Proteoglycan Synthesis In Articular Cartilage Research Articles

Comparative Effects of Azapropazone on Cellular Events at Inflamed Sites. Influence on Joint Pathology in Arthritic Rats, Leucocyte Superoxide and Eicosanoid Production, Platelet Aggregation, Synthesis of Cartilage Proteoglycans, Synovial Production and Actions of Interleukin-1 in Cartilage Resorption Correlated with Drug Uptake into Cartilage In-vitro

Azapropazone (APZ) has been compared with standard NSAIDs in title systems to establish aspects of its mode of action on cellular events at inflamed sites. APZ (150 mg kg-1 day-1) given for 10-13 days exhibited a reduction in joint pathology in established adjuvant arthritis in rats comparable with that of indomethacin (2 mg kg-1 day-1) and clobuzarit (20 mg kg-1 day-1). APZ was shown to be a potent inhibitor of the production of leucocyte superoxide and synovial interleukin-1 (IL-1)-like activity and stimulated articular cartilage proteoglycan synthesis, but was ineffective as an inhibitor of platelet aggregation or IL-1 induced cartilage degradation in-vitro. These in-vitro effects may have relevance to the mode of action of this weak inhibitor of prostaglandin synthesis.

Oral administration of the NADPH-oxidase inhibitor apocynin partially restores diminished cartilage proteoglycan synthesis and reduces inflammation in mice

Apocynin, an inhibitor of NADPH-oxidase, is known to partially reverse the inflammation-mediated cartilage proteoglycan synthesis in chondrocytes. More recently, it was reported that apocynin prevents cyclooxygenase (COX)-2 expression in monocytes. The present study aimed to investigate whether these in vitro features of apocynin could be confirmed in vivo. In a mouse model of zymosan-induced acute arthritis apocynin was administered orally (0, 3.2, 16 and 80 μg/ml in the drinking water) and the effects on cartilage proteoglycan synthesis were monitored. In a mouse model of zymosan-induced inflammation of the ears apocynin was administered orally (14 mg/kg/day by gavage) and the effects on ear swelling and ex vivo produced prostaglandin E 2 (PGE 2) by lipopolysaccharide (LPS)-stimulated blood cells were measured. In this study, ibuprofen was used as a positive control (50 mg/kg/day by gavage) and animals received vehicle as a negative control. Apocynin dose-dependently reversed the inhibition of proteoglycan synthesis in articular cartilage of the arthritic joint. A statistically significant increase in proteoglycan synthesis was found at a dose of 80 μg/ml apocynin. Apocynin did not affect the proteoglycan synthesis of the control knee joints. Apocynin significantly decreased the zymosan-induced ear swelling at 1, 2 and 4 h (hours) after zymosan injection versus the vehicle treated group at 14 mg/kg/day. The ex vivo production of PGE 2 by LPS-stimulated blood cells was significantly decreased after in vivo apocynin treatment. Ibuprofen decreased ear swelling at the same time-points as apocynin and inhibited the ex vivo produced PGE 2. In conclusion, the present study confirmed two important features of apocynin in vivo: (1) oral administration of apocynin can partially reverse the inflammation-induced inhibition of cartilage proteoglycan synthesis, and (2) oral administration of apocynin has COX inhibitory effects similar to the non-steroidal anti-inflammatory drug (NSAID) ibuprofen. Therefore, apocynin might be of potential use during the treatment of chronic inflammatory joint diseases like osteoarthritis or rheumatoid arthritis.

The effect of link peptide on proteoglycan synthesis in equine articular cartilage.

The basal rate of in vitro proteoglycan (PG) synthesis in explants of equine articular cartilage was subject to considerable variation in animals of the same age but was greater in younger than older animals. Synthesis of PGs in explant cultures was stimulated by a synthetic link peptide, identical in sequence to the N-terminus of the link protein (LP) of PG aggregates, in a similar manner to that demonstrated previously for human articular cartilage [Biochem. Soc. Trans. 25 (1997) 427; Arthritis Rheum. 41 (1998) 157]. Stimulation occurred in tissue from animals ranging from 1 to 30 years old but older animals required higher concentrations of peptide to produce a measurable response. Synthesis of PGs increased in a concentration-dependent manner and was paralleled by increases in the ability of aggrecan monomers to form aggregates with hyaluronan (HA). In addition to its effect on synthesis of PGs, link peptide also increased synthesis of both aggrecan and LP mRNA. Cartilage explant and chondrocyte cultures secreted small amounts of biologically active interleukin 1 (IL 1) and secretion of this cytokine was reduced considerably by the addition of link peptide. Reduction in the activity of this catabolic cytokine coupled with the increased synthesis of mRNA for aggrecan and link peptide may be the mechanism by which link peptide exerts its positive effect on the rate of PG synthesis in articular cartilage.

Role of nitric oxide in the inhibition of BMP-2-mediated stimulation of proteoglycan synthesis in articular cartilage

Objective Bone morphogenetic protein-2 (BMP-2)-mediated stimulation of articular cartilage proteoglycan (PG) synthesis is suppressed in arthritic murine knee joints and by interleukin-1 (IL-1). The goal of this study was to investigate whether the gaseous mediator nitric oxide (NO) plays a crucial role in the inhibition of BMP-2 effects by IL-1.Methods Bone morphogenetic protein-2 alone or in combination with IL-1 was injected into the right knee joint of wild-type and NOS2 deficient C57Bl/6×129/Sv mice. Proteoglycan synthesis was measured ex vivo by incorporation of35S-sulfate on day 1, 2 and 3 after injection. To study the role of NO in the inhibition BMP-2-mediated stimulation of PG synthesis in arthritic joints, BMP-2 was injected intra-articularly in the joints of wild-type and NOS2 deficient mice with zymosan-induced arthritis. To check for NOS2 deficiency, NO production was measured in conditioned medium after challenge of patellae with surrounding tissue with IL-1.Results BMP-2 potently stimulated proteoglycan synthesis in articular cartilage of normal knees (up to 4-fold) but not in arthritic knees. Co-injection of BMP-2 with tumor necrosis factor α had no effect on BMP-2-mediated stimulation of PG synthesis but co-injection with IL-1 α resulted in a nearly total inhibition of BMP-2-mediated stimulation. In contrast, in NOS2 deficient mice IL-1 had no effect on BMP-2-mediated stimulation of PG synthesis. However, injection of BMP-2 into arthritic knee joints of NOS2 knock out mice did not result in significant stimulation of PG synthesis.Conclusions In this study we show that NO plays a role in the inhibition of BMP-2-mediated stimulation of PG synthesis by IL-1. However, NO, or at least NOS2, plays no dominant role in the inhibition of BMP-2 effects in arthritic knee joints.

In vitro stimulation of equine articular cartilage proteoglycan synthesis by hyaluronan and carprofen

The effects of hyaluronan and carprofen (both racemic mixture and separate R and S enantiomers) on proteoglycan (PG) synthesis by equine cultured chondrocytes and cartilage explants were examined. Hyaluronan stimulatedPG synthesis in both cell and explant cultures. The concentration–response curve of the latter was bell-shaped. Racemic carprofen and R and S enantiomers also stimulated PG synthesis, although concentration–response relationships varied for each preparation and high concentrations inhibited synthesis. It was concluded that (a) hyaluronan exerts a stimulatory effect on PG synthesis at low concentrations and (b) stimulatory effects of carprofen on PG synthesis are, to some degree, enantioselective with the carprofen S-enantiomer exerting the greatest effect. Hyaluronan and carprofen are used clinically despite incompletely understood mechanisms of action. These results suggest (a) hyaluronan and carprofen might exert an anti-arthritic action through stimulation of PG synthesis and (b) there is possible justification for therapeutic administration of enantiomeric rather than racemic carprofen.

Effect of dimethylsulfoxide on articular cartilage proteoglycan synthesis and degradation, chondrocyte viability, and matrix water content.

To determine the effects of dimethylsulfoxide (DMSO) exposure on cartilage proteoglycan (PG) synthesis, PG degradation, chondrocyte viability, and matrix water content. Using a cartilage explant culture system, PG synthesis, PG degradation, matrix water content, and chondrocyte viability were determined for cartilage exposed to DMSO daily for selected periods of time. Juvenile bovine (calf) carpometacarpal joint cartilage explants. PG synthesis: Explants (n = 30/group) were separated into 10 groups based on the time of daily exposure to 10% DMSO. Exposure time was repeated daily for 3 days. The control group was incubated in basal medium alone for 3 days, with daily medium changes. Once all DMSO exposure times were complete for the third day, PG synthesis was determined by analysis of incorporation of radiolabelled sulfate. Cell viability: Explants (n = 3/group) were subjected to an identical DMSO exposure protocol, and examined histologically. The percentage of viable cells/high power field (hpf) was calculated for each group. PG degradation: Explants (n = 21/group) were preincubated with radiolabelled sulfate, then subjected to a similar DMSO exposure protocol. The medium was collected from all explants daily and assayed for PG content. After 3 days, the explants were digested and total labelled PG content determined. Percent of total explant labelled PG content released into the medium daily was determined for each group. Water content: Explants (n = 21/group) were separated into three treatment groups, one of which had no treatments performed, whereas the other two groups were incubated in basal medium for 72 hours, one with, and one without, 10% DMSO. Wet and dry weights were determined, and percent water calculated, for all three groups. Separate 1-way ANOVA were performed, with appropriate post hoc tests (P < .05). PG synthesis was significantly lower than control for all time periods of DMSO exposure except for 1 and 3 hours, and decreased in a time-dependent manner after the 1-hour exposure time. The mean percentage of viable cells/hpf was significantly lower than control for the 1-, 3-, 9-, 12-, and 24-hour treatment groups. There was no significant difference in PG degradation for any group compared with control for the first 2 days of incubation. All groups except the 24-hour group had a significantly higher degradation compared with control for the third day of incubation. Cartilage exposed to DMSO for 72 hours had a significantly lower water content, and cartilage incubated in basal medium alone for 72 hours had a significantly higher water content than cartilage that received no DMSO and no incubation. DMSO, in relatively low concentration, is detrimental to articular cartilage PG synthesis in a time-dependent manner. Dehydration of the cartilage and chondrocyte death also occur with increasing time of DMSO exposure. Significant PG degradation occurs on the third day of culture with daily DMSO exposure. As a joint lavage solution, DMSO has potentially deleterious effects on the metabolism of chondrocytes.

Differential effects of local application of BMP-2 or TGF-β1 on both articular cartilage composition and osteophyte formation

Objective: The related molecules bone morphogenetic protein-2 (BMP-2) and transforming growth factor beta-1 (TGF-β1) have both been shown to stimulate chondrocyte proteoglycan (PG) synthesisin vitro. We investigated thein-vivoeffects of these factors on articular cartilage PG metabolism.Design: Several doses of BMP-2 or TGF-β1 were injected into the murine knee joint, once or repeatedly. Patellar cartilage PG synthesis was measured by [35S]-sulfate incorporation and reverse transcriptase polymerase chain reaction (RT-PCR). PG content was analyzed by measuring safranin O staining intensity on histologic sections.Results: A single injection of 200 ng BMP-2 induced a much earlier and more impressive stimulation of articular cartilage PG synthesis, than 200 ng TGF-β1. RT-PCR revealed that both factors upregulated mRNA of aggrecan more than that of biglycan and decorin. However, 21 days after a single injection of 200 ng TGF-β1 PG synthesis still was significantly increased, while stimulation by BMP-2 only lasted for 3 to 4 days. Stimulation by BMP-2 could be prolonged to at least 2 weeks by triple injections of 200 ng each, at alternate days. Remarkably, even after this intense exposure to BMP-2, stimulation of PG synthesis was not reflected in long-lasting enhancement of PG content of articular cartilage. In contrast, even a single injection with 200 ng of TGF-β1 induced prolonged enhancement of PG content. After repeated injections, both BMP-2 and TGF-β1 induced chondrogenesis at specific sites. ‘Chondrophytes’ induced by BMP-2 were found predominantly in the region where the growth plates meet the joint space, while those triggered by TGF-β1 originated from the periosteum also at sites remote from the growth plates.Conclusions: BMP-2 and TGF-β stimulate PG synthesis and PG content with different kinetics, and these factors have different chondro-inductive properties.

Load-Controlled Compression of Articular Cartilage Induces a Transient Stimulation of Aggrecan Gene Expression

The effects of short- and long-term load-controlled compression on the levels of aggrecan mRNA have been determined. Results show that a compressive stress of 0.1 MPa on bovine articular cartilage explants for 1, 4, 12, and 24 h produces a transient up-regulation of aggrecan mRNA synthesis. At 1 h, aggrecan mRNA levels in loaded explants were increased 3.2-fold compared to control explants. At longer times (≥4 h), the levels of aggrecan mRNA returned to baseline values or stayed slightly higher. There is a dose dependence in the response of the explant to increasing levels of compressive stress (0–0.5 MPa) for 1 h. Aggrecan mRNA levels increased 2- to 3-fold at 0–0.25 MPa. At 0.5 MPa, the level of aggrecan mRNA was lower than those at 0.1 and 0.25 MPa. This dose-dependent effect suggests a reversal of the stimulatory effects of compression on aggrecan gene expression at higher loads. After 24 h of compression, the levels of aggrecan mRNA in explants subjected to any of the stress levels were not significantly different from those in control explants. The stimulatory effect of 0.1 MPa compressive stress on aggrecan mRNA levels was blocked by Rp-cAMP and U-73122, indicating the involvement of the classical signal transduction pathways in the mechanical modulation of aggrecan gene expression. The responses of link protein mRNA to compression paralleled those of aggrecan, while there was no significant change in expression of the gene for the housekeeping protein elongation factor-1α. The results indicate that articular cartilage chondrocytes can respond to short-term compressive loads by transiently up-regulating expression of the aggrecan gene. The fact that long-term compression did not significantly alter aggrecan mRNA levels suggests that previously observed inhibitory effects of prolonged static compression on proteoglycan synthesis in articular cartilage may be, for the most part, mediated through mechanisms other than suppression of aggrecan mRNA levels.

Bone morphogenetic protein 2 stimulates articular cartilage proteoglycan synthesis in vivo but does not counteract interleukin-1alpha effects on proteoglycan synthesis and content.

To study the effect of bone morphogenetic protein 2 (BMP-2) on articular cartilage proteoglycan (PG) synthesis in vivo and to investigate whether BMP-2 is able to counteract the effects of interleukin-1 (IL-1) on articular cartilage PG synthesis and content. BMP-2 alone or in combination with IL-1alpha was injected into murine knee joints. PG synthesis was measured by 35S-sulfate incorporation using an ex vivo method or autoradiography. Cartilage PG content was analyzed by measuring Safranin O staining intensity on histologic sections. BMP-2 appeared to be a potent stimulator of articular cartilage PG synthesis in vivo. However, BMP-2 was not able to counteract the deleterious effects of IL-1alpha on articular cartilage PG synthesis and content. In addition, intraarticular injections of BMP-2 induced chondrophytes. Although BMP-2 is a very potent stimulator of cartilage PG synthesis in vivo, the therapeutic applications of BMP-2 are limited due to the inability of BMP-2 to counteract the effects of IL-1 and the induction of chondrophytes.

Elevated levels of insulin-like growth factor (IGF) binding protein-3 in rheumatoid arthritis synovial fluid inhibit stimulation by IGF-I of articular chondrocyte proteoglycan synthesis

The objective of this study was to quantify insulin-like growth factor (IGF) binding proteins (IGFBPs) in the synovial fluid (SF) and plasma of patients with rheumatic diseases and to study the role of these proteins in the regulation of cartilage proteoglycan (PG) synthesis. Immunological determination of IGFBP-2, IGFBP-3, IGF-I, IGF-II, interleukin-1 beta (IL-1 beta) and tumour necrosis factor alpha (TNF alpha) was undertaken in the SF and plasma of 115 patients with rheumatoid arthritis (RA; n = 53), osteoarthritis (OA; n = 44) and other rheumatic disorders. We also determined the effects of SF on bovine cartilage PG synthesis in culture. IGFBP-2 and IGFBP-3 were elevated in the plasma (by 38% and 28%, respectively) and SF (by 56% and 59%, respectively) of patients with RA compared to age- and sex-matched OA controls (determined by RIA and confirmed by Western ligand blot). IGF-I and IGF-II did not differ significantly between the two groups. OA SF, and, to a lesser extent, RA SF stimulated cartilage PG synthesis in culture, and more than 60% of this activity was neutralised by a specific monoclonal anti-IGF-I antibody. Human IGFBP-3 dose-dependently inhibited the stimulation of cartilage PG synthesis effected by SF or human IGF-I. In RA patients, the SF concentration of IGFBP-3 was positively correlated with SF levels of IL-1 beta and TNF alpha, with the serum levels of C-reactive protein and with the erythrocyte sedimentation rate. We concluded that IGF-I is, under the conditions studied, the most important anabolic factor in human SF with respect to articular cartilage PG synthesis. The bioactivity of IGF-I in joints is modulated by IGFBP-3, which is elevated in RA SF compared to OA SF. Elevated IGFBP-3 in RA SF may reduce the availability of IGF-I to articular chondrocytes, thus interfering with cartilage PG synthesis in RA.

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)

In vivo protection against interleukin-1-induced articular cartilage damage by transforming growth factor-beta 1: age-related differences.

Transforming growth factor-beta (TGF-beta) has been shown to antagonise interleukin-1 (IL-1) effects in different systems. Investigations were carried out to study whether TGF-beta 1 modulates IL-1 induced inflammation and IL-1 effects on articular cartilage in the murine knee joint. IL-1, TGF-beta 1 or both factors together were injected into the knee joint. Inflammation was studied in whole knee histological sections. Patellar cartilage proteoglycan synthesis was measured using 35S-sulphate incorporation while patellar cartilage glycosaminoglycan content was determined with automated image analysis on joint sections. Co-injection of TGF-beta 1 and IL-1 resulted in synergistic attraction of inflammatory cells. In contrast, TGF-beta 1 counteracted IL-1 induced suppression of articular cartilage proteoglycan synthesis. Proteoglycan depletion was similar shortly after the last injection of IL-1 or IL-1/TGF-beta 1, but accelerated recovery was found with the combination at later days. This protective effect of TGF-beta 1 could not be demonstrated in older mice. TGF-beta 1 aggravates IL-1 induced knee joint inflammation, but counteracts the deleterious effects of IL-1 on articular cartilage proteoglycan synthesis and content. The data indicate that TGF-beta 1 could play an important part in articular cartilage restoration after IL-1 induced proteoglycan depletion.

Regulation of IGF-1 receptors on rabbit articular chondrocytes by inflammatory mediators

Insulin-like growth factor 1(IGF-1) is a known stimulator of proteoglycan synthesis in articular cartilage. However, arthritic cartilage shows a reduced responsiveness to IGF-1, resulting in depletion of proteoglycan moieties.

Independent effects of interleukin 1 on proteoglycan synthesis and proteoglycan breakdown of bovine articular cartilage in vitro.

We studied the effects of human recombinant interleukin-1 beta on proteoglycan metabolism of bovine articular cartilage in organ culture. IL-1 was more potent in inhibiting synthesis (IC50 4 ng/mL) than in stimulating breakdown of proteoglycans (EC50 200 ng/mL). Inhibition of proteoglycan synthesis began to plateau earlier (2 days) than stimulation of proteoglycan release (4 days). Both effects could be neutralized with a polyclonal anti-IL-1 beta antibody; however, higher antibody titers were required to block IL-1 effects on proteoglycan synthesis than to neutralize those on proteoglycan release. Chloroquine, but not hydrocortisone, blocked IL-1-mediated proteoglycan breakdown. Both drugs, however, augmented IL-1-induced inhibition of proteoglycan synthesis. Our data suggest that the effects of IL-1 on articular cartilage proteoglycan synthesis and proteoglycan breakdown can be regulated independently.

Oxidation of articular cartilage glyceraldehyde-3-phosphate dehydrogenase (G3PDH) occurs in vivo during carrageenin-induced arthritis

Articular cartilage proteoglycan biosynthesis was substantially inhibited by the competitive glycolytic inhibitor 2-deoxyglucose (approximately 65% at 100 mM), but to a much lesser degree (approximately 10%) by the oxidative phosphorylation uncoupler, 2,4-dinitrophenol. These results confirm that articular cartilage proteoglycan synthesis mostly utilises ATP which is generated by glycolysis. In addition, we have utilised the loss of the relatively specific labelling of glyceraldehyde-3-phosphate dehydrogenase (G3PDH) by [3H]-iodoacetic acid to show that rabbit articular G3PDH is oxidised in vivo during the animal model of acute arthritis, carrageenin-induced arthritis, in the same way as we have previously shown that cartilage G3PDH is oxidised after in vitro exposure to sublethal doses of H2O2. The oxidation of rabbit G3PDH in vivo (18 hr post-injection) corresponds with the maximal influx of PMNL cells into the arthritic synovial fluid and with substantial inhibition of proteoglycan core protein synthesis. We propose that H2O2 released from "activated" PMNLs and macrophages is responsible for the "down-regulation" of biosynthetic processes found in cartilage during acute inflammation.

Nonsteroidal Antiinflammatory Drugs in Treatment of Osteoarthritis

It is clear that some synovial inflammation occurs in joints affected by osteoarthritis (OA) and it is well recognized that many patients with OA experience a decrease in pain and joint stiffness following administration of salicylates or other nonsteroidal antiinflammatory drugs (NSAIDs). However, neither the extent to which synovitis contributes to the cartilage breakdown in OA nor the effects of chronic administration of NSAIDs on the natural history of OA in humans is known. Recent studies indicate that several NSAIDs, including salicylates, suppress proteoglycan synthesis in articular cartilage in vitro. The effect on OA cartilage is more marked than that on normal cartilage. Other studies show that salicylate feeding may suppress proteoglycan metabolism in degenerating cartilage in vivo, aggravating the decrease in proteoglycan content caused by the disease itself. However, no effect of salicylates on normal articular cartilage has been observed in vivo. In damaged cartilage the magnitude of NSAID-induced suppression of proteoglycan metabolism appears to be related inversely to the proteoglycan content of the tissue. In addition, the NSAIDs used in treatment of arthritis today may differ with respect to their in vivo effects on articular cartilage metabolism due, in part, to differences between the molar concentrations of these drugs in synovial fluid.

Anti-inflammatory drugs, prostanoid and proteoglycan production by cultured bovine articular chondrocytes

The effect of various anti-inflammatory drugs on the production of prostaglandins E 2 and F 2α, 6 keto PGF 1α and thromboxane B 2 by bovine articular chondrocytes was measured by radioimmunoassay. While indomethacin and meclofenamic acid caused a dose-dependent inhibition of all prostanoids measured, the effects of hydrocortisone and colchicine varied with respect to different prostanoids. Hydrocortisone (10 −7M – 10 −3M) both in the presence and absence of added arachidonic acid, resulted in an inhibition of prostaglandins E 2 and F 2, and to a lesser extent, 6 keto PGF 1α, but T×B 2 production was only slightly inhibited by the drug in the absenced of arachidonic acid and markedly increased in its presence. Colchicine (10 −7M – 10 −3M) had the opposite effect, causing an inhibition of T×B 2 and stimulating PGE 2 and 6 keto PGF 1α production. These findings suggest that certain anti-inflammatory drugs may, in addition to their action on phospholipase A 2 and cyclo-oxygenase, exert potent effects at the level of the different synthetases. In order to see whether these alterations in relative prostanoid levels affected proteoglycan metabolism, the effect of anti-inflammatory drugs on proteoglycan synthesis by cultured chondrocytes was tested using 35SO 4 labeling methodology. The results showed that the concentrations tested (10 −5M to 10 −7M), indomethacin, dexamethasone, hydrocortisone and colchicine inhibited 35SO 4 incorporation into newly synthesized proteoglycan molecules both in the presence (10 −6M) and absence of exogenous arachidonic acid. In the same concentration range choroquine had no effect. These results do not support the hypothesis of direct prostanoid involvement in the modulation of proteoglycan synthesis in articular cartilage.

Effect of Prostaglandin E2 on Adult Pig Articular Cartilage Slices in Culture

Confirming earlier work by other investigators in isolated chondrocyte cultures, prostaglandin E2 (PGE2) (25 micrograms/ml) causes rapid inhibition of in vitro articular cartilage proteoglycan synthesis in adult pig cartilage slices. The potential impact of E prostaglandins on articular cartilage should be considered in clinical situations associated with elevated intra-articular prostaglandin levels (trauma, meniscal injury, arthritis, etc.).

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.