Although mankind has been suffering from osteoarthritis (OA) dating to the dawn of humankind, its pathogenesis remains poorly understood. OA is no longer considered a “wear and tear” condition but rather one driven by proteases where chronic low-grade inflammation may play a role in perpetuating proteolytic activity. While multiple factors are likely active in this process, recent evidence has implicated the importance of the innate immune system, the older or more primitive part of our body’s immune defense mechanisms. The role of some of the components of the innate immune system have been tested in OA models in vivo including the role of synovial macrophages and the complement system. This review is a selective overview of a large and evolving field. Insights into these mechanisms might inform our ability to phenotype patient subsets and give hope for the advent of novel OA therapies.

BackgroundChondroitin Sulphate (CS), a natural glycosaminoglycan of the extracellular matrix, has clinical benefit in symptomatic osteoarthritis but has never been tested in gout. In vitro, CS has anti-inflammatory and positive effects on osteoarthritic chondrocytes, synoviocytes and subchondral bone osteoblasts, but its effect on macrophages is unknown. The purpose of our study was to evaluate the in vitro effects of CS on monosodium urate (MSU)-stimulated cytokine production by macrophages.MethodsTHP-1 monocytes were differentiated into mature macrophages using a phorbol ester, pretreated for 4 hours with CS in a physiologically achievable range of concentrations (10–200 μg/ml) followed by MSU crystal stimulation for 24 hours. Cell culture media were analyzed by immunoassay for factors known to be upregulated during gouty inflammation including IL-1β, IL-8 and TNFα. The specificity of inflammasome activation by MSU crystals was tested with a caspase-1 inhibitor (0.01 μM-10 μM).ResultsMSU crystals ≥10 mg/dl increased macrophage production of IL-1β, IL-8 and TNFα a mean 7-, 3- and 4-fold respectively. Induction of IL-1β by MSU was fully inhibited by a caspase-1 inhibitor confirming inflammasome activation as the mechanism for generating this cytokine. In a dose-dependent manner, CS significantly inhibited IL-1β (p = 0.003), and TNFα (p = 0.02) production from macrophages in response to MSU. A similar trend was observed for IL-8 but was not statistically significant (p = 0.41).ConclusionsCS attenuated MSU crystal induced macrophage inflammation, suggesting a possible role for CS in gout prophylaxis.Electronic supplementary materialThe online version of this article (doi:10.1186/1471-2474-15-318) contains supplementary material, which is available to authorized users.

Background Chondroitin Sulphate (CS) has shown clinical benefit in symptomatic osteoarthritis (OA). EULAR has endorsed the use of CS in OA but its mechanism is unknown. Studies have shown that high levels of CS could potentially cause precipitation of monosodium urate (MSU) crystals leading to inflammasome activation. In vitro studies have shown that CS has some anti-inflammatory effects on chondrocytes and synoviocytes from OA patients. However, the effect of CS is unclear on macrophages which are key in OA pathogenesis. Objectives To evaluate the in vitro effects of CS on cytokine production by macrophages. Methods THP-1 cells, a human monocytic line, were induced to differentiate into mature macrophages using a phorbol diester. To test the effects of CS on uric acid (UA) solubility, we incubated sterile solutions of CS/UA in Opti-MEM at various concentrations (CS 10-10000µg/ml and UA 10-500µg/ml). These solutions were added to the cells in vitro to monitor for pro-inflammatory effects; the solutions were also subjected to high speed centrifugal ultra-filtration to quantify, by HPLC, potential particulate formation through analysis of the remaining soluble UA in the supernatant. MSU crystals were used as a positive pro-inflammatory stimulus. Cell culture medium was removed at 24 hrs and analyzed by high-sensitivity immunoassay for IL1β. Experiments were repeated with various concentrations of a caspase-1 inhibitor (0.01µM-10 µM) to identify the component of IL1β production attributable to inflammasome activation. Finally, macrophages were pretreated with the highly purifiedbovine CS for 4 hrs prior to the addition of MSU crystals (100µg/ml) or Lipopolysaccharide (LPS) at 50µg/ml, which served as a positive control. CS doses in the physiologic range (10-200µg/ml) were used. Culture medium was collected at 24 hrs and IL1β levels were determined as above. Results The CS/UA solutions did not lead to inflammasome activation of THP-1 macrophages (data not shown). MSU 100µg/ml consistently resulted in increased IL-1β levels by macrophages but was inhibitable by the caspase-1 inhibitor (at 1 µM or greater) confirming activation of the inflammasome as the source of this cytokine (data not shown). CS decreased IL-1 β levels in both the LPS and MSU treatment groups. Increasing doses of CS lead to a dose-dependent inhibition of IL-1β production from macrophages (Figure 1). Image/graph Conclusions High concentrations of a highly pure bovine CS do not facilitate formation of pro-inflammatory UA microparticulates or microcrystals. In contrast, CS decreases IL-1β levels in a dose-dependent manner at physiologically achievable concentrations of CS. The anti-inflammatory mechanism of CS appears compatible with inflammasome inhibition. Further research is needed to understand the means by which CS has its anti-inflammatory effect. Acknowledgements Supported by Bioibérica (Barcelona, Spain), NIH 5T32AI007217-30 (EO) & P01 AR050245. Disclosure of Interest E. Orlowsky Grant/research support from: Bioberica, Barcelona, Spai...

important process in OA progression, where several immune mediators, such as immunoregulatory neuropeptides, play an important role. The vasoactive intestinal peptide (VIP) and the corticotropin-releasing factor (CRF)/urocortins (UCNs) family are neuropeptides expressed in central and peripheral tissues, including immune cells, that modulate the expression of inflammatory and extracellular matrix remodelling mediators. VIP has previously shown a plethora of beneficial effects, both in inflammatory disorder animal models and in human OA, being a potential therapeutic agent. Besides, it has shown that high VIP levels are correlated with a decrease of the OA severity progress. In addition, CRF and Urocortin1 (UCN1) are secreted to the OA joint microenvironment exerting an autocrine and paracrine immuno/inflammatory regulation. Chondroitin sulfate (CS) is a Symptomatic Slow Action Drug for Osteoarthritis (SYSADOA) described to improve the symptoms of OA disease. The NIH-funded GAIT study demonstrated that CS is an effective drug in reducing OA patients' synovitis. The aim of this study was to compare the effect of CS vs. paracetamol on synovitis in OA patients, and to evaluate their impact on VIP, CRF and UCN1 concentrations. Methods: 71 OA patients with synovitis (synovial hyper-trophy+effusion4mm) were treated with CS (CondrosanÒ, CS Bio-ActiveTM, Bioibérica S.A., Barcelona, Spain) (800mg/day) or paracetamol (4g/day) for 6 months. Patients were followed-up until month 9 to evaluate the CS carry-over effect. In each visit (0, 6 and 9 months) synovitis was evaluated by sonography and plasma and synovial fluid were collected for the quantification of VIP, CRF and UCN1 by EIA (Enzyme Immunoassay). Once the clinical data have been collected, CS treated patients were subdivided into two groups, as responding and non-responding to treatment. A responding patient was defined by a sinovitis reduction at 6 months greater than 20% from basal value. Time-course analysis study was performed by a Wilcoxon two-related samples test. The comparation between responding and nonresponding patients was analyzed by a Mann-Whitney U test. P values less than or equal to 0.05 were considered significant. Results: The analysis of the results obtained showed that CS but not paracetamol reduces effectively the synovitis observed in OA patients. The improvement remained after 3 months treatment cessation. Synovial fluid presents a progressive decrease neuropeptides levels along the CS treatment, reaching significancy VIP reduction at 9 months. This tendency is more pronounced when only the responding patients are analyzed. In contrast no tendency was observed with the paracetamol group, showing a lonely significant decrease of UCN1 at 6 months. The neuropeptides levels in plasma did not show significant differences neither in the chondroitin treated patients nor in the responding group. However, the paracetamol grup present a progressive increment of CRF/UCN levels being significant the UCN1 increase at 9 months. When comparing the basal level...