Proteoglycan aggregate synthesis in normal and chronically hydrocortisone-suppressed rabbit articular cartilage

Treatment recommendations for chronic knee osteoarthritis

Primary osteoarthritis (OA) hinders an aging global population as one of the leading causes of years-lost-to-disability (YLD). OA in most patients is considered to be an overuse injury that results in degenerative inflammation of the joints with the associated formation of bony outgrowths. Due to the escalating nature of this chronic pain disease, treatment management for OA can initially begin with a more conservative approach. It can eventually lead to more invasive surgical procedures. At present, the standard of care remains initial conservative management with lifestyle changes, including weight loss with concurrent anti-inflammatory regimens. Injections are frequently used for the escalation of care, but a significant number of patients ultimately resort to total knee arthroplasty. This review will focus specifically on knee OA, providing a brief overview of risk factors and early management and in-depth exploration of the invasive interventions that can offer symptomatic relief and return of function.

The Effect of Intra-articular Corticosteroids on Articular Cartilage: A Systematic Review

Background:

Intra-articular (IA) corticosteroid therapy has been used for the treatment of inflammation and pain in the knee since the 1950s.

Purpose:

To review the current literature on the effects of IA corticosteroids on articular cartilage.

Study Design:

Systematic review.

Methods:

A MEDLINE and SCOPUS database search was performed, and studies were selected for basic science and clinical trial research on corticosteroids with direct outcome measures of cartilage health. Preliminary searches yielded 1929 articles, and final analysis includes 40 studies.

Results:

Methylprednisolone, dexamethasone, hydrocortisone, betamethasone, prednisolone, and triamcinolone were reported to display dose-dependent deleterious effects on cartilage morphology, histology, and viability in both in vitro and in vivo models. The beneficial animal in vivo effects of methylprednisolone, hydrocortisone, and triamcinolone occurred at low doses (usually <2-3 mg/dose or 8-12 mg/cumulative total dose in vivo), at which increased cell growth and recovery from damage was observed; the single human clinical trial indicated a beneficial effect of triamcinolone. However, at higher doses (>3 mg/dose or 18-24 mg/cumulative total dose in vivo), corticosteroids were associated with significant gross cartilage damage and chondrocyte toxicity. Dose and time dependency of corticosteroid chondrotoxicity was supported in the in vitro results, however, without clear dose thresholds.

Conclusion:

Corticosteroids have a time- and dose-dependent effect on articular cartilage, with beneficial effects occurring at low doses and durations and detrimental effects at high doses and durations. Clinically, beneficial effects are supported for IA administration, but the lowest efficacious dose should be used.

Biochemical changes in articular cartilage after joint immobilization by casting or external fixation

Knees of mature dogs were immobilized for 6 weeks by long-leg casts allowing 8 degrees-15 degrees of motion, a model studied by others, or with external fixators, a new, more severe model that kept the joints rigid. Some animals were allowed to recover for 1 week after the immobilization period. Articular cartilage was examined histologically and biochemically. After 6 weeks of immobilization, water increased 7% in both casted and fixator-immobilized joints compared with normal knee cartilage, while hexuronic acid was 23 and 28% lower, respectively. The limited motion permitted by the casts resulted in a smaller depression of proteoglycan synthesis and less proteoglycan loss during immobilization than occurred in the rigid external fixator group. The protective effect of limited motion was shown clearly during the recovery period: as measured by hexuronic acid content, cartilage from the casted joints had almost recovered within 1 week, whereas the external fixator group experienced little or no recovery during the week after treatment. In contrast to previous studies by others with casted joints, both newly synthesized [35S]sulfate-labeled and accumulated unlabeled proteoglycans from both casted and fixator-immobilized cartilages were able to form complexes with exogenous hyaluronic acid to the same extent as those from control cartilage. Thus, in immobilized cartilage, failure of the newly synthesized proteoglycan to bind to hyaluronate is not a mechanism of accelerated proteoglycan loss. The accelerated proteoglycan turnover appears to be caused by a combination of decreased synthesis and increased proteolysis of the secreted proteoglycans.(ABSTRACT TRUNCATED AT 250 WORDS)

Use of synovial fluid markers of cartilage synthesis and turnover to study effects of repeated intra-articular administration of methylprednisolone acetate on articular cartilage in vivo

In vivo the effects of intra-articular (IA) corticosteroids on articular cartilage remain controversial. This study was designed to examine this issue using synovial fluid (SF) markers of cartilage metabolism. Paired radiocarpal joints, without clinical or radiographic signs of joint disease, were studied in 10 adult horses. Aseptic arthrocentesis was performed weekly for 13 weeks. IA injections of methylprednisolone acetate (MPA) into the treatment joint and the vehicle into the control joint were performed at weeks 3, 5 and 7. We used radioimmunoassays on SF samples which measure a keratan sulfate epitope (KS) and the 846 epitope on cartilage aggrecan (PG) and the C-propeptide (CPII) of cartilage type II procollagen which is released following synthesis of this molecule. Gel chromatography was performed on selected SF samples to evaluate the sizes of SF PG molecules. The total joint KS and the 846 epitopes were both present on a heterogeneous population of mainly molecules which, from chromotographic analysis, appeared to be mainly fragments of the articular cartilage aggrecan. They were significantly elevated in MPA joints whereas CPII was significantly reduced compared to the control during the treatment period. These results indicate that the repeated use of IA MPA leads to a potentially harmful inhibition of procollagen II synthesis and an increased release of degradation products of the PG aggrecan from articular cartilage.

The pathobiology of osteoarthritis and the rationale for the use of pentosan polysulfate for its treatment

OBJECTIVES

Structure-modifying osteoarthritis (OA) drugs (SMOADs) may be defined as agents that reverse, retard, or stabilize the underlying pathology of OA, thereby providing symptomatic relief in the long-term. The objective of this review was to evaluate the literature on sodium pentosan polysulfate (NaPPS) and calcium pentosan polysulfate (CaPPS), with respect to the pathobiology of OA to ascertain whether these agents should be classified as SMOADs.

METHODS

Published studies on NaPPS and CaPPS were selected on the basis of their relevance to the known pathobiology of OA, which also was reviewed.

RESULTS

Both NaPPS and CaPPS exhibit a wide range of pharmacological activities. Of significance was the ability of these agents to support chondrocyte anabolic activities and attenuate catabolic events responsible for loss of components of the cartilage extracellular matrix in OA joints. Although some of the anti-catabolic activities may be mediated through direct enzyme inhibition, NaPPS and CaPPS also have been shown to enter chondrocytes and bind to promoter proteins and alter gene expression of matrix metalloproteinases and possibly other mediators. In rat models of arthritis, NaPPS and CaPPS reduced joint swelling and inflammatory mediator levels in pouch fluids. Moreover, synoviocyte biosynthesis of high-molecular-weight hyaluronan, which is diminished in OA, was normalized when these cells were incubated with NaPPS and CaPPS or after intraarticular injection of NaPPS into arthritic joints. In rabbit, canine, and ovine models of OA, NaPPS and CaPPS preserved cartilage integrity, proteoglycan synthesis, and reduced matrix metalloproteinase activity. NaPPS and CaPPS stimulated the release of tissue plasminogen activator (t-PA), superoxide dismutase, and lipases from vascular endothelium while concomitantly decreasing plasma levels of the endogenous plasminogen activator inhibitor PAI-1. The net thrombolytic and lipolytic effects exhibited by NaPPS and CaPPS may serve to improve blood flow through subchondral capillaries of OA joints and improve bone cell nutrition. In geriatric OA dogs, NaPPS and CaPPS reduced symptoms, as well as normalized their thrombolytic status, threshold for platelet activation, and plasma triglyceride levels. These hematologic parameters were shown to be abnormal in OA animals before drug treatment. Similar outcomes were observed in OA patients when CaPPS or NaPPS were given orally or parenterally in both open and double-blind trials.

CONCLUSIONS

The data presented in this review support the contention that NaPPS and CaPPS should be classified as SMOADs. However, additional long-term clinical studies employing methods of assessing joint structural changes will be needed to confirm this view.

Chondrocytes in culture produce a mechanically functional tissue

A mechanically testable tissue was grown in vitro from rabbit chondrocytes that were initially plated at high density (approximately 80,000 cells/cm2). The DNA, collagen, and proteoglycan content, as well as the tissue thickness, tensile stiffness, and synthesis rates, were measured at 4, 6, and 8 weeks. The biochemical properties were similar to those for immature cartilage, with predominantly type-II collagen produced; this indicated that the cells retained their chondrocytic phenotype. The tissue formed a coherent mechanical layer with testable tensile stiffness as early as 4 weeks. The tensile elastic modulus reached 1.3 MPa at 8 weeks, which is in the range of values for native cartilage from the midzone. Collagen density was approximately 24 mg/ml at 8 weeks, which is about one-half the value for native cartilage, and the collagen fibril diameters were smaller. Chondrocytes in culture responded to culture conditions and were stimulated by cytokine interleukin-1beta. When culture conditions were varied to RPMI nutrient medium with lower fetal bovine serum and higher ascorbic acid concentrations, the thickness decreased and the modulus increased significantly. Interleukin-1beta, added to the 8-week culture for 2 weeks, caused a decrease of 60% in thickness, a decrease of 81% in proteoglycan content, and a decrease of 31% in collagen content; this is similar to the response of cartilage explants to interleukin-1beta. This cartilage analog may be useful as a model system to study structure-function relationships in cartilage or as cartilage-replacement tissue.

Antioxidant effects of hyaluronan and its alpha-methyl-prednisolone derivative in chondrocyte and cartilage cultures

OBJECTIVE

To compare hyaluronan and its alpha-methyl prednisolone derivative (HYC-141) with respect to their potential to directly cause tissue damage and to protect tissues from attack by reactive oxygen species.

METHODS

Cartilage samples and chondrocytes were isolated from 15-day chick embryos and were exposed to enzyme-based and activated inflammatory cell-free radical generating systems in the presence of varying concentrations of alpha-methyl prednisolone, hyaluronan, and HYC-141. Tissue and cell vitality was measured by determining the incorporation of radioactive sulphate into newly synthesized glycosaminoglycans.

RESULTS

Only alpha-methyl prednisolone caused a significant decrease in biosynthetic activity. All the tested substances were capable, to some extent, of protecting tissues and cells from damage by reactive oxygen species; HYC-141 demonstrated the greatest protective effect.

CONCLUSION

These data suggest that HYC-141 may possess certain advantages over the individual component molecules in the local treatment of arthropathies.

Anti-rheumatic drugs and cartilage

In this chapter an attempt has been made to draw together the known biology of cartilage and some of the mechanisms thought to be responsible for its failure in arthritis. The picture is far from complete but we are now in a good position to use this information to help appraise the pros and cons of the wide range of drugs now available to treat articular disorders. For convenience, these drugs were classified as NSAIDs, corticosteroids and chondroprotective agents. The influence of each of these classes on the metabolism of cartilage was examined in the light of published laboratory and clinical studies. It has been clearly shown that not all NSAIDs are the same. While many of the older drugs provided no benefit to cartilage metabolism, and in some instances suppressed it, the more recently discovered molecules appear to be free of these undesirable effects. Tiaprofenic acid, diclofenac and piroxicam emerged as drugs with little or no harmful effects on cartilage metabolism when used at concentrations within the human therapeutic range. For all NSAIDs, their potential effects on cartilage must be weighed against their respective anti-inflammatory potency, half-life, and effects on the gastric mucosa and other tissues. Other chapters in this book have addressed these important problems. The long-acting corticosteroids, betamethasone and triamcinolone hexacetonide, also appear to offer some benefit in the management of OA; however, as in RA, their use should be restricted to short-term applications. In terms of cartilage metabolism the chondroprotective agents pentosan polysulphate, Arteparon and Rumalon have been the most extensively studied class of drugs. While the laboratory studies have provided convincing evidence of their chondroprotective efficacy, it has been difficult to prove this clinically. This dichotomy of opinion (laboratory versus clinical) stems largely from the inadequacy of the methodologies currently available for the objective clinical assessment of patient response to anti-rheumatic drug therapy. With the advent of nuclear magnetic resonance imaging techniques and monoclonal antibodies to detect specific proteoglycan breakdown fragments in synovial fluid and plasma, the prospects for a unified research approach for the evaluation of these agents may now be possible.

Decrease of proteoglycan granule number but increase of their size in articular cartilage of young rabbits after physical exercise and immobilization by splinting

The effects of physical exercise (running) and immobilization by splinting on the number and size of proteoglycan (PG) granules and the diameter of collagen fibers of the articular cartilage were studied with the transmission electron microscope with a stereological method. The lateral tibial condyles of 24 young rabbits were examined. The analysis was carried out in the superficial, middle, and deep zones of uncalcified articular cartilage and also in the pericellular, territorial, and interterritorial regions of each zone. PGs were demonstrated in situ by using en bloc staining with the cationic dye ruthenium red, which binds to negative groups of glycosaminoglycans. Results of the control group showed that there was a large pericellular number of PG granules, and the number of granules tended to increase through cartilage depth. The mean diameter of PG granules was highest in the superficial zone and decreased through cartilage depth. The collagen fibers were thicker in the interterritorial than in the territorial region and their diameters increased from superficial toward the deep zone of uncalcified cartilage. Results of the experimental groups showed that the number of ruthenium-red-positive PG granules decreased by 3-46% in all zones and regions after both physical exercise and joint immobilization. On the other hand, the diameter of PG granules increased by 4-42% in all zones and regions in all groups. Collagen fibers in the territorial region of the middle zone were thinner in the exercised and in the splinted knee, while thicker in the contralateral knee to the splinted limb, as compared with the controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibition of proteoglycan synthesis by hydrogen peroxide in cultured bovine articular cartilage

Oxygen-derived reactive species, generated enzymatically by the action of xanthine oxidase upon hypoxanthine, significantly inhibit proteoglycan synthesis by cultured bovine articular cartilage (Bates, E.J., Lowther, D.A. and Handley, C.J. (1984) Ann. Rheum. Dis. 43, 462-469). Here we extend these investigations and show, through the use of catalase and the specific iron chelator diethylenetriaminepentaacetic acid, that the active species involved is H2O2 and not the hydroxyl radical. Incubations of cartilage with H2O2 at concentrations of 1 X 10(-4) M and above are also inhibitory to proteoglycan synthesis. Subsequent recovery of the tissue is dependent upon the initial dose of xanthine oxidase or H2O2. Xanthine oxidase at 84 mU per incubation results in a prolonged inhibition of proteoglycan synthesis which is still apparent after 14 days in culture. Lower concentrations of xanthine oxidase (21-66 mU) are inhibitory to proteoglycan synthesis, but the tissue is able to synthesise proteoglycans at near normal rates after 3 days in culture. The inhibition of proteoglycan synthesis by 1 X 10(-4) M H2O2 is completely reversed after 5 days in culture, whereas 1 X 10(-3) M H2O2 results in a more prolonged inhibition. The synthesis of the proteoglycan core protein is inhibited, but the ability of the newly formed proteoglycans to aggregate with hyaluronic acid is unimpaired.

Microinjury to the synovial membrane may cause disaggregation of proteoglycans in rabbit knee joint articular cartilage

Proteoglycans (PGs) isolated from articular cartilage (AC) of mature rabbits subjected to two or more consecutive intraarticular (IA) injections of sterile saline 24 h apart showed an aggregation defect in the presence of excess hyaluronic acid (HA). Although the PG contents of experimental and control cartilages were indistinguishable, a higher proportion of PGs were extractable from the 3 X IA tissues, as assessed by uronic acid analysis. Proteoglycans from experimental and control cartilages when examined by Sepharose CL-2B chromatography showed two subunit populations, the smaller (KAV = 0.70) containing more ketatan sulphate than the larger (KAV = 0.31). Cultures of AC from IA joints released more 35SO4-labelled PGs into the media over 72 h than control tissues and consisted mainly of PG degradation products although 20% could aggregate in the presence of HA. Examination of PG aggregation 2 weeks after 2 X IA or 3 X IA injections showed that the defect initiated was still present; however, cartilage of immature rabbits was not affected by the 2 X IA procedure.

A comparison of the proteoglycans produced by rabbit articular chondrocytes in monolayer and spinner culture and those of bovine nasal cartilage

The structural and immunological properties of the glycosaminoglycans and the core proteins of bovine nasal cartilage proteoglycan and the proteoglycans produced by rabbit articular chondrocytes in spinner and monolayer culture were compared. Culture medium with 35SO4- or 3H-serine-labeled proteoglycan was mixed with bovine nasal cartilage 4M guanidine-HCl extract and digested with trypsin. The proteoglycan fragments were then isolated by DEAE-cellulose chromatography and fractionated by dissociative CsCl density gradient centrifugation. Approximately 90% of the 35SO4 incorporated into proteoglycan by the cultured chondrocytes was in chondroitin sulfates and about 5% in keratan sulfate. Although there was considerable overlap in the Sepharose 4B elution of the tryptic proteoglycan fragments of highest buoyant density, some monolayer-produced proteoglycan fragments eluted earlier and some spinner-produced proteoglycan fragments eluted later than the proteoglycan fragments from bovine nasal cartilage. These differences in apparent fragment size could relate to differences in glycosaminoglycan chain length, since the glycosaminoglycans released by treatment with alkali from monolayer-produced proteoglycan in part eluted from Sepharose 4B earlier and those from spinner-produced proteoglycan in part eluted later than the chondroitin sulfate chains released from bovine cartilage proteoglycan. After digestion with chondroitinase ABC, 3H-serine-labeled high density tryptic proteoglycan fragments from monolayer and spinner culture yielded Sepharose 6B elution profiles which were similar to each other but did not coincide with the peaks of carbazole reactivity found with similarly treated fragments of bovine nasal cartilage proteoglycan. Cross-reactivity was demonstrated by radioimmunoautography between bovine cartilage and rabbit chondrocyte proteoglycan fragments restricted to gradient fractions of low buoyant density, but immunological cross-reactivity was not found for the antigens associated with the keratan sulfate-rich and chondroitin sulfate-bearing tryptic fragments of bovine nasal cartilage proteoglycan. These studies indicate that the proteoglycan core proteins produced by rabbit articular chondrocytes in monolayer and spinner culture are, in part, different from the core protein of bovine nasal cartilage proteoglycan and that the three proteoglycans differ in the length of some of their chondroitin sulfate chains.

Proteoglycan alterations in rabbit knee articular cartilage following physical exercise and immobilization

Rabbit knee articular cartilage was studied after the joint was submitted to immobilization, running or increased weight bearing for 24-27 days. Immobilization with a plastic splint reduced the fraction of proteoglycans not extractable with 4 M guanidinium chloride (GdnHCl). In the immobilized joints the chondroitin sulfate content was elevated as calculated from the galactosamine/glucosamine ratio. The ability of these proteoglycans to reform aggregates with endogenous hyaluronic acid in Sepharose CL-2B chromatography was reduced. Increased exercise was associated with an elevation of proteoglycans extractable with 4 M GdnHCl. The increased weight bearing occurring in the contralateral knee elevated the content of proteoglycans not extractable with 4 M GdnHCl. Other effects of weight bearing included increased glucosamine concentration, suggesting accumulation of keratan sulfate-rich proteoglycans, and an elevated hydroxyproline concentration.