The role of cyclic-3',5'-adenosine monophosphate in prostaglandin-mediated inhibition of basic calcium phosphate crystal-induced mitogenesis and collagenase induction in cultured human fibroblasts

Role of inflammation in the pathogenesis of osteoarthritis: latest findings and interpretations

Osteoarthritis (OA) has traditionally been classified as a noninflammatory arthritis; however, the dichotomy between inflammatory and degenerative arthritis is becoming less clear with the recognition of a plethora of ongoing immune processes within the OA joint and synovium. Synovitis is defined as inflammation of the synovial membrane and is characteristic of classical inflammatory arthritidies. Increasingly recognized is the presence of synovitis in a significant proportion of patients with primary OA, and based on this observation, further studies have gone on to implicate joint inflammation and synovitis in the pathogenesis of OA. However, clinical OA is not one disease but a final common pathway secondary to many predisposing factors, most notably age, joint trauma, altered biomechanics, and obesity. How such biochemical and mechanical processes contribute to the progressive joint failure characteristic of OA is tightly linked to the interplay of joint damage, the immune response to perceived damage, and the subsequent state of chronic inflammation resulting in propagation and progression toward the phenotype recognized as clinical OA. This review will discuss a wide range of evolving data leading to our current hypotheses regarding the role of immune activation and inflammation in OA onset and progression. Although OA can affect any joint, most commonly the knee, hip, spine, and hands, this review will focus primarily on OA of the knee as this is the joint most well characterized by epidemiologic, imaging, and translational studies investigating the association of inflammation with OA.

Carbonated apatite-induced arthropathy: a consideration in cases of polyarthritis

BACKGROUND

A 79-year-old woman was referred for evaluation of her painful and swollen joints. She had a medical history of congestive heart failure, renal insufficiency and peptic ulcer disease. For the past 3 years she had experienced recurrent bouts of debilitating arthritis, lasting approximately 3-4 weeks at a time. The symptoms were most severe in the hands and knees, where the joints were warm, swollen and tender. During each flare-up, the patient was housebound and required therapeutic dosing of nonsteroidal anti-inflammatory drugs and codeine to control joint pain.

INVESTIGATIONS

Physical examination, fine-detailed radiographs of the hands, standing radiographs of the knees, arthrocentesis including cell count and gram stain, compensated polarized light microscopy, alizarin-red staining, X-ray diffraction, scanning and transmission electron microscopy with energy dispersive spectrometry, electron microprobe analysis with energy dispersive spectrometry, Fourier transform infrared spectroscopy, and atomic force microscopy.

DIAGNOSIS

Carbonated-substituted apatite arthropathy.

MANAGEMENT

Both knees were aspirated and large volumes of a straw-colored synovial fluid was removed. The knees were injected with corticosteroid, resulting in excellent symptomatic response.

Hydroxyapatite deposition disease of the joint

Basic calcium phosphate (BCP) crystals include partially carbonate-substituted hydroxyapatite, octacalcium phosphate, and tricalcium phosphate. They may form deposits, which are frequently asymptomatic but may give rise to a number of clinical syndromes including calcific periarthritis, Milwaukee shoulder syndrome, and osteoarthritis, in and around joints. Recent data suggest that magnesium whitlockite, another form of BCP, may play a pathologic role in arthritis. Data from the past year have provided further understanding of the mechanisms by which BCP crystals induce inflammation and degeneration. There remains no specific treatment to modify the effects of BCP crystals. Although potential drugs are being identified as the complex pathophysiology of BCP crystals is unraveled, much work remains to be done in order to translate research advances to date into tangible clinical benefits.

Phosphocitrate as a potential therapeutic strategy for crystal deposition disease

The deposition of basic calcium phosphate and calcium pyrophosphate dihydrate crystals in articular tissues is probably an under-recognized event. Clinical observations indicate that exaggerated and uniquely distributed cartilage degeneration is associated with these deposits. Measurements of putative markers of cartilage breakdown suggest that these crystals magnify the degenerative process. In vitro studies reveal two potential mechanisms by which crystals cause degeneration. These involve the stimulation of mitogenesis in synovial fibroblasts and the secretion of metalloproteinases by cells that phagocytose these crystals. Approaches that may ameliorate the degenerative process may ensue from new information about how crystals form and how they exert their biologic effects.

Transduction mechanisms of porcine chondrocyte inorganic pyrophosphate elaboration

OBJECTIVE

To investigate cellular signaling mechanisms that influence chondrocyte production of inorganic pyrophosphate (PPi), which promotes calcium pyrophosphate dihydrate (CPPD) crystal deposition.

METHODS

Articular chondrocyte and cartilage cultures were stimulated with protein kinase C (PKC) activator and adenyl cyclase activator. Generation of extracellular PPi was measured.

RESULTS

Adenyl cyclase activation resulted in diminished pyrophosphate generation. PKC activation stimulated pyrophosphate elaboration.

CONCLUSION

Two signaling pathways, cAMP and PKC, modulate generation of extracellular pyrophosphate by cartilage and chondrocytes. They are novel targets for potentially diminishing extracellular pyrophosphate elaboration that leads to CPPD crystal deposition.

Posttranscriptional regulation of collagenase-1 gene expression in synoviocytes by adenosine receptor stimulation

OBJECTIVE

To characterize the transcriptional and posttranscriptional regulation of collagenase-1 by adenosine receptor stimulation in interleukin-1 (IL-1)-stimulated fibroblast-like synoviocytes (FLS).

METHODS

FLS were stimulated with IL-1 and either the nonselective adenosine agonist 5'-N-ethylcarboxamidoadenosine (NECA) or the adenylate cyclase activator forskolin. Electrophoretic mobility shift assays were performed to determine AP-1 and cAMP-responsive element binding protein (CREB) activation. Transcriptional activation was determined by transfecting HS68 dermal fibroblasts with a collagenase-chloramphenicol acetyltransferase construct. Finally, collagenase messenger RNA (mRNA) half-life was determined by activating cells in the presence of IL-1, IL-1 + NECA, or IL-1 + forskolin and culturing cells in the presence of actinomycin D.

RESULTS

NECA and forskolin had no effect on AP-1 activation, c-jun or c-fos gene expression, or CREB phosphorylation. IL-1 markedly increased collagenase promoter activity, and neither NECA nor forskolin blocked this action. Studies of mRNA half-life showed that both NECA and forskolin decreased the half-life of collagenase mRNA in IL-1-stimulated FLS and HS68 cells.

CONCLUSION

The findings of this study demonstrate that NECA and forskolin decrease collagenase gene expression in FLS and dermal fibroblasts due to enhanced mRNA degradation.

Inhibition of synoviocyte collagenase gene expression by adenosine receptor stimulation

OBJECTIVE

To characterize the regulation of matrix metalloproteinases (MMPs) by adenosine.

METHODS

Cultured fibroblast-like synoviocytes (FLS) were stimulated with interleukin-1 (IL-1) in the presence or absence of adenosine receptor agonists. Immunoreactive MMPs were measured using specific enzyme-linked immunosorbent assays, and gene expression was assessed by Northern blot analysis.

RESULTS

The nonselective adenosine receptor agonist 5'-N-ethylcarboxamidoadenosine (NECA) decreased collagenase production by IL-1-stimulated synoviocytes from 196 +/- 28 ng/ml (mean +/- SEM) to 66 +/- 9 ng/ml (P < 0.001). There was minimal effect on stromelysin production (decrease from 107 +/- 16 ng/ml to 97 +/- 15 ng/ml). Selective adenosine receptor agonists implicated the A2b adenosine receptor in this activity, and reverse transcriptase-polymerase chain reaction studies confirmed that FLS express this receptor. Northern blot analysis demonstrated that the mechanism of action was pre-translational since NECA decreased collagenase, but not stromelysin or tissue inhibitor of metalloproteinases 1 (TIMP-1), messenger RNA levels. Cyclic AMP levels were increased by NECA, and a direct adenylate cyclase activator (forskolin) also suppressed collagenase gene expression. These data suggest that cAMP mediates the inhibitory effect of NECA on collagenase production.

CONCLUSION

Stimulation of the A2b receptor on FLS decreases collagenase gene expression, with little or no effect on stromelysin and TIMP-1. The combination of antiinflammatory and MMP-regulating properties of adenosine or adenosine-regulating agents suggest that treatment based on this approach might be useful in rheumatoid arthritis.

Specific inhibition of basic calcium phosphate and calcium pyrophosphate crystal-induction of metalloproteinase synthesis by phosphocitrate

Calcium pyrophosphate dihydrate (CPPD) and basic calcium phosphate (BCP) crystal deposition diseases are a group of heterogeneous arthritides which are a significant source of morbidity in the elderly. Both crystals induced mitogenesis and metalloproteinase (MP) synthesis and secretion by fibroblasts and chondrocytes which may promote degradation of intra-articular tissue. We have previously shown that phosphocitrate (PC), an inhibitor of hydroxyapatite crystallization, specifically blocks BCP crystal-induced mitogenesis in 3T3 cells. This led us to examine the effect of PC on BCP and CPPD crystal induction of MP synthesis in human fibroblasts. PC (10(-3) to 10(-4) M) specifically inhibited the crystal-induced collagenase and stromelysin mRNA accumulation while having no effect on epidermal growth factor-induced or basal levels of mRNA for both enzymes. Western blots (collagenase) of conditioned media confirmed that PC blocked crystal-induced proteinase secretion as well. Moreover, PC (10(-3) M) also blocked the crystal induction of c-fos and c-jun. Since FOS and JUN proteins form a transacting activator (AP-1) for expression of collagenase and stromelysin genes, PC may block the synthesis of both enzymes by inhibiting the transcription of c-fos and c-jun.