Chondromucoprotein-degrading neutral protease activity in rheumatoid synovial fluid

Synovial fluid glycosaminoglycan (acid mucopolysaccharide) analysis in assessment of temporomandibular joint dysfunction. A pilot study

Temporomandibular joint (TMJ) synovial fluid was aspirated from normal control subjects and patients undergoing surgery for TMJ dysfunction. The glycosaminoglycan (GAG) composition of this fluid was analysed and compared with the clinical diagnosis and histological appearance of the condylar tissues. Changes in GAG composition were observed where a histologically hyperplastic response was seen in joint tissues, but these findings did not necessarily correlate with the initial clinical diagnosis. It is suggested that the fluid composition reflects the current metabolic activities of the tissues and may provide a useful marker of such processes.

Quantitative histologic studies on the pathogenesis of periarticular osteoporosis in rheumatoid arthritis

The pathogenesis of periarticular osteopenia in rheumatoid arthritis (RA) was investigated by histomorphometry on juxtaarticular bone removed during joint surgery. Twenty areas from 12 RA patients were compared with 14 areas from 6 osteoarthritis (OA) patients. There was no difference between the 2 groups in the percent of total bone volume. However, increased bone formation was suggested by an increase in the percent of active osteoid surface in RA compared with that in OA. Bone resorption was also increased in RA, as evidenced by increases versus OA in percent total resorptive surface, percent active resorptive surface, and number of osteoclasts. These results demonstrate increased turnover of bone in RA, especially in the resorptive phase of the periarticular trabecular bone. It is proposed that soluble factor(s) synthesized in the contiguous rheumatoid synovium may be transferred to the periarticular bone space, stimulating osteoclasts to resorb bone.

An electron microscopic study of the synovial-bone junction in rheumatoid arthritis

The cellular characteristics of the rheumatoid synovial-bone junction (SBJ) were examined in the electron microscope. Large numbers of mononuclear inflammatory cells along the bone suggested the advance of the rheumatoid inflammatory lesion into bone tissue. The SBJ contained macrophage-rich and osteoclast-rich areas. The presence of the macrophage as a predominant cell type and the marked collagenolysis of the eroded bone matrix suggested that collagenase released by macrophages was responsible for a major portion of the bone erosion. The observation of osteoclasts with ruffled borders, containing free bone crystals in close contact with the bone, indicated that these osteoclasts were stimulated by the rheumatoid synovium. It seems likely that articular bone resorption depends upon the local host response to the macrophage and osteoclast in the rheumatoid joint.

Proteolytic enzymes in joint destruction

An increase in both neutral and acid proteolytic activity and proteinase inhibitors is reported in synovial fluid of osteoarthrotic and rheumatoid joints, compared with controls, but in subchondral bone and articular cartilage only Cathepsin D and in synovial tissue only neutral caseinolysis were elevated. Especially high proteolytic activities were found in joint compartments of seronegative rheumatoid and in sera of osteoarthrotic patients. The source of the main part of neutral caseinolytic activity in joint fluid is inflammatory cells, in the case of Cathepsin D the tissues of origin seem to be bone and cartilage.

Influence of antigen-induced arthritis on connective tissue call metabolism

Loss of hyaline articular cartilage during chronic joint inflammation may be due to enzymatic breakdown of cartilage proteoglycans and inhibition of proteoglycan biosynthesis. In vivo study in the mouse on the influence of antigen-induced arthritis on articular cartilage chondrocyte function revealed that proteoglycan synthesis was severely inhibited during active joint inflammation. In addition, autoradiographs showed that inhibition of chondrocyte synthetic function and chondrocyte death at later stages of the arthritis were most pronounced in the central part of patellar hyaline articular cartilage without pannus tissue being present nearby.

Antigen-induced arthritis. Decreased proteoglycan content and inhibition of proteoglycan synthesis in articular cartilage

An arthritis was induced in rabbits immunized with human serum albumin by injection of antigen into the hind knee joint. Histological changes in the synovial membrane and an increase in polymorphonuclear granulocytes in the synovial fluid indicated an inflammatory response similar to that described with fibrin as antigen (1). The arthritis was accompanied by no significant change in the collagen content, but a marked decrease in the proteoglycan content of the cartilage was noted. Cartilage from inflamed joints generally exhibited a decreased ability to synthesize proteoglycan in vitro.

[Human joint capsule in osteoarthrosis (morpholocical changes) (author's transl)]

Morphological investigations of the joint capsules in osteoarthrotic-changed joints have given rise to doubts about the present theory of the causal aetiology of the osteoarthrosis. In every inspected and demonstrated illustration beside the partly normal capsules segments could be found every transition between mild regressive alterations and most massive proliferative changes of the conective tissue and the lining cell layer. It was extraordinary, that the strongly dilated vessels were filled with red blood cells. In another part of the same case was found a massive stricture caused by concentrically deposited substances, which were impregnated with collagenous fibers. Regeneration of the vessels frequently happened adjacent totally obstructed ones. Round-cell infiltrations, granulocytes or other indications of an inflammatory synovitis are found only in a few cases. The intracartilaginous enzymatic reactions, which have been much talked of and which were explained as characteristic of the osteoarthrosis cannot be the cause of the degradation of the cartilage, particularly, because of the normal cell count which is to be found in the synovial fluid. We can answer this problem, if we can prove that the substrates of the chondral metabolism themselves exert a direct or indirect influence on the interstitial connective tissue with induction of the powerful proliferation of the same tissue. The changes in the transit zone would be secondary and their effect on the lining cell layer would increase the progression of the arthrotic events.

Surface ultrastructure of rheumatoid articular cartilage

Six rheumatoid articular cartilage specimens, which appeared grossly normal and were shown to be free of pannus when examined under the light microscope, were examined electron microscopically. For comparison, normal-appearing cartilage specimens from 2 patients with meniscus injury and 2 with degenerative joint disease (DJD) were also examined. In all cases the normal-appearing joint surface of rheumatoid cartilage was abnormal. Amorphous-appearing material was present to a depth varying between 6 and 25 micron. Some of this material had the appearance of fibrin deposited at the cartilage surface, but much appeared to represent breakdown products of the cartilage matrix, i.e. degraded collagen and proteoglycan. DJD cartilage did not show similar changes. The findings suggest that the surface of rheumatoid articular cartilage, even when grossly normal in appearance, is degraded by enzymes either present in the synovial fluid or released by polymorphonuclear cells in close contact with the cartilage surface.

Carrageenin-induced arthritis. IV. Rate changes in cartilage matrix proteoglycan synthesis

A localized inflammatory response was initiated by both single and repeated injections of carrageenin into femorotibial joints. Histologic changes were observed 24 hours after a single intraarticular injection, and an inhibition in the in vitro rate of proteoglycan synthesis was detected 72 hours after the injection. This inhibition was relieved in vitro by the addition of beta-D-xyloside, an exogenous initiator of glycosaminoglycan biosynthesis. Following repeated carrageenin injections, most cells appeared to be dead on histologic examination and no in vitro proteoglycan synthesis could be detected; nor could any stimulation be achieved by adding exyloside.

Carrageenin-induced arthritis. III. Proteolytic enzymes present in rabbit knee joints after a single intraarticular injection of carrageenin

A single intraarticular injection of carrageenin into the rabbit knee joint initiates an inflammatory reaction in the synovial tissues. the exudate from the joint was able to degrade proteoglycan at pH 5.2 and pH 7.2. Further characterization of proteolytic enzymes in the inflamed synovial tissues showed the presence of cathepsin D, a neutral protease, and cathepsin B1. Maximum activities of two lysosomal enzymes, acid phosphatase and cathepsin D, were observed within 7 days of injection. Most of this activity was found to be associated with cells in the synovial fluid.

Carrageenin-induced arthritis. I. The effect of intraarticular carrageenin on the chemical composition of articular cartilage

A single intraarticular injection of carrageenin into rabbit knee joints initiated a localized synovial inflammatory response. This response was accompanied by a 20% loss of proteoglycan from the articular cartilage within 24 hours and by a further 30-60% loss within 5-7 days. The chondrocytes replaced the lost proteoglycan within 42 days. More than two injections caused only a further small decrease in proteoglycan content; the cartilage was then unable to replace the lost proteoglycan. The absence of recovery coincided with the appearance of erosion of the cartilage surface.

Electron microscopic demonstration of immunoglobulin deposition in rheumatoid cartilage

Horseradish peroxidase (HRPO) conjugated with goat antihuman IgG, goat antihuman IgM, and aggregated human IgG has been used as a enzymatic marker to stain IgG, IgM, and rheumatoid factor in rheumatoid cartilage. When Hrpo-anti IgG and HRPO-anti IgM were used, immunoglobulin deposits were not observed in nonrheumatoid cartilage. However 7 of 8 rheumatoid cartilage specimens stained with HRPO-anti IgG showed electron-dense deposits. Three rheumatoid specimens stained with HRPO-anti IgM showed similar findings. Both of 2 rheumatoid specimens also stained positively with HRPO conjugated with aggregated IgG, a finding indicating that rheumatoid factor was present. The deposits were seen between the collagen fibers of the superficial layer of the cartilage to a maximal depth of 22 mu from the surface (average: 7 mu). The amorphous fibrinous material on the surface of the cartilage was also stained. The demonstration of IgG, IgM, and rheumatoid factor in the superficial zone of rheumatoid cartilage suggests that immune complexes are deposited in the cartilage in this disease.

Purification of granulocyte neutral protease from human blood and rheumatoid synovial fluid

The neutral protease activity of human synovial fluid cells, like that of peripheral blood leucocytes, is located in a granule fraction. It can be solubilised by various agents but only 1 M neutral salts do so without inactivation. Salt-solubilised neutral protease has been purified (300 X) from synovial fluid cells; like preparations obtained in the same way (600 X purified) from peripheral blood leucocytes, it has a broad pH profile of activity (pH 7--10.5) and in this, as well as in substrate specificity and sensitivity to activators and inhibitors, it behaves as a serine-histidine type protease similar to elastase (EC 3.4.21.11). The product showed two major components on polyacrylamide gel electrophoresis. Collagenase or chymotrypsin-like activity were not detected.

Neutral proteases and cathepsin D in human articular cartilage

Proteolytic enzymes have been studied in extracts of human articular cartilage by the use of micromethods. The digestion of hemoglobin at pH 3.2 and of cartilage proteoglycan at pH 5 was shown to be due chiefly to cathepsin D. Cathepsin D was purified 900-fold from human patellar cartilage. Its identity was established by its specific cleavage of the B chain of insulin. At least six multiple forms of cathepsin D are present in cartilage; these corresponded to bovine forms 4-9. Cathepsin D had no action on proteins at pH 7.4. However, cartilage extracts digested proteoglycan, casein, and histone at this pH. The proteolytic activities against these three substrates were purified about 170-, 160-, and 70-fold, respectively. Each activity appeared in multiple forms on DEAE-Sephadex chromatography. The three activities appear to be different since cysteine inhibited casein digestion, aurothiomalate inhibited histone digestion, and neither inhibited proteoglycan digestion. Tests with a wide range of inhibitors and activators suggest that these three activities differ from other neutral proteases described in the literature.