Proinflammatory cytokines increase iron uptake into human monocytes and synovial fibroblasts from patients with rheumatoid arthritis.
BACKGROUND
It has been hypothesized that iron is stored in the synovium of patients with rheumatoid arthritis which perpetuates inflamation by aiding the production of oxygen free radicals. Proinflammatory cytokines are produced by macrophages and lymphocytes present within synovium and by mononuclear cells of in synovial fluid from patients with rheumatoid arthritis. There are two known systems for iron uptake. The first involves binding of iron to transferrin and uptake via transferrin receptors. The second involves uptake by low molecular weight organic anions such as ascorbate and citrate (non-transferrin bound uptake).


METHODS
Proinflammatory cytokines (IL-1, IL-6, TNFalpha and interferon gamma) were added to fibroblasts isolated from patients with rheumatoid arthritis and human monocytes in culture and their effect on 59Fe-transferrin and citrate uptake was determined.


RESULTS
Proinflammatory cytokines increase transferrin and non-transferrin bound iron uptake into human monocytes and increase transferrin-bound iron uptake by synovial fibroblasts, but have no effect on non-transferrin bound uptake into fibroblasts.


CONCLUSIONS
Proinflammatory cytokines produced in human rheumatoid arthritis synovium and synovial fluid may contribute to the accumulation of iron that occurs in rheumatoid arthritis synovium which may lead to damage to synovial fibroblasts, macrophages and lymphocytes.
Telfer
Joan F
JF
Department of Immunology, Western Infirmary, University of Glasgow, United Kingdom. j.f.telfer@dundee.ac.uk
Brock
Jeremy H
JH
D001172:Arthritis, Rheumatoid / Q000378:metabolism*; D002478:Cells, Cultured; D002951:Citrates / Q000378:metabolism; D016207:Cytokines / Q000494:pharmacology*; D005347:Fibroblasts / Q000187:drug effects / Q000378:metabolism*; D006801:Humans; D007501:Iron / Q000378:metabolism*; D009000:Monocytes / Q000187:drug effects / Q000378:metabolism*; D013583:Synovial Membrane / Q000187:drug effects / Q000378:metabolism*; D014168:Transferrin / Q000378:metabolism
D002951:Citrates; D016207:Cytokines; D014168:Transferrin; D007501:Iron