An Overview of Molecular Aspects of Iron Metabolism

Iron (Fe) is an essential, but potentially noxious, metal for almost all organisms. Its precise cellular regulation is necessary to ensure synthesis of numerous iron-containing proteins required for metabolic processes yet at the same time avoiding the build-up of potentially toxic levels of iron. In humans, iron-deficiency results in anemia, while excess iron can lead to organ damage as a result of a build-up of non-transferrin-bound iron (NTBI). In recent years, the cloning of novel proteins has clarified the mechanisms of iron uptake, storage and metabolic regulation. Our current knowledge of the molecular aspects of mammalian iron metabolism and NTBI are presented in this review.     

Erythropoietin Administration May Potentiate Mobilization of Storage Iron in Patients on Oral Iron Chelation Therapy

Five, repeatedly transfused, patients with refractory anemia (RA) or RA with ringed sideroblast (RARS) subtypes of myelodysplastic syndrome (MDS), with serum ferritin (SF) levels of >2,000 μg/L, and one female with Hb E [β26(B8)Glu→Lys]/β⁰-thalassemia (thal) with an SF level of 1,760 μg/L, were treated with deferiprone (L1) at the dose of 4–6 g per day for at least 26 months. Beginning in the second month, all patients received recombinant human erythropoietin (rHuEPO) at the dose of 150 IU/kg thrice weekly, subcutaneously for 24 months. A significant increase in iron excretion after combined administration of L1 and rHuEPO compared to treatment with L1 as a single agent, was observed in all patients. The amount of excreted iron in urine ranged from 7.5 to almost 20 mg per day. In one patient, a response to rHuEPO resulted in transfusion independence and her SF decreased from 2086 to 879 μg/L. In four MDS patients, who remained dependent on red blood cell (RBC) transfusions, simultaneous administration of L1 and rHuEPO enabled the stabilization of SF levels, despite continuing iron load from the transfusions. Combined administration of rHuEPO and oral iron chelators may potentiate mobilization of storage iron and maintain iron balance in transfusion-dependent iron overloaded early MDS patients.     

Insights on regulation and function of the iron regulatory protein 1 (IRP1)

Iron regulatory protein 1 (IRP1) controls the translation or stability of several mRNAs by binding to iron responsive elements (IREs) within their untranslated regions. Its activity is regulated by an unusual iron-sulfur cluster (ICS) switch. Thus, in iron-replete cells, IRP1 assembles a cubane [4Fe-4S] cluster that prevents RNA-binding activity and renders the protein to cytosolic aconitase. We show that wild type or mutant forms of IRP1 that fail to assemble a [4Fe-4S] cluster are sensitized for iron-dependent degradation by the ubiquitin-proteasome pathway. The regulation of IRP1 abundance poses an alternative mechanism to prevent accumulation of inappropriately high IRE-binding activity when the ICS assembly pathway is impaired. To study functional aspects of IRP1, we overexpressed wild type or mutant forms of the protein in human H1299 lung cancer cells in a tetracycline-inducible fashion, and analyzed how this affects cell growth. While the induction of IRP1 did not affect cell proliferation in culture, it dramatically reduced the capacity of the cells to form solid tumor xenografts in nude mice. These data provide a first link between IRP1 and cancer.     

支气管哮喘患者外周血ET-1、TXB2水平变化及临床意义

目的 探讨支气管哮喘患者外周血中内皮素(ET-1)、血栓素B2(TXB2)的动态变化及临床意义.方法 支气管哮喘急性发作期患者75例(其中轻度42例,中重度33例),健康对照组38例.采用放射免疫法测定血浆中ET-1、TXB2的水平.结果 1、血浆中ET-1、TXB2水平轻度与中重度哮喘组患者高于健康对照组,差异有统计学意义(P<0.01).中重度哮喘组高于轻度组,差异有统计学意义(P<0.01).2、哮喘组血浆中ET-1与TXB2水平呈正相关(r=0.601,P<0.01).结论 ET-1、TXB2可能在哮喘的急性发病过程中起作用,以及影响哮喘的发生、发展.     

Effectiveness of the intestinal polypeptides,IRP, GIP,VIP and motilin on insulin release in the rat

Summary Intestinal insulin releasing polypeptide (IRP) and Gastric inhibitory polypeptide (GIP) have a similar effect on intravenous glucose tolerance in the rat. Both augment the insulin response to intravenous glucose and increase the rate of glucose disappearance. VIP and motilin have no discernible effect. Plasma insulin dose-response curves to IRP and GIP are similar; both peptides stimulate insulin release in the presence of small blood glucose increments. A direct comparison of the insulin releasing potency of IRP and GIP is not possible as the former is not yet available in pure form.     

Iron Mobilization From Transferrin And Non-Transferrin-Bound-Iron by Deferiprone. Implications in the Treatment of Thalassemia,Anemia of Chronic Disease,Cancer and Other Conditions

Iron mobilization from transferrin is one of the most important screening methods for the selection of chelators intended for clinical use in the treatment of iron overload in thalassemia and other conditions. In vitro and in vivo screening of approved and experimental chelating drugs has shown that only the α-ketohydroxypyridines deferiprone (L1) and 1-allyl-2 methyl-3-hydroxypyrid-4-one (L1NAll), are effective in the mobilization of iron from transferrin. Iron mobilization from transferrin and non-transferrin-bound-iron (NTBI) can be used to optimize existing chelation therapy protocols for the treatment of iron loaded patients. New chelation strategies involving L1 and its combination with deferoxamine (DFO) and other chelators can be used to increase iron excretion and reduce or prevent excess iron deposition in the heart and other vital organs of iron loaded patients by comparison to monotherapies. Deferiprone and its combinations may also have potential applications in the treatment of cancer, the anemia of chronic disease and other conditions.     

The Effect of Iron(III) on the Activity of Selenoenzymes and Oxidative Damage in the Liver of Rats. Interaction with Natural Antioxidants and Deferiprone

Iron is an essential element which, under certain conditions, can have prooxidant and cancerogenic effects. The effect of iron and iron chelators on the activity of selenoenzymes has been studied. Acute experiments in male Wistar rats demonstrated the prooxidant effect of iron on the selenoenzymes thioredoxin reductase (TrxR) and glutathione peroxidase (GPx). These enzymes represent an important part of the antioxidant defense system. Deferiprone (L1) has been shown to abolish the stimulating effect of iron on lipid peroxidation and reduced glutathione (GSH) levels, and also to inhibit the influence of iron on the activity of TrxR and GPx. Similarly, the flavonoid quercetin abolished the influence of iron on the activity of TrxR. The activity of both selenoenzymes has also been shown to be stimulated using L1, naringin (NAR), quercetin (QUE) and myricetin (MYR) in the absence of iron. Further studies including the combination of synthetic and natural compounds (e.g., flavonoids) are being considered for their possible development and clinical use in antioxidant therapies.     

Myocyte Damage and Loss of Myofibers is the Potential Mechanism of Iron Overload Toxicity in Congestive Cardiac Failure in Thalassemia. Complete Reversal of the Cardiomyopathy and Normalization of Iron Load by Deferiprone

Cardiac damage caused by iron overload toxicity is the main cause of death in thalassemia patients. Biopsy samples of poorly chelated thalassemia patients who suffered congestive cardiac failure (CCF) show extensive iron deposition in the myocardium. In one patient who survived CCF, a cardiac biopsy was performed during the removal of a thrombus caused by a port-a-cath, which was used for the administration of intravenous (iv) deferoxamine (DFO). Ultrastructural pathology studies of the cardiac biopsy indicated extensive iron deposition in myocytes with accumulation of iron mainly in lysosomes, leading in some cases to their disruption. Damage to other intracellular components of the myocytes and loss of myofibers was also observed. The patient became intolerant to iv and subcutaneous (sc) DFO 2 years after the CCF, and was then treated with deferiprone (L1) for 7 years. Within 1 year of L1 treatment at 75–80 mg/kg/day, serum ferritin levels were reduced to <0.45 mg/L and she became asymptomatic, needing no further drugs for her cardiomyopathy. Lowering the L1 dose to 50–70 mg/kg/day caused an increase in serum ferritin levels. Maintenance of normal iron stores during the last 3 years as detected by cardiac and liver magnetic resonance imaging (MRI) T2 and T2* and normalization of serum ferritin levels (<0.15 mg/L) was observed following L1 therapy at 80–85 mg/kg/day. Deferiprone (>80 mg/kg/day) appears to be effective in the rapid clearance of cardiac iron, in the reversal of iron overload related cardiomyopathy, in the maintenance of normal iron stores and the overall long-term survival of thalassemia patients.     

Poly(rC)-Binding Protein 1 Limits Hepatitis C Virus Virion Assembly and Secretion

The hepatitis C virus (HCV) co-opts numerous cellular elements, including proteins, lipids, and microRNAs, to complete its viral life cycle. The cellular RNA-binding protein, poly(rC)-binding protein 1 (PCBP1), was previously reported to bind to the 5′ untranslated region (UTR) of the HCV genome; however, its importance in the viral life cycle has remained unclear. Herein, we sought to clarify the role of PCBP1 in the HCV life cycle. Using the HCV cell culture (HCVcc) system, we found that knockdown of endogenous PCBP1 resulted in an overall decrease in viral RNA accumulation, yet resulted in an increase in extracellular viral titers. To dissect PCBP1’s specific role in the HCV life cycle, we carried out assays for viral entry, translation, genome stability, RNA replication, as well as virion assembly and secretion. We found that PCBP1 knockdown did not directly affect viral entry, translation, RNA stability, or RNA replication, but resulted in an overall increase in infectious particle secretion. This increase in virion secretion was evident even when viral RNA synthesis was inhibited, and blocking virus secretion could partially restore the viral RNA accumulation decreased by PCBP1 knockdown. We therefore propose a model where endogenous PCBP1 normally limits virion assembly and secretion, which increases viral RNA accumulation in infected cells by preventing the departure of viral genomes packaged into virions. Overall, our findings improve our understanding of how cellular RNA-binding proteins influence viral genomic RNA utilization during the HCV life cycle.     

老年颈动脉粥样斑块与胰岛素样生长因子-1及血脂的相关性研究

目的探讨胰岛素样生长因子1(IGF1)对老年颈动脉斑块(CAP)的影响及其在脂代谢中的作用。方法检测48例经颅多普勒超声确诊的老年CAP患者的血清IGF1水平和血脂指标,并与40例无CAP的老年人对照,并将两组的数据进行相关性分析。结果老年CAP组血清IGF1水平明显低于对照组(P<0.05);而TC、TG、LDL水平均较对照组高(P<0.01);HDL水平无显著差异。斑块组TC、TG、LDL均与IGF1呈负相关;HDL与IGF1无相关性。结论脂代谢紊乱是动脉粥样斑块形成的主要危险因素,IGF1作为一种重要的循环内分泌多肽,参与CAP的形成及脂代谢的调节。     

Low Serum Ferritin Levels are Misleading for Detecting Cardiac Iron Overload and Increase the Risk of Cardiomyopathy in Thalassemia Patients. The Importance of Cardiac Iron Overload Monitoring Using Magnetic Resonance Imaging T2 and T2*

The incidence of cardiomyopathy was monitored in a 6-year follow-up study involving 56 transfused thalassemia patients treated with deferoxamine (DFO), deferiprone (L1) or their combination. During this period, five female patients on regular subcutaneous or intravenous DFO presented with cardiac complications. Three patients suffered congestive heart failure and the other two arrhythmias. Four of the five patients maintained serum ferritin levels of about 1 mg/L or below and the fifth about 1.5 mg/L for several years prior to the cardiomyopathy. Cardiac magnetic resonance imaging (MRI) T2* and T2 was performed in four patients after the cardiomyopathy, identifying the presence of moderate-to-heavy siderosis. The treatment of the five patients has since changed, involving mainly the use of L1. Low serum ferritin levels appear to be misleading for detecting cardiac iron overload and this may increase the risk of cardiomyopathy. The MRI T2 and T2* relaxation time measurements are a more accurate method of detecting cardiac iron overload. Chelation therapy using L1 or appropriate L1/DFO combinations can reduce cardiac iron overload and the mortality rate in thalassemia patients.     

Regulation of innate immune responses by DAI (DLM-1/ZBP1) and other DNA-sensing molecules

DNA, whether it is microbe-derived or host-derived, evokes immune responses when exposed to the cytosol of a cell. We previously reported that DNA-dependent activator of IFN regulatory factors (DAI), also referred to as DLM-1/ZBP1, functions as a DNA sensor that activates the innate immune system. In the present study, we examined the regulation of the complex DNA-sensing system by DAI and other molecules. We first show that DAI directly interacts with DNA in vitro and that it requires three DNA-binding domains for full activation in vivo. We also show that the artificially induced dimerization of DAI results in the DNA-independent activation of type I IFN genes, thereby providing a better understanding for the molecular basis of DAI activation. Furthermore, we provide evidence for the presence of additional DNA sensors, either positively or negatively regulating cytosolic DNA-mediated innate immune responses. These results in toto provide insights into the mechanism of DAI activation and reveal the complex regulatory mechanisms underlying DNA-mediated protective and pathologic immune responses.     

Ang-(1-7)在急性呼吸窘迫综合征中的肺保护作用

肺组织局部的肾素-血管紧张素系统(RAS)与急性呼吸窘迫综合征(ARDS)关系密切,血管紧张素Ⅱ(AngⅡ)通过其1型受体激活肺部炎症反应,促进ARDS发生发展.血管紧张素-(1-7)[Ang-(1-7)]也是RAS中得重要重要组分之一,能拮抗AngⅡ的生物学作用,被认为是AngⅡ的内源性拮抗剂.在ARDS中,Ang-(1-7)可能通过抑制炎症反应、减轻肺组织纤维化以及抗肺动脉高压等途径发挥肺保护作用,在ARDS中具有广阔的应用前景.     

Effect of Deferiprone on Liver Iron Overload and Fibrosis in Hepatitis C Virus-Infected Thalassemia

To assess the effects of liver iron overload and fibrosis after treatment with a chelating agent in hepatitis C virus (HCV)-infected thalassemia, from April 1999 to July 2004, 45 patients with thalassemia major (age range 9–33 years, mean 19.3) received daily deferiprone (L1) for 23–60 months (75 mg/kg). The patients were divided into two groups on the basis of their hepatitis status (27 with, 18 without). Their serum was analyzed for alanine aminotransferase (GPT), aspartate aminotransferase (GOT), bilirubin (total/direct), r-glutamyl transpeptidase (r-GT), alkaline phosphatase (Alk-P), and ferritin. Liver iron overload and fibrosis were defined by a senior pathologist. No significant differences were demonstrated in serum levels of GPT, GOT, bilirubin, r-GT, Alk-P or ferritin; comparison was made for each group before and after L1 treatment. Iron scores were 2.3 ± 0.9 and 2.8 ± 0.9 for the hepatitis C negative and positive groups, respectively (p = 0.07), with liver fibrosis scores of 1.0 ± 0.5 and 0.4 ± 0.52 (p = 0.56). The two scores were not higher for the positive group. There was no evidence of: 1) greater iron overload and fibrosis in the HCV-infected thalassemic patients; 2) L1 inducing progressive hepatic fibrosis or worsening iron overload in HCV-infected thalassemic patients after long-term therapy; 3) further damage to liver cells associated with L1 treatment.     

TNF,TNF inducers,and TNFR2 agonists: A new path to type 1 diabetes treatment

In the past decade, interest in the century‐old tuberculosis vaccine, bacillus Calmette‐Guerin (BCG), has been revived for potential new therapeutic uses in type 1 diabetes and other forms of autoimmunity. Diverse clinical trials are now proving the value of BCG in prevention and treatment of type 1 diabetes, in the treatment of new onset multiple sclerosis and other immune conditions. BCG contains the avirulent tuberculosis strain Mycobacterium bovis, a vaccine originally developed for tuberculosis prevention. BCG induces a host response that is driven in part by tumour necrosis factor (TNF). Induction of TNF through BCG vaccination or through selective agonism of TNF receptor 2 (TNFR2) has 2 desired cellular immune effects: (1) selective death of autoreactive T cells and (2) expansion of beneficial regulatory T cells (Tregs). In human clinical trials in both type 1 diabetes and multiple sclerosis, administration of the BCG vaccine to diseased adults has shown great promise. In a Phase I trial in advanced type 1 diabetes (mean duration of diabetes 15 years), 2 BCG vaccinations spaced 4 weeks apart selectively eliminated autoreactive T cells, induced beneficial Tregs, and allowed for a transient and small restoration of insulin production. The advancing global clinical trials using BCG combined with mechanistic data on BCGs induction of Tregs suggest value in this generic agent and possible immune reversal of the type 1 diabetic autoimmune process.