Reduction of the concentration and total amount of keratan sulphate in synovial fluid from patients with osteoarthritis during treatment with piroxicam

Synovial fluid markers in osteoarthritis

Exploration of the mechanisms responsible for breakdown and repair of articular cartilage in osteoarthritis has promoted interest in the potential use of cartilage-derived molecules as markers of cartilage metabolism in this disease. Many of the macromolecules detectable in synovial fluid have been evaluated as possible surrogate markers of the severity or activity of disease processes. Measurements of the synovial fluid concentration of any marker without due consideration of the fate of the molecule in the joint cavity are likely to be misleading and insufficient to cement a relationship between marker concentration and the severity of articular pathology.

Current pharmacological treatment of osteoarthritis

In this overview, the currently available symptomatic treatments of osteoarthritis from the published literature are evaluated. Paracetamol attracts growing interest as a less toxic yet potent alternative to NSAIDs. These latter agents are, however, used more widely than paracetamol, although adverse reactions associated with their use are of increasing concern among both patients and physicians. New NSAIDs are still under development. While there is not much evidence of important differences between NSAIDs in overall efficacy, they do vary with regard to toxicity. The cytoprotective effect of misoprostol in at-risk patients on NSAIDs is established but the cost-effectiveness is unclear. Furthermore, percutaneous administration of NSAIDs, capsaicin, and other substances may have some merit. Opioids, such as dextropropoxyphene, are used in combination with paracetamol in patients intolerant to NSAIDs or when pain is not controlled with NSAIDs. Locally administered glucocorticoids may have a disease-modifying effect and are of symptomatic use in certain situations. The role, if any, of hyaluronan therapy remains to be established. Although this agent appears to have a good safety profile, it is expensive. Chondroprotection is an interesting field for future research, although there is no good evidence supporting its existence in clinical medicine as practised now.

Even low-grade synovitis significantly accelerates the clearance of protein from the canine knee. Implications for measurement of synovial fluid "markers" of osteoarthritis

OBJECTIVE

In recent studies, the synovial fluid concentration of molecules derived from the extracellular matrix of articular cartilage has been used to deduce the magnitude of cartilage destruction or repair in osteoarthritic (OA) joints. Because low-grade synovitis is often present in such joints, we assessed the effect of synovial inflammation on the clearance of a prototypical protein, albumin, from synovial fluid.

METHODS

131I-labeled albumin (RISA) was injected into 1 (control) knee of each of 14 dogs. The concentration of RISA in synovial fluid aspirated 7 hours after the injection and serial measurements of surface radioactivity were used to calculate the volume of distribution (Vd) and clearance of RISA. One week later, synovitis was induced in the contralateral knee by intraarticular injection of various quantities of calcium pyrophosphate dihydrate (CPPD) crystals, after which RISA was injected into that joint and these measurements were repeated.

RESULTS

Intraarticular injection of 500 micrograms of CPPD crystals produced intense synovitis, with a mean synovial fluid white blood cell (WBC) count of 43,200 cells/mm3, and values for RISA Vd and RISA clearance (36.5 ml and 33.7 microliters/minute) were much higher than those for saline-injected control knees (2.7 ml and 1.5 microliters/minute, respectively). Injection of 0.5 microgram of CPPD also produced marked synovitis and values for Vd and RISA clearance that were 2-3-fold greater than those in the contralateral knee. The low-grade synovitis produced by only 0.05 microgram of CPPD, which resulted in synovial fluid WBC counts as low as 1,000-2,000 cells/mm3, was accompanied by increases in the clearance and Vd of RISA to levels approximately 40% and approximately 80% higher, respectively, than those for the contralateral knee.

CONCLUSION

Even mild synovitis, as seen in OA, may significantly increase the clearance of a protein from the joint. Synovitis is a significant variable which must be considered in studies of putative chondroprotective drugs if conclusions about the effects of drugs on cartilage metabolism are to be drawn from changes in the synovial fluid concentration of a "marker" protein.

Leg lengthening and glycosaminoglycans in the rabbit knee

We investigated the effects of tibial lengthening by callotasis on glycosaminoglycan (GAG) metabolism of the knee articular cartilage in 30 rabbits. The distraction rate was 1 mm per day. On the right side, the daily distraction was in 2 steps, while on the left it was in 120 steps. The animals were divided into 3 subgroups based on length gain; 10, 20, and 30 percent, respectively. The knee joint fluid and medial tibial cartilage were examined by quantitative analysis of the GAG content and/or synthesis. The immunoreactivity for chondroitin sulfate in the cartilage was also examined by immunohistochemistry. For all length gains, the GAG concentration in the synovial fluid was higher on both sides than in controls, with no difference between sides. The GAG content and synthesis in the cartilage on the 2-step side decreased gradually with increasing length. On the 120-step side, the content did not differ from control values in any length gain, and the level of synthesis at 20 and 30 percent lengthening was higher than the control level. Our findings indicate that the alterations in GAG metabolism are attributable to increased mechanical stress on the articular cartilage, suggesting a moderate increase on the 120-step side compared to an excessive one on the 2-step side.

Articular cartilage and osteoarthrosis. The role of molecular markers to monitor breakdown, repair and disease

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ELISA for the core protein of the cartilage large aggregating proteoglycan, aggrecan: comparison with the concentrations of immunogenic keratan sulphate in synovial fluid, serum and urine

Immunological assays for fragments of the cartilage large aggregating proteoglycan, aggrecan, have been widely used to monitor cartilage turnover. These assays have commonly employed the monoclonal keratan sulphate antibody, 5D4. Keratan sulphate, however, is present in many tissues and 5D4 affinity is critically dependent on antigen structure. We have therefore raised and characterized a monoclonal antibody (1-F21) that reacts with the core protein of aggrecan without interference from the glycosaminoglycan side chains and, using this antibody, we have optimized a sensitive, competitive ELISA. The within-assay and between-assay coefficients of variation were 4.9-8.9% and 11.1-13.0%, respectively. The mean concentrations of core protein in synovial fluid, serum and urine were 76.4 micrograms/ml, 104.0 ng/ml and 81.0 ng/ml, respectively. In synovial fluids the concentrations were closely correlated with the concentrations of keratan sulphate as determined by 5D4 (r = 0.94), whereas in serum and urine there was no obvious correlation between the determinations. These findings show that measurement of both core protein and keratan sulphate results in a more precise description of aggrecan turnover.