The cytokinome in osteoarthritis, a new paradigm in diagnosis and prognosis of cartilage disease

At present, diagnosis and progression monitoring of osteoarthritis (OA) is made through radiological and clinical assessment. Several studies investigated the role of synovial fluid analysis, to find out whether joint disease could be characterized by the pattern of cytokines, which acts during the pathogenic process or in specific stages of it. Online PubMed-Medline search was performed in order to retrieve evidence concerning synovial fluid analysis of cytokines involved in OA degenerative process. Concerning pro-inflammatory cytokines, it has been shown that interleukin (IL)-6, TNF-α and IL-17 are mainly over-expressed in the synovial fluid of OA joints, as well as anti-inflammatory cytokine IL-10. Variations of cytokines levels occur with radiological and clinical progression. It was also reported that metalloproteinases are involved. Synovial fluid analysis may be helpful in defining stage and type of OA, but more research is needed, especially focusing on the variation of sets of cytokines during OA stages and correlating these patterns with clinical features.

Age-related NADPH Oxidase (arNOX) Activity Correlated with Cartilage Degradation and Bony Changes in Age-related Osteoarthritis

The purpose of this study was to investigate the age-related NADPH oxidase (arNOX) activity in patients with age-related knee osteoarthritis (OA). Serum and cartilage arNOX activities were determined using an oxidized ferricytochrome C reduction assay. Full-thickness knee joint cartilages obtained through total knee replacement surgery were graded according to the Outerbridge (OB) classification. Radiographic severity of OA was determined on Knee X-rays according to the Kellgren-Lawrence (K/L) grading system. Cartilage β-galactosidase, HIF-1α, and GLUT-1 expression levels were evaluated as markers for tissue senescence, hypoxia, and glycolysis. Higher arNOX activities occurred with higher levels of cartilage β-galactosidase, HIF-1α, and GLUT-1 (P = 0.002). arNOX activity in cartilages with surface defects (OB grade II, III) was higher than in those without the defects (OB grade 0, I) (P = 0.012). Cartilage arNOX activity showed a positive correlation with serum arNOX activity (r = -0.577, P = 0.023). Serum arNOX activity was significantly higher in the OA subgroup with bilateral ROA than in the OA with no or unilateral ROA (2.449 ± 0.81, 2.022 ± 0.251 nM/mL, respectively, P = 0.019). The results of this study demonstrate that OA itself is not a cause to increase arNOX activities, however, arNOX hyperactivity is related to a high degree of cartilage degradation, and a high grade and extent of ROA in age-related OA.

A Selective p38α Mitogen-Activated Protein Kinase Inhibitor Reverses Cartilage and Bone Destruction in Mice with Collagen-Induced Arthritis

Destruction of cartilage and bone is a poorly managed hallmark of human rheumatoid arthritis (RA). p38 Mitogen-activated protein kinase (MAPK) has been shown to regulate key proinflammatory pathways in RA, including tumor necrosis factor alpha, interleukin (IL)-1beta, and cyclooxygenase-2, as well as the process of osteoclast differentiation. Therefore, we evaluated whether a p38alpha MAPK inhibitor, indole-5-carboxamide (SD-282), could modulate cartilage and bone destruction in a mouse model of RA induced with bovine type II collagen [collagen-induced arthritis (CIA)]. In mice with early disease, SD-282 treatment significantly improved clinical severity scores, reduced bone and cartilage loss, and reduced mRNA levels of proinflammatory genes in paw tissue, including IL-1beta, IL-6, and cyclooxygenase-2. Notably, SD-282 treatment of mice with advanced disease resulted in significant improvement in clinical severity scoring and paw swelling, a reversal in bone and cartilage destruction as assessed by histology, bone volume fraction and thickness, and three-dimensional image analysis. These changes were accompanied by reduced osteoclast number and lowered levels of serum cartilage oligomeric matrix protein, a marker of cartilage breakdown. Thus, in a model of experimental arthritis associated with significant osteolysis, p38alpha MAPK inhibition not only attenuates disease progression but also reverses cartilage and bone destruction in mice with advanced CIA disease.

Histone deacetylases--a new target for suppression of cartilage degradation?

Increased expression of metalloproteinases is a fundamental aspect of arthritispathology and its control is a major therapeutic objective. In cartilage cultured in the presence of the cytokines interleukin-1 and oncostatin M, chondrocytes produce enhanced levels of metalloproteinases of the ADAMTS (a disintegrin and metalloproteinase with thrombospondin motifs) and MMP (matrix metalloproteinase) families, resulting in the degradation of aggrecan and collagen. The histone deacetylase inhibitors trichostatin A and butyrate were shown to drastically reduce expression of these enzymes relatively selectively, with concomitant inhibition of breakdown of matrix components. This family of enzymes is therefore a promising target for therapeutic intervention.

Neoepitopes as biomarkers of cartilage catabolism

Progressive degradation of articular cartilage is a central feature of arthritis and a major determinant of long term joint dysfunction. There are no treatments able to halt the progression of cartilage destruction presently available, and monitoring the benefit of potential therapies is hampered by our inability to measure the "health" of articular cartilage. Serial radiographic assessment of joint space narrowing, the current gold standard, requires measurements over a prolonged time (1-5 years) and is prone to technical difficulties. Other strategies for evaluating cartilage degradation are needed to enable both short and long term monitoring of disease progression and response to therapy. One avenue that holds promise is the use of biomarkers that accurately reflect the degradative state of the articular cartilage. Antibodies that recognise terminal amino acid sequences generated by proteolysis at specific sites in the core protein of both aggrecan and type II collagen (neoepitope antibodies) have become available in recent years. These antibodies have been invaluable for identifying the proteinases responsible for cartilage breakdown both in vitro and in vivo. The presence of neoepitope sequences generated by specific metalloenzyme cleavage of aggrecan and type II collagen correlates well with the progression of cartilage degeneration, both in vitro and in mouse models of arthritis. Preliminary results with quantitative assays of type II collagen neoepitopes suggest that they may be useful markers of joint disease in humans. Long term studies correlating neoepitope concentration with clinical and radiographic disease are now required to validate the utility of neoepitopes as surrogate markers of cartilage degeneration and joint disease.

Aggrecanase-mediated cartilage degradation

Increasing evidence is accumulating for the importance of the aggrecanases ADAMTS-4 and ADAMTS-5 in cartilage degradation in arthritis. Recent work from a number of laboratories has begun to provide insight into the regulation of the expression and activity of these proteins and the molecular basis of their role in aggrecan catabolism. Recombinant ADAMTS-4 and ADAMTS-5 cleave aggrecan at five distinct sites along the core protein and aggrecan fragments generated by cleavage at all of these sites have been identified in cartilage explants undergoing matrix degradation. This proteolytic activity of the aggrecanases can be modulated by several means, including altered expression, activation by proteolytic cleavage at a furin-sensitive site, binding to the aggrecan substrate through the C-terminal thrombospondin motif, activation through post-translational processing of a portion of the C-terminus and inhibition of activity by the endogenous inhibitor TIMP-3. ADAMTS-4 and ADAMTS-5 activity is detected in joint capsule and synovium in addition to cartilage, and may be upregulated in arthritic synovium at either the message level or through post-translational processing. Additional substrates have now been identified, including the chondroitin-sulfate proteoglycans brevican and versican. Finally, advances are occurring in the development of selective aggrecanase inhibitors designed to serve as therapeutics for the treatment of arthritis.

Activation of stress-activated protein kinase in osteoarthritic cartilage: evidence for nitric oxide dependence

OBJECTIVE

We have demonstrated in bovine chondrocytes that nitric oxide (NO) mediates IL1 dependent apoptosis under conditions of oxidant stress. This process is accompanied by activation of c-Jun NH2-terminal kinase (JNK; also called stress-activated protein kinase). In these studies we examined activation of JNK in explant cultures of human osteoarthritic cartilage obtained at joint replacement surgery and we characterized the role of peroxynitrite to act as an upstream trigger.

DESIGN

A novel technique to isolate chondrocyte proteins (<10% of total cartilage protein) from cartilage specimens was developed. It was used to analyse JNK activation by a western blot technique. To examine the hypothesis that chondrocyte JNK activation is a result of increased peroxynitrite, in vitro experiments were performed in which cultured chondrocytes were incubated with this oxidant.

RESULTS

Activated JNK was detected in the cytoplasm of osteoarthritis (OA) affected chondrocytes but not in that of controls. In vitro, chondrocytes produce NO and superoxide anion. IL-1 (48 h), which induces nitric oxide synthase, resulted in an activation of JNK; this effect was reversed by N-monomethylarginine (NMA). TNFalpha treated chondrocytes at 48 h produce superoxide anion (EPR method). Exposure of cells to peroxynitrite led to an accumulation of intracellular oxidants, in association with JNK activation and cell death by apoptosis.

CONCLUSION

We suggest that JNK activation is among the IL-1 elicited responses that injure articular chondrocytes and this activation of JNK is dependent on intracellular oxidant formation (including NO peroxynitrite). In addition, the extraction technique here described is a novel method that permits the quantitation and study of proteins such as JNK involved in the signaling pathways of chondrocytes within osteoarthritic cartilage.

An experimental study of surface injury to articular cartilage and enzyme responses within the joint

An experimental model of degenerative joint disease on chondromalacia consists of a surgically-scarified articular surface of the adult dog knee joint. In 52 dogs, evaluated by histologic and enzymatic assays over a period of 1 to 110 weeks post-surgery, the levels of acid hydrolase activity varied on various areas of articular cartilage within the same joint. There was a transient rise in most of the acid hydrolases in the synovium as a response to arthrotomy of the knee joint. All of the acid hydrolases studied did not respond uniformly to surgically created trauma. There was evidence of repair of the cartilage lacerations even when the subchondral zone was not breached. Lacerations in the central portion of the patella rarely showed healing in contrast to those placed more to the periphery of the articular surface. There was no gross or histologic evidence of progressive degenerative joint disease up to 2 years post-surgery. Thus an injury inflicted to the surface of the articular cartilage may be in itself insufficient in severity to produce destructive changes in the joint. This should not be too surprising, since, clinically, all joint surface injury does not lead to degenerative arthritis. The joint seems to have an injury threshold whereby chondrocytes are capable of repairing surface injury if the damage is not massive or repetitive. Insofar as lacerations in the center of the patella rarely healed, while the peripheral ones showed consistent signs of healing, the site of injury, as well as the magnitude of injury, may be critical.

Angiotensin converting enzyme in human synovium: increased stromal [(125)I]351A binding in rheumatoid arthritis

OBJECTIVE

To determine whether tissue angiotensin converting enzyme (ACE) is increased in synovia from patients with rheumatoid arthritis, osteoarthritis or chondromalacia patellae.

METHODS

Sections of synovia from patients with rheumatoid arthritis (n = 7), osteoarthritis (n = 7) or chondromalacia patellae (n = 6) were tested for immunoreactivity for ACE, and for binding of the ACE inhibitor [(125)I]351A. The amount of ACE was measured with computer assisted image analysis as the proportion of synovial section area occupied by ACE-immunoreactive cells, and the density of [(125)I]351A binding.

RESULTS

[(125)I]351A binding sites had characteristics of ACE and colocalised with ACE-like immunoreactivity to microvascular endothelium and fibroblast-like stromal cells in inflamed and non-inflamed human synovium. Stromal [(125)I]351A binding densities (B(eq)) and the fraction of synovial section area occupied by ACE-immunoreactivity (fractional area) were higher in synovia from patients with rheumatoid arthritis (B(eq) 28 amol/mm(2), fractional area 0.21) than from those with osteoarthritis (B(eq) 9 amol/mm(2), fractional area 0.10) or chondromalacia patellae (B(eq) 9 amol/mm(2), fractional area 0.09)(p < 0.05). Density of [(125)I]351A binding to stroma was similar to that to blood vessels in rheumatoid arthritis, but less dense than vascular binding in chondromalacia patellae and osteoarthritis. Increases in [(125)I]351A binding densities were attributable to increases in the numbers of binding sites, and were consistent with an increase in the density of ACE bearing stromal cells.

CONCLUSION

ACE is upregulated in synovial stroma in rheumatoid arthritis. Increased tissue ACE may result in increased local generation of the vasoconstrictor and mitogenic peptide angiotensin II and thereby potentiate synovial hypoxia and proliferation in rheumatoid arthritis.

Bronchial cartilage atrophy in chronic bronchitis: observations on chondrolytic processes

The status of bronchial cartilage degeneration in chronic bronchitis is unclear, and little is known about the chondrolytic mechanisms involved. The potential contributions of various inflammatory cells, chondrocytes and cartilage-degrading enzymes to cartilage atrophy have been examined. Bronchial cartilage specimens were obtained at autopsy from lobar secondary bronchi from chronic bronchitics and age-matched controls; each was examined by light microscopy and immunohistology for the distributions of mast cells, macrophages, eosinophils, collagenase 1, collagenase 3, and degradation products of cartilage collagen. Most bronchitic specimens showed hypertrophic chondrocytes, some of which were immunostained for collagenase 3, and occasionally for collagenase 1. Evidence for collagen degradation products was demonstrated around the lacunae of a proportion of chondrocytes, and both collagenases were also observed in the soft inflammatory tissues in close association with the cartilage surface, together with variable distributions of mast cells and macrophages. Such observations were generally absent or very much reduced in the control, non-bronchitic specimens. Degenerative changes, atrophy and loss of bronchial cartilage were common features of most chronic bronchitic specimens, this usually being related to intrinsic changes in the chondrocyte phenotype, including proliferative and matrix-degrading properties. Mast cells and macrophages were often observed in close association with the bronchial cartilage, suggesting that inflammatory cells may also contribute to the mechanisms of bronchial cartilage degradation and loss. These observations of bronchial cartilage degeneration were generally lacking in age-matched non-bronchitic control specimens.

Expression and regulation of collagenase-3 (MMP-13) in human malignant tumors

Human collagenase-3 (MMP-13) is a matrix metalloproteinase originally identified in breast carcinomas. Recent studies have revealed that this enzyme is also produced by a variety of malignant tumors including head and neck carcinomas, chondrosarcomas and basal cell carcinomas of the skin. In all cases, the expression of collagenase-3 is associated with aggressive tumors. Different cytokines, growth factors and tumor promoters are able to up-regulate collagenase-3 expression in tumor cells or in stromal cells surrounding epithelial tumor cells. Functional analysis of the collagenase-3 gene promoter has allowed the identification of AP-1 and OSE-2 elements mediating, at least in part, its expression in both normal and pathological conditions.

[Overview of the current status of measurable parameters of cartilage metabolism in various body fluids]

The human cartilage and bone is characterized by a remodeling during the life, well balanced by neosynthesis and degradation of matrix components. In different joint diseases, it becomes imbalanced and the destruction of the cartilage supersedes the repair. In tissue processes in disease and in normal turnover of the matrix, these molecules are fragmented and released into surrounding fluids, in the synovial fluid, and then in the blood and the urine, where they can be detected. The quantitative measurement in the synovial fluid is more specific than in the other body fluids. The research process in recent years has suggested that these molecular markers of cartilage and bone matrix metabolism can be used to determine diagnosis, the disease severity rather than its presence or absence, the prognosis, and the response to therapy. They should help to identify the disease mechanism in different joint diseases not only on the tissue but also on the molecular level. The specific cartilage matrix markers promise to become useful tools in the future in clinical use. The research in this area is still in the early stages, with most results dated from the end of the 1980s and the 1990s.

Localization of matrix metalloproteinase 3 (stromelysin) in osteoarthritic cartilage and synovium

Degradation of proteoglycans is an initial change in osteoarthritic cartilage. Matrix metalloproteinase-3 (MMP-3; stromelysin) capable of degrading cartilage proteoglycans and type IX collagen was immunolocalized in osteoarthritic and normal cartilage. Immunohistochemical studies showed MMP-3 in chondrocytes of the superficial and transition zones in approximately 90% of osteoarthritic cartilage (60 of 67 samples) and in 31% of those of the superficial zone in some normal cartilage (4 of 13 samples). MMP-3 staining correlated directly with the histological histochemical scores of Mankin and with proteoglycan depletion, up to a certain grade of severity. Chondrocytes in the deep radial zone, clusters, and osteophytes were immunostained only when proteoglycan depletion and fissures affected them. Culture media from osteoarthritic cartilage contained significantly higher levels of metalloproteinase activity that was identified as MMP-3 by immunoblotting and lower amounts of tissue inhibitor of metalloproteinases compared with those in the control samples. MMP-3 was also immunolocalized in the lining cells of most osteoarthritic synovium (20 of 23 specimens, 87%) with a direct correlation with scores of inflammatory cell infiltration in the synovium, but it was not detected in the normal synovium. Light and electron microscopic studies demonstrated that MMP-3 digests proteoglycan aggregates in human articular cartilage. Treatment of normal and osteoarthritic cartilage slices with tumor necrosis factor-alpha and/or interleukin-1 alpha increased the number of MMP-3-immunoreactive chondrocytes and the intensity of the staining. These data suggest that MMP-3 produced by the chondrocytes and synovial lining cells under stimulation with these cytokines may be important in proteoglycan degradation in human ostoearthritic cartilage.

The role of proteinases in cartilage destruction

Most of the organic, extracellular matrix of articular cartilage consists of collagens and proteoglycans. Their degradation is initiated extra- or peri-cellularly by proteinases produced locally by cells in and around the joint. Although enzymes from all four classes of proteinases can degrade the cartilagenous matrix, serine proteinases, particularly plasmin, and various neutral metalloproteinases (NMPs) are likely to be the key enzymes in this process. Much attention has been paid to members of the latter group, which are synthesised both by the resident, mesenchymal cells of the joint and by various types of white blood cells which colonise it during inflammation. NMPs can be conveniently grouped into three classes, the collagenases, the stromelysins and the gelatinases. Two members are known for each class, with the recently identified "pump" (Putative Metalloproteinase) probably constituting a third member of the stromelysin group. Regulation of these enzymes is complex. Cells normally synthesise NMPs at low rates, but their production increases markedly following cellular activation by cytokines or certain other stimuli. Major control points for enzyme synthesis occur at the levels of transcription and the conversion of proenzyme to active enzyme; enzyme activity is further regulated through the action of inhibitors. Alpha-2 macroglobulin is the major systemic inhibitor, while a number of tissue inhibitors act as local regulators. These include at least two TIMPs and several IMPs. Pharmacologic manipulation of NMP activity holds promise as an approach to anti-erosive therapy in arthritis.

Mechanisms of human neutrophil-mediated cartilage damage in vitro: the role of lysosomal enzymes, hydrogen peroxide and hypochlorous acid

Cartilage is a focal point of attack by cellular and molecular elements of the inflammatory response which occurs in arthritic diseases. Neutrophils damage articular cartilage by degrading matrix components and inhibiting their synthesis. The aim of this study was to elucidate mechanisms of this damage. Human neutrophils were isolated from blood by centrifuging through Ficoll-Hypaque and granule extract prepared from them. Articular cartilage from adult humans and cattle was maintained in organ culture. Cartilage degradation (release of 35S-labelled proteoglycan) or synthesis (incorporation of 35S into proteoglycan) was determined after various treatments. Human neutrophils and neutrophil granule extract degraded proteoglycan and inhibited proteoglycan synthesis. The specific leucocyte elastase inhibitor N-methoxysuccinyl-(ala)2-pro-val-chloromethylketone (MAAPVCMK) partially reversed these effects. H2O2, a product of the neutrophil respiratory burst, when added directly at 10(-6)mol/L, or generated by glucose oxidase (GO)/glucose inhibited proteoglycan synthesis but had no effect on degradation. Hypochlorous acid (OHCl), a product of the myeloperoxidase (MPO)/H2O2/Cl system at 50 mumol/L degraded proteoglycan and inhibited its synthesis. OHCl produced by granule extract (as a source of MPO) + GO-generated H2O2 + Cl- degraded proteoglycan. The results indicate that neutrophil-mediated proteoglycan degradation and inhibition of synthesis is largely attributable to elastase and secondarily to OHCl, whereas H2O2 impairs synthesis without affecting degradation of proteoglycan.

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.

Isozymes of glycogen phosphorylase in human cartilage and cartilage tumors

Isozyme patterns of glycogen phosphorylase in normal fetal and adult human cartilage and benign and malignant cartilage tumors were investigated by means of polyacrylamide gel disc electrophoresis. In both normal cartilage and cartilage tumors four distinct bands were observable: these were of the liver, liver-like and fetal types and of a hybrid type between the muscle and fetal types judging by their mobilities in the small-pore gels containing 0.01% and 0.1% glycogen. The isozyme pattern of benign cartilage tumors was almost identical with that of normal cartilage. In normal fetal and adult cartilage and benign cartilage tumors, the liver and liver-like types were predominant, whereas in malignant cartilage tumors they were minor and the fetal type was predominant. These results indicate fetal deviation of phosphorylase isozymes in malignant transformation of cartilage cells.

The brachymorphic mutation of mice and altered developmental patterns of limb bud 3':5' cyclic adenosine monophosphate

Concentrations of cyclic AMP (cAMP) were determined in paired fore and hind limbs from day 12-16 of development in murine fetuses homozygous for the brachymorphic (bm) mutation and normal controls. A developmental rise in cAMP occurred 1 day earlier in bm/bm than in +/+ hind limbs and cAMP was higher in day-13 bm/bm than in +/+ fore limbs. Since cAMP is well documented to stimulate chondrogenic differentiation, premature cartilage determination secondary to altered levels of cAMP could play a role in bm/bm short-limbed dwarfism.

Comparison of phosphohydrolase activities from articular cartilage in calcium pyrophosphate deposition disease and primary osteoarthritis

One abnormality in calcium pyrophosphate deposition disease (CPDD) which fosters consistently high synovial fluid pyrophosphate ion (PPi) and large accumulations of calcium pyrophosphate dihydrate crystals (Ca pyrophosphate) might be an aberration in chondrocytes involving elaboration of PPi and failure of its hydrolysis within cartilage matrix. Exploration of this hypothesis required further information on the phosphohydrolases in relevant human articular cartilages. Triton X-100 extracts of whole homogenized cartilage from 18 patients with primary osteoarthritis (OA), 10 patients with CPDD and secondary OA, as well as 6 "normal" subjects were partially purified by DE-52 chromatography and eluates studied for phosphohydrolase activity in a variety of substrates, inhibitors, and environmental conditions. Almost all the protein as well as crude alkaline phosphatase and pyrophosphatase activities were clustered in peaks designated I and II. Findings in CPDD cartilage not observed in OA controls were: 1) consistent alkaline phosphatase activity in the void volume of DE-52 columns, 2) high levels of 5'nucleotidase activity, 3) abundant generation of PPi by CPDD cartilage during in vitro incubation of cartilage extract fractions with ATP. This enzymatic behavior is likely to bear a regulatory relationship to PPi production by chondrocytes in CPDD.

[Regulatory effects of proteases in articular inflammation]

The role of proteases in the stimulation of cells participating in a chronic inflammatory reaction is reviewed. Several neutral proteases stimulate B lymphocytes to produce both specific and unspecific antibodies and such enzymes can replace, at least in vitro, T-helper cells. Proteases might influence macrophages as well, by a MIF-like activity, by increasing spreading in vitro or by liberating from C3 the C3b component which has an activating effect on these cells. Endocytosis of protease - alpha-2 macroglobulin complexes by macrophages induces production of neutral proteases as well. A stimulation of fibroblasts by proteases is possible but not yet clearly proven.

The possible role of neutrophil proteinases in damage to articular cartilage

The proteolytic degradation of articular cartilage that is seen in the arthritides affects both of the major structural components of the tissue, proteoglycan and collagen. Neutrophil leucocytes are abundant in the synovial fluid of the inflamed joints, and we have considered whether the large quantities of neutral proteinases carried by these cells could contribute to the cartilage degradation. The two neutrophil serine proteinases have been isolated, and shown to break down both proteoglycan and collagen in articular cartilage. The enzymes attacked the non-helical terminal peptides of the collagen, eliminating the cross-links, thus destabilizing and solubilizing, the fibres. The soluble collagen then denatured spontaneously, and was further degraded. Although large quantities of the neutrophil proteinases are probably released in the synovial fluid each day, the inhibitory capacity of the fluid is seldom, if ever, saturated. Nevertheless, immunologically mediated release of the neutrophil enzymes in 'frustrated endocytosis' at the cartilage surface could give rise to the generalized damage that has been reported by others.

Enzyme histochemistry of bone and cartilage cells

Initial studies indicated that bone and cartilage, when treated with a hypertonic glutaraldehyde fixative for a short period, retained significant enzyme activity for histochemistry and also maintained excellent fine structure. We used 6% glutaraldehyde in 0.1 M cacodylate buffer, pH = 7.2, 4 degrees C to fix small pieces of bone or cartilage for three hours while the tissues were being constantly agitated. These samples were demineralized in 10% ethylene diamine tetraacetic acid, buffered to pH = 7.2 with 0.1 M Tris HC1, at 4 degrees C. The demineralized tissue was frozen and cryostat sections 32 microns thick were taken for incubation at 37 degrees C in various media for histochemistry. For electron microscopic localization of enzymes a heavy metal capturing method had to be used. For light microscopy, the azo dye methods were frequently used, but these were not usable for electron microscopy. Alkaline phosphatase was found on the outer surface of osteoblast and hypertrophic cartilage cell membranes. The only intracellular enzyme activity was found on the mitochondrial membranes of the osteoclast and only when the pH of the media was lowered from the optimum 9.5 to 8.5. Alkaline phosphatase was not found along the osteocyte or young cartilage cell membranes...

Effects of acute cartilaginous injury on serum and cartilage lysozyme levels

Acute cartilage degradation was produced in rabbits by the intravenous injection of crude papain. This resulted in a significant rise in serum lysozyme in 97% of the animals, as well as a fall in the residual lysozyme content of auricular and costal cartilage. The rise in serum lysozyme paralleled the rise in serum chondroitin sulfate. The source of the rise in lysozyme appeared to be the release of extracellular, nonlysosomal lysozyme from the cartilage matrix. Serum lysozyme elevation in arthritic disorders may reflect cartilage degradation.