Metabolic changes in rabbit articular cartilage due to inflammation

The effects of inflammation on the articular cartilage of rabbit knee joints were studied. The inflammation was induced by intraarticular injections of croton oil or rabbit peritoneal leukocyte lysates. An increase in the activities of various lysosomal enzymes was observed in the synovial fluid as well as in the cartilage of the inflamed joints. Loss of proteoglycans, increased rate of degradation of collagen and proteoglycans, and increased rate of their synthesis were evident in the treated cartilage. The rate of uptake of ³H-thymidine was also increased. A significant change was observed in the type of collagen synthesized by these explants in vitro. In addition to synthesizing their characteristic Type II collagen, the cartilage explants from the treated joints synthesized Type I collagen.     

Osteoarthritis-related changes in human articular cartilage

We report the use of immunologic methods for detecting specific alterations in human osteoarthritic cartilage. Monoclonal antibodies with specificities for proteoglycans and link proteins have been used to define immunogenic sites in these molecules. We have identified 1 site in the protein core, 1 site in the link proteins, and another site that is common to both proteoglycan and link proteins, which are not modified in osteoarthritic cartilage. In addition, an antigenic determinant in link proteins that is altered in osteoarthritic cartilage has been identified. These results suggest that the structure of the ternary complex (hyaluronic acid binding region-link proteins-hyaluronic acid) could be altered in osteoarthritic cartilage. These modifications may be due to a genetic defect or to partial enzymatic degradation of these sites.     

Proteoglycan structural changes in human rheumatoid articular cartilage.

Human rheumatoid arthritic (RA) cartilage contains elevated levels of proteolytic enzymes in which the metalloproteases are believed to be the prime enzyme system involved in cartilage metabolism. We examined the effects of these enzymes and the serine proteases on endogenous proteoglycans (PGs) and newly synthesized PGs of seven RA cartilages. The data was further analyzed with regard to the therapy received by the patients prior to surgery. A structural heterogeneity among the PGs from RA cartilage was found, and two subsets were distinguished. While in the first subset more than 35% of the PGs were in aggregate form, no appreciable amount of PG aggregate was found in the second subset. Interestingly, in all but one specimen the subsets appeared to be a function of prior therapy received by the patients. In subset I patients had received prednisone and/or DMARD in addition to NSAIDs, while those from subset II had all received NSAIDs only, with one exception. Our findings also suggest that PG structure alterations could result from the action of already active and APMA-activated metalloproteases; these reduced the PG aggregation capability and caused extensive cleavage in the PG core protein. The serine proteases did not seem to play a major role. Moreover, when the endogenous latent metalloproteases were activated with APMA, high-density PGs (the A1D1 fraction) showed a reduction in their capacity to reaggregate, and in their hydrodynamic size. Using an immunological technique we demonstrated the presence, in subset I, of the hyaluronan binding region domain (HABR) of the core protein. For subset II this domain could not be found.(ABSTRACT TRUNCATED AT 250 WORDS)     

Osteoarthritis-related changes in human articular cartilage. An immunologic study.

We report the use of immunologic methods for detecting specific alterations in human osteoarthritic cartilage. Monoclonal antibodies with specificities for proteoglycans and link proteins have been used to define immunogenic sites in these molecules. We have identified 1 site in the protein core, 1 site in the link proteins, and another site that is common to both proteoglycan and link proteins, which are not modified in osteoarthritic cartilage. In addition, an antigenic determinant in link proteins that is altered in osteoarthritic cartilage has been identified. These results suggest that the structure of the ternary complex (hyaluronic acid binding region-link proteins-hyaluronic acid) could be altered in osteoarthritic cartilage. These modifications may be due to a genetic defect or to partial enzymatic degradation of these sites.     

Neutral metalloproteases and age related changes in human articular cartilage.

A decrease in proteoglycan (Pg) content and disturbances in the collagen network have been reported in aging cartilage. This study aims to determine whether these changes are associated with proteolytic enzymes such as neutral metalloproteases. Eighty lateral tibial plateaus were collected from subjects after death. The age, topographical area, and lesion severity (macroscopic grading) of each specimen were noted and the effects of neutral metallo-Pg-degrading and collagenolytic enzymes on these specimens were compared. The specimens were divided into two age groups: 20-50 years (group 1) and greater than 50 years (group 2). They were selected from both weight bearing and non-weight bearing areas. In some cartilage tissues the superficial layer was separated from the deep zone. Our data for the two neutral metalloenzymes examined showed: no correlation between enzyme activity and age when the specimens were of the same grade and a statistically significant rise in the enzyme levels of the older specimens, which increased as the lesions progressed. Neutral metallo-Pg-degrading enzyme activity was higher in non-weight bearing areas than in weight bearing areas, and this reached a statistical difference in the older cartilage with advanced lesions. The Pg-degrading enzyme activity was raised in the superficial layers of damaged cartilage tissue. Our data suggest that neutral metalloproteases are closely associated with the appearance and progression of the changes seen in aging cartilage.     

Metabolic and ultrastructural changes in articular cartilage of rats fed dietary supplements of omega-3 fatty acids

A "marginally deficient" essential fatty acid state was produced in male Sprague-Dawley rats by dietary supplementation with omega 3 fatty acids. Animals fed diets containing the highest amounts of these fatty acids (10% menhaden fish oil) demonstrated a 70% maximum decrease in the linoleic and arachidonic acid content of articular cartilage, a 30-40% decrease in cartilage hexosamine content, with little effect on hydroxyproline levels, and a 32% inhibition of proteoglycan synthesis. Histologic analysis revealed an occasional surface irregularity and localized depletion of Safranin O and toluidine blue staining of articular cartilage on the femoral heads from animals taking the higher doses. Electron microscopic analysis revealed a marked decrease in "dark-staining" chondrocytes relative to "light-staining" cells in all animals fed menhaden fish oil. The cartilaginous changes noted in this study reflect a causal relationship between chondrocyte metabolism and an altered unsaturated fatty acid content. The observed responses of chondrocytes to omega 3 fatty acids may be similar to those commonly associated with the development of early osteoarthrosis. It is not known whether similar changes are induced in other species, including humans, but these observations suggest that some caution must be taken in the long-term administration of menhaden fish oil or other omega 3 fatty acid-containing preparations in rheumatoid arthritis patients.     

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.     

In vitro rabbit articular cartilage organ model I. Morphology and glycosaminoglycan metabolism

A new in vitro adult articular cartilage organ model is described. Cartilage explants from adult rabbits have maintained a maximum glycosaminoglycan synthetic rate from day 7 to day 14 of incubation and normal morphology through day 10. The metabolic and histologic stability of this articular cartilage model suggests its suitability for investigating synthesis and degradation in normal, pharmacologically altered, and diseased cartilage.     

Chondrons from articular cartilage. III. Morphologic changes in the cellular microenvironment of chondrons isolated from osteoarthritic cartilage

Chondrons were isolated from human and canine osteoarthritic cartilage using low-speed homogenization techniques. Changes in chondron morphology were evaluated using differential interference-contrast microscopy, phase-contrast microscopy, and histochemical and ultrastructural methods. Chondrocyte viability was assessed using fluorescein diacetate staining, and chondron metabolism was investigated using autoradiography. The results suggest that initial changes in the collagen and proteoglycan distribution within the chondron are followed by chondrocyte proliferation to form clusters. These techniques offer the potential to study cell matrix interactions in degenerative osteoarthritis.     

Pressure related changes in human lumbosacral zygapophyseal joint articular cartilage

A brief histomorphologic study is presented of pressure related changes in the hyaline cartilage of paired left and right lumbosacral zygapophyseal joints in 6 cadavers. A comparison of the histology of the left and right zygapophyseal joint cartilages by light microscopy and dark field microscopy showed that, when dark field microscopy is used, a different histological reaction to staining can be highlighted. A similar change was not found using polarized light. It is not within the scope of this brief report to investigate the changes observed in this histological study.     

Extracellular matrix changes regulate calcium crystal formation in articular cartilage

PURPOSE OF REVIEW: The pathologic matrix mineralization seen in calcium pyrophosphate dihydrate and basic calcium phosphate deposition diseases identifies a subset of osteoarthritis patients with an unusual joint distribution and rapid progression of disease. Several factors contribute to pathologic matrix mineralization, including changes in the extracellular matrix of articular cartilage. The factors contributing to extracellular matrix changes that promote crystal formation are important and not well understood. Better characterization of these factors will enhance the understanding of the pathogenesis of pathologic matrix mineralization and may identify potential targets for novel therapeutic interventions. RECENT FINDINGS: Histologic studies of cartilage from patients affected by calcium crystal arthritis show changes in the pericellular matrix of articular chondrocytes. The amounts and types of collagens, proteoglycans, and calcium-binding proteins are altered. The mechanisms by which these changes occur remain poorly understood. Recent work, however, has implicated alterations in the chondrocyte phenotype and post-translational matrix-modulating enzymes such as the transglutaminases. SUMMARY: Changes in extracellular matrix are associated with the pathologic matrix mineralization seen in calcium pyrophosphate dihydrate and basic calcium phosphate crystal deposition diseases. The literature on growth plate cartilage provides observations and mechanisms through which extracellular matrix contributes to normal matrix mineralization, and has served as a model on which to base studies in articular cartilage. More studies are warranted to enhance the understanding of how changes in extracellular matrix contribute to crystal deposition diseases.     

Degradative changes in human articular cartilage induced by chemotherapeutic agents

We determined the effects of cytotoxic drugs on human articular cartilage by studying patients who received cancer chemotherapy. Tissue morphology and the biochemical findings of the "treated" cartilage were compared with those of "normal" human cartilage. The histological and ultrastructural studies showed that degeneration and repair occurred simultaneously. Degenerative changes included: chondrocytic alterations, collagen network disruption, decreased safranin-O staining at the superficial layer and pericellular area of the midlayer chondrocytes. Repair was shown by cartilage hypercellularity and clone formation. Some chondrocytes showed intense perilacunar metachromasia. Abnormal biochemistry included increased amounts of DNA content; total neutral collagenolytic enzyme and metalloproteoglycan-degrading enzyme (NMPE) activities; and the active form of the neutral collagenolytic enzyme. The cartilage proteoglycan content was lower in treated patients than in controls. Thus, chemotherapeutic agents can induce cartilage changes similar to those of early osteoarthritis. The reversibility of these changes and drug effects on diseased cartilage remain to be determined.     

Immunohistochemical demonstration of fibronectin in the most superficial layer of normal rabbit articular cartilage.

OBJECTIVE--To locate fibronectin ultrastructurally in the most superficial layer of normal articular cartilage of rabbits, in order to clarify its role in joint physiology. METHODS--Articular cartilage was obtained from the femoral condyle of seven normal adult rabbits and prepared by a method that included tannic acid fixation. Polyclonal antibodies against rabbit fibronectin were used in an immunohistochemical electron microscopic study, without any enzymic digestion but with a pre-embedding method for the transmission electron microscopy. RESULTS--The cartilage surface was successfully preserved by tannic acid fixation. The most superficial layer in electron photomicrographs was approximately 200-300 nm thick, cell free, and appeared to have two parallel components: the more superficial lamina and the deeper lamina. Gold labelled fibronectin lined this layer in immunohistochemical electron photomicrographs. CONCLUSIONS--Fibronectin covering the surface of the articular cartilage may have a role in joint lubrication and protection of the cartilage by binding with the collagenous matrix and hyaluronic acid in synovial fluid. Chondroitin sulphates may act as a charge barrier in close relationship with the collagen fibrils in the deeper lamina. Significant alteration in these functions may be one of the first causal steps leading to destruction of the articular cartilage.     

Differential responses of human articular cartilage to retinol.

An in-vitro study has been made of the response of aged human articular cartilage to the catabolic agent retinol. Weight bearing cartilage from the femoral condyle degrades and releases proteoglycan with an associated reduction of sulphate incorporation. Similar cartilage from the femoral head responds to the retinol with an inhibition of sulphate incorporation but no degradation or loss of proteoglycan. Extraction of the proteoglycan from the femoral head samples failed to demonstrate any evidence of breakdown.     

辛伐他汀对兔关节软骨组织中蛋白多糖降解的作用

目的探讨辛伐他汀对关节软骨的保护作用。方法取兔膝关节软骨建立软骨组织块培养模型,用5ng/ml浓度的IL-1α诱导软骨蛋白多糖降解,并以不同浓度辛伐他汀、双氯芬酸钠及地塞米松处理。培养60h后收集培养上清,检测软骨释放至其中的氨基聚糖的含量以评价蛋白多糖的降解程度。结果在1～10μmol/L的浓度间,辛伐他汀均能抑制软骨蛋白多糖的降解,并呈剂量依赖性;而双氯芬酸钠和地塞米松对蛋白多糖的降解没有明显的抑制作用。结论辛伐他汀对IL-1α诱导的软骨蛋白多糖降解具有抑制作用,提示它对关节软骨具有保护作用,可能影响骨关节炎疾病的进程。