthritis in most knee compartments, exceeding the variability of these measurements. SUMMARY: Magnetic resonance imaging provides reliable and quantitative data on cartilage status throughout all compartments of the knee, and robust acquisition protocols for multicenter trials are now available. Magnetic resonance imaging technology should hopefully reduce the number of patients needed in clinical trials, improve retention of these patients, and reduce the overall costs and the length of clinical trials of treatment response to disease-modifying osteoarthritis drugs.     

Synovial,articular cartilage and bone changes in rapidly destructive arthropathy (osteoarthritis) of the hip

Summary We studied ten femoral heads from eight patients suffering from rapidly destructive arthropathy (RDA) of the hip. At surgery, 1–3.5 ml of synovial fluid, ranging from citrous to hemorrhagic, was aspirated from six joints. This fluid was viscous, pauci-cellular and did not contain calcium pyrophosphate dihydrate (CaPPD) crystals, although significant amounts of alizarin S-positive material was found in three joints. Significant synovial hyperplasia was found in four joints and moderate hyperplasia in two. Synovium was hypertrophic, hypercellular and slightly to moderately fibrotic. It lacked evidence of perivascular inflammatory infiltrates. Synovium often contained amyloid micro-deposits and alizarin S-positive osteocartilagenous debris surrounded by macrophages. Synovial hyperplasia had a good correlation with osteocartilagenous debris and a poor correlation with amyloid infiltration. Femoral heads were usually flattened and exhibited large areas of exposed bone spotted by plugs of fibro-cartilagenous tissue. Subchondral bone contained large ischemic and necrotic areas, remodeling. Subchondral bone necrosis and ischemia were the most significant findings of this study and their role in the development of RDA is discussed.     

骨关节炎软骨基质蛋白多糖变化的实验研究

目的：观察骨关节炎（OA）不同时期关节软骨基质蛋白多糖的变化，探索与软骨基质代谢相关的OA的发病机制。方法：以家兔制作OA动物模型，在病变的早、中晚期获取关节软骨，提取葡糖氨基聚糖（GAG），用生化和放射免疫技术测定其中不同种类GAG及其功能基团的含量。结果：在病变的不同时期，GAG的总量、透明质酸的含量和其中所含的硫酸基团的含量均减少，而硫酸软骨素与硫酸角质素的比例增高。这些改变均随病变的进展而渐不明显。结论：OA时，软骨基质蛋白多糖各组分和功能基团均发生了有意义的变化，这种变化有助于阐明OA的发病机制。     

Articular cartilage repair using dedifferentiated articular chondrocytes and bone morphogenetic protein 4 in a rabbit model of articular cartilage defects

OBJECTIVE: To observe redifferentiation of dedifferentiated chondrocytes after transplantation into the joint, and to evaluate the ability of dedifferentiated chondrocytes transduced with adenovirus containing bone morphogenetic protein 4 (BMP-4) to redifferentiate in vitro and in vivo in a rabbit model of articular cartilage defects. METHODS: Monolayer and pellet culture systems were used to evaluate the redifferentiation of dedifferentiated chondrocytes transduced with BMP-4. A rabbit model of partial-thickness articular cartilage defects was used to evaluate cartilage repair macroscopically and histologically, 6 and 12 weeks after transplantation with first-passage, fifth-passage, or transduced fifth-passage chondrocytes. Histologic grading of the repaired tissue was performed. Expression of BMP-4 and the ability of transplanted cells to recover a chondrocytic phenotype were also assessed. RESULTS: BMP-4--expressing dedifferentiated chondrocytes recovered a chondrocytic phenotype in vitro. After transplantation into the joint, some of the dedifferentiated chondrocytes in the defect sites could undergo redifferentiation and formed matrix that displayed positive toluidine blue staining for glycosaminoglycans. Histologic scores of the regenerative tissue revealed significantly better cartilage repair in rabbits transplanted with BMP-4--expressing cells than in the other treatment groups. Staining with toluidine blue revealed expression of BMP-4 in the cells and in the matrix surrounding the cells. CONCLUSION: Some dedifferentiated chondrocytes can redifferentiate after transplantation into the load-bearing joint. BMP-4 can be used to induce redifferentiation of dedifferentiated chondrocytes in vitro and in vivo, which could help enhance articular cartilage repair.