Interleukin-1 inhibits keratan sulfate production by rabbit chondrocytes: possible role of prostaglandin E2

Celecoxib inhibits nitric oxide production in chondrocytes of ligament-damaged osteoarthritic rat joints

The purpose of this study was to demonstrate the direct effects of celecoxib, one of the selective cyclo-oxygenase (COX)-2 inhibitors, on nitric oxide (NO) and prostaglandinE2 (PGE2) synthesis in cultured osteoarthritic chondrocyte comparing with those of indomethacin. Articular chondrocytes were isolated from rat osteoarthritic knee joint with damaged anterior cruciate ligament and also from the sham knee joint. Chondrocytes were preincubated with or without IL-1 alpha, and were exposed to celecoxib, indomethacin (non-selective COX inhibitor), or nothing. The amounts of NO and PGE2 in culture supernatants of chondrocytes were measured by EIA or the Griess reaction. In a series of experiments preincubated with or without IL-1 alpha and exposed to nothing, PGE2 and NO levels were significantly higher in osteoarthritic chondrocytes than in sham chondrocytes. Celecoxib and indomethacin inhibited the increase of PGE2 in osteoarthritic chondrocytes. Celecoxib inhibited and indomethacin did not inhibit the increase of NO levels in osteoarthritic chondrocytes.

Repetitive mechanical stretching modulates IL-1beta induced COX-2, MMP-1 expression, and PGE2 production in human patellar tendon fibroblasts

While mechanical loading is known to be essential in maintaining tendon homeostasis, repetitive mechanical loading has also been implicated in the etiology of tendon overuse injuries. The purpose of this study was to determine whether cyclic mechanical stretching regulates inflammatory responses induced by interleukin-1beta (IL-1beta) treatment in human patellar tendon fibroblasts (HPTFs). HPTFs were grown in microgrooved silicone dishes, where they became elongated in shape and aligned with the microgrooves, which is similar to the shape and organization of tendon fibroblasts in vivo. Cyclic uniaxial stretching was then applied to silicone culture dishes with a 4% or 8% stretch at a stretching frequency of 0.5 Hz for a duration of 4 h in the presence or absence of 10 pM IL-1beta treatment. Non-stretched cells in the presence or absence of IL-1beta were used for controls, respectively. The expression of cyclooxygenase-2 (COX-2), matrix metalloproteinase-1 (MMP-1), and the production of prostaglandin E2 (PGE2) were measured. In the absence of stretching, it was found that 10 pM of IL-1beta markedly induced higher levels of COX-2, MMP-1 gene expression, and PGE2 production than non-treated cells. Furthermore, cells with 4% stretching decreased the COX-2 and MMP-1 gene expression and PGE2 production that were stimulated by IL-1beta, whereas cells with 8% stretching further increased these gene products and/or expression levels in addition to the effects of IL-1beta stimulation. Thus, the results suggest that repetitive, small-magnitude stretching is anti-inflammatory, whereas large-magnitude stretching is pro-inflammatory. Therefore, moderate exercise may be beneficial to reducing tendon inflammation.

Activation of histamine H1 receptor results in enhanced proteoglycan synthesis by human articular chondrocyte: involvement of protein kinase C and intracellular Ca(2+)

In earlier work, we obtained evidence for the presence of histamine H1 and H2 receptors on chondrocytes. Activation of the H1 receptor enhanced keratan sulfate synthesis, and protein kinase C (PKC) inhibitors antagonized histamine-stimulated keratan sulfate (KS) synthesis. These data do indicate the involvement of PKC in activation of H1 receptor, but precise mechanisms remained to be clarified. Human articular chondrocytes were treated with different concentrations of histamine and its antagonist. Intracellular Ca(2+) and proteoglycan synthesis was measured, using the fluorescent indicator dye Fura-2 AM and [35S]-sulfate incorporation, respectively. Activation of the H1 receptor led to stimulation of proteoglycan synthesis and evoked increases in levels of intracellular Ca(2+). Activity of PKC was also enhanced with activation of the H1 receptor. Intracellular Ca(2+) and activation of PKC are involved in the signal transduction pathway of H1 receptor-mediated stimulation of proteoglycan synthesis.

Tumor necrosis factor alpha-dependent proinflammatory gene induction is inhibited by cyclic tensile strain in articular chondrocytes in vitro

OBJECTIVE

To understand the intracellular mechanisms of the action of mechanical strain on articular chondrocytes during inflammation.

METHODS

One of the major mediators responsible for cartilage destruction in inflamed articular joints is tumor necrosis factor alpha (TNFalpha). Therefore, in this study we examined the intracellular mechanisms of actions of cyclic tensile strain (CTS) on the recombinant human TNFalpha (rHuTNFalpha)-induced proinflammatory pathways in primary cultures of chondrocytes. The expression of messenger RNA (mRNA) for TNFalpha-dependent proinflammatory proteins was examined by semiquantitative reverse transcriptase-polymerase chain reaction. The synthesis of proinflammatory proteins was examined by Western blot analysis in cell extracts, followed by semiquantitative measurement of bands using densitometric analysis. Nitric oxide production was measured by Griess reaction, and prostaglandin E2 production was assessed by radioimmunoassays. The proteoglycan synthesis in chondrocytes was assessed by incorporation of Na2(35)SO4 in chondroitin sulfate proteoglycans.

RESULTS

By exposing chondrocytes to CTS in the presence of TNFalpha in vitro, we showed that CTS is an effective antagonist of TNFalpha actions and acts as both an antiinflammatory signal and a reparative signal. CTS of low magnitude suppresses TNFalpha-induced mRNA expression of multiple proinflammatory proteins involved in catabolic responses, such as inducible nitric oxide synthase, cyclooxygenase 2, and collagenase. CTS also counteracts cartilage degradation by augmenting induction of tissue inhibitor of metalloproteinase 2. Additionally, CTS augments the reparative process via abrogation of TNFalpha-induced suppression of proteoglycan synthesis. Nonetheless, CTS acts on chondrocytes in a TNFalpha-dependent manner, since exposure of chondrocytes to CTS alone had no effect on these parameters.

CONCLUSION

CTS of low magnitude acts as an effective antagonist of TNFalpha not only by inhibiting the TNFalpha-dependent induction of proinflammatory proteins upstream of mRNA transcription, but also by augmenting the proteoglycan synthesis that is inhibited by TNFalpha.

Cyclic tensile strain suppresses catabolic effects of interleukin-1beta in fibrochondrocytes from the temporomandibular joint

OBJECTIVE

To discern the effects of continuous passive motion on inflamed temporomandibular joints (TMJ).

METHODS

The effects of continuous passive motion on TMJ were simulated by exposing primary cultures of rabbit TMJ fibrochondrocyte monolayers to cyclic tensile strain (CTS) in the presence of recombinant human interleukin-1beta (rHuIL-1beta) in vitro. The messenger RNA (mRNA) induction of rHuIL-1beta response elements was examined by semiquantitative reverse transcriptase-polymerase chain reaction. The synthesis of nitric oxide was examined by Griess reaction, and the synthesis of prostaglandin E2 (PGE2) was examined by radioimmunoassay. The synthesis of proteins was examined by Western blot analysis of the cell extracts, and synthesis of proteoglycans via incorporation of 35S-sodium sulfate in the culture medium.

RESULTS

Exposure of TMJ fibrochondrocytes to rHuIL-1beta resulted in the induction of inducible nitric oxide synthase (iNOS) and cyclooxygenase 2 (COX-2), which were paralleled by NO and PGE2 production. Additionally, IL-1beta induced significant levels of collagenase (matrix metalloproteinase 1 [MMP-1]) within 4 hours, and this was sustained over a period of 48 hours. Concomitant application of CTS abrogated the catabolic effects of IL-1beta on TMJ chondrocytes by inhibiting iNOS, COX-2, and MMP-1 mRNA production and NO, PGE2, and MMP-1 synthesis. CTS also counteracted cartilage degradation by augmenting expression of mRNA for tissue inhibitor of metalloproteinases 2 that is inhibited by rHuIL-1beta. In parallel, CTS also counteracted rHuIL-1beta-induced suppression of proteoglycan synthesis. Nevertheless, the presence of an inflammatory signal was a prerequisite for the observed CTS actions, because fibrochondrocytes, when exposed to CTS alone, did not exhibit any of the effects described above.

CONCLUSION

CTS acts as an effective antagonist of rHuIL-1beta by potentially diminishing its catabolic actions on TMJ fibrochondrocytes. Furthermore, CTS actions appear to involve disruption/regulation of signal transduction cascade of rHuIL-1beta upstream of mRNA transcription.

Cyclic tensile strain acts as an antagonist of IL-1 beta actions in chondrocytes

Inflammatory cytokines play a major role in cartilage destruction in diseases such as osteoarthritis and rheumatoid arthritis. Because physical therapies such as continuous passive motion yield beneficial effects on inflamed joints, we examined the intracellular mechanisms of mechanical strain-mediated actions in chondrocytes. By simulating the effects of continuous passive motion with cyclic tensile strain (CTS) on chondrocytes in vitro, we show that CTS is a potent antagonist of IL-1 beta actions and acts as both an anti-inflammatory and a reparative signal. Low magnitude CTS suppresses IL-1 beta-induced mRNA expression of multiple proteins involved in catabolic responses, such as inducible NO synthase, cyclo-oxygenase II, and collagenase. CTS also counteracts cartilage degradation by augmenting mRNA expression for tissue inhibitor of metalloproteases and collagen type II that are inhibited by IL-1 beta. Additionally, CTS augments the reparative process via hyperinduction of aggrecan mRNA expression and abrogation of IL-1 beta-induced suppression of proteoglycan synthesis. Nonetheless, the presence of an inflammatory signal is a prerequisite for the observed CTS actions, as exposure of chondrocytes to CTS alone has little effect on these parameters. Functional analysis suggests that CTS-mediated anti-inflammatory actions are not mediated by IL-1R down-regulation. Moreover, as an effective antagonist of IL-1 beta, the actions of CTS may involve disruption/regulation of signal transduction cascade of IL-1 beta upstream of mRNA transcription. These observations are the first to show that CTS directly acts as an anti-inflammatory signal on chondrocytes and provide a molecular basis for its actions.

Expression of both P1 and P2 purine receptor genes by human articular chondrocytes and profile of ligand-mediated prostaglandin E2 release

OBJECTIVE

To assess the expression and function of purine receptors in articular chondrocytes.

METHODS

Reverse transcriptase-polymerase chain reaction (RT-PCR) was used to screen human chondrocyte RNA for expression of P1 and P2 purine receptor subtypes. Purine-stimulated prostaglandin E2 (PGE2) release from chondrocytes, untreated or treated with recombinant human interleukin-1alpha (rHuIL-1alpha), was assessed by radioimmunoassay.

RESULTS

RT-PCR demonstrated that human articular chondrocytes transcribe messenger RNA for the P1 receptor subtypes A2a and A2b and the P2 receptor subtype P2Y2, but not for the P1 receptor subtypes A1 and A3. The P1 receptor agonists adenosine and 5'-N-ethylcarboxamidoadenosine did not change PGE2 release from chondrocytes. The P2Y2 agonists ATP and UTP stimulated a small release of PGE2 that was potentiated after pretreatment with rHuIL-1alpha. PGE2 release in response to ATP and UTP cotreatment was not additive, but release in response to coaddition of ATP and bradykinin (BK) or UTP and BK was additive, consistent with ATP and UTP competition for the same receptor site. The potentiation of PGE2 release in response to ATP and UTP after rHuIL-1alpha pretreatment was mimicked by phorbol myristate acetate.

CONCLUSION

Human chondrocytes express both P1 and P2 purine receptor subtypes. The function of the P1 receptor subtype is not yet known, but stimulation of the P2Y2 receptor increases IL-1-mediated PGE2 release.

Modulation of IL-1-induced cartilage injury by NO synthase inhibitors: a comparative study with rat chondrocytes and cartilage entities

Nitric oxide (NO) is produced in diseased joints and may be a key mediator of IL-1 effects on cartilage. Therefore, we compared the potency of new [aminoguanidine (AG), S-methylisothiourea (SMT), S-aminoethylisothiourea (AETU)] and classical [Nomega-monomethyl-L-arginine (L-NMMA), Nomega-nitro-L-arginine methyl ester (L-NAME)] NO synthase (NOS) inhibitors on the inhibitory effect of recombinant human interleukin-1beta (rhIL-1beta) on rat cartilage anabolism. Three different culture systems were used: (1) isolated chondrocytes encapsulated in alginate beads; (2) patellae and (3) femoral head caps. Chondrocyte beads and cartilage entities were incubated in vitro for 48 h in the presence of rhIL-1beta with a daily change of incubation medium to obtain optimal responses on proteoglycan synthesis and NO production. Proteoglycan synthesis was assessed by incorporation of radiolabelled sodium sulphate [Na2(35)SO4] and NO production by cumulated nitrite release during the period of study. Chondrocytes and patellae, as well as femoral head caps, responded concentration-dependently to IL-1beta challenge (0 to 250 U ml(-1) and 0 to 15 U ml(-1) respectively) by a large increase in nitrite level and a marked suppression of proteoglycan synthesis. Above these concentrations of IL-1beta (2500 U ml(-1) and 30 U ml(-1) respectively), proteoglycan synthesis plateaued whereas nitrite release still increased thus suggesting different concentration-response curves. When studying the effect of NOS inhibitors (1 to 1000 microM) on NO production by cartilage cells stimulated with IL-1beta (25 U ml(-1) or 5 U ml(-1)), we observed that: (i) their ability to reduce nitrite level decreased from chondrocytes to cartilage samples, except for L-NMMA and AETU; (ii) they could be roughly classified in the following rank order of potency: AETU > L-NMMA > or = SMT > or = AG > or = L-NAME and (iii) AETU was cytotoxic when used in the millimolar range. When studying the effect of NOS inhibitors on proteoglycan synthesis by cartilage cells treated with IL-1beta, we observed that: (i) they had more marked effects on proteoglycan synthesis in chondrocytes than in cartilage samples; (ii) they could be roughly classified in the following rank order of potency: L-NAME > or = L-NMMA > > AG > SMT > > AETU and (iii) potentiation of the IL-1 effect by AETU was consistent with cytotoxicity in the millimolar range. D-isomers of L-arginine analog inhibitors (1000 microM) were unable to correct nitrite levels or proteoglycan synthesis in IL-1beta treated cells. L-arginine (5000 microM) tended to reverse the correcting effect of L-NMMA (1000 microM) on proteoglycan synthesis, thus suggesting a NO-related chondroprotective effect. However, data with L-NAME and SMT argued against a general inverse relationship between nitrite level and proteoglycan synthesis. Dexamethasone (0.1 to 100 microM) (i) failed to inhibit NO production in femoral head caps and chondrocytes beads whilst reducing it in patellae (50%) and (ii) did not affect or worsened the inhibitory effect of IL-1beta on proteoglycan synthesis. Such results suggested a corticosteroid-resistance of rat chondrocyte iNOS. Data from patellae supported a possible contribution of subchondral bone in NO production. In conclusion, our results suggest that (i) NO may account only partially for the suppressive effects of IL-1beta on proteoglycan synthesis, particularly in cartilage samples; (ii) the chondroprotective potency of NOS inhibitors can not be extrapolated from their effects on NO production by joint-derived cells and (iii) L-arginine analog inhibitors are more promising than S-substituted isothioureas for putative therapeutical uses.

Factors related to degradation of articular cartilage in osteoarthritis: a review

OBJECTIVES

Osteoarthritis (OA) is a common joint deterioration initiated by multiple factors. To better understand related factors in the development of this disease, we focused on the mechanical stress loaded on articular cartilage.

MATERIALS AND METHODS

The anterior cruciate ligaments of rabbit knee joints were transected, and expression of protein kinase C (PKC) examined immunohistochemically. The PKC activator 12-o-tetradecanoyl-phorbol-13-acetate (TPA) was then administered intraarticularly. To determine the involvement of gas mediators, a cartilage defect was made on the medical femoral condyle of rabbit knee joints. Hydrostatic pressure was loaded on the cartilage taken from the surrounding defects, and levels of superoxide anion and nitric oxide (NO) were measured. Bovine chondrocytes were subjected to cyclic mechanical stretch using a Flexercell Strain Instrument. Proteoglycan synthesis and PKC activity were measured. Expression of matrix metalloproteinase (MMP)-3 and tissue inhibitor of metalloproteinase (TIMP)-1 in articular cartilages obtained from OA patients were examined using Northern blots.

RESULTS

Chondrocytes from experimentally induced OA were stained positively with anti-alpha-PKC antibody. Intraarticular administration of TPA prevented the development of OA changes. Cyclic tensile stretch loaded on chondrocytes decreased proteoglycan synthesis and PKC activity. Thus, PKC is involved in the stress-mediated degradation of articular cartilage. Cartilage defects led to degradation of surrounding cartilage and to enhanced superoxide anion and NO synthesis. We also noted increased and decreased expressions of MMP-3 and TIMP-1 mRNA in human OA cartilage, respectively.

CONCLUSION

PKC, gas mediators (superoxide anion, NO), and proteinases are all involved in OA.

A role for histamine receptors in rheumatoid arthritis

Although neurotransmitters and various chemical mediators play an important role in the pathogenesis of rheumatoid arthritis (RA), precise underlying mechanisms have yet to be determined. Histamine is a classical mediator of inflammation and three types of receptors are known. We investigated the presence and functions of histamine receptors of lymphocytes, bone marrow cells, synovial fibroblasts, and chondrocytes in experimentally-induced arthritis and human RA. The function of H2 receptors in peripheral blood lymphocytes and bone marrow cells were down regulated as measured by increments of intracellular cAMP and IL-6 production. Synovial fibroblasts from RA patients did not respond to H2 agonist to synthesize hyaluronic acid. It is evident that H2 receptors are down-regulated in lymphocytes, bone marrow cells, and synovial fibroblasts. The reduced function of H2 receptors in collagen-induced arthritis was normalized by transfer of the receptor-bearing lymphocytes and bone marrow cells. These data suggest that histamine is involved in the pathogenesis of RA.

Zonal differences in nitric oxide synthesis by bovine chondrocytes exposed to interleukin-1

To determine the role of nitric oxide (NO) in the inhibition of aggrecan synthesis, we measured levels of NO produced by bovine chondrocytes from different layers of articular cartilage in the presence of interleukin-1 (IL-1). Chondrocytes from the superficial layer showed a large increase in NO synthesis in response to IL-1. Although chondrocytes from the deep layer also produced NO in response to IL-1, the amount was less than that from the superficial layer. Enhanced NO production evoked by IL-1 was accompanied by a significant inhibition of aggrecan synthesis. These data suggest that chondrocytes in both superficial and deep layer of articular cartilage inhibit aggrecan synthesis with IL-1 via NO production. In addition, superficial layer cells respond to lower amounts of IL-1 with respect to NO-production and inhibition of proteoglycan synthesis.