Body iron metabolism and pathophysiology of iron overload. Int J Hematol. 2008;88:7-15. [PMID: 18594779 DOI: 10.1007/s12185-008-0120-5]

Body iron store as a predictor of oxidative DNA damage in healthy men and women

While iron plays an important role in many cellular functions, excess iron storage induces DNA damage by generating hydroxyl radicals and thus promotes carcinogenesis. However, it remains unclear whether body iron levels that are commonly observed in a general population are related to oxidative DNA damage. We examined the association between serum ferritin concentrations and levels of urinary 8-hydroxydeoxyguanosine (8-OHdG), a biomarker of systemic oxidative DNA damage and repair, in 528 Japanese men and women aged 21-67 years. Men had much higher ferritin levels than in women, and the levels were significantly greater in women aged 50 years or older than in women aged less than 50 years. Urinary 8-OHdG concentrations were significantly and positively associated with serum ferritin levels in all the subgroups. The Spearman rank correlation coefficients were 0.47, 0.76, and 0.73 for men overall, women aged less than 50 years, and women aged 50 years or older, respectively. These associations were materially unchanged after adjustment for potential confounding variables. In men, a more pronounced association was observed in nonsmokers than in smokers. Our results suggest body iron storage is a strong determinant of levels of systemic oxidative DNA damage in a healthy population.

Clinical consequences of iron overload from chronic red blood cell transfusions, its diagnosis, and its management by chelation therapy

Iron overload from chronic transfusion therapy can be extremely toxic. Excess transfusional iron is deposited in the liver, heart, and other organs as free iron, which can cause organ dysfunction and damage over time. Increased awareness of the risk of iron overload in patients requiring chronic transfusion therapy is needed, and such patients should be screened for hyperferritinemia. Those with serial serum ferritin levels exceeding 1000 ng/mL and a total infused red blood cell volume of 120 mL/kg of body weight or more should be treated with chelation therapy and then monitored to ensure that treatment adequately reduces iron levels.

Oncostatin M and leukemia inhibitory factor increase hepcidin expression in hepatoma cell lines

Overproduction of hepcidin by interleukin-6 (IL-6) is considered to be the main factor responsible for the development of anemia in inflammatory conditions. Since oncostatin M (OSM), a member of the IL-6 family, plays an important role in immune and inflammatory responses, we assessed the effect of OSM on hepcidin expression, as well as that of leukemia inhibitory factor (LIF), another member of the IL-6 family. We found that hepcidin expression was markedly induced by OSM and LIF in a time- and dose-dependent manner in hepatoma cell lines, and this expression was induced independent of IL-6/IL-6 receptor signaling. Luciferase assay revealed that OSM and LIF stimulated a -1.3-kb hepcidin promoter. This effect was markedly reduced when the signal transducer and activator of transcription (STAT) site of the promoter was mutated, and was almost completely abolished in the presence of AG-490, a Janus kinase (JAK) inhibitor. Hence, the JAK/STAT pathway plays a major role in OSM- and LIF-induced activation of the hepcidin promoter. In conclusion, we demonstrated that OSM and LIF can induce hepcidin expression mainly through the JAK/STAT pathways. Further studies are warranted to evaluate the clinical significance of OSM and LIF in the development of anemia in various inflammatory diseases.

Iron overload and toxicity: the hidden risk of multiple blood transfusions

BACKGROUND

The quantity of iron in body is carefully regulated, primarily by control of iron absorption, and excess total body iron can be extremely toxic. Since humans have no mechanism for elimination of excess iron, multiple transfusions of red blood cells, which are required for the management of a number of disorders, inevitably result in iron overload. Cumulative iron overload, in turn, leads to iron toxicity with organ dysfunction and damage.

MATERIALS

This review examines the relationship between iron metabolism and hematologic disorders treated with multiple transfusions, with emphasis on the diagnosis and current methods of management of iron overload and toxicity in transfusion-dependent patients. Primarily using key words, we identified and reviewed more than 100 pertinent articles in English and other languages in the Medline database plus an additional number of abstracts of presentations at recent meetings of relevant scientific associations.

RESULTS

Transfusion-dependent disorders include those characterized by decreased red blood cell production, increased red blood cell destruction, or chronic blood loss. Patients receiving chronic transfusion therapy should be screened and monitored for iron overload, yet in our opinion, this is not always done routinely. Once iron overload has been identified, it should be treated to reduce the risk of morbidity and mortality from iron toxicity, which particularly affects the liver and heart.

CONCLUSION

Increased awareness of the risks of iron overload from chronic transfusion therapy should result in greater use of interventions such as iron chelation to reduce total body iron and the risk of long-term sequelae.

Transferrin and ferritin response to bacterial infection: the role of the liver and brain in fish

Iron is essential for growth and survival, but it is also toxic when in excess. Thus, there is a tight regulation of iron that is accomplished by the interaction of several genes including the iron transporter transferrin and iron storage protein ferritin. These genes are also known to be involved in response to infection. The aim of this study was to understand the role of transferrin and ferritin in infection and iron metabolism in fish. Thus, sea bass transferrin and ferritin H cDNAs were isolated from liver, cloned and characterized. Transferrin constitutive expression was found to be highest in the liver, but also with significant expression in the brain, particularly in the highly vascularized region connecting the inferior lobe of the hypothalamus and the saccus vasculosus. Ferritin, on the other hand, was expressed in all tested organs, but also significantly higher in the liver. Fish were subjected to either experimental bacterial infection or iron modulation and transferrin and ferritin mRNA expression levels were analyzed, along with several iron regulatory parameters. Transferrin expression was found to decrease in the liver and increase in the brain in response to infection and to increase in the liver in iron deficiency. Ferritin expression was found to inversely reflect transferrin in the liver, increasing in infection and iron overload and decreasing in iron deficiency, whereas in the brain, ferritin expression was also increased in infection. These findings demonstrate the evolutionary conservation of transferrin and ferritin dual functions in vertebrates, being involved in both the immune response and iron metabolism.

Iron behaving badly: inappropriate iron chelation as a major contributor to the aetiology of vascular and other progressive inflammatory and degenerative diseases

BACKGROUND

The production of peroxide and superoxide is an inevitable consequence of aerobic metabolism, and while these particular 'reactive oxygen species' (ROSs) can exhibit a number of biological effects, they are not of themselves excessively reactive and thus they are not especially damaging at physiological concentrations. However, their reactions with poorly liganded iron species can lead to the catalytic production of the very reactive and dangerous hydroxyl radical, which is exceptionally damaging, and a major cause of chronic inflammation.

REVIEW

We review the considerable and wide-ranging evidence for the involvement of this combination of (su)peroxide and poorly liganded iron in a large number of physiological and indeed pathological processes and inflammatory disorders, especially those involving the progressive degradation of cellular and organismal performance. These diseases share a great many similarities and thus might be considered to have a common cause (i.e. iron-catalysed free radical and especially hydroxyl radical generation).The studies reviewed include those focused on a series of cardiovascular, metabolic and neurological diseases, where iron can be found at the sites of plaques and lesions, as well as studies showing the significance of iron to aging and longevity. The effective chelation of iron by natural or synthetic ligands is thus of major physiological (and potentially therapeutic) importance. As systems properties, we need to recognise that physiological observables have multiple molecular causes, and studying them in isolation leads to inconsistent patterns of apparent causality when it is the simultaneous combination of multiple factors that is responsible.This explains, for instance, the decidedly mixed effects of antioxidants that have been observed, since in some circumstances (especially the presence of poorly liganded iron) molecules that are nominally antioxidants can actually act as pro-oxidants. The reduction of redox stress thus requires suitable levels of both antioxidants and effective iron chelators. Some polyphenolic antioxidants may serve both roles.Understanding the exact speciation and liganding of iron in all its states is thus crucial to separating its various pro- and anti-inflammatory activities. Redox stress, innate immunity and pro- (and some anti-)inflammatory cytokines are linked in particular via signalling pathways involving NF-kappaB and p38, with the oxidative roles of iron here seemingly involved upstream of the IkappaB kinase (IKK) reaction. In a number of cases it is possible to identify mechanisms by which ROSs and poorly liganded iron act synergistically and autocatalytically, leading to 'runaway' reactions that are hard to control unless one tackles multiple sites of action simultaneously. Some molecules such as statins and erythropoietin, not traditionally associated with anti-inflammatory activity, do indeed have 'pleiotropic' anti-inflammatory effects that may be of benefit here.

CONCLUSION

Overall we argue, by synthesising a widely dispersed literature, that the role of poorly liganded iron has been rather underappreciated in the past, and that in combination with peroxide and superoxide its activity underpins the behaviour of a great many physiological processes that degrade over time. Understanding these requires an integrative, systems-level approach that may lead to novel therapeutic targets.