Iron-binding proteins and free iron in synovial fluids of rheumatoid arthritis patients.

Iron-binding proteins (lactoferrin, transferrin and ferritin) and free iron were measured in synovial fluid (SF) from 30 patients with rheumatoid arthritis (RA) and 20 osteoarthritis (OA) patients. The iron-binding proteins except transferrin were significantly increased in RA SF as compared with OA SF. Similarly, free iron was also significantly higher in RA SF than in OA SF, whereas the ferritin saturation index, transferrin saturation index and bound iron were more significantly decreased in RA SF than in OA SF. These results suggest that RA SF contains sufficient micromolar amounts of free iron to allow hydroxyl radical formation. Also the capacity of iron-binding proteins to bind free iron is inadequate in the presence of a large amount of iron-binding proteins which are present in RA SF.