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The aim of this study was to determine the involvement of pro-inflammatory phospholipase A2 (PLA2) enzymes in human chondrocytes from patients with osteoarthritis (OA).PLA2 involvement in OA chondrocytes was analysed by (a) arachidonic acid (AA) and oleic acid release, (b) PLA2 mRNA analysis, and (c) prostaglandin E2 (PGE2) production in cultured OA chondrocytes in response to various cytokines and platelet activating factor (PAF).Pro-inflammatory cytokines and PAF stimulation led to increased AA release, interleukin (IL)-1β and tumour necrosis factor (TNF) being the strongest inducers. The pattern of oleic acid release was similar to but less prominent than AA release, suggesting that predominantly arachidonyl selective enzymes were activated. IL-1β, TNF, IL-6, and IL-8 upregulated secretory group IIA, IID, and V phospholipase A2 (sPLA2-IIA, -IID, -V) and cytosolic group IVA phospholipase A2 (cPLA2-IVA) expression, where induction of chondrocyte sPLA2-IID is a novel finding. Furthermore, IL-1β, TNF, and IL-6 also induced COX2 expression. PAF induced expression of group IIA, IID and IVA PLA2, and COX2. In line with its anti-inflammatory properties, IL-4 was unable to induce either AA release or expression of PLA2s or COX2. IL-1β and TNF strongly increased PGE2 production, with IL-1β as the most prominent inducer.Multiple PLA2 isoforms are expressed and influenced by pro-inflammatory stimuli in OA chondrocytes. Hence, several PLA2 enzymes may contribute to chondrocyte function by their upregulation and activation, and increased AA release and PGE2 production may therefore be important effectors in OA pathophysiology. PLA2 enzymes and cPLA2-IVA in particular are thus possible therapeutic targets in OA.

Rheumatic diseases are often associated with changes in bone metabolism. Excessive production and release of cytokines and other growth factors due to inflammation, e.g. tumor necrosis factor-alpha (TNF-alpha), receptor activator of NF-kappaB ligand (RANKL), interleukins such as IL-1 and IL-6, may cause alterations in bone homeostasis leading to bone degradation. Other components such as osteoprotegerin (OPG) and possibly the ligand-receptor pair hepatocyte growth factor (HGF) and c-met may counteract this destruction, we have measured the levels of OPG, and HGF c-met, in serum, synovial fluid (SF), and cartilage from patients with rheumatoid arthritis (RA) and other arthritides. We found a) elevated levels of both OPG and HGF in SF from RA patients relative to arthritides of other causes, b) increased levels of both OPG and HGF in SF from seropositive RA patients (RA+) compared to seronegative RA patients (RA-), c) elevated levels or both OPG and HGF in serum from RA patients compared to healthy controls, d) no correlation between severity of inflammation and levels of OPG or HGF, and e) presence of HGF c-met in both cartilage and synovial tissue. The most significant elevations of OPG and HGF were found in patients with RA, the rheumatic disease most frequently associated with the development of secondary osteoporosis.

Cytokines are signalling glycoproteins mediating acute inflammation, chronic inflammation, and connective tissue destruction. The present study was designed to characterize the profile of cytokine message in normal human articular cartilage and from patients with rheumatoid arthritis (RA) and osteoarthritis (OA), by means of the reverse transcriptase-polymerase chain reaction (RT-PCR). Message RNA (mRNA) was extracted from fresh or frozen cartilage. The results showed expression of mRNA for IL-6, IL-6R, IL-7, IL-8, IL-10, and IL-12 (p35 and p40) exclusively in the RA cartilage. Except for mRNA for IL-8 and IL-10, no other cytokine or cytokine receptor was expressed in OA and control cartilage. mRNA for IL-1beta, IL-4, TNF-alpha, and TNFR-p75, was not detected in any cartilage sample except for one RA specimen expressing IL-1beta mRNA. However, the expression of message for pro-inflammatory cytokines was far more prominent than anti-inflammatory cytokines. This may suggest a disturbed balance of pro- and anti-inflammatory activity in RA cartilage.