Objective To evaluate the sites of expression of interleukin‐1β (IL‐1β), tumor necrosis factor α (TNFα), and inducible nitric oxide synthase (iNOS) in patients with inflammatory and degenerative joint diseases. Methods Cytokines and iNOS were detected by immunohistochemistry analysis of synovial and cartilage biopsy specimens obtained at knee arthroscopy in patients with rheumatoid arthritis (RA), psoriatic arthritis (PsA), osteoarthritis (OA), and traumatic knee arthritis. Cytokine and iNOS expression was quantified using computerized image analysis. Results IL‐1β, TNFα, and iNOS were highly expressed by synovial cells (lining layer cells, infiltrating leukocytes, endothelial cells) from patients with inflammatory arthritides and significantly less by synovial cells from patients with OA and traumatic arthritis. In contrast, the latter patients showed high chondrocyte expression of cytokines and iNOS while RA and PsA patients had only minor chondrocyte positivity. In both joint compartments, IL‐1β expression, TNFα expression, and iNOS expression were strongly correlated. Conclusion The enhanced and coordinated expression of IL‐1β, TNFα, and iNOS by chondrocytes strongly supports the hypothesis that chondrocytes are the major site of production of mediators of inflammation in human OA, thus playing a primary role in the pathogenesis of this disease.

Our findings suggest the existence in human chondrocytes of a novel catabolic pathway, primed by chemokines and their receptors, that leads to the breakdown of cartilage matrix components.

Chemokines play a key role in modulating leukocyte functions at sites of inflammation. To assess chondrocyte contribution to the chemotactic environment of inflamed joints the intracellular content of CC and CXC chemokines was investigated. IL-8, GROK K, MCP-1, RANTES, MIP-1K K and MIP-1L L expression was evaluated by flow cytometric analysis and RT-PCR in chondrocytes isolated from cartilage specimens obtained from patients with osteoarthritis and rheumatoid arthritis and multiorgan donors as normal controls. All the chemokines except RANTES were found in normal chondrocytes, with different degrees of staining intensity. In osteoarthritis and rheumatoid arthritis patients, an enhancement of IL-8, GROK K, MIP-1K K and MIP-1L L was observed.z 1999 Federation of European Biochemical Societies.

Besides the well-known activities of the prototypical inflammatory cytokines (IL-1␤, TNF␣), a role for chemokines and their receptors in cartilage degradation in osteoarthritis has recently been reported. Human chondrocytes can produce CC and CXC chemokines and express chemokine receptors for both chemokine subfamilies. Engagement of these receptors can induce the release of matrix degrading enzymes such as matrix metalloproteinases 1, 3, and 13, and N-acetyl-␤-Dglucosaminidase. Furthermore GRO␣, a CXC chemokine acting on CXCR2, can activate an apoptotic pathway in chondrocytes that leads to chondrocyte cell death. These findings suggest that chemokines can act as an autocrine or paracrine loop on chondrocytes and can contribute to many pathophysiological patterns present in osteoarthritis. Chemokines and their downstream signaling pathways can be considered novel therapeutic targets in osteoarthritis.Cartilage degradation in osteoarthritis (OA) results from phenotypical instability of the chondrocytes that sets up different cellular reaction patterns (dedifferentiation, release of matrix degrading enzymes, hypertrophy and apoptosis) under the control of a number of soluble factors, mainly released by the chondrocytes themselves. 24,77 Recent reports would establish the concept that OA-affected chondrocytes behave as activated macrophages 28 and share the release of similar inflammatory mediators. 3 However, because cartilage is an avascular, alymphatic, and aneural tissue, OA does not fit to the classic definition of inflammatory disease.Osteoarthritis might be considered as the result of the loss of the differentiated phenotype of the chondrocytes, with an enhancement of both catabolism and anabolism. 77 In this perspective, the huge base of literature currently available concerning the protagonist role of interleukin-1 (IL-1) cannot also account for the pattern of frustrated anabolism seen in OA. Furthermore, enhanced catabolism and enhanced anabolism seem to be distinct or at least heterogeneous within the various layers of articular cartilage, with superficial layers more susceptible to the catabolic effects of IL-1␤. 27 Chondrocytes of the deeper layers exhibit higher rates of proliferation and higher collagen and proteoglycan synthesis. 36 This discloses a pathogenic role also for growth and/or anabolic factors besides that of classical-proinflammatory cytokines (IL-1␤ and tumor necrosis factor alpha [TNF␣]).Data obtained by means of gene-chip analysis of osteoarthritic chondrocytes versus normal chondrocytes indicate strong up-regulation of members of the chemokine family beyond that of classic proinflammatory cytokines. 3 On the protein side, available current data obtained in supernatants of normal and OA cartilage explants show that IL-8 and monocyte chemoattractant protein-1 (MCP-1) are present at concentrations that are one order of magnitude higher than those of IL-1 and TNF␣. 3 This strongly supports a role for chemokines in cartilage physiology and pathology.Chemoattractive cytokines (chemokines) ...

Objective. To extend the study of the chemokine receptor repertoire on human chondrocytes to receptors with reported housekeeping functions (CXCR3, CXCR4, CXCR5, and CCR6) and to evaluate whether ligands of these receptors play a role in chondrocyte phenotype modulation and proliferation.Methods. Chemokine receptor expression was determined by flow cytometry. Subcultures of chondrocytes were collected and fixed at confluence or during the exponential phase of growth and analyzed for chemokine receptor modulation. The effects of chemokines on isolated cells as well as chondrocytes cultured within an intact extracellular matrix were investigated. Isolated human chondrocytes were stimulated with 100 nM Osteoarthritis (OA) is characterized by loss of the functional integrity of articular cartilage due to an imbalance between catabolic and anabolic chondrocyte activity. The biosynthetic and degradative activities of chondrocytes are regulated by extracellular influences that include interactions with the extracellular matrix (ECM), mechanical stress, and soluble factors, such as cytokines and growth factors. We and other investigators have recently reported that CC and CXC chemokines may also play an important role in OA cartilage degradation (1-3).Human chondrocytes express a variety of chemokine receptors, including CCR1, CCR2, CCR3, CCR5, CXCR1, and CXCR2 (1-3), which belong to the socalled inducible inflammatory receptors (4). Interaction of these receptors with the corresponding ligands, which are also produced by chondrocytes themselves (2,3,5-8), induces the release of matrix-degrading enzymes and the enhancement of ECM catabolism (1-3). These observaSupported by grants from MIUR (ex-quota 40%) and by the Ricerca Corrente Istituti Ortopedici Rizzoli,