Synthesis of articular cartilage proteoglycans by isolated bovine chondrocytes. Effect of autogenous conditioned synovial medium in vitro

Do arachidonic acid and its metabolites, secreted by rheumatoid and osteoarthritic synovial tissue, account for the strong inhibition of DNA synthesis in cultured human articular chondrocytes? A novel approach to the mechanism of tissue damage

AIMS

To further characterize factors secreted in vitro by osteoarthritic and rheumatoid arthritis synovial membranes that inhibit DNA synthesis by cultured human articular chondrocytes, and extend these findings to synovial fluid.

MATERIAL AND METHODS

Synovial tissue, synovial fluid and articular cartilage were obtained at surgery from two patients suffering rheumatoid arthritis and two other patients suffering from osteoarthritis. Synovial tissue was incubated in DMEM, then condition media and synovial fluids were extracted with methanol. Methanol extracts and extracted residues (hyaluronic acid, proteins) were assayed for their capacity to inhibit DNA synthesis in articular chondrocytes. Methanol extracts were also fractionated by thin layer chromatography on silica-coated plates and recovered fractions similarly tested.

RESULTS

All extracts exhibited strong and concentration-dependent inhibition of [3H]-thymidine incorporation. The most potent inhibition was obtained with the extracts from rheumatoid joints and the least potent inhibition was with synovial fluids. The removal of active substances with methanol leaves an inactive residue. Methanol extraction does not alter the mitogenic activity of five exogenous growth factors and two cytokines, thus suggesting that such activity is entirely due to lipids. The bulk of anti-mitotic factors extracted by methanol co-migrate when fractionated by thin layer chromatography on silica-coated plates with arachidonic acid and its lipo-oxygenase metabolites.

IN CONCLUSION

Inflamed synovium produces and releases lipids, most probably arachidonic acid metabolites that inhibit cell proliferation thus limiting inflammation and pannus formation in arthritis.

Sulfated glycosaminoglycans and glucosamine may synergize in promoting synovial hyaluronic acid synthesis

High-molecular-weight hyaluronic acid (HA) produced by the synovium may function physiologically to aid preservation of cartilage structure and prevent arthritic pain; both the size and concentration of HA in synovial fluid are diminished in osteoarthritis (OA). Glucosamine therapy for OA can be expected to increase synovial HA production by providing rate-limiting substrate. In addition, certain sulfated glycosaminoglycans and polysaccharides - including chondroitin sulfate (CS), dermatan sulfate, and pentosan polysulfate - stimulate synovial HA production, apparently owing to a hormone-like effect triggered by the binding of these polymers to membrane proteins of synovial cells. Surprisingly, a significant proportion of orally administered CS is absorbed as intact polymers - apparently by pinocytosis. These considerations may rationalize clinical studies concluding that oral CS provides slow-onset but durable pain relief and functional improvement in OA. The possibility that oral glucosamine and CS may interact in a complementary or synergistic fashion to improve synovial fluid HA content in OA should be assessed in clinical studies, and the potential of adjunctive CS administration to improve the clinical response achievable with optimal intakes of glucosamine should likewise be evaluated. In light of the fact that the synovium virtually functions as a 'placenta' for cartilage, focusing on synovium as the target for therapeutic intervention in OA may be a rational strategy.

Does chondroitin sulfate defend the human uterine cervix against ripening in threatened premature labor?

OBJECTIVE

This study was undertaken to investigate changes in chondroitin sulfate levels in the cervix and the physiologic role of chondroitin sulfate isomers in the process of cervical ripening.

STUDY DESIGN

Uterine cervical mucus samples were obtained from 57 women (7 nonpregnant women, 19 at preterm gestation, 9 at term gestation, 16 during the first stage of term labor, and 6 with threatened premature labor). Chondroitin sulfate isomer (chondroitin 0-sulfate, 4-sulfate, and 6-sulfate) concentrations in cervical mucus were measured by high-performance liquid chromatography. The effect of exogenous chondroitin sulfate on hyaluronidase activity in cervical mucus was evaluated by gel permeation chromatography of fluorolabeled hyaluronic acid.

RESULTS

Chondroitin sulfate concentrations in cervical mucus were increased significantly (P <. 05) in the threatened premature labor group compared with the preterm and term groups. However, the same finding was not observed in the first stage of term labor. Exogenous chondroitin sulfate inhibited hyaluronidase activity in mucus.

CONCLUSION

Chondroitin sulfate may defend against cervical ripening in threatened premature labor.

Effects of anti-inflammatory drugs on cartilage recovery from catabolin-induced degradation

Effects of aspirin (200 micrograms/ml), hydrocortisone (10 micrograms/ml), sodium aurothiomalate (100 micrograms/ml), and indomethacin (10 micrograms/ml) on recovery of cartilage from interleukin 1 or catabolin-induced degradation were examined in this initial in vitro study. The experimental protocol involved a "degradative phase" of eight days during which cartilage plugs were incubated in the presence or absence of spent human rheumatoid synovial culture media. A "recovery" period of six days followed during which the effects of the aforementioned drugs on treated cartilage were analyzed. Incorporation of [35S]sulfate and [3H]proline precursors, and total contents of hydroxyproline and glycosaminoglycan in cartilage were determined two, four, and six days after insult. Aspirin treatment caused a rise in total proteoglycan content over degraded controls (p less than 0.002), however, this increase was not associated with increased [35S]sulfate incorporation into glycosaminoglycans. Hydrocortisone resulted in a delayed rise in proteoglycan content concommitant with increased [35S]sulfate uptake, whereas sodium aurothiomalate treatment was without effect on proteoglycans. Indomethacin treatment was associated with an increased release of newly synthesized macromolecules by cartilage into the media (p less than 0.01). These results suggest that common anti-inflammatory drugs may exhibit distinctly different effects on the in vitro synthesis and retention of proteoglycans by cartilage explants previously exposed to a degradative phase. Further work is necessary to assess the influence of drug concentration in this experimental system.

Incorporation of [35S]sulphate and [3H]thymidine into isolated bovine articular chondrocytes in vitro. Effect of autogenous conditioned synovial medium

The present work is a part of a study series concerned with the metabolic events taking place in the synovial joint tissues. We have previously reported that synovial products not only enhance the degradation of articular cartilage proteoglycans but also inhibit the synthesis of articular cartilage proteoglycans, and that these cellular interactions may be partly modulated by arachidonic acid metabolites. In the experiments reported here we show that the addition of conditioned synovial medium to confluent monolayer cultures of articular chondrocytes not only inhibits the synthesis of proteoglycans, measured as the incorporation of radiosulphate into cartilage proteoglycans but also inhibits the synthesis of DNA, measured as the incorporation of radiothymidine into the chondrocytes, in a dose-dependent manner. In our culture system, calf knee-joint synovial tissue produces PGE, and it has been reported that previous exposure to PGE2 affects the ability of the cell to respond to that same hormone. In these experiments, previous exposure to conditioned synovial medium affected neither the inhibition of the incorporation of radiosulphate nor the inhibition of the incorporation of radiothymidine.

Effect of indomethacin and hydrocortisone upon joint tissue in vitro. Incorporation of [35S]sulphate into chondrocyte proteoglycans

It has previously been shown that products from the synovial tissue influence the behaviour of the chondrocyte in such a way that, not only is the degradation enhanced, but the synthesis of cartilage proteoglycans too is inhibited. In the case of cartilage degradation, these cellular interactions within the joint tissues have been shown to be partly modulated by arachidonic acid metabolites. The experiments reported here show that these cellular interactions cannot be completely ruled out in the case of cartilage synthesis either. Conditioned medium from synovial tissue (control SM) reduced the incorporation of [35S]sulphate into the monolayer cultures of chondrocytes. This reduction was not affected with the simultaneous addition of indomethacin (1.4 X 10(-6) mol/l) to the chondrocyte cultures. However, conditioned synovial medium from synovial tissue that had been cultured with indomethacin (1.4 X 10(-5) mol/l) enhanced radiosulphate incorporation, somewhat, as compared with control SM. Control SM together with hydrocortisone (2.2 X 10(-8) mol/l, 2.2 X 10(-7) mol/l, 2.2 X 10(-6) mol/l) reduced radiosulphate incorporation into the chondrocyte cultures in a dose-dependent manner. Conditioned synovial medium from synovial tissue that had been cultured with hydrocortisone (2.2 X 10(-8) mol/l, 2.2 X 10(-7) mol/l, 2.2 X 10(-6) mol/l) enhanced radiosulphate incorporation, as compared with control SM.

Continuous mechanical pressure and joint tissue. Effect of synovial membrane products and indomethacin in vitro

We have previously reported that a continuous mechanical pressure of approximately 30 kgfcm-2 greatly inhibited the degradation of articular proteoglycans in calves. In the present report it is shown that indomethacin (5 micrograms/ml) failed to inhibit cartilage degradation caused by mechanical pressure. It is therefore suggested that prostaglandins do not mediate the inhibition of cartilage degradation exerted by continuous mechanical pressure. We have also reported previously that bovine-conditioned synovial medium (SM) greatly enhances the degradation of calf articular cartilage proteoglycans. We now show that the catabolic activity of SM was greatly (but not entirely) inhibited by the application of a continuous mechanical pressure. Simultaneous addition of indomethacin (5 micrograms/ml) to the cartilage cultures did not affect this result. However, the addition of indo-SM (SM from synovial tissue cultured in the presence of 5 micrograms/ml indomethacin) to cartilage cultures subjected to continuous mechanical pressure did not increase cartilage degradation, compared with the addition of DMEM alone. A hypothesis is proposed that continuous mechanical pressure may cause a change in the state of synovial factor receptors on the membranes of chondrocytes.