Ferritin as a source of iron for oxidative damage.

The generation of deleterious activated oxygen species capable of damaging DNA, lipids, and proteins requires a catalyst such as iron. Once released, ferritin iron is capable of catalyzing these reactions. Thus, agents that promote iron release may lead to increased oxidative damage. The superoxide anion formed enzymatically, radiolytically, via metal-catalyzed oxidations, or by redox cycling xenobiotics reductively mobilizes ferritin iron and promotes oxidative damage. In addition, a growing list of compounds capable of undergoing single electron oxidation/reduction reactions exemplified by paraquat, adriamycin, and alloxan have been reported to release iron from ferritin. Because the rapid removal of iron from ferritin requires reduction of the iron core, it is not surprising that the reduction potential of a compound is a primary factor that determines whether a compound will mobilize ferritin iron. The reduction potential does not, however, predict the rate of iron release. Therefore, ferritin-dependent oxidative damage may be involved in the pathogenesis of diseases where increased superoxide formation occurs and the toxicity of chemicals that increase superoxide production or have an adequate reduction potential to mobilize ferritin iron.     

Non-anemic iron deficiency,oral iron supplementation,and oxidative damage in college-aged females

Oxidative damage, as indicated by protein carbonyl and lipid hydroperoxide concentrations, was assessed in the plasma of college-aged females with adequate iron status and with non-anemic iron deficiency before and after eight weeks of iron supplementation. At baseline, the mean serum ferritin, iron, transferrin saturation, and total iron binding capacity of the iron deficient group (n = 13) was significantly different from the iron adequate controls (n = 24). Mean plasma lipid hydroperoxide and protein carbonyl concentrations did not differ between groups at baseline. Following eight weeks of iron supplementation, the mean serum ferritin, iron, and transferrin saturation significantly increased and the total iron binding capacity significantly decreased in the iron deficient group. No significant differences in plasma lipid hydroperoxide or protein carbonyl concentrations were found between groups at the end of the study period. When plasma lipid hydroperoxide and protein carbonyl concentrations of subjects within groups were compared at the start versus at the end of the study, no significant differences were found for either group. Neither non-anemic iron deficiency nor its treatment with oral iron supplements is associated with oxidative damage in the plasma of college-aged females.     

Ferritin and ferritin isoforms II: protection against uncontrolled cellular proliferation, oxidative damage and inflammatory processes

Ferritin is a major iron storage protein involved in the regulation of iron availability. Each ferritin molecule comprises 24 subunits. Various combinations of H-subunits and L-subunits make up the 24-subunit protein structure and these ferritin isoforms differ in their H-subunit to L-subunit ratio, as well as in their metabolic properties. Ferritin is an acute-phase protein and its expression is up-regulated in conditions such as uncontrolled cellular proliferation, in any condition marked by excessive production of toxic oxygen radicals, and by infectious and inflammatory processes. Under such conditions ferritin up-regulation is predominantly stimulated by increased reactive oxygen radical production and by cytokines. The major function of ferritin in these conditions is to reduce the bio-availability of iron in order to stem uncontrolled cellular proliferation and excessive production of reactive oxygen radicals. Ferritin is not, however, indiscriminately up-regulated in these conditions as a marked shift towards a predominance in H-subunit rich ferritins occurs. Preliminary indications are that, while the L-subunit primarily fulfils the conventional iron storage role, the H-subunit functions primarily as rapid regulator of iron availability, and perhaps indirectly as regulator of other cellular processes. It is suggested that the optimum differential expression of the two subunits differ for different cells and under different conditions and that the expression of appropriate isoferritins offers protection against uncontrolled cellular proliferation, oxidative stress and against side effects of infectious and inflammatory conditions.     

Ferritins control interaction between iron homeostasis and oxidative stress in Arabidopsis

Ferritin protein nanocages are the main iron store in mammals. They have been predicted to fulfil the same function in plants but direct evidence was lacking. To address this, a loss-of-function approach was developed in Arabidopsis. We present evidence that ferritins do not constitute the major iron pool either in seeds for seedling development or in leaves for proper functioning of the photosynthetic apparatus. Loss of ferritins in vegetative and reproductive organs resulted in sensitivity to excess iron, as shown by reduced growth and strong defects in flower development. Furthermore, the absence of ferritin led to a strong deregulation of expression of several metal transporters genes in the stalk, over-accumulation of iron in reproductive organs, and a decrease in fertility. Finally, we show that, in the absence of ferritin, plants have higher levels of reactive oxygen species, and increased activity of enzymes involved in their detoxification. Seed germination also showed higher sensitivity to pro-oxidant treatments. Arabidopsis ferritins are therefore essential to protect cells against oxidative damage.     

Gastrins, iron homeostasis and colorectal cancer

The peptide hormone gastrin has been identified as a major regulator of acid secretion and a potent mitogen for normal and malignant gastrointestinal cells. The importance of gastric acid in the absorption of dietary iron first became evident 50 years ago when iron deficiency anemia was recognized as a long-term consequence of partial gastrectomy. This review summarizes the connections between circulating gastrins, iron status and colorectal cancer. Gastrins bind two ferric ions with micromolar affinity and, in the case of non-amidated forms of the hormone, iron binding is essential for biological activity in vitro and in vivo. The demonstration of an interaction between gastrin and transferrin by biochemical techniques led to the proposal that gastrins catalyze the loading of transferrin with iron. Several lines of evidence, including the facts that the concentrations of circulating gastrins are increased in mice and humans with the iron overload disease hemochromatosis and that transferrin saturation positively correlates with circulating gastrin concentration, suggest the potential involvement of gastrins in iron homeostasis. Conversely, recognition that ferric ions play an unexpected role in the biological activity of gastrins may assist in the development of useful therapies for colorectal carcinoma and other disorders of mucosal proliferation in the gastrointestinal tract.     

Intralysosomal iron chelation protects against oxidative stress-induced cellular damage

Oxidant-induced cell damage may be initiated by peroxidative injury to lysosomal membranes, catalyzed by intralysosomal low mass iron that appears to comprise a major part of cellular redox-active iron. Resulting relocation of lytic enzymes and low mass iron would result in secondary harm to various cellular constituents. In an effort to further clarify this still controversial issue, we tested the protective effects of two potent iron chelators--the hydrophilic desferrioxamine (dfo) and the lipophilic salicylaldehyde isonicotinoyl hydrazone (sih), using cultured lysosome-rich macrophage-like J774 cells as targets. dfo slowly enters cells via endocytosis, while the lipophilic sih rapidly distributes throughout the cell. Following dfo treatment, long-term survival of cells cannot be investigated because dfo by itself, by remaining inside the lysosomal compartment, induces apoptosis that probably is due to iron starvation, while sih has no lasting toxic effects if the exposure time is limited. Following preincubation with 1 mM dfo for 3 h or 10 microM sih for a few minutes, both agents provided strong protection against an ensuing approximately LD50 oxidant challenge by preventing lysosomal rupture, ensuing loss of mitochondrial membrane potential, and apoptotic/necrotic cell death. It appears that once significant lysosomal rupture has occurred, the cell is irreversibly committed to death. The results lend strength to the concept that lysosomal membranes, normally exposed to redox-active iron in high concentrations, are initial targets of oxidant damage and support the idea that chelators selectively targeted to the lysosomal compartment may have therapeutic utility in diminishing oxidant-mediated cell injury.     

Early-stage iron deficiency alters physiological processes and iron transporter expression,along with photosynthetic and oxidative damage to sorghum

Iron (Fe) starvation in Strategy II plants is a major nutritional problem causing severe visual symptoms and yield reductions. This prompted us to investigate the physiological and molecular consequences of Fe deficiency responses at an early stage in sorghum plants. The Fe-starved sorghum did not show shoot biomass reduction, but the root length, biomass, and chlorophyll synthesis were severely affected. The chlorophyll a fluorescence analysis showed that the quantum yield efficiency of PSII (Fv/Fm) and photosynthesis performance index (Pi_ABS) in young leaves significantly reduced in response to low Fe. Besides, Fe concentration in root and shoot significantly declined in Fe-starved plants relative to Fe-sufficient plants. Accordingly, this Fe reduction in tissues was accompanied by a marked decrease in PS-release in roots. The qPCR experiment showed the downregulation of SbDMAS2 (deoxymugineic acid synthase 2), SbNAS3 (nicotianamine synthase 3), and SbYSL1 (Fe-phytosiderophore transporter yellow stripe 1) in Fe-deprived roots, suggesting that decreased rhizosphere mobilization of Fe(III)-PS contributes to reduced uptake and long-distance transport of Fe. The cis-acting elements of these gene promoters are commonly responsive to abscisic acid and methyl jasmonate, while SbYSL1 additionally responsive to salicylic acid. Further, antioxidant defense either through metabolites or antioxidant enzymes is not efficient in counteracting oxidative damage in Fe-deprived sorghum. These findings may be beneficial for the improvement of sorghum genotypes sensitive to Fe-deficiency through breeding or transgenic approaches.     

Fur controls iron homeostasis and oxidative stress defense in the oligotrophic alpha-proteobacterium Caulobacter crescentus

In most bacteria, the ferric uptake regulator (Fur) is a global regulator that controls iron homeostasis and other cellular processes, such as oxidative stress defense. In this work, we apply a combination of bioinformatics, in vitro and in vivo assays to identify the Caulobacter crescentus Fur regulon. A C. crescentus fur deletion mutant showed a slow growth phenotype, and was hypersensitive to H₂O₂ and organic peroxide. Using a position weight matrix approach, several predicted Fur-binding sites were detected in the genome of C. crescentus, located in regulatory regions of genes not only involved in iron uptake and usage but also in other functions. Selected Fur-binding sites were validated using electrophoretic mobility shift assay and DNAse I footprinting analysis. Gene expression assays revealed that genes involved in iron uptake were repressed by iron-Fur and induced under conditions of iron limitation, whereas genes encoding iron-using proteins were activated by Fur under conditions of iron sufficiency. Furthermore, several genes that are regulated via small RNAs in other bacteria were found to be directly regulated by Fur in C. crescentus. In conclusion, Fur functions as an activator and as a repressor, integrating iron metabolism and oxidative stress response in C. crescentus.     

Body iron is a contributor to oxidative damage of DNA

The transition metal iron is catalytically highly active in vitro, and not surprisingly, body iron has been suggested to promote oxidative stress in vivo. In the current analysis we studied the association of serum ferritin concentration and serum soluble transferrin receptor concentration with daily urinary 8-hydroxydeoxyguanosine excretion, a marker of oxidative stress, in 48 mildly dyslipidemic men in East Finland. In multivariate linear regression analyses allowing for age, smoking, body mass index and physical exercise, serum ferritin concentration predicted the excretion rate at B = 0.17 (95% CI 0.08–0.26, P = 0.001), and serum soluble transferrin receptor to ferritin concentration ratio (TfR/ferritin) predicted the excretion rate at B = ? 0.13 (95% CI ? 0.21 to ? 0.05, P = 0.002). Our data suggest that body iron contributes to excess oxidative stress already at non-iron overload concentrations in these subjects.     

Body iron is a contributor to oxidative damage of DNA

The transition metal iron is catalytically highly active in vitro, and not surprisingly, body iron has been suggested to promote oxidative stress in vivo. In the current analysis we studied the association of serum ferritin concentration and serum soluble transferrin receptor concentration with daily urinary 8-hydroxydeoxyguanosine excretion, a marker of oxidative stress, in 48 mildly dyslipidemic men in East Finland. In multivariate linear regression analyses allowing for age, smoking, body mass index and physical exercise, serum ferritin concentration predicted the excretion rate at B = 0.17 (95% CI 0.08-0.26, P = 0.001), and serum soluble transferrin receptor to ferritin concentration ratio (TfR/ferritin) predicted the excretion rate at B = - 0.13 (95% CI - 0.21 to - 0.05, P = 0.002). Our data suggest that body iron contributes to excess oxidative stress already at non-iron overload concentrations in these subjects.     

Bacterial iron homeostasis

Iron is essential to virtually all organisms, but poses problems of toxicity and poor solubility. Bacteria have evolved various mechanisms to counter the problems imposed by their iron dependence, allowing them to achieve effective iron homeostasis under a range of iron regimes. Highly efficient iron acquisition systems are used to scavenge iron from the environment under iron-restricted conditions. In many cases, this involves the secretion and internalisation of extracellular ferric chelators called siderophores. Ferrous iron can also be directly imported by the G protein-like transporter, FeoB. For pathogens, host-iron complexes (transferrin, lactoferrin, haem, haemoglobin) are directly used as iron sources. Bacterial iron storage proteins (ferritin, bacterioferritin) provide intracellular iron reserves for use when external supplies are restricted, and iron detoxification proteins (Dps) are employed to protect the chromosome from iron-induced free radical damage. There is evidence that bacteria control their iron requirements in response to iron availability by down-regulating the expression of iron proteins during iron-restricted growth. And finally, the expression of the iron homeostatic machinery is subject to iron-dependent global control ensuring that iron acquisition, storage and consumption are geared to iron availability and that intracellular levels of free iron do not reach toxic levels.     

Ferritin, a physiological iron donor for microsomal lipid peroxidation

In the process of lipid peroxidation of microsomes induced either by oxygen radicals generated by xanthine oxidase or by NADPH, ferritin is able to donate the necessary iron. The amount of ferritin necessary to catalyze the process of lipid peroxidation is in the physiological range. In contrast to the finding with phospholipid liposomes, catalase hardly stimulates the lipid peroxidation of microsomes.     

Lymphocyte DNA damage and oxidative stress in patients with iron deficiency anemia

Oxidant stress has been shown to play an important role in the pathogenesis of iron deficiency anemia. The aim of this study was to investigate the association between lymphocyte DNA damage, total antioxidant capacity and the degree of anemia in patients with iron deficiency anemia. Twenty-two female with iron deficiency anemia and 22 healthy females were enrolled in the study. Peripheral DNA damage was assessed using alkaline comet assay and plasma total antioxidant capacity was determined using an automated measurement method. Lymphocyte DNA damage of patients with iron deficiency anemia was significantly higher than controls (p<0.05), while total antioxidant capacity was significantly lower (p<0.001). While there was a positive correlation between total antioxidant capacity and hemoglobin levels (r=0.706, p<0.001), both total antioxidant capacity and hemoglobin levels were negatively correlated with DNA damage (r=-0.330, p<0.05 and r=-0.323, p<0.05, respectively). In conclusion, both oxidative stress and DNA damage are increased in IDA patients. Increased oxidative stress seems as an important factor that inducing DNA damage in those IDA patients. The relationships of oxidative stress and DNA damage with the severity of anemia suggest that both oxidative stress and DNA damage may, in part, have a role in the pathogenesis of IDA.     

Ferritin in bone marrow and serum in iron deficiency and iron overload

Nonheme iron and ferritin in the bone marrow and serum ferritin was investigated in patients with iron deficiency anaemia or iron overload. As controls served patients without any disturbance of the iron metabolism. There is a precise correlation between the nonheme iron and ferritin in the bone marrow of patients with and without disturbance of iron metabolism. A correlation was also found between the ferritin in the bone marrow and the serum. Nonheme iron and ferritin in the bone marrow and serum ferritin was decreased in patients with iron deficiency anaemia. Conversely, the same parameters were increased in patients with iron overload.