Nozokomiální methemoglobinemie

Congenital methemoglobinemia in a dog with a promoter deletion and a nonsynonymous coding variant in the gene encoding cytochrome b₅.

Methemoglobinemia is not a rare condition arising from the exposure to hemoglobin-oxidizing agents such as nitrates-nitrites present in well water or vegetables. Infants <3 months of age are more susceptible than adults because of lower amounts of a key enzyme, NADH-cytochrome b5 reductase, which converts methemoglobin back to hemoglobin. We report 2 infants, aged respectively 2 and 1 months, suffering from methemoglobinemia, fed with a formula that was reconstituted with a high concentration of courgette soup to resolve constipation. They developed a severe cyanosis with methemoglobinemia (respectively 30.4 and 27%) and were hospitalized and treated with methylene blue at 1%. After 12 h the syndrome was completely resolved. Home-prepared infant foods containing vegetables are potential causes of methemoglobinemia. It is important not to feed infants with vegetables having a high nitrate content (e.g., courgette, spinach, beets and green beans) to resolve constipation since, particularly in the first months of life, they may cause severe methemoglobinemia.

Iron is an essential element for the growth and survival of nearly all living organisms. However, it is difficult for most organisms to get enough iron from the environment, because of the extremely low solubility of ferric ion. One of the strategies for iron acquisition is to use the ATP-binding cassette (ABC) transport system. In Gram-negative bacteria, a typical iron uptake ABC transporter consists of a ferric ion-binding protein (Fbp) located in periplasm (FbpA), two transmembrane proteins that form a pathway for ferric ions (FbpB), and two peripheral ATP-binding proteins located at the cytoplasm side of the inner membrane (FbpC). TtFbpA is a ferric ion-binding protein of a putative iron uptake ABC transporter from Thermus thermophilus HB8. Here we report the crystal structures of the apo-form and ferric ion-bound form of TtFbpA at 1.8-Å and 1.7-Å resolutions, respectively [1]. The crystal structure of the ferric ion-bound TtFbpA shows that a ferric ion binds to a specific site of TtFbpA to form a six-coordinated complex by three tyrosine residues, two bicarbonates and a water molecule, revealing a novel mode of coordination to a ferric ion. Another crystal structure of ferric ion-bound TtFbpA reported earlier showed the bound ferric ion is five-coordinated by three tyrosine residues and a carbonate bound in the bidentate manner [2]. The different modes of the coordination would probably result from the different pHs used for crystallization: pH 5.5 (six-coordinated) vs. pH 7.5 (five-coordinated). The Gram negative bacterium T. thermophilus HB8 can live in a wide pH range of 3.4–9.6. We propose that TtFbpA, a periplasmic protein of T. thermophilus HB8, can act as a ferric ion-binding protein over the wide pH range by taking at least two different coordination manners to a ferric ion depending on pH. This is the first example of a periplasmic ferric iron-binding protein that can coordinate a ferric ion via multiple types of coordination complex formation.

Symbiosomes and bacteroids isolated from soybean (Glycine max Merr.) nodules are able to take up ferrous iron. This uptake activity was completely abolished in the presence of ferrous-iron chelators. The kinetics of uptake were characterized by initially high rates of iron internalization, but no saturation was observed with increasing iron concentration. This process does not appear to involve the ferric reductase of the peribacteroid membrane. The transport of ferrous iron was inhibited by other transition metals, particularly copper. Ferrous iron was taken up by symbiosomes more efficiently than the ferric form. This indicates that the iron transport from the plant host cell to the microsymbiont in vivo may occur mainly as the ferrous form.

Published corrosion studies have demonstrated the formation of a passive layer and assessed corrosion rate in a NaCl matrix fluid. However, a critical issue for corrosion laboratory tests is to simulate realistic downhole and reservoir brine composition and conditions, which includes a complex matrix of Na+, K+, Mg2+, Ca2+, Sr2+, Ba2+, Fe2+, HCO3–, CO2(aq), and others. Just as crucial, dissolved oxygen concentration should be controlled at reservoir conditions which are strictly anoxic (&amp;lt;&amp;lt; 1 ppb dissolved O2), especially for projects dealing with ferrous iron. Strictly anoxic conditions are crucial for evaluating efficiency and degradation of corrosion inhibitors because dissolved oxygen may interfere and even react with corrosion inhibitors under production temperatures and pressures. Flow-through corrosion tests were performed for 3 weeks at 200 °C and 1,380 bar. The feed solutions were prepared to represent realistic field brines with complex mixtures of cations and anions, instead of using only NaCl, as is commonly done. All solutions were strictly anoxic (&amp;lt;&amp;lt; 1 ppb dissolved O2). Ferrous iron is from the dissolution of carbon steel 1010 due to corrosion. Mineral deposits on the inner surface of test tubings were collected for XRD and SEM analyses. A single phase of ankerite (CaMg0.27Fe0.73(CO3)2) was observed instead of siderite (FeCO3), calcite (CaCO3), or magnetite (Fe3O4), which are commonly reported as corrosion products at temperatures above 150 °C. Strictly anoxic conditions allow iron to exist in its ferrous form causing it to incorporate into the ankerite structure, as would be seen in the reservoir and production stream. SEM images and XRD composition of the corrosion products showed that the inner surface of test tubing was uniformly covered by ankerite. These results demonstrate that more complicated corrosion products can form under simulated downhole environment by using realistic brine compositions under strictly anoxic conditions. The surface properties, solubility, and density of this passive layer could be very different from siderite (FeCO3) and magnetite (Fe3O4), which could cause different protection properties. As a result, corrosion rates may be different than previously reported under extreme conditions and should be studied further.

Spectrophotometry of hemoglobin: a criticism.

Pregnancy with methemoglobinemia (metHb) poses several challenges to the anaesthesiologist. MetHb is characterized by iron moiety of Hb in the ferric ( Fe 3+) state. MetHb has decreased oxygen carrying capacity and increased oxygen affinity resulting in cyanosis and tissue hypoxia. Clinical features are proportional to the concentration of the MetHb, which range from asymptomatic state to seizures and cardiac arrthymia to fatality. We present a case of primigravida with Methemoglobinemia posted for emergency cesarean section.At presentation she had cyanosis, dyspnoea and pain in abdomen. Her methemoglobin levels were 25%. She was treated with Methylene blue before induction. This article addresses the anaesthetic challenges and precautions to be taken for a successful anaesthetic management of a patient with methemoglobinemia.

Background:there is an intimate relation between transition metals and cell homeostasis due to the physiological necessity of metals in vivo. Particularly, iron (ferrous and ferric state) is utilized in many physiological processes of the cell but in excess has been linked with negative role contributing in many neurodegenerative processes.Objective:the aim of this study was to investigate which oxidation state of ionic iron (Ferrous (II) versus Ferric (III)) is more toxic to neuronal cells (SHSY5Y).Materials and Methods:The neuroblastoma (SHSY5Y) cells were exposed to varying concentration of ferric and ferrous iron. Morphological studies using immunofluorescence staining and microscopic analysis as confirmed by intracellular glutathione (GSH) test demonstrated oxidative stress to cells in iron microenvironment. In addition, MTT assay was performed to evaluate the viability and metabolic state of the cells.Results:the results showed that ferrous form has significantly higher toxicity compared to the ferric ionic state of higher concentration. In addition, microscopic analysis shows cell fenestration at higher concentrations and swelling at intermediate ferric dosages as demonstrated by atomic force microscopy (AFM). Interestingly, the addition of a differentiation inducing factor, trans-retinoic rcid (RA) retains significant viability and morphological features of the cells irrespective of the ionic state of the iron. AFM images revealed clustered aggregates arising from iron chelation with RA.Conclusions:the results indicate that Fe (II) has more toxic effects on cells. In addition, it could be an interesting finding with respect to the antioxidant properties of RA as a chelating agent for the neurodegenerative therapeutics.

Iron deficiency has long been considered to be the most difficult of nutrient deficiencies in plants to understand and to correct. After the landmark discovery in 1843 that lime‐induced chlorosis was a form of iron deficiency, progress was slow for the next 100 years. Many, but not all, of the scientific giants who made significant progress on understanding iron chlorosis and iron physiology in plants in the 1940's and 1950's have passed away. Thome was certain that ferrous iron was the key to understanding the disorder. Kliman had suggested uptake of Pe in the ferrous form. Iljin found that iron chlorotic leaves had high levels of free amino acids, high levels of citrate and total organic acids, were high in P and K and low in Ca concentrations. These are the criteria that generally identify iron chlorosis. Shive and his students found an Fe‐Mn interaction through which Fe deficiency can be induced. Warm found that lime‐induced chlorosis in grapes could be largely prevented if resistant rootstocks were chosen. Those workers represented a generation gone but it will not be forgotten. Leeper did critical evaluations which demonstrated that chlorotic leaves often— very often—contain more iron than do green leaves. Oserkowsky and Lindner and Harley found that green leaves contained more “active” iron than chlorotic leaves. The role of bicarbonate was better elucidated by many workers. While the nature of iron chlorosis was being subjected to many studies, same breakthroughs occurred in its control. Jacobson used iron chelate (EDTA) as the Fe source in nutrient solutions. Stewart and Leonard successfully took FeEDTA to the field for control of Fe deficiency on orange trees. Kroll synthesized a chelating agent with 108 higher stability with Fe than FeEOTA. It found many applications. There were many other pioneers in this period. The 1960's and 1970's saw modem biochemical techniques move into the field. Iron deficient roots excrete more protons than normal roots. Iron inefficient plants are genetically controlled (one gene in at least some situations). They have less reducing ability at the root surface and excrete fewer protons than Fe efficient plants. Citrate functions in the xylem transport of Fe (ferric yet). Iron deficiency can be identified through analysis of certain enzymes before the chlorophyll begins to disappear. The role of Fe in synthesis of chlorophyll is better elucidated. The modern pioneers include Brown, Evans, Marshner, DeKock, Chaney, Tiffin, Bar‐Akiva and many others. But the next pioneers probably will be the plant breeders who will wipe out the problem—at least in important plant species.

A potters clay from the Gorgan plain, in N. E. Iran, has been fired successively at temperatures up to the melting point 1 200 °C in an atmosphere of air or 5 % CO in moist CO2. Mossbauer spectra at 296 K and 4.2 K allow the determination of the relative amounts of iron in well-crystallised haematite or magnetite, of poorly-crystallised and fine-particle ferric oxide or hydroxide, and of iron diluted in the ferrous or ferric form in silicate minerals. In an oxidizing atmosphere there is no ferrous iron in firings above 500 °C and at 1 200 °C, all the ferric iron is diluted in the silicate matrix. A peak in the magnetization which reaches 5 emu/g. Fe near 1 100 °C is associated with a decrease in the size of ferric oxide fine particles before their disappearance at 1 200 °C. In a reducing atmosphere, some ferric iron persists up to about 1 200 °C, 12 % of the iron is in the form of magnetite between 600 and 800 °C, and its progressive disappearance from 850 °C accounts for the drop in magnetization from 16 emu/g. Fe at 800 °C to zero at 1 100 °C.

Iron is an indispensable micronutrient for virtually all microorganisms, where it acts as a cofactor of many enzymes involved in regulation of multiple cellular and physiological functions. This metal is also considered an important determinant contributing to the pathogenesis of fungal infectious diseases, and therefore the identification of iron-regulated metabolic processes occurring within the invading fungal cell can help the development of new antifungal therapeutic strategies. In this study, we examined relationships between iron availability and neutral storage lipids in Histoplasma capsulatum, a dimorphic fungus responsible for the most common respiratory and systemic mycosis in humans. Yeast cells were grown in a defined minimal medium supplemented with or without iron. Lipids were extracted from cells at the log and late stationary growth phases, then separated by thin-layer chromatography, and fatty acids were analyzed by gas chromatography. A culture age-related decrease in the unsaturated fatty acid content was observed in all four neutral lipid classes examined. Iron-related alterations could be seen in relation to triacylglycerol and free fatty acid pools, whereas no iron-dependent effects were detected in diacylglycerol and steryl ester fractions. Regarding triacylglycerols, the presence of iron positively affected the content of unsaturated fatty acids, and this stabilizing action of iron was notably increased when ferrous ions were added. Subsequent iron uptake studies showed a definite preference of H. capsulatum to acquire iron in its reduced, more soluble, ferrous form, and therefore, the availability of iron may be the underlying reason for the observed iron-maintained homeostasis in H. capsulatum triacylglycerols.

Acid and ferric sulfate bioleaching of uranium ores: A review #

Researchers have speculated as to the molecular basis of O(2) sensing for decades. In more recent years, since the discovery of ion channels as identified effectors for O(2) sensing pathways, research has focussed on possible pathways coupling a reduction in hypoxia to altered ion channel activity. The most extensively studied systems are the K(+) channels which are inhibited by hypoxia in chemoreceptor tissues (carotid and neuroepithelial bodies). In this review, we consider the evidence supporting the involvement of well defined enzymes in mediating the regulation of K(+) channels by hypoxia. Specifically, we focus on the roles proposed for three enzyme systems; NADPH oxidase, heme oxygenase and AMP activated protein kinase. These systems differ in that the former two utilise O(2) directly (to form superoxide in the case of NADPH oxidase, and as a co-factor in the degradation of heme to carbon monoxide, bilirubin and ferrous iron in the case of heme oxygenase), but the third responds to shifts in the AMP:ATP ratio, so responds to changes in O(2) levels more indirectly. We consider the evidence in favour of each of these systems, and highlight their differential importance in different systems and species. Whilst the evidence for each playing an important role in different tissues is strong, there is a clear need for further study, and current awareness indicates that no one specific cell type may rely on a single mechanism for O(2) sensing.

Fundamental investigations were made on the oxidation of pyrite and consequent dissolution of iron by pure and mixed cultures of Thiobacillus ferrooxidans and Thiobacillus thiooxidans. The release of iron from pyrite was remarkably enhanced with large inocula above ca. 109 cells per flask (or 1% pulp density) of 2-day (active) cultures of T. ferrooxidans, but not with inoculum of 108 cells or less. Furthermore, a phenomenon was observed that the enhanced oxidation of pyrite always proceeded with the coexistence of a 108 cells or less inoculum of T. ferrooxidans and T. thiooxidans incapable of oxidizing pyrite. During the bacterial oxidation of pyrite, high iron oxidation ratios (Fe3+/total Fe) above 90% were maintained, coincident with the enhanced release of iron from pyrite. Contrarily, in the absence of T. ferrooxidans, a major portion of iron was in the ferrous form and iron release was not promoted. Thus, it was thought that T. ferrooxidans contributes to the oxidation of pyrite through the regeneration reaction of ferric iron.

The phase equilibria in the Fe–Zn–O system in the range 900–1580°C in air have been experimentally studied using equilibration and quenching techniques. The compositions of the phases at equilibrium were determined using electron probe X‐ray microanalysis (EPMA). The ferrous and ferric bulk iron concentrations were measured with a wet chemical analysis using the ammonium metavanadate technique. X‐ray powder diffraction analysis (XRD) was used to characterise the phases. Iron oxide dissolved in zincite was found to be present principally in the ferric form. The XRD analysis and the composition measurements both indicate that zincite is the only phase stable in the ZnO‐rich area in the range of conditions investigated. The solubility of the iron oxide in zincite rapidly increases at temperatures above 1200°C; the morphology of the zincite crystals also sharply changes between 1200 and 1300°C from rounded to plate‐like crystals. The plate‐like zincite forms a refractory network—the type of microstructure beneficial to the Imperial Smelting Process (ISP) sinter performance. The software program FactSage with a thermodynamically optimised database was used to predict phase equilibria in the Fe–Zn–O system.