Polycyclic Aromatic Hydrocarbon Increases mRNA Level for Interleukin 1 Beta in Human Fibroblast-Like Synoviocyte Line via Aryl Hydrocarbon Receptor

Rheumatoid arthritis (RA) is characterized by proliferation of synoviocytes that produce proinflammatory cytokines, which is implicated in the pathogenesis of the disease. Among the cytokines, IL-1 is the critical mediator of the disease. When human fibroblast-like synoviocytes line, MH7A, was treated with 3-methylcholanthrene (3-MC), a polycyclic aromatic hydrocarbon (PAH), mRNA of IL-1β was up-regulated. MH7A cells express functional aryl hydrocarbon receptor (AhR) as shown by 3-MC-inducible CYP1A1 mRNA expression. The effect of 3-MC was inhibited by α-napthoflavone, an AhR antagonist, indicating that the effect of 3-MC is mediated via AhR. Benzo[a]pyrene (B[a]P) and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) also up-regulated mRNA level of IL-1β in the cells via AhR. As PAHs are much contained in cigarette smoke, these findings provide the possible basis for epidemiological studies indicating a strong association between heavy cigarette smoking and outcome of RA.