Cartilage Proteoglycan Depletion Research Articles

Effects of exercise on synovium and cartilage from normal and inflamed knees

The effect of running activity on normal and inflamed knees was determined by light microscopic (LM) and scanning electron microscopic (SEM) observations on hamster articular cartilage. Animals were split into two groups; one housed in standard cages and one given free access to running wheels. Twenty-one days prior to analysis, half of each group was given an intra-articular injection of lipopolysaccharide (LPS) to cause an inflammation, the other half were uninjected. No remarkable changes were observed by LM in either the control running or nonrunning groups. In contrast, cartilage proteoglycan depletion, and pannus and synovial hyperplasia were equally observed in both groups of LPS-injected animals. SEM observations on the patellae from control animals found them to be free from damage to the articular cartilage. The joints of both the LPS nonrunning and running animals contained synovial hypertrophy with villus projection from the synovial lining. However, only the LPS-injected running hamsters had cartilage fraying over large areas of the articular surface, as well as areas in which the villus projections had been flattened. These results demonstrated that mechanical stress applied to a proteoglycan-depleted cartilage enhances the breakdown of the collagen matrix as judged by fibrillation, and may aggravate the inflammation by crushing the swollen synovial lining where it encroaches on the joint space.

Insulin-like growth factor I accelerates recovery of articular cartilage proteoglycan synthesis in culture after inhibition by interleukin 1.

Interleukin 1 (IL-1) is a cytokine which induces cartilage proteoglycan (PG) depletion by inhibiting PG synthesis and increasing PG breakdown. Insulin-like growth factor I (IGF-I), in contrast, is known to promote matrix formation. We examined the effects of both mediators in a bovine tissue culture model. IL-1 dose-dependently inhibited PG formation of articular cartilage [half-maximal effect (EC50) at 4 ng/ml], while PG synthesis was increased by IGF-I (EC50 = 15 ng/ml). After inhibition of PG formation with IL-1 for 2 days and subsequent removal of free IL-1, addition of IGF-I dose-dependently accelerated restoration of the original rate of synthesis with a half-maximal effect at 20 ng/ml and a maximal effect at 50 ng/ml. The IGF-I concentration required to elicit a half-maximal effect on cartilage PG synthesis remained constant in the absence or presence of IL-1. We therefore conclude that inhibition of cartilage PG synthesis by IL-1 is not effected by damage to the IGF receptor. Synovial fluid (SF) of 40 patients with rheumatoid arthritis (RA) was found to contain 64 +/- 6 ng IGF-I/ml (mean +/- SEM). The reported effects of IGF-I in vitro therefore occurred at concentrations comparable to those present in joints in vivo. IL-1 beta was detectable (> 0.5 pg/ml) in 38 of 40 RA-SF samples (mean 28 +/- 6 pg/ml).(ABSTRACT TRUNCATED AT 250 WORDS)

Proteoglycan depletion of intact articular cartilage by retinoic acid is irreversible and involves loss of hyaluronate

Intact sesamoid bones from bovine metacarpophalangeal joints were cultured with retinoic acid for 9 days and allowed to recover in control medium for up to 17 days. Retinoic acid (300 ng/ml) induced 91.8% inhibition of glycosaminoglycan (GAG) synthesis and 50.6% loss of sulfated GAGs from the cartilage. Retinoic acid also induced 38.2% loss of hyaluronate from the matrix. The synthesis and content of the large aggregating proteoglycan (aggrecan) were preferentially decreased compared with that of the small nonaggregating species. The aggrecan synthesized was similar to control aggrecan in size, aggregation capacity, and composition of its GAGs. GAG synthesis was almost completely restored in control medium within the next 6 days. The GAGs synthesized during recovery were slightly shorter than control GAGs and showed a higher ratio of chondroitin-6-sulfate over chondroitin-4-sulfate. Neither the proteoglycan content nor the hyaluronate content recovered within 17 days. The aggregation capacity of newly synthesized aggrecan was normal. However, the retention of proteoglycans synthesized in the recovery period was much lower in treated cartilage than in control cartilage (T1/2 of 17 and 38 days, respectively). In conclusion, the retinoic-acid-induced proteoglycan depletion was irreversible in spite of the restored synthesis of aggrecan with a normal aggregation capacity. The reduced retention of newly synthesized aggrecan during recovery might be caused by a lack of hyaluronate. This model seems suitable to study aspects of cartilage destruction and repair.

Cartilage proteoglycan‐induced arthritis in BALB/c mice. Antibodies that recognize human and mouse cartilage proteoglycan and can cause depletion of cartilage proteoglycan with little or no synovitis

Human fetal cartilage proteoglycan (PG) induces the development of an erosive polyarthritis and spondylitis in BALB/c mice. We have examined the properties of 3 monoclonal antibodies (MAb) to human fetal cartilage PG isolated from immunized mice that cross-react with mouse cartilage PG. Compared with sera from arthritic mice, which contain antibodies reactive with keratan sulfate, MAb 202 (IgG1) reacted only with a protein-related epitope that is distributed on both hyaluronic acid-binding and chondroitin sulfate-attachment regions. MAb 813 (IgG1) reacted with the same fragments and recognized an epitope with the immunologic characteristics of keratan sulfate. MAb 945 (IgM) remains to be further characterized. Introduction of hybridomas secreting MAb 202 and MAb 945 into irradiated mice resulted in the loss of PG from articular cartilage and from growth plate cartilage (with MAb 202 only), as revealed by a loss of staining with toluidine blue. There was no synovial hyperplasia with MAb 202, but some hyperplasia and mononuclear cell infiltration was seen with MAb 945. This was accompanied by the binding of immunoglobulins to articular cartilage, as demonstrated by immunofluorescence. The hybridoma secreting MAb 813 produced no cartilage changes or synovitis, and there was no immunoglobulin binding to cartilage. Polymorphonuclear leukocyte infiltration was never observed with these antibodies. These studies indicate that MAb reactive with mouse cartilage PG can cause the depletion of PG from hyaline cartilage by mechanisms that may be both complement dependent and complement independent. Antibodies may serve to release and expose PG antigen to immune cells, as well as causing a loss of the mechanical properties of cartilage that are PG dependent.

Metalloproteinases and cartilage proteoglycan depletion in chronic arthritis

Chronic monarticular arthritis can be induced in ovalbumin-sensitized rabbits by intraarticular injection of ovalbumin (antigen-induced arthritis) or in naive rabbits by injecting hyaluronic acid mixed with the polycation poly-D-lysine (polycation-induced arthritis). Both models show some points of similarity, including joint swelling, the presence of inflammatory leukocytes and the inflammatory mediator prostaglandin E2, and the kinetics of cartilage proteoglycan loss. However, the assessment of the capacity of synovial lining and articular cartilage to synthesize and secrete neutral metalloproteinases reveals a difference between these models. We found that articular cartilage from the inflamed joints of rabbits with antigen-induced arthritis did not synthesize neutral metalloproteinases, although the synovial lining did. In contrast, both the synovial lining and the articular cartilage from the inflamed joints of rabbits with polycation-induced arthritis synthesized neutral metalloproteinases. These findings suggest that in inflammatory synovitis, different mechanisms can operate to produce damage to the matrix of articular cartilage.

Effect of indomethacin on swelling, lymphocyte influx, and cartilage proteoglycan depletion in experimental arthritis.

The effects of indomethacin on antigen induced arthritis in rabbits have been investigated. Arthritis was induced in the knee joints of sensitised rabbits by intra-articular injection of antigen. Swelling of the joints was measured for 14 days after antigen challenge, and groups of animals were killed on days 1, 7, or 14 for collection of synovial fluids and tissues. Indomethacin (1 mg/kg, three times daily) reduced joint swelling and the prostaglandin E2 concentrations in synovial fluid. In addition, indomethacin increased the loss of proteoglycan from articular cartilage and the numbers of lymphocytes in the inflamed synovial lining. These findings suggest that the symptomatic benefits of indomethacin and related drugs in inflammatory arthritis may be achieved at the expense of significant adverse effects on joint tissues.

Cartilage proteoglycan depletion in acute and chronic antigen‐induced arthritis

We examined the kinetics of proteoglycan (PG) depletion in rabbits with antigen-induced arthritis. There was a rapid loss of PG from arthritic cartilage, reaching 35-40% at day 7. Thereafter, the rate of PG depletion declined, and by day 42, the maximum loss was 55-60%. The initial loss of PG was accompanied by the appearance of large amounts of sulfated glycosaminoglycans (GAGs) in the joint fluid (measured as total sulfated GAGs by dye binding and as keratan sulfate by radioimmunoassay). However, by day 14, the levels of sulfated GAGs in arthritic joint fluid declined to control levels, even though the cartilage demonstrated a sustained depletion of PG. The cartilage PG degradation observed in antigen-induced arthritis could also be produced in normal animals by a single intraarticular injection of recombinant interleukin-1. The acute loss of cartilage PG occurred independently of neutrophil accumulation, both in the case of antigen-induced arthritis and after injection of interleukin-1.

Effect of steroid hormones on endotoxin-mediated cartilage degradation.

Cartilage degradation is a characteristic feature of various types of human arthritis, notably rheumatoid arthritis and osteoarthritis. The influence of glucocorticoid and other steroid hormones on cartilage proteoglycan breakdown was examined in a model system in which breakdown is readily quantified by the release of proteoglycan from cultured bovine nasal cartilage discs. Endotoxin (bacterial lipopolysaccharides) treatment enhanced the depletion of cartilage proteoglycan by 2-3 fold. This was inhibited in a concentration-dependent manner by hydrocortisone (10(-9) to 10(-5) M) or other glucocorticoid hormones (dexamethasone, prednisolone, cortisone). Inhibition required the continued presence of the steroid. Removal of hydrocortisone (3 x 10(-7) M) after 4 days from endotoxin-treated cultures resulted in the rapid restoration of an endotoxin response, so that proteoglycan release approached maximum levels during a second 4-day culture period. Other C-21 steroid hormones (progesterone, aldosterone) were also inhibitory at 10(-5) M, but testosterone and beta-estradiol showed little influence on endotoxin action. Proteoglycan products of smaller average mol wt (Sepharose CL-2B chromatography), consistent with core protein cleavages, were released from endotoxin-treated cartilage. Cleavage was unaffected by beta-estradiol, partially blocked by aldosterone and largely prevented by hydrocortisone administration.

Bacterial lipopolysaccharides induce in vitro degradation of cartilage matrix through chondrocyte activation.

The present studies demonstrate that bacterial lipopolysaccharides (LPS) induce cartilage matrix degradation in live explants in organ culture. Quintuplicate bovine nasal fibrocartilage explants cultured for 8 d with three different purified LPS preparations derived from Escherichia coli and Salmonella typhosa at concentrations ranging from 1.0 to 25.0 micrograms/ml resulted in matrix proteoglycan depletion of 33.3 +/- 5.8 to 92.5 +/- 2.0% (medium control depletion 17.7 +/- 0.7 to 32.4 +/- 1.4%). Matrix degradation depended on the presence of live chondrocytes because frozen-thawed explants incubated with LPS failed to show any proteoglycan release. Moreover, the addition of Polymyxin B (25 micrograms/ml) to live explants incubated with LPS abolished matrix release, whereas Polymyxin B had no effect on the matrix-degrading activity provided by blood mononuclear cell factors. A highly purified Lipid A preparation induced matrix degradation at a concentration of 0.01 micrograms/ml. Cartilage matrix collagen and proteoglycan depletion also occurred with porcine articular cartilage explants (collagen release: 18.3 +/- 3.5%, medium control: 2.1 +/- 0.5%; proteoglycan release: 79.0 +/- 5.9%, medium control: 28.8 +/- 4.8%). Histochemical analysis of the cultured explants confirmed the results described above. Gel chromatography of the proteoglycans released in culture indicated that LPS induced significant degradation of the high molecular weight chondroitin sulfate-containing aggregates. These findings suggest that bacterial products may induce cartilage damage by direct stimulation of chondrocytes. This pathogenic mechanism may play a role in joint damage in septic arthritis and in arthropathies resulting from the presence of bacterial products derived from the gastrointestinal tract.

Early rheumatoid-like lesions in rabbits injected with foreign serum: relationship to localization of immune complexes in the lining tissues of joints and cellular content of synovial fluid.

Immune complex localization in joint tissues and white cell effusion into the joint space as well as synovial lesions are shown to occur in rabbits injected intravenously with bovine serum. Synovial lesions of one knee were found to be associated with immune complexes in joint tissues of the contralateral knee (because of the experimental design very few rabbits had both immunofluorescence and histology performed on the same joint). There was also a week correlation between moderate and gross synovial lesions and cellular effusions of the same joint. Cartilage proteoglycan depletion was seen in some injected animals and this was related to lining cell hyperplasia. Rabbits from different breeding colonies displayed different incidences of lesions suggesting an environmental or genetic influence on the development of rheumatoid-like lesions.