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Resolving the paradigm crisis in intravenous iron and erythropoietin management.

Despite the proven benefits of intravenous (i.v.) iron therapy in anemia management, it remains underutilized in the hemodialysis population. Although overall i.v. iron usage continues to increase slowly, monthly usage statistics compiled by the US Renal Data System suggest that clinicians are not implementing continued dosing regimens following repletion of iron stores. Continued therapy with i.v. iron represents a key opportunity to improve patient outcomes and increase the efficiency of anemia treatment. Regular administration of low doses of i.v. iron prevents the recurrence of iron deficiency, enhances response to recombinant human erythropoietin therapy, minimizes fluctuation of hemoglobin levels, hematocrit levels, and iron stores, and may reduce overall costs of care. This article reviews the importance of i.v. iron dosing on a regular basis in the hemodialysis patient with iron-deficiency anemia and explores reasons why some clinicians may still be reluctant to employ these protocols in the hemodialysis setting.

Anemia, Iron-Deficiency↗

Sodium o-iodobenzoate and hemoglobin-oxygen affinity: in vivo effects.

Sodium o-iodobenzoate (OISB) was given intravenously to 15 dogs to test the in vivo effect of this drug on the oxyhemoglobin dissociation curve. Administration of a single dose of 500 mg/kg was followed by an average increase in P50 (PO2 at 50% oxyhemoglobin saturation) of 3.6 mmHg from 26.8 +/- 0.5 to 30.4 +/- 1.8 mmHg (corrected to pH 7.4). This elevation was sustained for 7 days. During intravenous infusions of 200 mg/kg every other day for 3 wk, there was a sustained increase in P50 of 2.6 mmHg from 27.8 +/- 1.1 to 30.4 +/- 0.9 mmHg. All dogs survived the experiment and no ill effects of the drug were noted. An increase in serum lactate and pyruvate occurred in all animals following acute or chronic exposure to the drug. There was no significant change in whole blood pH, 2,3-diphosphoglycerate concentrations, intracellular pH, or serum total phosphate. Multiple infusions of sodium cyanate (50 mg/kg per day) reduced P50 by an average of 12.2 +/- 0.3 mmHg. A subsequent single infusion of OISB (500 mg/kg) failed to increase P50. Our preliminary data indicate that pharmacological manipulation of hemoglobin O2 affinity is possible with organic compounds unrelated to erythrocyte metabolism.

Animals↗

Schiff base adducts of hemoglobin. Modifications that inhibit erythrocyte sickling.

Normal and sickle erythrocytes were exposed in vitro to millimolar concentrations of 31 different carbonyl compounds. Schiff base (imine) linkages were formed with amino groups of intracellular hemoglobin. Adducts were isolated by gel electrofocusing and could be dissociated by dialysis. Aromatic aldehydes proved more reactive than aliphatic aldehydes, and ketones were unreactive. The influence of various ring substituents on the reactivity of aromatic aldehydes was found to conform closely to traditional concepts regarding electronic and steric effects. Several of the aromatic aldehydes were shown to markedly increase the oxygen affinity of hemoglobins A and S. In particular, 2,4-dihydroxybenzaldehyde and o-vanillin, at concentrations of 5 mM, produced 2- to 3-fold reductions in the P50 (partial pressure of oxygen at half-saturation) of sickle hemoglobin in whole blood. Since low degrees of oxygen saturation promote erythrocyte sickling, compounds of this type significantly inhibit sickling at reduced partial pressures of oxygen.

Adult↗

Spectral analysis of Fe(III)-complex reduction by hemoglobin: possible mechanisms of interaction.

1. Hemoglobin is capable of electron transfer to Fe(III)-complexes of ATP, EDTA, NTA, and citrate leading to formation of reduced Fe(II) and its concurrent release from these chelating compounds as evident in the formation of a Fe(II)-Tris 2,2' bipyridine complex. 2. Multi-component analysis of kinetic spectra in the visible region (700-500 nm) has permitted a determination of the effect of various chelating molecules bound to Fe(III), pH, the effects of ionic strength, temperature, and the molecular nature of the Fe(III)-complex on reaction rates. 3. We have examined and compared the reactivities of normal adult hemoglobin A (alpha 2 beta 2) to reduce these Fe(III)-complexes and suggest possible mechanism(s) for the electron transfer process.

2,2'-Dipyridyl↗

Iron deficiency and intestinal malabsorption in HIV disease.

Children with human immunodeficiency virus (HIV) infection have a higher prevalence of intestinal malabsorption. Anemia is also a common feature in these children. The aims of this work were (a) to establish the prevalence of iron deficiency in HIV-infected children, (b) to test the hypothesis that iron deficiency is related to intestinal malabsorption, (c) to see whether it may contribute to anemia, and (d) to evaluate the sensitivity of oral iron load in the investigation of intestinal function. To accomplish these goals, 71 HIV-infected symptomatic children were enrolled. Iron serum values were determined before and after oral load with ferrous sulfate. The correlation between basal and post-load iron levels was evaluated by linear regression. Xylose level after oral load, fecal fat, and fecal alpha 1-antitrypsin concentration were also determined. Iron deficiency was detected in 48% of patients, and it was significantly associated with intestinal iron malabsorption. Sugar malabsorption, steatorrhea, and fecal protein loss were detected in 26, 36, and 17% of patients, respectively. Low hemoglobin levels were detected in 66% of patients. The majority of children with iron deficiency also had anemia. Preliminary data showed that oral iron administration was sufficient for raising hemoglobin in children with normal iron absorption, whereas parenteral administration was required in those with iron malabsorption. We conclude that (a) iron deficiency is a major feature of pediatric HIV infection, (b) it is related to intestinal malabsorption, and (c) it contributes to anemia. Finally, oral iron load is a sensitive test for investigating intestinal function.

Child↗

Identification of a two-component signal transduction system from Corynebacterium diphtheriae that activates gene expression in response to the presence of heme and hemoglobin.

Corynebacterium diphtheriae, the causative agent of diphtheria, utilizes various host compounds to acquire iron. The C. diphtheriae hmuO gene encodes a heme oxygenase that is involved in the utilization of heme and hemoglobin as iron sources. Transcription of the hmuO gene in C. diphtheriae is controlled under a dual regulatory mechanism in which the diphtheria toxin repressor protein (DtxR) and iron repress expression while either heme or hemoglobin is needed to activate transcription. In this study, two clones isolated from a C. diphtheriae chromosomal library were shown to activate transcription from the hmuO promoter in Escherichia coli. Sequence analysis revealed that these activator clones each carried distinct genes whose products had significant homology to response regulators of two-component signal transduction systems. Located upstream from each of these response regulator homologs are partial open reading frames that are predicted to encode the C-terminal portions of sensor kinases. The full-length sensor kinase gene for each of these systems was cloned from the C. diphtheriae chromosome, and constructs each carrying one complete sensor kinase gene and its cognate response regulator were constructed. One of these constructs, pTSB20, which carried the response regulator (chrA) and its cognate sensor kinase (chrS), was shown to strongly activate transcription from the hmuO promoter in a heme-dependent manner in E. coli. A mutation in chrA (chrAD50N), which changed a conserved aspartic acid residue at position 50, the presumed site of phosphorylation by ChrS, to an asparagine, abolished heme-dependent activation. These findings suggest that the sensor kinase ChrS is involved in the detection of heme and the transduction of this signal, via a phosphotransfer mechanism, to the response regulator ChrA, which then activates transcription of the hmuO promoter. This is the first report of a bacterial two-component signal transduction system that controls gene expression through a heme-responsive mechanism.

Alleles↗

The development of hemoglobin solutions as red cell substitutes: hemoglobin solutions.

Although the efficacy of hemoglobin-based oxygen carriers was established more than 60 years ago, all prior clinical trials have demonstrated significant toxicity characterized by renal dysfunction, gastrointestinal distress, and systemic vasoconstriction. The mechanisms of these toxicities now appear to be understood. Tetrameric forms of the hemoglobin molecule extravasate from the circulation and interact with endothelial derived relaxing factor, leading to unopposed vasoconstriction. Although numerous efforts are underway to chemically modify the native tetramer, it is likely that all tetrameric forms of the hemoglobin molecule will continue to extravasate. We have focused on developing a polymerized form of hemoglobin that is virtually free of unreacted tetramer. The development and characterization of this polymerized pyridoxylated hemoglobin solution (Poly SFH-P) is described. Clinical trials have been completed successfully in volunteers, and are now underway to assess the safety and efficacy of Poly SFH-P as a clinically useful red cell substitute in the treatment of acute blood loss in the setting of trauma and surgery.

Animals↗

Allylic nitro compounds as nitrite donors.

Allylic nitro compounds were synthesized and evaluated as organic sources of nitrite and nitric oxide. Unactivated allylic nitro compounds do not spontaneously release nitrite and nucleophile promoted nitrite release is slow. However, 2-(nitromethyl)-cyclohex-1-ene-3-one spontaneously dissociates in buffer (pH = 7.4) to release nitrite with a kobs = 1.6 x 10(-5) s(-1). In the presence of L-cysteine, this compound rapidly yields nitrite and reacts with hemoglobin similarly to sodium nitrite. Structural modifications and the nature and amount of nucleophile modulate the rate of nitrite release. In the presence of L-cysteine and ascorbic acid, this compound forms nitric oxide. Together, these results reveal a new structural architecture for the tunable liberation of nitrite and nitric oxide from organic compounds.

Molecular Structure↗

Radiation-induced changes of structural and functional properties of human hemoglobin. I. Spectral characterization of irradiated deoxyhemoglobin.

Structural changes of human deoxyhemoglobin (deoxyHb) induced by water and ethanol radicals were investigated in this study using absorption spectroscopy. Spectra of deoxyHb samples irradiated under various conditions (the atmosphere of argon or N2O in the absence or presence of ethanol) indicate their conversion into methemoglobin (metHb), hemichrome- and cholehemichrome-like products. The absorbance at the characteristic maxima of these derivatives and also of the oxidized or reduced samples following irradiation depends on the dose of radiation and the conditions employed.

Ferric Compounds↗

Alkylation of DNA and hemoglobin in the mouse following exposure to propene and propylene oxide.

Male CBA mice were exposed to propene, unlabelled or 14C-labelled, by inhalation, or to 14C-labelled propylene oxide by intraperitoneal injection. 2-Hydroxypropyl adducts to guanine-N-7 in DNA of various organs and to N-terminal valine and histidine-N pi in hemoglobin were measured. The adduct levels observed show that propylene oxide is the major primary metabolic product of propene. A direct comparison of propylene oxide with the homologous compound ethylene oxide on the basis of adduct levels introduced (in DNA and in hemoglobin) at equimolar injected amounts, shows that propylene oxide is 6-10 times less effective than ethylene oxide.

Alkenes↗

Effect of oral iron supplementation during pregnancy on maternal and fetal iron status.

The known increased need for iron during pregnancy appears to be met only in part by increased iron absorption and amenorrhea. Considerable demands are made on maternal iron stores and, since many women lack sufficient storage iron, pregnancy may be expected to cause iron deficiency. This may lead to anemia in pregnancy and post partum and could also have a bearing on the iron status of the fetus and the neonate. Based on these considerations, prophylactic supplementation of dietary iron is advocated but remains a disputed issue. In the present controlled, prospective and longitudinal study changes in hematologic status, and in particular in iron stores, during pregnancy were investigated in 44 healthy Caucasian women with uncomplicated pregnancies and deliveries. They were randomly assigned to a study group (n = 21) receiving oral iron supplements from the 16th week of amenorrhea until 6 weeks post partum, and a control group (n = 23) without iron supplementation. Maternal concentrations of hemoglobin, serum iron, serum transferrin and serum ferritin were determined at 16, 28 and 36 weeks of amenorrhea, at delivery, and 6 and 12 weeks post partum. The same variables were determined in cord blood. Iron supplementation appeared to prevent the physiologic fall in hemoglobin and serum iron concentrations which occurred in the control group, but had little influence on the observed rise in transferrin concentrations. Ferritin levels in serum, which are known to reflect mobilisable iron stores, fell to 30% of the initial values in the control group and to 70% in the study group. Six and 12 weeks post partum ferritin levels were still low in the nonsupplemented group (Tab. I).(ABSTRACT TRUNCATED AT 250 WORDS)

Administration, Oral↗

Iron supplementation in adolescent hemodialysis patients.

AIMS: Iron supplementation is necessary in children on hemodialysis, but the optimal protocol remains unknown. We studied the effects of changing our unit's protocol from oral iron with periodic doses of parenteral iron dextran to routine administration of parenteral sodium ferric gluconate on anemia and iron parameters. METHODS: We followed seven hemodialysis patients aged 15 20 years (mean 17 years). Hemoglobin, hematocrit, serum iron, transferrin saturation, ferritin, erythropoietin dose, total elemental iron dose and total iron cost for the six months prior to the protocol change were compared to the same variables during the six months following the change. RESULTS: There was no statistically significant difference between the doses of parenteral iron between the two protocols; however, the total dose of elemental iron administered in the oral iron plus iron dextran protocol was greater than in the sodium ferric gluconate protocol (19.6+/-13.1 (mean+/-SD) mg/kg/week versus 1.1+/-0.3 mg/kg/week; p = 0.03). Both protocols had equivalent efficacy with respect to hemoglobin, ferritin and other measures of iron stores. On the other hand, the costs of sodium ferric gluconate were significantly higher than those of oral iron plus intermittent iron dextran (157.75+/-45.94 $/patient/month versus 52.08+/-49.88 $/patient/month; p = 0.01). CONCLUSIONS: Routine administration of sodium ferric gluconate is equivalent if not superior to use of oral iron plus iron dextran for maintenance of iron stores in adolescents on hemodialysis, but more expensive.

Administration, Oral↗

[A specific spectrophotometric method for determining plasma and/or serum hemoglobin. Use of the chromogen 2,2'-azino-di-(3-ethylbenzothiazoline)-6-sulfonate (ABTS)].

The authors describe a method for the determination of the plasma and/or serum haemoglobin, based on the peroxidase properties of the Haemoglobin-Haptoglobin complex, following the action of a solution of ABTS and hydrogen peroxide. The colour observed after a defined period of time is measured by spectrophotometry at 402 nm and is proportional to the haemoglobin concentration of the sample. A statistical study of the plasma haemoglobin concentration performed in male and female blood donors aged between 18 and 60 years is also presented.

Adolescent↗

The interaction of hemoglobin with hexadecyltrimethylammonium bromide.

The interaction of hemoglobin (Hb) with hexadecyltrimethylammonium bromide (CTAB) is investigated by UV-vis absorption spectra and fluorescence spectra method. CTAB monomer can convert methemoglobin (metHb) to hemichrome, and CTAB molecular assemblies, such as micelle, microemulsion and lamellar liquid crystal, can induce heme monomer to leave the hydrophobic cavity of Hb. TEM results show that Hb maintains the spherical structure in CTAB microemulsions while it is unfolded in CTAB lamellar liquid crystals. The existence of proton in the above systems can increase the stability of metHb.

Cetrimonium↗

Characterization of structural xenobiotic modifications in proteins by high sensitivity tandem mass spectrometry. Human hemoglobin treated in vitro with styrene 7,8-oxide.

Alkylation of DNA by xenobiotic agents, or their electrophilic metabolites, is believed to be the major initiating process that may result ultimately in carcinogenesis. The study of hemoglobin alkylated in vivo by chemical carcinogens has previously been proposed as an indicator for DNA alkylation. Xenobiotically modified proteins, however, are not readily amenable to conventional methods for amino acid sequencing. Tandem mass spectrometry allows unambiguous structural elucidation of chemically modified proteins. Styrene is a widely used chemical in the plastics industry and its major metabolite, styrene 7,8-oxide, is both mutagenic and carcinogenic in rodents. Human hemoglobin was modified in vitro with styrene 7,8-oxide and digested with trypsin. Tryptic peptides from unmodified hemoglobin were isolated by high performance liquid chromatography, and their molecular weights were determined by liquid secondary ion mass spectrometry. This allowed confirmation of the known sequence of the protein and provided a reference for the identification of modified peptides. High performance tandem mass spectrometry of modified peptides allowed unambiguous assignment of specific residues modified. The externally accessible histidines were found to be the dominant sites for alkylation at high modification levels of the protein.

Alkylation↗

Possible contribution of oxyhemoglobin to the iron-induced hemolysis simultaneous effect of iron and hemoglobin on lipid peroxidation.

The mechanism of iron toxicity in iron overloaded patients is not well established. A hypothesis was put forward that free radical processes are involved. Our earlier study indicates that iron-induced hemolysis is preceded by peroxidation of the membrane lipids. In the present work the simultaneous effect of iron and hemoglobin on lipid peroxidation was studied. It was found that in hemoglobin-containing liposome suspensions Fe2+ in concentrations above 10(-5) M inhibits the peroxidation, while Fe3+ drastically potentiates it, with concomitant transformation of oxyhemoglobin to methemoglobin. The experiments with scavengers of activated oxygen indicate superoxide anion radical (O-.2), hydroxyl radical (OH.) and singlet oxygen (1O2) participation. The possible mechanism of the phenomenon is discussed. A conclusion is drawn that the toxic effect of Fe3+ may be associated not only with iron--membrane interaction, but also with increased methemoglobin formation and O-.2 release.

Animals↗

Bioavailability of Petit-Suisse cheese as food vehicle for iron fortification estimated by the prophylactic method.

Microencapsulated ferrous sulfate (SFE-171) and ferric orthophosphate in Petit-Suisse cheese were examined for iron bioavailability by the prophylactic method. The iron sources were industrially added to different samples of Petit-Suisse cheese, which were mixed with other food components in our laboratory before use. A reference standard diet inclusive of nonmicroencapsulated ferrous sulfate and a control diet low in iron content were prepared in the laboratory. The final iron content in the fortified diets was approximately 15 mg Fe/kg diet. These diets were administered to weaning rats for 23 days. The iron bioavailability was evaluated as the ratio of iron incorporated into hemoglobin to oral iron intake, thereby being estimated as 62.6 +/- 8.8% for ferrous sulfate and 59.2 +/- 10.6% for SFE-171, which were significantly effective at p < 0.01 compared to 43.4 +/- 10.5% for ferric orthophosphate. It thus turned out that SFE-171 was stable through industrial processing with Petit-Suisse cheese as the food vehicle and served as an iron fortifier equal to ferrous sulfate in bioavailability.

Administration, Oral↗