Nature of anaemia in rheumatoid arthritis. VII. Storage of iron in rheumatoid disease.

Disturbance of iron metabolism is a prominent feature of the anaemia of rheumatoid arthritis. The plasma iron concentration is almost always reduced in the presence of active disease (Bruzzone and Massimello, 1940; Nilsson, 1948). Despite intensive investigation (Raymond, Bowie, and Dugan, 1965), the metabolic pathways of iron in rheumatoid disease and the relationship between the levels of plasma iron, the degree of anaemia, and the activity of the disease remain obscure. The rapid clearance from the plasma of iron given intravenously (Roy, Alexander, and Duthie, 1955; Freireich, Ross, Bayles, Emerson, and Finch, 1957; Weinstein, 1959) may be due to an abnormal uptake by the reticulo-endothelial system. Gardner and Roy (1961) estimated the iron content of postmortem material from rheumatoid and control subjects and showed that there was no increase in iron content in rheumatoid tissues as compared with controls. However, hyperplasia of the reticuloendothelial system was observed and, in particular, the spleens of rheumatoid patients were significantly larger than those of controls. These results suggested that there was a greater absolute amount of iron in the reticulo-endothelial systems of the patients. Muirden (1966), using electron microscopy, showed large quantities of ferritin in the cells of rheumatoid synovium. One explanation for this observation could be that iron may be diverted from the plasma and deposited in the inflamed synovial tissue. Further evidence of increased iron deposition in rheumatoid arthritis, even in the presence of a low plasma iron, was provided by studies of the handling of endogenous iron released from erythrocytes after intravenous injection of nicotinic acid or aged autologous blood in patients with rheumatoid arthritis (Owen and Lawson, 1966). These studies showed that there was a smaller rise and amore rapid fall in plasma iron levels in rheumatoid patients compared with healthy control subjects. The authors suggested that these observations could be explained by an abnormally slow release of endogenous iron from the reticulo-endothelial system. On the assumption that iron might be stored in excessive amounts in the reticulo-endothelial system or inflamed tissue, it was decided to study the metabolism of iron in rheumatoid arthritis following administration of the iron-chelating agent desferrioxamine. A screening test for iron storage disease was suggested by Keberle (1964), using desferrioxamine B ("Desferal", Ciba), a tri-hydroxamic acid with a highly-specific ability to chelate trivalent iron. The simple desferrioxamine test indicates that iron storage disease may be suspected if there is an increase in urinary iron excretion in excess of ten times the amount present in the urine before injecting the chelating agent (Unseld, 1964; W6hler, 1964). The simple desferrioxamine test does not allow for possible alterations in the excretion of the chelate, ferrioxamine, which has been shown to vary in different types of anaemia (Bannerman, Callender, and Williams, 1962). Also, the test does not permit calculation of chelation of iron in vivo. The more refined differential ferrioxamine test was devised by Fielding (1965) to overcome these defects. This procedure involves collection of urine for 6 hours before and after an intramuscular injection of 500 mg. desferrioxamine together with labelled ferrioxamine given in a dose of 50 mg./60 kg. body weight. The upper range of normal chelation in vivo is stated to be 500 psg./kg. These tests were used in this study, but Fielding's differential desferrioxamine test was modified to avoid the use of radioactive isotopes. The urinary excretion pattern of ferrioxamine after an intramuscular injection of ferrioxamine (50 mg./60kg. body weight) was measured in a series of patients and healthy subjects to confirm that the modification of the differential desferrioxamine test was satisfactory. In addition, the pattern of iron excretion after daily intramuscular injection of desferrioxamine was