The role of crystals in articular tissue degeneration

Osteoarthritis gene therapy

Osteoarthritis (OA) is the Western world's leading cause of disability. It is incurable, costly and responds poorly to treatment. This review discusses strategies for treating OA by gene therapy. As OA affects a limited number of weight-bearing joints and has no major extra-articular manifestations, it is well suited to local, intra-articular gene therapy. Possible intra-articular sites of gene transfer include the synovium and the cartilage. Most experimental progress has been made with gene transfer to synovium, a tissue amenable to genetic modification by a variety of vectors, using both in vivo and ex vivo protocols. The focus so far has been upon the transfer of genes whose products enhance synthesis of the cartilaginous matrix, or inhibit its breakdown, although there is certainly room for alternative targets. It is possible to build a convincing case implicating interleukin-1 (IL-1) as a key mediator of cartilage loss in OA, and the therapeutic effects of IL-1 receptor anatagonist (IL-1Ra) gene transfer have been confirmed in three different experimental models of OA. As transfer of IL-1Ra cDNA to human arthritic joints has already been accomplished safely, we argue that clinical studies of intra-articular IL-1Ra gene transfer in OA are indicated and should be funded. Of the available vector systems, recombinant adeno-associated virus may provide the best combination of safety with in vivo delivery using current technology.

Basic calcium phosphate crystals stimulate the endocytotic activity of cells—inhibition by anti-calcification agents

Pathological calcifications are associated with many medical conditions including diabetes, breast cancer, and crystals-associated osteoarthritis. The deposition of calcium-containing crystals on cells induces detrimental cellular effects and speeds up the progression of associated diseases. We carried out the present study to test the hypotheses that calcium-containing crystals may stimulate the influx of other molecules existing in the extracellular fluid disturbing normal molecular signaling and that anti-calcification agent will inhibit such endocytotic process. We found that basic calcium phosphate (BCP) crystals greatly stimulated the endocytotic activity of cells by rendering the cells more permeable and that the anti-calcification agent phosphocitrate and several others inhibited the crystals-mediated endocytosis. This is the first study reporting that the endocytotic activity of cells is affected by BCP crystals and that such endocytotic activity can be inhibited by anti-calcification agents. Since calcium-containing crystals are associated with many human diseases and in many circumstances are associated with apoptotic bodies, extracellular and matrix vesicles where DNA fragments, small peptides, and minerals are released into extracellular space, the findings reported here are important for our understanding of the complex biological effects and the potential pathological role of calcium-containing crystals in crystals-associated diseases, and for the development of disease modifying agents as well.

Inhibitors of articular calcium crystal formation

The coexistence of calcium phosphate and calcium pyrophosphate crystals in osteoarthritis is a well-described phenomenon. In addition to deposition in articular cartilage, the crystals induce numerous changes to biochemical parameters in the surrounding fluid. This survey discusses crystal-inhibitor interactions whereby defining the molecular structure of crystals assists in an optimal inhibitor design. Crystal growth studies in the presence and absence of a test compound can generate data on crystal face changes. Together with knowledge of the inhibitors' molecular structure, computer modeling can portray crystal-inhibitor interactions. Few inhibitors have been tested in both in vitro and in vivo phases. One exception is phosphocitrate. This compound inhibits both the development of specific calcium crystals and crystal-induced intracellular changes. Animal studies confirm a strong action on pathologic calcification. The recently described phosphocitrate in a mixed calcium and sodium salt, yet to be tested in a guinea pig osteoarthritis model, appears to be an even more powerful inhibitor.

Molecular mechanism of the induction of metalloproteinases 1 and 3 in human fibroblasts by basic calcium phosphate crystals. Role of calcium-dependent protein kinase C alpha

Synovial fluid basic calcium phosphate (BCP) crystals are common in osteoarthritis and are often associated with destructive arthropathies involving cartilage degeneration. These crystals are mitogenic and induce oncogene expression and matrix metalloproteinase (MMP) synthesis and secretion in human fibroblasts. To date, BCP crystal-elicited signal transduction pathways have not been completely studied. Because protein kinase C (PKC) is known to play an important role in signal transduction, we investigated the participation of this pathway in the BCP crystal induction of MMP-1 and MMP-3 mRNA and protein expressions in human fibroblasts. Using reverse transcription/polymerase chain reaction (RT-PCR) and Northern and Western blotting techniques, we show here that BCP crystal stimulation of MMP-1 and MMP-3 mRNA and protein expressions in human fibroblasts is dependent upon the calcium-dependent PKC signal transduction pathway and that the PKC alpha isozyme is specifically involved in the pathway. We have previously shown that BCP crystal induction of MMP-1 and MMP-3 is also dependent on the p44/42 mitogen-activated protein kinase (p44/42 MAPK) signal transduction pathway. We now show that these two pathways operate independently and seem to complement each other. This leads to our hypothesis that the two pathways initially function independently, ultimately leading to an increase in mitogenesis and MMP synthesis, and may converge downstream of PKC and p44/42 MAPK to mediate BCP crystal-induced cellular responses.

Basic calcium phosphate crystals up-regulate metalloproteinases but down-regulate tissue inhibitor of metalloproteinase-1 and -2 in human fibroblasts

OBJECTIVE

To examine the effect of basic calcium phosphate (BCP) crystals on expression of tissue inhibitors of metalloproteinases (TIMP)-1 and -2 in human fibroblasts.

METHOD

Using a semi-quantitative reverse transcription-polymerase chain reaction method and phosphocitrate (PC), a specific inhibitor of the biological effects of BCP crystals, we examined the effects of BCP on the steady state transcript levels of metalloproteinase (MMP)-1, -3, -9 and -13 and TIMP-1 and -2 in human fibroblasts. DNA primers against elongation factor were used as internal controls. RNAs isolated from human fibroblasts treated with BCP crystals (50 microg/ml) in the presence or absence of PC (10(-3) M) were used as templates, and RNA from untreated control cultures and cultures treated with Interleukin-1-beta (IL-1beta) were used as negative and positive controls, respectively.

RESULTS

We observed increases in MMP-1, -3, -9 and -13 transcripts by BCP crystals. BCP crystal down-regulated TIMP-1 and -2 over untreated controls. Western blot analysis confirmed that BCP crystals down-regulate the synthesis of TIMP-1 and -2. While IL-1beta up-regulated MMP-1, -3, -9 and -13, it had no significant effect on expression of either TIMP. In all cases, PC specifically reversed the differential regulation of MMPs and TIMPs by BCP crystals but had no effect on IL-1beta induction of MMP expression.

CONCLUSION

The ability of BCP to induce the synthesis of degradative MMPs while down-regulating the synthesis of the naturally occurring counterpart TIMPs may explain the changes consistent with a role of BCP crystal in the pathogenesis of degenerative changes in osteoarthritis. The ability of PC to reverse both degradative effects of BCP crystal suggests that PC can be a potential therapeutic agent for BCP crystal deposition diseases.