Effects of riboflavin and desferrioxamine B on Fe(Ⅱ)oxidation by 0_(2)

Flavins and siderophores secreted by various plants,fungi and bacteria under iron(Fe)deficient conditions play important roles in the biogeochemical cycling of Fe in the environment.Although the mechanisms of flavin and siderophore mediated Fe(Ⅱ)reduction and dissolution under anoxic conditions have been widely studied,the influence of these compounds on Fe(ID)oxidation under oxic conditions is still unclear.In this study,we investi-gated the kinetics of aqueous Fe(Ⅱ)(17.8μM)oxidation by O_(2)at pH 5-7 in the presence of riboflavin(oxidized(RBF)and reduced(RBFH_(2)))and desferrioxamine B(DFOB)as representative flavins and siderophores,respec-tively.Results showed that the addition of RBF/RBFH_(2)or DFOB markedly accelerates the oxidation of aqueous Fe(Ⅱ)by O_(2).For instance,at pH 6,the rate of Fe(Ⅱ)oxidation was enhanced 20-70 times when 10μM RBFH_(2)was added.The mechanisms responsible for the accelerated Fe(Ⅰ)oxidation are related to the redox reactivity and complexation ability of RBFH_(2),RBF and DFOB.While RBFH_(2)does not readily complex Fe(Ⅰ)/Fe(Ⅱ),it can activate O_(2)and generate reactive oxygen species,which then rapidly oxidize Fe(Ⅱ).In contrast,both RBF and DFOB do not reduce O_(2)but react with Fe(Ⅱ)to form RBF/DFOB-complexed Fe(Ⅱ),which in turn accelerates Fe(Ⅰ)oxidation.Furthermore,the lower standard reduction potential of the Fe(Ⅰ)-DFOB complex,compared to the Fe(Ⅰ)-RBF complex,correlates with a higher oxidation rate constant for the Fe(Ⅰ)-DFOB complex.Our study reveals an overlooked catalytic role of flavins and siderophores that may contribute to Fe(Ⅱ)/Fe(Ⅱ)cycling at oxic-anoxic interfaces.

Liver iron content determination by magnetic resonance imaging

Accurate evaluation of iron overload is necessary to establish the diagnosis of hemochromatosis and guide chelation treatment in transfusion-dependent anemia. The liver is the primary site for iron storage in patients with hemochromatosis or transfusion-dependent anemia, therefore, liver iron concentration (LIC) accurately re? ects total body iron stores. In the past 20 years, magnetic resonance imaging (MRI) has emerged as a promising method for measuring LIC in a variety of diseases. We review the potential role of MRI in LIC determination in the most important disorders that are characterized by iron overload, that is, thalassemia major, other hemoglobinopathies, acquired anemia, and hemochromatosis. Most studies have been performed in thalassemia major and MRI is currently a widely accepted method for guiding chelation treatment in these patients. However, the lack of correlation between liver and cardiac iron stores suggests that both organs should be evaluated with MRI, since cardiac disease is the leading cause of death in this population. It is also unclear which MRI method is the most accurate since there are no large studies that have directly compared the different available techniques. The role of MRI in the era of genetic diagnosis of hemochromatosis is also debated, whereas data on the accuracy of the method in other hematological and liver diseases are rather limited. However, MRI is a fast, non-invasive and relatively accurate diagnostic tool for assessing LIC, and its use is expected to increase as the role of iron in the pathogenesis of liver disease becomes clearer.

A Comparative Study on the Enhancement Efficacy of Specific and Non-specific Iron Chelators for Protoporphyrin Ⅸ Production and Photosensitization in HaCat Cells

The iron chelators can be utilized in target cells to improve 5-aminolaevulinic acid （ALA）-based photodynamic therapy （PDT）. The purpose of this study is to compare the effect of two kinds of iron chelators, desferrioxamine （DFO） and ethylenediaminetetraacetic acid （EDTA） on the enhancement of ALA-PDT. HaCat cells were cultured in medium containing 2.0 mmol/L of ALA and 0.5 mmol/L of DFO or EDTA. After 3-h incubation in the dark, the concentration of cellular pro-toporphyrin Ⅸ （PpⅨ） was detected by high performance liquid chromatography （HPLC）, and the fluorescence of PpⅨ was observed at 630 nm emission under confocal laser scanning microscope. For PDT, HaCat cells were irradiated using 632.8 nm laser, and the fractions of apoptotic and necrotic cells were flow cytometrically assayed. Related differences in morphology and ultrastructure of Ha-Cat cells were observed using optical microscope or transmission electron microscope. Compared to incubation with ALA alone, the addition of DFO or EDTA increased the concentration of cellular PpⅨ and the fluorescent density of PpⅨ, and also increased cell death ratio after PDT. PDT using ALA plus DFO produced the highest cellular PpⅨ level, greatest cell death ratio and most severe structural damage to the cells. It was concluded that both DFO and EDTA could enhance ALA-based PpⅨ production and PDT. Compared to the non-specific iron chelator of EDTA, the specific chelator, DFO, showed more potential for the enhancement.

Liver cirrhosis as a consequence of iron overload caused by hereditary nonspherocytic hemolytic anemia

Nonspherocytic hereditary anemias are occasionally accompanied by significant iron overload but the significance for the development of chronic liver disease is not clear. We described two cases of patients with chronic liver d isease and severeiron overload due to chronic hereditary hemolysis. Both patients have had signs of liver cirrhosis and severe hemolysis since childhood. A hereditary pyruvate kinase deficiency (PKD) was discovered as the underlying reason for the hemolysis.Sequencing of the pyruvate kinase gene showed a mutation within exon 11. Liver histology in both patients revealed cirrhosis and a severe iron overload but primary hemochromatosis was excluded by HFE-gene analysis.An iron reduction therapy with desferrioxamine led to significant decrease of serum ferritin and sustained clinical improvement. PKD-induced hemolysis may cause severe iron overload even in the absence of HFE-genotype abnormalities. This secondary iron overload can lead to chronic liver disease and cirrhosis. Therefore, the iron metabolism of PKD patients has to be closely monitored and iron overload should be consequently treated.

Correction of Severe Anemia in a Patient with End Stage Renal Disease and Myelodysplastic Syndrome

Background: Anemia is a common complication of end-stage renal disease (ESRD) and is effectively managed by Erythropoietin Stimulating Agents (ESAs) and intravenous iron therapy. Management of anemia in ESRD patients with myelodysplastic syndrome (MDS) poses a unique challenge. ESAs even at extremely high doses do not result in a desired response, especially if the patients are iron-overloaded. Case: A 72-year-old man with history of ESRD and MDS on hemodialysis since September 2009 was severely anemic requiring massive doses of ESA in excess of 90,000 units/week. Iron saturation was consistently >60%;ferritin was >2500. Desferrioxamine (DFO) 125 mg IV/week was begun in November 2010. His PRBC transfusion and ESA requirements declined after the initiation of this therapy. He had 33 ER visits for PRBC transfusions (1 - 3 transfusions/visit) from September 2009 to November 2010 (average: 2.35/month), which decreased to 18 visits in 20 months (average: 0.9/month) after getting DFO. Conclusion: We report a case of MDS with ESRD on hemodialysis where anemia was managed with Desferrioxamine therapy along with ESA, after which it was noted that there was a significant reduction in the number of PRBC transfusions that the patient received along with a decrease in ESA requirements and a decrease in number of hospitalizations, which in the long term could be cost effective.

Determination of bacterial viability by selective capture using surface-bound siderophores

A significant challenge in bacterial detection is the identification of viable bacteria over debris, specifically post decontamination. Of increasing concern are antibiotic resistant strains that require accurate and rapid post decontamination analysis. Current strategies are fraught with disadvantages and most of them are not selective for viable bacteria. However, bacteria are critically dependent upon iron sequestration, synthesizing and releasing siderophores (SDPs) to tightly bind iron, with the subsequent uptake of iron bound SDPs. This is a highly conserved process that occurs only in intact bacteria. Herein we report a facile method to use bacterial SDPs to selectively and rapidly identify only viable bacteria in complex matrices, and discriminate them from their dead counterparts. Desferrioxamine B (Desf B) tethered to a glass slide is used to specifically capture viable bacteria from a mixture of viable and dead Escherichia coli, as demonstrated by fluorescence microscopy. We re- port both direct conjugation of Desf B on thin-film-coated glass slides as well as biotin-streptavidin conjugation strategies, both of which are successful in the said goal. We have analyzed the density of images obtained upon fluorescence staining using edge detection with a Canny edge detector. This novel application of a software analysis tool originally developed for satellite imaging to biological staining allows for accurate quantitation of observed data.

去铁敏干预蛛网膜下腔出血后溶酶体组织蛋白酶表达研究

目的:探讨大鼠蛛网膜下腔出血(SAH,Subarachnoid Hemorrhage)早期脑损伤中溶酶体组织蛋白酶B(Cathepsin B)、溶酶体组织蛋白酶D(Cathepsin D)的表达变化及去铁敏(DFO)对其的影响。方法:将24只SD大鼠随机分为四组:正常对照组(6只),SAH模型组(6只),安慰剂组(6只),DFO药物组(6只),视交叉前池注血法(APC)制作大鼠SAH模型,免疫组化分别检测Cathepsin D、Cathepsin B的蛋白表达,干湿法测定48 h脑含水量。结果:与正常组比较,SAH模型组大鼠48 h后Cathepsin D、Cathepsin B的蛋白表达明显增强,水肿指数增高,DFO药物组大鼠48h后Cathepsin D、Cathepsin B的蛋白表达较SAH组明显减低,水肿指数减低。结论:Cathepsin D、Cathepsin B在大鼠蛛网膜下腔出血后表达增强,DFO能减少其表达并对早期脑损伤有保护作用,溶酶体可能参与了蛛网膜下腔出血早期脑损伤的过程,稳定溶酶体膜,减少Cathepsin B/D的释放可能为SAH后早期脑损伤提供新的治疗途径。