Involvement of prostaglandins from rheumatoid synovium in inhibition of articular cartilage metabolism

Metabolic effects of avocado/soy unsaponifiables on articular chondrocytes

Avocado/soy unsaponifiable (ASU) components are reported to have a chondroprotective effect by virtue of anti-inflammatory and proanabolic effects on articular chondrocytes. The identity of the active component(s) remains unknown. In general, sterols, the major component of unsaponifiable plant material have been demonstrated to be anti-inflammatory in vitro and in animal models. These studies were designed to clarify whether the sterol content of ASU preparations were the primary contributors to biological activity in articular chondrocytes. ASU samples were analyzed by high pressure liquid chromatography (HPLC) and GC mass spectrometry. The sterol content was normalized between diverse samples prior to in vitro testing on bovine chondrocytes. Anabolic activity was monitored by uptake of 35-sulfate into proteoglycans and quantitation of labeled hydroxyproline and proline content after incubation with labeled proline. Anti-inflammatory activity was assayed by measuring reduction of interleukin-1 (IL-1)-induced synthesis of PGE2 and metalloproteases and release of label from tissue prelabeled with S-35.All ASU samples exerted a similar time-dependent up-regulation of 35-sulfate uptake in bovine cells reaching a maximum of greater than 100% after 72 h at sterol doses of 1–10 μg/ml. Non-collagenous protein (NCP) and collagen synthesis were similarly up-regulated. All ASU were equally effective in dose dependently inhibiting IL-1-induced MMP-3 activity (23–37%), labeled sulfate release (15–23%) and PGE2 synthesis (45–58%). Up-regulation of glycosaminoglycan and collagen synthesis and reduction of IL-1 effects in cartilage are consistent with chondroprotective activity. The similarity of activity of ASU from diverse sources when tested at equal sterol levels suggests sterols are important for biologic effects in articular chondrocytes.

Biomarkers of antioxidant status, inflammation, and cartilage metabolism are affected by acute intense exercise but not superoxide dismutase supplementation in horses

Objectives were to evaluate effects of (1) repetitive arthrocentesis on biomarkers of inflammation (prostaglandin E(2), PGE(2)) and aggrecan synthesis (chondroitin sulfate-846; CS) in synovial fluid (SF); (2) exercise and superoxide dismutase (SOD) supplementation on biomarkers of inflammation, antioxidant status, and aggrecan synthesis, in horses. Preliminary trial. Standardbreds underwent four arthrocentesis procedures within 48 h and exhibited elevated CS and no changes in PGE(2). Exercise trial. this randomized crossover design used twelve Standardbred mares which received either treatment (3000 IU d(-1) oral SOD powder) or placebo (cellulose powder) for 6 wks which culminated with them running a repeated sprint exercise test (RSET). Samples were collected before (PRE), during (PEAK), and following exercise (POST). Exercise resulted in increased (P < 0.05) antioxidant defenses including erythrocyte SOD, total glutathione, glutathione peroxidase, gene transcripts for interferon-gamma, interleukin-10, and interleukin-1β in blood, and decreased plasma nitric oxide. Exercise increased (P < 0.05) SF CS and adjusted-PGE(2), and higher (P < 0.05) CS and PGE(2) were found in hock versus carpus joints. No treatment effects were detected. Results suggest normal adaptive responses likely due to exercise-induced tissue microdamage and oxidative stress. Additional research is needed to identify benefit(s) of SOD supplementation in horses.

Prostaglandin E2 receptor type 2-selective agonist prevents the degeneration of articular cartilage in rabbit knees with traumatic instability

Introduction

Osteoarthritis (OA) is a common cause of disability in older adults. We have previously reported that an agonist for subtypes EP2 of the prostaglandin E2 receptor (an EP2 agonist) promotes the regeneration of chondral and osteochondral defects. The purpose of the current study is to analyze the effect of this agonist on articular cartilage in a model of traumatic degeneration.

Methods

The model of traumatic degeneration was established through transection of the anterior cruciate ligament and partial resection of the medial meniscus of the rabbits. Rabbits were divided into 5 groups; G-S (sham operation), G-C (no further treatment), G-0, G-80, and G-400 (single intra-articular administration of gelatin hydrogel containing 0, 80, and 400 μg of the specific EP2 agonist, ONO-8815Ly, respectively). Degeneration of the articular cartilage was evaluated at 2 or 12 weeks after the operation.

Results

ONO-8815Ly prevented cartilage degeneration at 2 weeks, which was associated with the inhibition of matrix metalloproteinase-13 (MMP-13) expression. The effect of ONO-8815Ly failed to last, and no effects were observed at 12 weeks after the operation.

Conclusions

Stimulation of prostaglandin E2 (PGE2) via EP2 prevents degeneration of the articular cartilage during the early stages. With a system to deliver it long term, the EP2 agonist could be a new therapeutic tool for OA.

Prostaglandin E2 and its cognate EP receptors control human adult articular cartilage homeostasis and are linked to the pathophysiology of osteoarthritis

OBJECTIVE

To elucidate the pathophysiologic links between prostaglandin E(2) (PGE(2)) and osteoarthritis (OA) by characterizing the catabolic effects of PGE(2) and its unique receptors in human adult articular chondrocytes.

METHODS

Human adult articular chondrocytes were cultured in monolayer or alginate beads with and without PGE(2) and/or agonists of EP receptors, antagonists of EP receptors, and cytokines. Cell survival, proliferation, and total proteoglycan synthesis and accumulation were measured in alginate beads. Chondrocyte-related gene expression and phosphatidylinositol 3-kinase/Akt signaling were assessed by real-time reverse transcription-polymerase chain reaction and Western blotting, respectively, using a monolayer cell culture model.

RESULTS

Stimulation of human articular chondrocytes with PGE(2) through the EP2 receptor suppressed proteoglycan accumulation and synthesis, suppressed aggrecan gene expression, did not appreciably affect expression of matrix-degrading enzymes, and decreased the type II collagen:type I collagen ratio. EP2 and EP4 receptors were expressed at higher levels in knee cartilage than in ankle cartilage and in a grade-dependent manner. PGE(2) titration combined with interleukin-1 (IL-1) synergistically accelerated expression of pain-associated molecules such as inducible nitric oxide synthase and IL-6. Finally, stimulation with exogenous PGE(2) or an EP2 receptor-specific agonist inhibited activation of Akt that was induced by insulin-like growth factor 1.

CONCLUSION

PGE(2) exerts an antianabolic effect on human adult articular cartilage in vitro, and EP2 and EP4 receptor antagonists may represent effective therapeutic agents for the treatment of OA.

Gender differences and protective effects of testosterone in collagen induced arthritis in rats

To understand the gender differences noticed in autoimmune disorders, particularly rheumatoid arthritis, we used a rat model of collagen induced arthritis (CIA). This study was carried out in two parts. In the first study, severity of inflammation was compared between male and female rats with respect to radiology, histology, activities of lysosomal enzymes, lipid peroxidation, immune response to type II collagen and the level of prostaglandin, a major inflammatory mediator. Since female rats developed severe inflammation, this study was extended to confirm if testosterone at physiological concentration had protective effect against CIA. Hence, studies were carried out on the effect of testosterone application on castrated arthritic rats. Female arthritic rats were also treated with testosterone to find out the effectiveness of the androgen in the presence of female hormones. Results of this study conclusively showed that testosterone possessed significant anti-inflammatory effects at physiological concentration and exerted its action in a gender nonspecific manner.

Effects and mechanisms of total glucosides of paeony on adjuvant arthritis in rats

Total glucosides of paeony (TGP) is the major active constituent of Paeonia lactiflora Pall. The present study was carried out to investigate the effects of TGP on adjuvant arthritis (AA) of rat and its possible mechanisms. AA was induced by metatarsal footpad injection with complete Freund's adjuvant in male Sprague-Dawley rats. The secondary inflammatory reaction was evaluated by hind paw swelling, polyarthritis index. Activity of interleukin-1 (IL-1) was detected by Con A-induced thymocytes proliferation of C57BL/6J mice assay. The tumor necrosis factor alpha (TNFalpha), prostaglandin E(2) (PGE(2)) and cyclic adenosine monophosphate (cAMP) levels in synoviocytes were assessed by radioimmunoassay (RIA). PGE(2) receptors, EP2 and EP4, were analyzed by Western blot analysis. The level of IL-6 was measured by ELISA. Intragastric administration of TGP (50,100 mg/kg) significantly decreased secondary inflammatory reaction in AA rats. Suppressing the activity of IL-1 and TNFalpha, decreased PGE(2) and increased cAMP levels in synoviocytes of AA rats were observed after administration of TGP. In the immunoblot analysis, TGP could up-regulate the expression of EP2 and EP4. These results showed TGP significantly inhibited the progression of AA, and the inhibitory effects might be associated with its ability to mediate the level of cAMP and inhibit the production of IL-1, TNFalpha, IL-6 and PGE(2) from activated synoviocytes.

Profiles of Fatty Acids in Different Bone Structures of Growing Chicks

This study was concerned with the dynamics of fatty acids in tissues involved in the growth and mineralization of the femur of Starbro chicks from 1 to 50 days of age. Four chickens that died of suffocation were obtained each day. Altogether, 400 femoral bones were studied in five age groups (I-V). Compact bone, spongy bone and articular cartilage were sampled. Lipids were extracted according to Folch and fatty acids were separated using gas chromatography. The fatty acid profile was found to change with age. Fatty acids with the highest content in bone were C(18:1), C(16:0), C(18:2) and C(18:0). The highest content of fatty acids was found in spongy bone and the lowest in articular cartilage. Several correlations were revealed between individual fatty acids. The following conclusions were drawn. (1) Fatty acid profiles in compact bone, spongy bone and articular cartilage change with age of chicks. (2) Oleic (C(18:1)), palmitic (C(16:0)), linoleic (C(18:2)), stearic (C(18:0)) and arachidonic (C(20:4)) acids accounted for most of the fatty acid pool. (3) Correlations in the content of fatty acids were noted between bone structures.

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.

PGE2 signal through EP2 promotes the growth of articular chondrocytes

EP2 was identified as the major PGE2 receptor expressed in articular cartilage. An EP2 agonist increased intracellular cAMP in articular chondrocytes, stimulating DNA synthesis in both monolayer and 3D cultures. Hence, the EP2 agonist may be a potent therapeutic agent for degenerative cartilage diseases.

INTRODUCTION

Prostaglandin E2 (PGE2) exhibits pleiotropic effects in various types of tissue through four types of receptors, EP1-4. We examined the expression of EPs and effects of agonists for each EP on articular chondrocytes.

MATERIALS AND METHODS

The expression of each EP in articular chondrocytes was examined by immunohistochemistry and RT-PCR. A chondrocyte cell line, MMA2, was established from articular cartilage of p53(-/-) mice and used to analyze the effects of agonists for each EP. A search for molecules downstream of the PGE2 signal through the EP2 agonist was made by cDNA microarray analysis. The growth-promoting effect of the EP2 agonist on chondrocytes surrounded by cartilage matrix was examined in an organ culture of rat femora.

RESULTS AND CONCLUSION

EP2 was identified as the major EP expressed in articular cartilage. Treatment of MMA2 cells with specific agonists for each EP showed that only the EP2 agonist significantly increased intracellular cAMP levels in a dose-dependent manner. Gene expression profiling of MMA2 revealed a set of genes upregulated by the EP2 agonist, including several growth-promoting and apoptosis-protecting genes such as the cyclin D1, fibronectin, integrin alpha5, AP2alpha, and 14-3-3gamma genes. The upregulation of these genes by the EP2 agonist was confirmed in human articular chondrocytes by quantitative mRNA analysis. On treatment with the EP2 agonist, human articular chondrocytes showed an increase in the incorporation of 5-bromo-2-deoxyuracil (BrdU), and the organ culture of rat femora showed an increase of proliferating cell nuclear antigen (PCNA) staining in articular chondrocytes surrounded by cartilage matrix, suggesting growth-promoting effects of the PGE2 signal through EP2 in articular cartilage. These results suggested that the PGE2 signal through EP2 enhances the growth of articular chondrocytes, and the EP2 agonist is a candidate for a new therapeutic compound for the treatment of degenerative cartilage diseases.

Human synovium produces substances that inhibit DNA and stimulate proteoglycan and collagen synthesis by cultured human articular chondrocytes and synovial fibroblasts

The effects of synovial conditioned medium (SCM) on DNA, proteoglycan (PG), and protein-collagen synthesis and respective gene expressions, in human articular chondrocytes (AC) and DNA synthesis in synovial fibroblasts (SFb), were studied in monolayer culture. All SCM exhibited concentration-dependent inhibition of [3H]thymidine incorporation in both AC and SFb. In contrast, SCM from three OA patients stimulated [35S]SO4 and [3H]glycine incorporations and the expression (RT-PCR) of aggrecan- and type II collagen-specific mRNAs in AC. The production of agents that inhibit DNA synthesis was blocked by indomethacin and dexamethasone and stimulated by IL-1 beta and TNF-alpha. The inhibitory substances were not produced by heat-inactivated tissue nor cultured SFb or AC and were completely solubles in methanol. It is postulated that synovial tissue secretes lipids, most probably arachidonic acid metabolites. These may counteract growth of an inflammatory synovial pannus by inhibiting SFb proliferation and enhance repair of damaged tissues by stimulating the matrix synthesis.

The use of ginger (Zingiber officinale Rosc.) as a potential anti-inflammatory and antithrombotic agent

The effect of an aqueous extract of ginger (Zingiber officinale) on serum cholesterol and triglyceride levels as well as platelet thromboxane-B(2) and prostaglandin-E(2) production was examined. A raw aqueous extract of ginger was administered daily for a period of 4 weeks, either orally or intraperitoneally (IP) to rats. Fasting blood serum was investigated for thromboxane-B(2), prostaglandin-E(2), cholesterol and triglycerides. A low dose of ginger (50 mg/kg) administered either orally or IP did not produce any significant reduction in the serum thromboxane-B(2) levels when compared to saline-treated animals. However, ginger administered orally caused significant changes in the serum PGE(2) at this dose. High doses of ginger (500 mg/kg) were significantly effective in lowering serum PGE(2) when given either orally or IP. However, TXB(2) levels were significantly lower in rats given 500 mg/kg ginger orally but not IP. A significant reduction in serum cholesterol was observed when a higher dose of ginger (500 mg/kg) was administered. At a low dose of ginger (50 mg/kg), a significant reduction in the serum cholesterol was observed only when ginger was administered IP. No significant changes in serum triglyceride levels were observed upon administration of either the low or high dose of ginger. These results suggest that ginger could be used as an cholesterol-lowering, antithrombotic and anti-inflammatory agent.

The role of prostaglandin E2 receptors in the pathogenesis of rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic inflammatory disorder leading to bone and cartilage destruction. A substantial body of evidence suggests that prostaglandin E2 (PGE2) contributes to the pathogenesis of RA, and nonsteroidal anti-inflammatory drugs, inhibitors of the synthesis of PGE2 and other prostanoids, continue to be used in the treatment of this disease. To begin to understand the mechanism by which prostaglandins modulate the pathophysiology of this disease, we examined mice lacking each of the four known PGE2 (EP) receptors after generation of collagen antibody-induced arthritis, an animal model of RA. Homozygous deletion of the EP1, EP2, or EP3 receptors did not affect the development of arthritis, whereas EP4 receptor-deficient mice showed decreased incidence and severity of disease. These animals also showed reduced inflammation as assessed by circulating IL-6 and serum amyloid A levels. Joint histopathology of EP4(-/-) animals revealed reduced bone destruction, proteoglycan loss, and type II collagen breakdown in cartilage compared with EP4(+/+) mice. Furthermore, liver and macrophages isolated from EP4(-/-) animals produced significantly less IL-1 beta and IL-6 than control samples. Thus, PGE2 contributes to disease progression at least in part by binding to the EP4 receptor. Antagonists of this receptor might therefore provide novel agents for the treatment of RA.

Effects of anti-arthritis preparations on gene expression and enzyme activity of cyclooxygenase-2 in cultured equine chondrocytes

OBJECTIVE

To determine the effects of recombinant equine interleukin -1beta (reIL-1beta) and 4 anti-inflammatory compounds on the expression and activity of cyclooxygenase (COX)-2 in cultured equine chondrocytes.

SAMPLE POPULATION

Articular cartilage from 9 young adult horses.

PROCEDURE

Reverse transcriptase-polymerase chain reaction methods were used to amplify a portion of equine COX-2 to prepare a cDNA probe. Northern blot analysis was used to quantify the expression of COX-2 in first-passage cultures of equine articular chondrocytes propagated in media containing dexamethasone (DEX), phenylbutazone (PBZ), polysulfated glycosaminoglycan, and hyaluronan, each at concentrations of 10 and 100 microg/ml and each with or without reIL-1beta. A commercial immunoassay was used to determine prostaglandin E2 (PGE2) concentrations in conditioned medium of similarly treated cells to quantify COX-2 activity.

RESULTS

Addition of reIL-1beta increased the expression of COX-2 in a dose-dependent manner, which was paralleled by an increased concentration of PGE2 in culture medium. Concentration of PGE2 in spent medium from reIL-beta-treated chondrocytes was significantly reduced by DEX and PBZ; however, only DEX significantly reduced gene expression of COX-2.

CONCLUSIONS AND CLINICAL RELEVANCE

Prostaglandin E2 is considered to be an important mediator in the pathophysiologic processes of arthritis, and cultured chondrocytes respond to interleukin-1 with enhanced expression and activity of COX-2. Palliative relief in affected horses is probably attributable, in part, to inhibition of PGE2 synthesis; however, analysis of these data suggests that of the 4 compounds tested, only DEX affects pretranslational regulation of the COX-2 gene in cultured equine chondrocytes.

Evaluation of the influence of prostaglandin E2 on recombinant equine interleukin-1beta-stimulated matrix metalloproteinases 1, 3, and 13 and tissue inhibitor of matrix metalloproteinase 1 expression in equine chondrocyte cultures

OBJECTIVE

To determine the effects of prostaglandin E2 (PGE2) on recombinant equine interleukin (IL)-1beta-stimulated expression of matrix metalloproteinases (MMP 1, MMP 3, MMP 13) and tissue inhibitor of matrix metalloproteinase 1 (TIMP 1) in vitro.

SAMPLE POPULATION

Cultured equine chondrocytes.

PROCEDURE

Stationary monolayers of first-passage chondrocytes were exposed to graduated concentrations of PGE2 with or without a subsaturating dose (50 pg/ml) of recombinant equine IL-1beta (reIL-1beta) to induce expression of MMP 1, MMP 3, MMP 13, and TIMP 1, followed by RNA isolation and northern blotting. In subsequent experiments, gene expression was similarly quantified from mRNA isolated from cultures pretreated with phenylbutazone to quench endogenous PGE2 synthesis, followed by exposure to reIL-1beta and exogenous PGE2 (5 mg/ml) with appropriate controls.

RESULTS

Exogenous PGE2 (10 mg/ml) significantly reduced reIL-1beta-induced expression of MMP 1, MMP 3, MMP 13, and TIMP 1. Abrogation of cytokine induction with this dose of PGE2 was comparable to that for dexamethasone (10(-5) M) control. Similarly, pretreatment with phenylbutazone, followed by exposure to relL-1beta and PGE2 (5 mg/ml), was associated with a reduced expression of the genes of interest, an effect that was significant for MMP 1, MMP 13, and TIMP 1.

CONCLUSIONS AND CLINICAL RELEVANCE

The MMP and TIMP 1 are important mediators in the pathophysiologic events in osteoarthritis. The potential for physiologically relevant regulation of expression of these genes by PGE2 is a consideration in the use of drugs that inhibit prostanoid synthesis in the treatment of equine arthropathies.

Characterization of PGE(2) receptors (EP) and their role as mediators of 1alpha,25-(OH)(2)D(3) effects on growth zone chondrocytes

Growth plate chondrocyte function is modulated by the vitamin D metabolite 1alpha,25-(OH)(2)D(3) via activation of protein kinase C (PKC). In previous studies with cells derived from prehypertrophic and upper hypertrophic zones of rat costochondral cartilage (growth zone cells), inhibition of prostaglandin production with indomethacin caused a decrease in the stimulation of PKC activity, suggesting that changes in prostaglandin levels mediate the 1alpha,25-(OH)(2)D(3)-dependent response in these cells. Growth zone cells also respond to PGE(2) directly, indicating that prostaglandins act as autocrine or paracrine regulators of chondrocyte metabolism in the growth plate. The aim of the present study was to identify which PGE(2) receptor subtypes (EP) mediate the effects of PGE(2) on growth zone cells. Using primers specific for EP1-EP4, reverse transcription-polymerase chain reaction (RT-PCR) amplified EP1 and EP2 cDNA in a RT-dependent manner. In parallel experiments, we used EP subtype-specific agonists to examine the role of EP receptors in 1alpha,25-(OH)(2)D(3)-mediated cell proliferation and differentiation. 17-Phenyl-trinor-PGE(2) (PTPGE(2)), an EP1 agonist, decreased [3H]-thymidine incorporation in a dose-dependent manner and augmented the 1alpha,25-(OH)(2)D(2)-induced inhibition of [3H]-thymidine incorporation. PTPGE(2) also caused significant increases in proteoglycan production, as measured by [35S]-sulfate incorporation, and alkaline phosphatase specific activity. 1alpha,25-(OH)(2)D(3)-induced alkaline phosphatase activity was only slightly stimulated by PTPGE(2). In contrast, 1alpha,25-(OH)(2)D(3)-induced PKC activity was synergistically increased by PTPGE(2), whereas EP1 antagonists SC-19220 and AH6809 inhibited PKC activity in a dose-dependent manner. The EP2, EP3 and EP4 agonists had no effect on the various cell-induced responses measured. EP1 receptor-induced responses were blocked by the phospholipase C inhibitor U73122, and reduced by PKA inhibitors. EP1 receptor-induced PKC activity was insensitive to pertussis toxin or choleratoxin but blocked by the G-protein inhibitor GDPbetaS, suggesting the involvement of G(q). These results suggest that the EP1 receptor subtype mediates various PGE(2)-induced cellular responses in growth zone chondrocytes leading to decreased proliferation and enhanced differentiation, as well as the effect of 1alpha,25-(OH)(2)D(3) on cellular maturation.

Characterization of prostaglandin E(2) receptors and their role in 24,25-(OH)(2)D(3)-mediated effects on resting zone chondrocytes

Resting zone chondrocyte differentiation is modulated by the vitamin D metabolite, 24,25-(OH)(2)D(3), via activation of protein kinase C (PKC). In previous studies, inhibition of prostaglandin production with indomethacin caused an increase in PKC activity, suggesting that changes in prostaglandin levels may mediate the 24, 25-(OH)(2)D(3)-dependent response and act as autocrine or paracrine regulators of chondrocyte metabolism. Supporting this hypothesis is the fact that resting zone cells respond directly to prostaglandin E(2) (PGE(2)). The aim of the present study was to identify which PGE(2) receptor subtypes (EP) mediate the effects of PGE(2) on resting zone cells. Using primers specific for EP1-EP4, reverse transcription-polymerase chain reaction (RT-PCR) amplified EP1 and EP2 cDNA in a RT-dependent manner. A variant form of the EP1 cDNA, EPlv, was also amplified in an RT-dependent manner. In parallel experiments, we used EP subtype-specific agonists to examine the role of EP receptors in 24,25-(OH)(2)D(3)-mediated cell proliferation and differentiation. 17-phenyl-trinor-PGE(2) (PTPGE(2)), an EP1 agonist, increased [(3)H]-thymidine incorporation in a dose-dependent manner and reversed the 24, 25-(OH)(2)D(2)-induced inhibition of [(3)H]-thymidine incorporation. SC-19220, an EP1 antagonist, caused a further dose-dependent decrease in 24,25-(OH)(2)D(3)-induced inhibition of [(3)H]-thymidine incorporation. PTPGE(2) also caused a biphasic increase in [(35)S]-sulfate incorporation and increased alkaline phosphatase enzyme activity at high concentrations (10(-8) M). 24, 25-(OH)(2)D(3)-induced alkaline phosphatase activity was synergistically stimulated in a dose-dependent manner by PTPGE(2). In contrast, 24,25-(OH)(2)D(3)-induced PKC activity was inhibited in a dose-dependent manner by PTPGE(2) and SC-19220, the EP1 antagonist, elevated PKC activity at high concentrations (10(-8) M). The EP2 agonist, misoprostol, only affected [(35)S]-sulfate incorporation, but in a dose-dependent manner. The EP3 and EP4 agonists had no effect on cell response. These results suggest that the EP1 receptor subtype mediates some of the PGE(2)-induced cellular responses in resting zone cells that lead to both increased proliferation and differentiation. Because 24,25-(OH)(2)D(3) inhibits PGE(2) synthesis in these cells, EP1-mediated induction of proliferation is blocked, encouraging cellular maturation and activation of PKC activity.

Effects of misoprostol and prostaglandin E2 on proteoglycan biosynthesis and loss in unloaded and loaded articular cartilage explants

The effects of misoprostol, a prostaglandin E1 analog, and prostaglandin E2 on proteoglycan biosynthesis and loss were studied in unloaded and mechanically loaded mature bovine articular cartilage explants. The prostaglandins were administered daily at dosages of 0, 10, 100 and 1000 eta g/ml for up to seven days, and proteoglycan biosynthesis determined by measurement of radiolabelled sulfate incorporation. The presence of misoprostol lead to a significant (p < 0.001) dose-dependent inhibition (30%-50%) in proteoglycan biosynthesis which was also dependent on exposure time (p < 0.05). A significant decrease in biosynthesis (34%) was also found for prostaglandin E2, but only at the highest dose (1000 eta g/ml). Proteoglycan catabolism rates were not affected by either substance as assessed by loss of newly synthesized proteoglycan. The application of a continuous cyclic mechanical compressive load (stress of 1.0 MPa at 1 hertz for 24 hours) resulted in a significant inhibition of proteoglycan biosynthesis (up to 50%) as compared to unloaded explants. However, there was no additive effect when mechanical load and misoprostol or prostaglandin E2 were combined. These results suggest that prostaglandins may have a role in the degenerative and repair process in various forms of arthritis where elevated intra-articular levels of prostaglandin E2 are present.

Inhibition of the effects of rheumatoid synovial fluid cells on chondrogenesis and cartilage breakdown in vitro: possible therapeutical conclusions. A morphological--biochemical study

Short-term co-cultivation of blastemal cells from 12-day-old mouse limb buds and human rheumatoid synovial fluid cells in high density cultures (Trowell culture system) resulted, depending on when co-cultivation started, either in (1) an inhibition of chondrogenesis (co-cultivation right from the start) or in (2) an extensive breakdown of cartilaginous matrix (co-cultivation after formation of embryonic cartilage). These synovial effects were markedly impeded if Avarol (a dioxygenase inhibitor) was applied singly or in combination with PAI-2 (a u-PA-inhibitor). PAI-2 alone, however, had no effect on the synovial-induced inhibition of chondrogenesis, but produced a pronounced inhibitory effect on matrix breakdown. The effects of both inhibitors were studied electron microscopically and biochemically (determination of sulfated-glycosaminoglycans in the high density cultures by Alcian Blue binding assay). The results of this study are consistent with the presumption that rheumatoid synovial cells are capable of inhibiting chondrogenesis and enhancing the breakdown of the cartilaginous matrix. Amongst others, the possible mediators involved are prostaglandins and plasminogen activators. The response to the inhibitors Avarol and PAI-2 is compatible with their mode of action. The chondroprotective action of these substances may be useful in developing potential antirheumatic drugs.

Ginger (Zingiber officinale) in rheumatism and musculoskeletal disorders

One of the features of inflammation is increased oxygenation of arachidonic acid which is metabolized by two enzymic pathways--the cyclooxygenase (CO) and the 5-lipoxygenase (5-LO)--leading to the production of prostaglandins and leukotrienes respectively. Amongst the CO products, PGE2 and amongst the 5-LO products, LTB4 are considered important mediators of inflammation. More than 200 potential drugs ranging from non-steroidal anti-inflammatory drugs, corticosteroids, gold salts, disease modifying anti-rheumatic drugs, methotrexate, cyclosporine are being tested. None of the drugs has been found safe; all are known to produce from mild to serious side-effects. Ginger is described in Ayurvedic and Tibb systems of medicine to be useful in inflammation and rheumatism. In all 56 patients (28 with rheumatoid arthritis, 18 with osteoarthritis and 10 with muscular discomfort) used powdered ginger against their afflictions. Amongst the arthritis patients more than three-quarters experienced, to varying degrees, relief in pain and swelling. All the patients with muscular discomfort experienced relief in pain. None of the patients reported adverse effects during the period of ginger consumption which ranged from 3 months to 2.5 years. It is suggested that at least one of the mechanisms by which ginger shows its ameliorative effects could be related to inhibition of prostaglandin and leukotriene biosynthesis, i.e. it works as a dual inhibitor of eicosanoid biosynthesis.

Influence of synovial cells on cartilage in vitro: induction of breakdown and inhibition of synthesis

Organoid or high density cultures of: (1) synovial cells from patients with rheumatoid arthritis, and (2) prechondrogenic mesenchymal cells from limb buds of 12-day-old mouse embryos, were co-cultured for 7-10 days using the Trowell culture system. Depending on the time of commencing co-cultivation, chondrogenesis was inhibited (co-cultivation from the start) or the cartilaginous matrix was partly degraded (co-cultivation after formation of embryonic cartilage, i.e. on day 4). These effects were obtained with cells from synovial fluid as well as from synovial tissue. Matrix degradation and the behaviour of the different cell types could be demonstrated well by electron microscopy under the in vitro conditions applied.

Influence of prostaglandins on DNA and matrix synthesis in growth plate chondrocytes

Prostaglandins are locally produced in a number of tissues in response to a variety of stimuli, including local growth factors and systemic hormones. The present investigation characterizes prostaglandin effects on growth plate chondrocytes. Since cyclic adenosine monophosphate (cAMP) may act as a prostaglandin-stimulated second messenger, the effects of prostaglandins A1, D2, E1, E2, F2 alpha, and I2 (10(-10)-10(-6) M) on cAMP levels and thymidine incorporation were evaluated. The stimulation of cAMP and thymidine incorporation by the various prostaglandin metabolites were dose dependent and highly correlated (r = 0.99, p less than 0.001). The magnitude of the effect varied but was maximal at 10(-6) M for each of the prostaglandins. Prostaglandins of the E series (E1 and E2) were the most potent, causing significant effects at 10(-10) M and with maximal 12- and 13-fold increases in DNA synthesis after a 24 h exposure. Prostaglandins D2 and A1 maximally stimulated thymidine incorporation by 4.7- and 3.1-fold but caused significant increases only at 10(-8) M. Prostaglandins F2 alpha and I2 were the least stimulatory, producing small but significant increases in thymidine incorporation at 10(-6) M (30 and 100% stimulations). A causal relationship between cAMP and thymidine incorporation was further verified by the ability of dibutyryl-cAMP to increase DNA synthesis. Long-term chondrocyte cultures treated continuously with PGE2 demonstrated an increase in cell number, confirming the proliferative effect. Indomethacin did not alter the potent dose-dependent stimulations of chondrocyte DNA synthesis by TGF-beta 1, basic FGF, or PTH, indicating that these known mitogens act independently of prostaglandin metabolism. PGE2 was further examined for its effects of matrix synthesis. PGE2 inhibited collagen synthesis with a maximal 42% decrease but did not alter noncollagen protein synthesis. In contrast, PGE2 maximally increased sulfate incorporation by 35% and caused a small dose-dependent inhibition in alkaline phosphatase activity. Thus, prostaglandins alter DNA and matrix synthesis in growth plate chondrocytes and may have an important role in chondrocyte metabolism in the growth plate, fracture callus, and other areas of endochondral ossification.

Metabolic and ultrastructural changes in articular cartilage of rats fed dietary supplements of omega-3 fatty acids

A "marginally deficient" essential fatty acid state was produced in male Sprague-Dawley rats by dietary supplementation with omega 3 fatty acids. Animals fed diets containing the highest amounts of these fatty acids (10% menhaden fish oil) demonstrated a 70% maximum decrease in the linoleic and arachidonic acid content of articular cartilage, a 30-40% decrease in cartilage hexosamine content, with little effect on hydroxyproline levels, and a 32% inhibition of proteoglycan synthesis. Histologic analysis revealed an occasional surface irregularity and localized depletion of Safranin O and toluidine blue staining of articular cartilage on the femoral heads from animals taking the higher doses. Electron microscopic analysis revealed a marked decrease in "dark-staining" chondrocytes relative to "light-staining" cells in all animals fed menhaden fish oil. The cartilaginous changes noted in this study reflect a causal relationship between chondrocyte metabolism and an altered unsaturated fatty acid content. The observed responses of chondrocytes to omega 3 fatty acids may be similar to those commonly associated with the development of early osteoarthrosis. It is not known whether similar changes are induced in other species, including humans, but these observations suggest that some caution must be taken in the long-term administration of menhaden fish oil or other omega 3 fatty acid-containing preparations in rheumatoid arthritis patients.

Ginger (Zingiber officinale) and rheumatic disorders

Oxygenation of arachidonic acid is increased in inflamed tissues. In this condition products of two enzymic pathways--the cyclooxygenase and the 5-lipoxygenase producing respectively prostaglandins and leukotrienes--are elevated. Of the cyclooxygenase products, PGE2 and of the lipoxygenase products, LTB4 are the strongest candidates for mediating inflammation. Non-steroidal anti-inflammatory drugs which inhibit the cyclooxygenase, and corticosteroids are used to treat such disorders. Both types of drugs produce adverse side-effects on prolonged use. Ginger is reported in Ayurvedic and Tibb systems of medicine to be useful in rheumatic disorders. Seven patients suffering from such disorders reported relief in pain and associated symptoms on ginger administration.

Independent effects of interleukin-1 on proteoglycan breakdown, proteoglycan synthesis, and prostaglandin E2 release from cartilage in organ culture

Exposure of bovine nasal cartilage in culture to interleukin-1 (IL-1) leads to a time- and concentration-dependent stimulation of proteoglycan breakdown and prostaglandin E2 (PGE2) release, and to inhibition of proteoglycan synthesis. The threshold levels of IL-1 required for initiating these effects were different, and IL-1 was 10 times more potent in inhibiting synthesis than in stimulating breakdown of proteoglycan. Kinetic studies indicated that the effects on proteoglycan metabolism occurred earlier (16-24 hours) than those for PGE2 release (48 hours). Selective effects were observed with inhibitors. Nonsteroidal antiinflammatory drugs blocked PGE2 production in response to IL-1, but had no effect on proteoglycan metabolism, and the antiarthritic drugs that blocked IL-1-stimulated breakdown augmented the inhibition of proteoglycan synthesis. We suggest that the effects of IL-1 on proteoglycan breakdown, proteoglycan synthesis, and PGE2 release are mediated by independent post-receptor mechanisms.

Insulin-like growth factor stimulation of chondrocyte proteoglycan synthesis by human synovial fluid

We investigated the role of insulin-like growth factors (IGFs) as regulating factors of cartilage metabolism in human synovial fluid (SF), using a bovine explant culture system that was shown to respond to recombinant IGF-1 in vitro. SF from rheumatoid arthritis (RA) patients and from control patients was found to stimulate chondrocyte proteoglycan synthesis in bovine articular cartilage. A monoclonal antibody directed primarily against IGF-1 (and to some extent, IGF-2) partially blocked the stimulatory action of serum and totally blocked the stimulation by SF. These findings indicate that IGFs are major regulating factors of cartilage proteoglycan synthesis in human SF. In addition, we measured serum and SF levels of IGF-1 in RA patients and control patients, using a radioimmunoassay. No difference in immunoreactive serum IGF-1 was detected between patients and controls. The IGF-1 levels in SF were consistently lower than in serum, for both patient groups. No differences in IGF-1 concentration were found between RA and non-RA SF. The relevance of these data with respect to joint inflammation is discussed.

Review of pathogenesis and treatment of degenerative joint disease

Treatment of degenerative joint disease (osteoarthritis) is discussed in relationship to pathogenesis of five clinical entities, defined to facilitate discussion:-1) occurring in high motion joints and associated with synovitis; 2) associated with low motion joints; 3) "non-progressive" articular cartilage erosion; 4) secondary to other identified problems (intra-articular fractures, ligamentous damage, wounds, septic arthritis, osteochondrosis); and 5) chondromalacia of the patella. In addition to direct damage to articular cartilage, synovitis and capsulitis and depletion of matrical glycosaminoglycans and proteoglycans play important roles. The natural healing response in damaged articular cartilage is inadequate. The principles of treatment are divided into: 1) prevention or treatment of primary causes. These include the effects of track surface, shoeing, and the appropriate resolution of intra-articular fractures, septic arthritis and osteochondritis dissecans. 2) treatment of active soft tissue disease contributing to articular cartilage degeneration, including rest, physical therapy, synovectomy and administration of anti-inflammatory drugs, sodium hyaluronate and polysulfated glycosaminoglycans. 3) attempts at treatment of articular cartilage loss or degeneration, including articular cartilage curettage, subchondral bone drilling, osteophyte removal, articular cartilage grafting and arthrodesis.

Chondrocyte activation in response to factor(s) produced by a continuous line of lapine synovial fibroblasts

We have established a permanent line of lapine synovial fibroblasts called HIG-82. Upon appropriate stimulation, these cells mimicked primary cultures of lapine synovial cells in producing substances which activated primary cultures of lapine articular chondrocytes. Activated chondrocytes secreted prostaglandin E2 (PGE2) and latent neutral collagenase, gelatinase, and caseinase, but not acid hydrolases, into their culture media. PGE2 itself did not activate the chondrocytes. Heating the crude, synovial-conditioned media at 70 degrees C for 30 min reduced their activating activity by 49.3 +/- 20.5% (n = 7). Production of PGE2 by chondrocytes was maximal during the first day of exposure to synovial conditioned media, whereas the production of neutral proteinases peaked during the second day. All the chondrocyte-stimulating activity was present in a fraction of Mr 10,000-25,000. Unlike the crude conditioned medium, this partially-purified material retained full activity following heating to 70 degrees C for 30 min. These data indicate that synovial fibroblasts (type B synoviocytes) are a source of chondrocyte activator(s) and that neutral, but not acid, proteinases may be involved in extracellular proteolysis which leads to the resorption of the cartilaginous matrix seen in bioassays of catabolin.

Human recombinant interleukin 1-mediated suppression of glycosaminoglycan synthesis in cultured rat costal chondrocytes

Effects of human recombinant interleukin 1 (IL-1) on the synthesis of glycosaminoglycan were examined with cultured rat costal chondrocytes. Incorporation of [35S]sulfate into glycosaminoglycan was strikingly diminished by the addition of IL-1 in a dose- and time- dependent manner. When the cells were cultured with 340 micrograms/ml of IL-1 for 72 hr, the synthesis of glycosaminoglycan was inhibited to 10% of the control. On the other hand, IL-1 had no effect on the morphology and proliferation of the chondrocytes. The suppression of glycosaminoglycan synthesis remained unchanged after the addition of indomethacin, indicating that the effect of IL-1 is independent of the enhanced synthesis of prostaglandins.

Carrageenin-induced arthritis. VI. Alterations in amino acid transport by articular cartilage in acute inflammatory arthritis

The mechanism of transport of alanine and aminoisobutyric acid into chondrocytes in rabbit articular cartilage was shown to be mediated by transport systems similar to that described for other eukaryotic cells namely the A, ASC, and L systems. Three days after the initiation of an acute inflammatory arthritis by the intra-articular injection of carrageenin into one knee joint the rate of transport of both these amino acids was decreased. Although all three transport systems were depressed, it appeared that the A and ASC systems were partially susceptible to damage by the induced inflammation. The rate of amino acid transport by the affected cartilage had recovered by 28 days after carrageenin treatment. This depression in amino acid transport is discussed in relation to a decrease in general metabolic processes in chondrocytes as a consequence of inflammation.

Influence of the severity and duration of murine antigen-induced arthritis on cartilage proteoglycan synthesis and chondrocyte death

Recent studies have shown that joint inflammation can suppress chondrocyte proteoglycan synthesis and can even kill chondrocytes. In the present study, we investigated the influence of the severity and chronicity of murine antigen-induced arthritis on the degree of these toxic effects on chondrocytes. Joint inflammation, quantitated by measurements of 99m technetium pertechnetate uptake, was significantly correlated with the inhibition of proteoglycan synthesis, measured by 35S-sulfate incorporation. Histologic grading of the extent of chondrocyte death on day 28 after arthritis induction correlated best with the degree of inflammation present on day 14. High scores for chondrocyte death were found only in mice with persistent, severe arthritis. Our data indicate that the severity of joint inflammation is a major determinant of the degree of chondrocyte proteoglycan synthesis inhibition, whereas both the severity and chronicity of the inflammation determine chondrocyte killing and, therefore, irreversible joint destruction.

Articular cartilage cultured with catabolin (pig interleukin 1) synthesizes a decreased number of normal proteoglycan molecules

A homogeneous preparation of catabolin from pig leucocytes caused a reversible dose-dependent (0.01-1 nM) decrease in the synthesis of proteoglycan in slices of pig articular cartilage cultured in serum-free medium. The monomers that were synthesized and secreted in the presence of catabolin had the same average hydrodynamic size and ability to aggregate as the controls, and the core protein was substituted with the same number of glycosaminoglycan chains. The chains were the same average length and charge as normal and were sulphated to the same extent as the controls. Newly synthesized extracellular proteoglycan was not preferentially degraded. A 2-3-fold increase in glycosaminoglycan synthesis occurred in control and catabolin-treated cartilage in the presence of beta-D-xyloside (1 mM), more than 80% being secreted into the medium as free chains. Decreased incorporation of sulphate was not reversed in the presence of lysosomal-enzyme inhibitors, and there was no evidence in pulse-chase experiments of increased intracellular degradation of glycosaminoglycan chains before secretion. It is concluded that catabolin-treated cartilage synthesizes a smaller number of normal proteoglycan molecules.

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.

The effects of prostaglandin E2 in rapidly growing rats: depressed longitudinal and radial growth and increased metaphyseal hard tissue mass

The effects of 0, 0.3, 1.0, 3.0, or 6.0 mg of prostaglandin E2 (PGE2)/kg/day administered subcutaneously for 3 weeks to triple fluorochrome-labeled weanling rats are reported. Microradiographs and undecalcified sections of proximal tibiae, tibial shafts, and seventh caudal vertebrae were evaluated by static and dynamic bone histomorphometry techniques. Significant changes were observed only at higher dose levels. Proximal tibial longitudinal growth rates were depressed in doses of 1, 3, or 6 mg PGE2/kg/day. Growth plate thickness and the size of hypertrophic cartilage cells were decreased in animals given 3 and 6 mg of PGE2/kg/day, but the calculated rate of cartilage cell production was unaffected. At doses of 6 mg PGE2/kg/day, periosteal bone apposition rates between Day -1 and Day +19 in both the tibial shafts and caudal vertebral cortices were depressed by less than 25%. Cortical bone mass and endosteal bone apposition rates in the tibial shaft and caudal vertebrae were unaffected. Hard tissue mass in the secondary spongiosa of the proximal tibial metaphysis increased dramatically (28%, 44%, and 60%, respectively) in rats treated with 1, 3, or 6 mg PGE2/kg/day. In addition, the secondary spongiosa contained numerous islands of woven trabecular bone along with an increased number of trabeculae. The study demonstrates that high doses of PGE2 stimulate new woven trabecular bone production and depress longitudinal and radial growth in rapidly growing rats.

Nonsteroidal anti-inflammatory drugs and modulation of cartilaginous changes in osteoarthritis and rheumatoid arthritis. Clinical implications

Nonsteroidal anti-inflammatory drugs have a potential for modifying the complex pathophysiologic events leading to cartilage destruction in various forms of arthritis. Following an evaluation of basic mechanisms in the pathogenesis of cartilaginous destructive lesions, the effects of nonsteroidal anti-inflammatory drugs on normal chondrocyte metabolism are discussed. Their capacity to modulate cartilage and bone lesions in experimental forms of arthritis is addressed, as is the manner in which they may modify the pathophysiology of cartilage destruction in human forms of arthritis. Different classes of nonsteroidal anti-inflammatory drugs produce different effects in certain in vivo or in vitro settings.

Changes in proteoglycan biosynthesis following leukocyte elastase treatment of bovine articular cartilage in culture

Treatment of bovine articular cartilage in culture with a low molecular weight elastase purified from rabbit polymorphonuclear leukocytes resulted in degradation and release of proteoglycans from the tissue, coupled with a prolonged inhibition of proteoglycan biosynthesis. These observations are consistent with those seen in experimental arthritis induced in rabbits. Comparison of the size of the proteoglycan degradation products extracted from elastase-treated cartilage in culture with that from arthritic cartilage showed marked similarities. The results strongly suggest that leukocyte elastase is a contributing factor in proteoglycan degradation and inhibition of synthesis in inflammatory joint disease.

Cytokine modulation of chondrocyte metabolism--in vivo and in vitro effects of piroxicam

Changes in the macromolecular proteolycan (PG) and collagen of the cartilage matrix may culminate in irreparable tissue destruction. Molecular modifications appear to result from: (A) exogenous proteinases, (B) endogenous chondrocyte proteinases whose synthesis and release is modulated by exogenous non-enzymatic cytokines (CKs) and (C) quantitative and/or qualitative alterations in chondrocyte PG and collagen synthesis which are potentially induced by exogenous CKs. Studies have recently been initiated to determine the effect of piroxicam on the synthesis and activity of such metabolic regulatory CKs in patients with rheumatoid arthritis and osteoarthritis, and in age-, sex-, and race-matched controls. Therapeutic doses of piroxicam alone had no effect on the anabolic or catabolic function of chondrocytes. Current studies concern the effect of piroxicam on: (a) spontaneous and lectin-driven production by peripheral blood monocytes and T-cells of trypsin-sensitive, heat-labile CKs (interleukin 1, lymphokine) which, in a protein- and RNA-synthesis-dependent manner, induce a concentration and duration of substrate exposure dependent release of chondrocyte PG- and collagen- degrading neutral proteinases in cartilage organ and chondrocyte suspension culture systems; (b) spontaneous and lectin-driven synthesis by peripheral blood T-cells of lymphokines capable of suppressing chondrocyte PG, glycosaminoglycan, protein, collagen and nucleic acid synthesis in a quantitatively reversible manner; (c) pathological synovial membrane synthesis of such catabolic-inducing and anabolic-modulatory CKs. These experimental model system are reviewed together with preliminary data on the effect of piroxicam.

Studies on the release of proteolytic enzymes during synovium-induced cartilage breakdown in vitro and the actions of anti-inflammatory drugs

Pig articular cartilage, overlaid with a minced preparation of synovium from the same joint, underwent extensive matrix degradation during a two-week culture period. This degradation was associated with de novo synthesis by the synovium of specific neutral proteoglycan- and collagen-degrading enzymes. Both enzymes exhibited neutral pH optima, and were inhibited by serum and the metal ion chelators EGTA and 1,10-phenanthroline. The neutral proteoglycanase cleaved the core protein of isolated proteoglycan. The effects of some anti-inflammatory drugs on synovial enzyme production and cartilage metabolism were investigated. The steroids, dexamethasone and prednisolone, inhibited production of both enzymes whereas the non-steroidal anti-inflammatory drugs (NSAID's), flurbiprofen and indomethacin, slightly increased medium enzyme levels. Flurbiprofen and indomethacin had no effect on the extent of synovium-mediated cartilage degradation as assessed histologically. Inhibition by the steroids of synovial collagenase production correlated with inhibition of cartilage collagen breakdown, whereas inhibition of synovial proteoglycanase production did not prevent extensive proteoglycan breakdown. Experiments using radiotracer techniques indicated that dexamethasone, whilst partially inhibiting synovium-mediated proteoglycan degradation, severely inhibited cartilage proteoglycan synthesis thus resulting in net proteoglycan loss.

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

It was previously reported that bovine conditioned synovial medium (SM) has a catabolic activity on articular cartilage proteoglycans in an organ culture system. The question thus arose whether SM had an anabolic effect as well on articular cartilage proteoglycans. In this report it is shown that addition of autogenous SM to isolated bovine articular chondrocytes inhibited the synthesis of proteoglycans as measured by the incorporation of radiosulphate. Already after 4 hours an inhibition was seen in the pericellular (matrix) chondroitin sulphate (MA-CS) fraction, and in the culture medium chondroitin sulphate (CM-CS) fraction it was significant after 72 hours. When the synovial tissue was cultured with indomethacin (1.4 X 10(-5) mol/l) and this indo-SM was added to the chondrocyte cultures, the ability of the chondrocytes to incorporate [35S]sulphate was decreased further. It therefore seems evident that the products from the synovial tissue influences the behaviour of the chondrocyte in such a way that not only is the degradation enhanced but also the synthesis of cartilage proteoglycans is inhibited.

The effect of synovial catabolin on cartilage synthetic activity

The effect of porcine synovial catabolin on the incorporation of [3H]amino acids and [35S]sulfate into bovine nasal cartilage was investigated. The rapid breakdown of matrix caused by partially purified catabolin had little affect on the incorporation of [3H]amino acids but there was inhibition of [35S]sulfate uptake. While the 35S-labelled material released into the medium was largely incapable of aggregation with hyaluronate, this was only a small part (less than 10%) of the total incorporated. The principal inhibitory action was in the formation of large molecular size material (guanidinium chloride extractable). The amount of newly synthesized glycosaminoglycans (GAG) during the 8 day culture period was too low (less than 0.8%) to influence the very rapid breakdown of the matrix under catabolin stimulation. Cartilage organ cultures recovered from inhibition of [35S]sulfate incorporation and from the catabolic stimulation after removal of catabolin. It is suggested that the two properties of the catabolin preparation demonstrated in this study may work synergistically both in causing and prolonging cartilage damage in vivo.

Enhanced production of prostaglandins and plasminogen activator during activation of human articular chondrocytes by products of mononuclear cells

We have examined the way in which products of cultured human blood mononuclear cells activate human articular chondrocytes. Conditioned medium from mononuclear cells enhanced the production of prostaglandin E by cultured human chondrocytes and also stimulated fibrinolytic activity in these cultures. These two effects may be interrelated, since the increased fibrinolysis in response to products of mononuclear cells was partially inhibited by indomethacin, an inhibitor of prostaglandin biosynthesis. The increased fibrinolysis is probably attributable to plasminogen activator, since it was strongly dependent on the presence of plasminogen. Increased amounts of PGE and chondroitin sulphate were also released from intact fragments of cartilage exposed to medium from cultured mononuclear cells. The time course and dose dependence of these effects were studied. The addition of exogenous arachidonic acid markedly enhanced production of PGE2. Ultrogel AcA54 was used to fractionate medium from cultured mononuclear cells and the chondrocyte-stimulating activity eluted with an apparent molecular weight between 12 000 and 25 000 daltons. Adherent and non-adherent mononuclear blood cells were also partially separated and conditioned medium from each was assayed for chondrocyte-stimulating factors. Both populations released factor(s) which increased the production of prostaglandin E by chondrocytes, but more activity came from the adherent mononuclear cells. The possible interrelationship between the chondrocyte activating factor studied here and others described in the literature is discussed.

The reversibility of osteoarthritis: a review

Osteoarthritis, usually considered a wear and tear, or age-associated disease, is generally regarded as inexorably progressive once it has become clinically symptomatic. Enormous advances in the understanding of the normal cell biology of hyaline cartilage, synovium, and bone have led some to suspect that the process can be arrested, or even reversed. Some of the lines of evidence, both experimental and clinical, supporting this proposition, are presented in this paper. I first noted an apparent partial reversal of severe osteoarthritis of the hips in an 85-year-old man, as assessed by reappearance of hip joint spaces, when examined radiologically. The favorable change persisted until his death at age 92. Since then a number of similar cases have been observed, other types of evidence of reversibility examined, and an extensive study of the literature made. Five main areas are described: Modern and ancient concepts of osteoarthritis; myths and misconceptions; theories of etiology and pathogenesis; advances in basic knowledge of tissue involved and lines of evidence of arrest or reversibility derived from these advances; and an outline of practical, clinical management based on the cell biology of hyaline cartilage, synovium, and bone, especially subchondral bone. Aspirin is emphasized as the drug of choice and a method of administration is described.

Correlation of the biosynthesis of prostaglandin and cyclic AMP in monolayer cultures of rabbit articular chondrocytes

We have utilized ionophores to test whether stimulation of chondrocyte prostaglandin biosynthesis is accompanied by an increase in cyclic nucleotide levels in these cells. Radioimmunoassay of prostaglandin E2, 6-oxo-prostaglandin F1 alpha (the stable metabolite of prostaglandin I2) and prostaglandin F2 alpha showed that synthesis of each was stimulated by the divalent-cation ionophore, A23187 after short-term incubation (1-7 min) in serum-free medium. No stimulation of thromboxane B2 was detected. Two monovalent ionophores, lasalocid and monensin failed to stimulate prostaglandin biosynthesis after short-term incubation. Ionophore A23187-stimulated prostaglandin biosynthesis was variably and partially inhibited by sodium meclofenamate, indomethacin and aspirin, but not by sodium salicylate. Ionophore A23187-stimulated prostaglandin biosynthesis was accompanied by a 7.5-fold increase in cyclic AMP levels after 15 min. Sodium meclofenamate, indomethacin and aspirin which inhibited prostaglandin E2 biosynthesis also reduced cyclic AMP levels. Exogenous prostaglandin E2 (1 microgram/ml) stimulated cyclic AMP biosynthesis, which was not inhibited by aspirin. These results indicated that prostaglandins can be considered as one of the local effectors controlling cyclic AMP production in articular cartilage.

Enhanced breakdown of bovine articular cartilage proteoglycans by conditioned synovial medium in vitro: a possible role for prostaglandins

Addition of conditioned medium derived from fragment cultures of synovium dissected from bovine knee joints (SM) to cultures of articular cartilage derived from the same animal resulted in a significant increase in breakdown of cartilage proteoglycans, measured as the release of [35S]sulphate from pre-labelled cartilage pieces. Culturing the synovium in the presence of indomethacin (indo-SM) at a concentration of 1.4 x 10(-5) mol/l reduced the breakdown-enhancing effect of the SM in some but not in all of the experiments. Addition of prostaglandins E1 or E2 (PGE1 or PGE2) (2.8 x 10(-7)-1.4 x 10(-5) mol/l) together with indo-SM resulted in a significant enhancement of breakdown of cartilage proteoglycans. PGA1, PGB1 and PGF2 alpha(less than 1.5 x 10(-5) mol/l) had, however, no effect in this system. Neither PGE1, PGE2 nor indomethacin at the concentrations mentioned above had any direct effect on breakdown of cartilage proteoglycans. No difference was found between the breakdown enhancing capacity of SM derived from synovium cultured in the presence of indo plus PGE1 or PGE2 (less than 4 x 10(-5) mol/l) and indo-SM. These findings are discussed in terms of cellular interactions.