Identification of tissue inhibitor of metalloproteinase-2 (TIMP-2)-progelatinase complex as the third metalloproteinase inhibitor peak in rheumatoid synovial fluid

Tissue inhibitor of metalloproteinases-4 (TIMP-4) gene expression is increased in human osteoarthritic femoral head cartilage

Tissue inhibitor of metalloproteinases-4 (TIMP-4), the newest member of the TIMP family, blocks the activities of several matrix metalloproteinases (MMPs) implicated in the arthritic cartilage erosion. By utilizing semi-quantitative RT-PCR, immunoblotting, and immunohistochemistry, we investigated whether the TIMP-4 gene is expressed in human non-arthritic and osteoarthritic (OA) cartilage. Directly analyzed femoral head cartilage showed TIMP-4 RNA expression in 2 of 9 non-arthritic and 12 of 14 OA patients. Femoral head cartilage from 6 of 9 OA patients had elevated TIMP-4 protein compared to the low-level expression in 3 of 8 non-arthritic controls. In most patients, there was correlation between TIMP-4 RNA and protein expression. TIMP-4 protein was also detected immunohistochemically in the upper zone of OA cartilage. The widespread TIMP-4 RNA and protein expression and augmentation in femoral OA cartilage suggests its important role in joint tissue remodeling and pathogenesis of OA. Increased TIMP levels in arthritic cartilage may not be a sufficiently effective defense against cartilage resorption by excessive multiple MMPs and aggrecanases.

Relationship of matrix metalloproteinases and their inhibitors to cartilage proteoglycan and collagen turnover: analyses of synovial fluid from patients with osteoarthritis

OBJECTIVE

To determine the relationship between matrix metalloproteinases (MMPs), their inhibitors, and the turnover of matrix molecules in articular cartilage from patients with osteoarthritis (OA).

METHODS

Synovial fluid samples were collected from the knees of 54 patients with OA. Radiographic evaluations and magnetic resonance imaging were performed on the knees of 34 OA patients to classify the stage of the disease. Biochemical analyses and immunoassays were used to measure the concentrations of MMP-1, MMP-3, tissue inhibitor of metalloproteinases 1 (TIMP-1), TIMP-2, the disaccharide of hyaluronic acid, the proteoglycan glycosaminoglycan disaccharides of chondroitin 4-sulfate (delta di-CS4) and chondroitin 6-sulfate (delta di-CS6), the 846 epitope on chondroitin sulfate of cartilage proteoglycan aggrecan (putative biosynthetic marker), the keratan sulfate (KS) epitope of aggrecan (putative degradation marker), and the C-propeptide of cartilage type II procollagen (CPII) (biosynthetic marker).

RESULTS

The concentration of TIMP-1 was directly correlated with the levels of MMP-1 and MMP-3 (both were also correlated with each other), confirming earlier results. There was an inverse correlation between the delta di-CS6:delta di-CS4 ratio and the concentration of MMP-3. The level of delta di-CS6 was correlated with that of the KS epitope, and to a lesser degree, with that of the 846 epitope (the latter was also correlated with the level of delta di-CS4). The concentration of TIMP-1 correlated with that of the 846 epitope, whereas TIMP-2 levels correlated with those of CPII. There were significantly lower concentrations of delta di-CS6, delta di-CS4, the 846 epitope, and CPII in synovial fluid from patients with late-stage OA.

CONCLUSION

These observations suggest a link between proteolysis and inhibitor concentrations in OA cartilage. Production of TIMPs appears to be individually linked to the synthesis of specific cartilage molecules. The reduction in the amount of cartilage-matrix structural components suggests that there is a measurable loss of cartilage in the late stages of the disease, as suggested previously. The resultant composition of the cartilage suggests that the loss may primarily involve "resident" molecules originally present in healthy cartilage.

Tissue inhibitor of metalloproteinase-2 (TIMP-2) mRNA is constitutively expressed in bovine, human normal, and osteoarthritic articular chondrocytes

Tissue inhibitors of metalloproteinases (TIMPs) inhibit the extracellular matrix (ECM) metalloproteinases (MMPs). To determine the source of TIMPs in synovial fluids of patients with osteoarthritis (OA), the ability of chondrocytes to express TIMP-2 and its regulation by agents found in inflammed joints was investigated. The constitutive TIMP-2 mRNA expression was demonstrated in chondrocytes from normal bovine, human OA and normal cartilage. The cross-hybridization of human and bovine TIMP-2 suggested its evolutionary conservation. Serum, IL-1, IL-6 and TGC-beta were unable to augment considerably the basal expression of TIMP-2 mRNA. TIMP-1 RNA expression in chondrocytes from human OA cartilage was elevated compared to non-OA chondrocytes, while TIMP-2 mRNA levels were similar in both. IL-1 beta, IL-6 and TGF-beta did not affect TIMP-2 expression but TGF-beta induced TIMP-1 mRNA in human OA chondrocytes. TIMP-2 and TIMP-1 are therefore differentially regulated in chondrocytes and the basal TIMP-2 levels may be needed for the cartilage ECM integrity.

Development of an enzyme-linked immunosorbent assay to measure total TIMP-1 (free TIMP-1 and TIMP-1 in combination with matrix-metalloproteinases) and measurement of TIMP 1 and CRP in serum

A panel of six monoclonal antibodies (MAbs) was raised against purified human fibroblast tissue inhibitor of metalloproteinase-1 (TIMP-1) and characterised. All possible antibody pairs were tested for their suitability as capture and revealing antibodies in a two-site enzyme-linked immunosorbent assay (ELISA) to measure total TIMP-1 (both free TIMP-1 and TIMP-1 together with matrix metalloproteinases (MMPs)). Using the best combination of MAbs the assay was optimised. The sensitivity of detection of the assay was 1.4 ng/ml, and inter- and intra-assay coefficients of variation were between 10.4-13.7% and 8.8-9.7%, respectively. Dilution series of human cerebrospinal and synovial fluids, plasma and sera paralleled those of the TIMP-1 standard curve indicating that the immunoreactivity detected in these samples was authentic TIMP-1. TIMP-2 shows no detectable cross reactivity in this assay confirming that this ELISA is specific for TIMP-1. The levels of total TIMP-1 and collagenase were measured in conditioned medium from A2058 human melanoma cells cultured in the absence or presence of human recombinant interleukin-1 alpha (hrIL-1 alpha). Total TIMP-1 was also measured in serum samples with known C-reactive protein (CRP) (n = 100) and alpha 1 antichymotrypsin (ACT) (n = 52) concentrations; no correlation was found between TIMP-1 levels and either of these acute phase reactants although the levels of TIMP-1 were raised when compared to normal sera. This ELISA provides a rapid and convenient procedure for the quantitation of total TIMP-1 in human biological fluids and supernatants from cultured cell lines.

Using inhibitors of metalloproteinases to treat arthritis. Easier said than done?

Collagenase and stromelysin have a premier role in the irreversible degradation of the extracellular matrix seen in rheumatic disease. It is therefore no surprise that considerable attention has been devoted to developing strategies to reduce their levels in diseased joints. Most efforts have focused on inhibiting the activity of the enzymes, either by increasing the concentration of natural inhibitors such as the TIMPs or by introducing into the joint synthetic compounds that will complex with the enzymes and inactivate them. There have also been studies directed at inhibiting enzyme synthesis. These preclinical studies have been carried out in cell-free and/or cell culture systems and in animal models. Despite promising preclinical data, there have been no stunning successes in the clinical arena. The reasons for this are several. In part, they are rooted in the technical difficulties associated with designing inhibitors of enzyme activity that are of high affinity, and then delivering them to the affected joints while still maintaining specificity and efficacy. The complicated structure of the proteoglycan and collagen that comprise articular cartilage, along with the biochemistry of inflamed synovial tissue, only compound the difficulties. In addition to these technical problems, the lack of fundamental knowledge about the biochemistry and molecular biology of the enzymes has handicapped our efforts. We are just resolving the crystal structure of the metalloproteinases (108) and beginning to understand the mechanisms controlling gene expression (67, 68, 70-72). These advances represent significant achievements in metalloproteinase enzymology and biology and should form the scientific basis for a new generation of effective therapies. For example, knowledge of the active site as derived from the crystal structure of the enzymes may facilitate the development of tightly-binding specific inhibitors which function well in vivo. Similarly, based on our current understanding of mechanisms controlling the regulation of both the TIMP genes and the MMP genes, we are beginning to elucidate how to turn these genes on or off, and hopefully, to modulate disease accordingly. Indeed, although some studies are still at a preclinical level, these possible approaches are becoming a reality (109). Arthritic diseases in general, and rheumatoid arthritis in particular, represent a complicated multifaceted set of clinical disorders. The clinical symptoms and pathologic features result from a cascade of biologic pathways that involve acute and chronic inflammation, the immune response, and metalloproteinase biochemistry.(ABSTRACT TRUNCATED AT 400 WORDS)