Lipoxygenase products and expression of 5-lipoxygenase and 5-lipoxygenase-activating protein in human cultured synovial cells.

5-Lipoxygenase products are pro-inflammatory mediators. Their roles and cellular origin in chronic inflammatory rheumatisms such as rheumatoid arthritis (RA) are poorly understood. The expression of arachidonate 5-lipoxygenase (5-LOX, arachidonate: oxygen 5-oxydoreductase; EC 1.13.11.34) and the 5-lipoxygenase activating protein (FLAP) genes in osteoarthritis and RA synoviocytes was studied at the transcriptional level by reverse transcription-polymerase chain reaction (RT-PCR) methodology. Arachidonic acid metabolism was analyzed by reverse-phase high pressure liquid chromatography. 5-LOX and FLAP mRNA were detectable using RT-PCR in all sources of synoviocytes tested. The expression of 5-LOX and FLAP mRNA led to the synthesis of 5-LOX metabolites. 12- and 15-LOX activities were also present. These LOX products can participate in inflammatory processes leading to joint destruction in RA.