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To examine the role of intracellular labile iron pool (LIP), ferritin (Ft), and antioxidant defence in cellular resistance to oxidative stress on chronic adaptation, a new H2O2-resistant Jurkat T cell line “HJ16” was developed by gradual adaptation of parental “J16” cells to high concentrations of H2O2. Compared to J16 cells, HJ16 cells exhibited much higher resistance to H2O2-induced oxidative damage and necrotic cell death (up to 3 mM) and had enhanced antioxidant defence in the form of significantly higher intracellular glutathione and mitochondrial ferritin (FtMt) levels as well as higher glutathione-peroxidase (GPx) activity. In contrast, the level of the Ft H-subunit (FtH) in the H2O2-adapted cell line was found to be 7-fold lower than in the parental J16 cell line. While H2O2 concentrations higher than 0.1 mM fully depleted the glutathione content of J16 cells, in HJ16 cells the same treatments decreased the cellular glutathione content to only half of the original value. In HJ16 cells, H2O2 concentrations higher than 0.1 mM increased the level of FtMt up to 4-fold of their control values but had no effect on the FtMt levels in J16 cells. Furthermore, while the basal cytosolic level of LIP was similar in both cell lines, H2O2 treatment substantially increased the cytosolic LIP levels in J16 but not in HJ16 cells. H2O2 treatment also substantially decreased the FtH levels in J16 cells (up to 70% of the control value). In contrast in HJ16 cells, FtH levels were not affected by H2O2 treatment. These results indicate that chronic adaptation of J16 cells to high concentrations of H2O2 has provoked a series of novel and specific cellular adaptive responses that contribute to higher resistance of HJ16 cells to oxidative damage and cell death. These include increased cellular antioxidant defence in the form of higher glutathione and FtMt levels, higher GPx activity, and lower FtH levels. Further adaptive responses include the significantly reduced cellular response to oxidant-mediated glutathione depletion, FtH modulation, and labile iron release and a significant increase in FtMt levels following H2O2 treatment.

SUMMARY Iron is an important catalyst of oxidative radical reactions and promotes the formation of the hydroxyl radical from the superoxide anion radical and hydrogen peroxide. The stimulatory effect of the hydroxyl radical on lipid peroxidation prompted the speculation that free iron may directly promote inflammation and that iron chelating agents may have useful anti-inflammatory properties. This hypothesis is tested in animal models of inflammation with a specific iron chelating agent, desferrioxamine. At low doses (6-6 mg/kg) intraperitoneal desferrioxamine stimulated the induction of acute foot pad swelling in rats by monosodium urate but at higher doses (above 200 mg/kg) it suppressed this inflammatory reaction. A similar anti-inflammatory effect was observed in carrageenan-induced foot pad swelling. In guinea-pigs in which a Glynn-Dumonde synovitis was induced with bovine gammaglobulin, desferrioxamine (100 mg/kg) stimulated the acute inflammatoivy induction phase of this chronic allergic monoarthritis model. Repeated administration of desferrioxamine (100 mg/kg) from the seventh to the twelfth day after intra-articular challenge with bovine gammaglobulin markedly depressed the chronic inflammatory phase. In-vitro experiments suggest that desferrioxamine inhibits iron-catalysed lipid peroxidation when it is poorly saturated with iron, but loses this effect when it is iron saturated. Such an effect may explain our results with desferrioxamine in the animal studies and suggests that effective iron chelation and its removal may modify the inflammatory process in man.Iron is an important catalyst in biological systems. Its easy access to 2 oxidation states, iron II and iron III, allows it to co-ordinate electron donors and to participate in redox processes. However, this property is potentially hazardous, since reactions involving oxygen favour a univalent reduction pathway which leads to the formation of unstable intermediates with unpaired electrons-free radicals.'The superoxide radical (02), the first univalent reduction product of oxygen, is released along with hydrogen peroxide during phagocytosis by polymorphonuclear leucocytes and macrophages.2 In the presence of traces of free iron salts, superoxide and hydrogen peroxide can react together

1. On exposure of synovial fluid to superoxide and hydrogen peroxide, generated enzymically or by activated polymorphonuclear leucocytes, hyaluronic acid is depolymerized and the fluid loses its lubricating properties. The ability of synovial fluid from rheumatoid patients to scavenge superoxide and hydrogen peroxide was therefore examined. 2. Synovial fluid from a range of rheumatoid patients contained no superoxide dismutase activity, insufficient caeruloplasmin to scavenge any superoxide radical and little, if any, catalase activity. 3. Total ascorbate (reduced ascorbate + dehydroascorbate) concentrations in the plasma and synovial fluid of rheumatoid patients were similar in each case. The values are at the low end of the normal range. 4. These results are discussed in relation to the role of oxygen radicals in inflammatory joint disease.

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