Prebiotics increase iron absorption and reduce the adverse effects of iron on the gut microbiome and inflammation: a randomized controlled trial using iron stable isotopes in Kenyan infants

BACKGROUND

Iron fortificants tend to be poorly absorbed and may adversely affect the gut, especially in African children.

OBJECTIVE

We assessed the effects of prebiotic galacto-oligosaccharides/fructo-oligosaccharides (GOS/FOS) on iron absorption and gut health when added to iron-fortified infant cereal.

METHODS

We randomly assigned Kenyan infants (n = 191) to receive daily for 3 wk a cereal containing iron and 7.5 g GOS/FOS (7.5 g+iron group), 3 g (3-g+iron group) GOS/FOS, or no prebiotics (iron group). A subset of infants in the 2 prebiotic+iron groups (n = 66) consumed 4 stable iron isotope-labeled test meals without and with prebiotics, both before and after the intervention. Primary outcome was fractional iron absorption (FIA) from the cereal with or without prebiotics regardless of dose, before and after 3 wk of consumption. Secondary outcomes included fecal gut microbiota, iron and inflammation status, and effects of prebiotic dose.

RESULTS

Median (25th-75th percentiles) FIAs from meals before intervention were as follows: 16.3% (8.0%-27.6%) without prebiotics compared with 20.5% (10.4%-33.4%) with prebiotics (Cohen d = 0.53; P < 0.001). FIA from the meal consumed without prebiotics after intervention was 22.9% (8.5%-32.4%), 41% higher than from the meal without prebiotics before intervention (Cohen d = 0.36; P = 0.002). FIA from the meal consumed with prebiotics after intervention was 26.0% (12.2%-36.1%), 60% higher than from the meal without prebiotics before intervention (Cohen d = 0.45; P = 0.007). After 3 wk, compared with the iron group, the following results were observed: 1) Lactobacillus sp. abundances were higher in both prebiotic+iron groups (P < 0.05); 2) Enterobacteriaceae sp. abundances (P = 0.022) and the sum of pathogens (P < 0.001) were lower in the 7.5-g+iron group; 3) the abundance of bacterial toxin-encoding genes was lower in the 3-g+iron group (false discovery rate < 0.05); 4) fecal pH (P < 0.001) and calprotectin (P = 0.033) were lower in the 7.5-g+iron group.

CONCLUSIONS

Adding prebiotics to iron-fortified infant cereal increases iron absorption and reduces the adverse effects of iron on the gut microbiome and inflammation in Kenyan infants. This trial was registered at clinicaltrials.gov as NCT03894358.

Impact of Flooding-Drainage Alternation on Fe Uptake and Transport in Rice: Novel Insights from Iron Isotopes

Iron (Fe) isotopes were utilized to provide insights into the temporal changes underlying Fe uptake and translocation during rice growth (tillering, jointing, flowering, and maturity stages) in soil-rice systems under typical flooding-drainage alternation. Fe isotopic composition (δ56Fe values) of the soil solution generally decreased at vegetative stages in flooding regimes but increased during grain-filling. Fe plaques were the prevalent source of Fe uptake, as indicated by the concurrent increase in the δ56Fe values of Fe plaques and rice plants during rice growth. The increasing fractionation magnitude from stem/nodes I to flag leaves can be attributed to the preferred phloem transport of light isotopes toward grains, particularly during grain-filling. This study demonstrates that rice plants take up heavy Fe isotopes from Fe plaque and soil solution via strategy II during flooding and the subsequent drainage period, respectively, thereby providing valuable insights into improving the nutritional quality during rice production.

Iron Isotopes in Acid Mine Drainage: Extreme and Divergent Fractionation between Solid (Schwertmannite, Jarosite, and Ferric Arsenate) and Aqueous Species

Examination of stable Fe isotopes is a powerful tool to explore Fe cycling in a range of environments. However, the isotopic fractionation of Fe in acid mine drainage (AMD) has received little attention and is poorly understood. Here, we analyze Fe isotopes in waters and Fe(III)-rich solids along an AMD flow-path. Aqueous Fe spanned a concentration and δ⁵⁶Fe range of ∼420 mg L^-1 and + 0.04‰ at the AMD source to ∼100 mg L^-1 and -0.81‰ at ∼450 m downstream. Aqueous As (up to ∼33 mg L^-1) and SO₄^2- (up to ∼2000 mg L^-1), like aqueous Fe, decreased in concentration down the flow-path. X-ray absorption spectroscopy indicated that downstream attenuation in aqueous Fe, As, and SO₄^2- was due to the precipitation of amorphous ferric arsenate (AFA), schwertmannite, and jarosite. The Fe(III) in these solids displayed extreme variability in δ⁵⁶Fe, spanning +3.95‰ in AFA near the AMD source to -1.34‰ in schwertmannite at ∼450 m downstream. Similarly, the isotopic contrast between solid Fe(III) precipitates and aqueous Fe (Δ⁵⁶Fe_ppt-aq) dropped along the flow-path from about +4.1 to -1.1‰. The shift from positive to negative Δ⁵⁶Fe_ppt-aq reflects divergence between competing equilibrium versus kinetic fractionation processes.

Large Fractionation in Iron Isotopes Implicates Metabolic Pathways for Iron Cycling in Boreal Shield Lakes

Stable Fe isotopes have only recently been measured in freshwater systems, mainly in meromictic lakes. Here we report the δ⁵⁶Fe of dissolved, particulate, and sediment Fe in two small dimictic boreal shield headwater lakes: manipulated eutrophic Lake 227, with annual cyanobacterial blooms, and unmanipulated oligotrophic Lake 442. Within the lakes, the range in δ⁵⁶Fe is large (ca. -0.9 to +1.8‰), spanning more than half the entire range of natural Earth surface samples. Two layers in the water column with distinctive δ⁵⁶Fe of dissolved (dis) and particulate (spm) Fe were observed, despite differences in trophic states. In the epilimnia of both lakes, a large Δ⁵⁶Fe_dis-spm fractionation of 0.4-1‰ between dissolved and particulate Fe was only observed during cyanobacterial blooms in Lake 227, possibly regulated by selective biological uptake of isotopically light Fe by cyanobacteria. In the anoxic layers in both lakes, upward flux from sediments dominates the dissolved Fe pool with an apparent Δ⁵⁶Fe_dis-spm fractionation of -2.2 to -0.6‰. Large Δ⁵⁶Fe_dis-spm and previously published metagenome sequence data suggest active Fe cycling processes in anoxic layers, such as microaerophilic Fe(II) oxidation or photoferrotrophy, could regulate biogeochemical cycling. Large fractionation of stable Fe isotopes in these lakes provides a potential tool to probe Fe cycling and the acquisition of Fe by cyanobacteria, with relevance for understanding biogeochemical cycling of Earth's early ferruginous oceans.

Laboratory study of iron isotope fractionation during dissolution of mineral dust and industrial ash in simulated cloud water

Atmospheric deposition is a key mode of iron (Fe) input to ocean regions where low concentrations of this micronutrient limit marine primary production. Various natural particles (e.g., mineral dust, volcanic ash) and anthropogenic particles (e.g., from industrial processes, biomass burning) can deliver Fe to the ocean, and assessment of their relative importance in supplying Fe to seawater requires knowledge of both their deposition flux and their Fe solubility (a proxy for Fe bioavailability). Iron isotope (⁵⁴Fe, ⁵⁶Fe, ⁵⁷Fe, ⁵⁸Fe) analysis is a potential tool for tracing natural and anthropogenic Fe inputs to the ocean. However, it remains uncertain how the distinct Fe isotopic signatures (δ⁵⁶Fe) of these particles may be modified by physicochemical processes (e.g., acidification, photochemistry, condensation-evaporation cycles) that are known to enhance Fe solubility during atmospheric transport. In this experimental study, we measure changes over time in both Fe solubility and δ⁵⁶Fe of a Tunisian soil dust and an Fe-Mn alloy factory industrial ash exposed under irradiation to a pH 2 solution containing oxalic acid, the most widespread organic complexing agent in cloud- and rainwater. The Fe released per unit surface area of the ash (∼1460 μg Fe m^-2) is ∼40 times higher than that released by the dust after 60 min in solution. Isotopic fractionation is also observed, to a greater extent in the dust than the ash, in parallel with dissolution of the solid particles and driven by preferential release of ⁵⁴Fe into solution. After the initial release of ⁵⁴Fe, the re-adsorption of A-type Fe-oxalate ternary complexes on the most stable surface sites of the solid particles seems to impair the release of the heavier Fe isotopes, maintaining a relative enrichment in the light Fe isotope in solution over time. These findings provide new insights on Fe mobilisation and isotopic fractionation in mineral dust and industrial ash during atmospheric processing, with potential implications for ultimately improving the tracing of natural versus anthropogenic contributions of soluble Fe to the ocean.

Iron Bioavailability from Ferrous Ammonium Phosphate, Ferrous Sulfate, and Ferric Pyrophosphate in an Instant Milk Drink-A Stable Isotope Study in Children

Ferrous ammonium phosphate (FAP) is an iron salt that has been developed for the fortification of food matrices sensitive to color and flavor changes. The objective of the study was to measure iron absorption from FAP in young children and compare it to a previous evaluation of FAP in young women. A double-blind randomized crossover study with two parallel arms was used to evaluate the iron absorption from FAP added to reconstituted milk powder in comparison to that from ferrous sulfate (FeSO4) and ferric pyrophosphate (FePP). Iron absorption was measured in 39 children aged 3- to 6-years-old using erythrocyte incorporation of stable Fe isotopes (57Fe, 58Fe). The geometric mean iron absorption in iron replete children from FAP, FeSO4 and FePP from milk was 8.3%, 7.6% and 2.1%, respectively. Iron absorption from FAP and FeSO4 fortified milk was not significantly different (p = 0.199); however, it was significantly higher than from FePP fortified milk (p < 0.001). Iron bioavailability from FAP and FePP relative to FeSO4 (relative bioavailability (RBV)) was 110% and 33%, respectively. The RBV of FAP (110%) in iron replete children was higher than previously reported RBV (71%) in mainly iron deficient women. The difference in iron status between the children and women in the respective studies may explain the different RBV values and is discussed.

Zinc regulation of iron uptake and translocation in rice (Oryza sativa L.): Implication from stable iron isotopes and transporter genes

Iron (Fe) is an essential nutrient for living organisms and Fe deficiency is a worldwide problem for the health of both rice and humans. Zinc (Zn) contamination in agricultural soils is frequently observed. Here, we studied Fe isotope compositions and transcript levels of Fe transporter genes in rice growing in nutrient solutions having a range of Zn concentrations. Our results show Zn stress reduces Fe uptake by rice and drives its δ⁵⁶Fe value to that of the nutrient solution. These observations can be explained by the weakened Fe(II) uptake through Strategy I but enhanced Fe(III) uptake through Strategy II due to the competition between Zn and Fe(II) combining with OsIRT1 (Fe(II) transporter) in root, which is supported by the downregulated expression of OsIRT1 and upregulated expression of OsYSL15 (Fe(III) transporter). Using a mass balance box model, we also show excess Zn reduces Fe(II) translocation in phloem and its remobilization from senescent leaf, indicating a competition of binding sites on nicotianamine between Zn and Fe(II). This study provides direct evidence that how Zn regulates Fe uptake and translocation in rice and is of practical significance to design strategies to treat Fe deficiency in rice grown in Zn-contaminated soils.

Iron isotope of suspended particulate matter in Zhujiang River, Southwest China: Characteristics, sources, and environmental implications

Understanding the environmental iron cycle influenced by natural and anthropogenic processes is significant to obtain the key information on earth-surface evolution. Iron isotope compositions and elemental compositions of the suspended particulate matter (SPM) in Zhujiang River were investigated to provide key insights for the earth-surface iron cycle. The δ⁵⁶Fe values of SPM display the range from -0.05‰ to 0.34‰ (averaged 0.19‰) while the iron contents range from 0.73 wt% to 7.63 wt% (averaged 4.15 wt%). The Chemical Index of Alteration (CIA) shows that the main weathering type of SPM is intermediate weathering (mean CIA value: 79.12). While the main chemical weathering types are similar, the δ⁵⁶Fe values vary dramatically, indicating that chemical weathering is not the governing factor of δ⁵⁶Fe values of SPM. Furthermore, evidence from the enrichment factors (EF, 0.78 to 1.29) of iron and Zinc isotopes reveals that the iron input from anthropogenic activities is quite limited. The significant correlation between (Fe/Ca)SPM and (Na/Ca)SPM, (Mg/Ca)SPM, (Al/Ca)SPM and (K/Ca)SPM (0.73 < r < 0.99, p < 0.01, n = 22) and the A-CN-K diagram could confirm that clay minerals (especially smectite and illite) are important components of SPM. Meanwhile, the higher enrichment rates of La, Pr and Nd with the increasing iron contents denote heavy minerals (mainly Fe oxides/oxy-hydroxides) are also important compositions of SPM. Based on the isotopic mass balance, it shows that the iron flux of SPM to the oceans during the wet season would reduce the δ⁵⁶Fe values of the bulk ocean by 0.3%. The present study reports the iron isotope and elemental compositions of Zhujiang SPM and identifies its influencing factors (weathering, anthropogenic inputs, and minerals effect), and also provides a quantitative reference for the intriguing question on the distinct δ⁵⁶Fe values of oceans, which is beneficial for understanding iron cycle in earth-surface system.

Iron absorption during pregnancy is underestimated when iron utilization by the placenta and fetus is ignored

BACKGROUND

Maternal iron absorption during pregnancy can be evaluated using RBC incorporation of orally administered stable iron isotope. This approach underestimates true maternal absorption of iron as it does not account for absorbed iron that is transferred to the fetus or retained within the placenta.

OBJECTIVE

Our objective was to re-evaluate maternal iron absorption after factoring in these losses and identify factors associated with iron partitioning between the maternal, neonatal, and placental compartments.

METHODS

This study utilized data from stable iron isotope studies carried out in 68 women during the third trimester of pregnancy. Iron status indicators and stable iron isotopic enrichment were measured in maternal blood, umbilical cord blood, and placental tissue when available. Factors associated with iron isotope partitioning between the maternal, neonatal, and placental compartments were identified.

RESULTS

On average, true maternal absorption of iron increased by 10% (from 19% to 21%) after accounting for absorbed iron present in the newborn (P < 0.001), and further increased by 7%, (from 39% to 42%, P < 0.001) after accounting for iron retained within the placenta. On average, 2% of recovered tracer was present in the placenta and 6% was found in the newborn. Net transfer of iron to the neonate was higher in women with lower total body iron (standardized β = -0.48, P < 0.01) and lower maternal hepcidin (standardized β = -0.66, P < 0.01). In women carrying multiple fetuses, neonatal hepcidin explained a significant amount of observed variance in net placental transfer of absorbed iron (R = 0.95, P = 0.03).

CONCLUSIONS

Maternal RBC iron incorporation of an orally ingested tracer underestimated true maternal iron absorption. The degree of underestimation was greatest in women with low body iron. Maternal hepcidin was inversely associated with maternal RBC iron utilization, whereas neonatal hepcidin explained variance in net transfer of iron to the neonatal compartment.These trials were registered at clinicaltrials.gov as NCT01019096 and NCT01582802.

Multi-domain cognitive assessment of male mice shows space radiation is not harmful to high-level cognition and actually improves pattern separation

Astronauts on interplanetary missions - such as to Mars - will be exposed to space radiation, a spectrum of highly-charged, fast-moving particles that includes 56Fe and 28Si. Earth-based preclinical studies show space radiation decreases rodent performance in low- and some high-level cognitive tasks. Given astronaut use of touchscreen platforms during training and space flight and given the ability of rodent touchscreen tasks to assess functional integrity of brain circuits and multiple cognitive domains in a non-aversive way, here we exposed 6-month-old C57BL/6J male mice to whole-body space radiation and subsequently assessed them on a touchscreen battery. Relative to Sham treatment, 56Fe irradiation did not overtly change performance on tasks of visual discrimination, reversal learning, rule-based, or object-spatial paired associates learning, suggesting preserved functional integrity of supporting brain circuits. Surprisingly, 56Fe irradiation improved performance on a dentate gyrus-reliant pattern separation task; irradiated mice learned faster and were more accurate than controls. Improved pattern separation performance did not appear to be touchscreen-, radiation particle-, or neurogenesis-dependent, as 56Fe and 28Si irradiation led to faster context discrimination in a non-touchscreen task and 56Fe decreased new dentate gyrus neurons relative to Sham. These data urge revisitation of the broadly-held view that space radiation is detrimental to cognition.

Iron Isotope Fractionation during Bio- and Photodegradation of Organoferric Colloids in Boreal Humic Waters

Biodegradation and photolysis of dissolved organic matter (DOM) in boreal high-latitude waters are the two main factors controlling not only the aquatic fluxes and residence time of carbon but also metal nutrients associated with DOM such as Fe. The DOM is usually present in the form of organic and organomineral colloids, which also account for the majority of dissolved Fe. Here, we use the stable Fe isotope approach to unravel the processes controlling Fe behavior during bio- and photodegradation of colloids in boreal Fe- and DOM-rich humic waters (a stream and a fen). The adsorption of Fe colloids onto heterotrophic bacteria Pseudomonas aureofaciens produced enrichment in +0.4‰ (δ⁵⁷Fe) in the heavier isotopes of the cell surface relative to the remaining solution. In contrast, long-term assimilation of Fe by live cells yielded preferential incorporation of lighter isotopes into the cells (-0.7‰ relative to aqueous solution). The sunlight-induced oxidation of Fe(II) in fen water led to the removal of heavier Fe isotopes (+1.5 to +2.5‰) from solution, consistent with Fe(III) hydroxide precipitation from Fe(II)-bearing solution. Altogether, bio- and photodegradation of organoferric colloids, occurring within a few days of exposure time, can produce several per mil isotopic excursions in shallow lentic and lothic inland waters of high-latitude boreal regions. Considerable daily scale variations of Fe isotopic composition should therefore be taken into account during the interpretation of the riverine flux of Fe isotopes to the ocean or tracing weathering processes using Fe isotopes in surface waters at high latitudes.

Probing Hydrogen Bonding Interactions to Iron-Oxido/Hydroxido Units by 57 Fe Nuclear Resonance Vibrational Spectroscopy

Hydrogen bonds (H-bonds) have been shown to modulate the chemical reactivities of iron centers in iron-containing dioxygen-activating enzymes and model complexes. However, few examples are available that investigate how systematic changes in intramolecular H-bonds within the secondary coordination sphere influence specific properties of iron intermediates, such as iron-oxido/hydroxido species. Here, we used 57 Fe nuclear resonance vibrational spectroscopy (NRVS) to probe the Fe-O/OH vibrations in a series of FeIII -hydroxido and FeIV/III -oxido complexes with varying H-bonding networks but having similar trigonal bipyramidal primary coordination spheres. The data show that even subtle changes in the H-bonds to the Fe-O/OH units result in significant changes in their vibrational frequencies, thus demonstrating the utility of NRVS in studying the effect of the secondary coordination sphere to the reactivities of iron complexes.

Iron(II)-Catalyzed Iron Atom Exchange and Mineralogical Changes in Iron-rich Organic Freshwater Flocs: An Iron Isotope Tracer Study

In freshwater wetlands, organic flocs are often found enriched in trace metal(loid)s associated with poorly crystalline Fe(III)-(oxyhydr)oxides. Under reducing conditions, flocs may become exposed to aqueous Fe(II), triggering Fe(II)-catalyzed mineral transformations and trace metal(loid) release. In this study, pure ferrihydrite, a synthetic ferrihydrite-polygalacturonic acid coprecipitate (16.7 wt % C), and As- (1280 and 1230 mg/kg) and organic matter (OM)-rich (18.1 and 21.8 wt % C) freshwater flocs dominated by ferrihydrite and nanocrystalline lepidocrocite were reacted with an isotopically enriched ⁵⁷Fe(II) solution (0.1 or 1.0 mM Fe(II)) at pH 5.5 and 7. Using a combination of wet chemistry, Fe isotope analysis, X-ray absorption spectroscopy (XAS), ⁵⁷Fe Mössbauer spectroscopy and X-ray diffraction, we followed the Fe atom exchange kinetics and secondary mineral formation over 1 week. When reacted with Fe(II) at pH 7, pure ferrihydrite exhibited rapid Fe atom exchange at both Fe(II) concentrations, reaching 76 and 89% atom exchange in experiments with 0.1 and 1 mM Fe(II), respectively. XAS data revealed that it transformed into goethite (21%) at the lower Fe(II) concentration and into lepidocrocite (73%) and goethite (27%) at the higher Fe(II) concentration. Despite smaller Fe mineral particles in the coprecipitate and flocs as compared to pure ferrihydrite (inferred from Mössbauer-derived blocking temperatures), these samples showed reduced Fe atom exchange (9-30% at pH 7) and inhibited secondary mineral formation. No release of As was recorded for Fe(II)-reacted flocs. Our findings indicate that carbohydrate-rich OM in flocs stabilizes poorly crystalline Fe minerals against Fe(II)-catalyzed transformation by surface-site blockage and/or organic Fe(II) complexation. This hinders the extent of Fe atom exchange at mineral surfaces and secondary mineral formation, which may consequently impair Fe(II)-activated trace metal(loid) release. Thus, under short-term Fe(III)-reducing conditions facilitating the fast attainment of solid-solution equilibria (e.g., in stagnant waters), Fe-rich freshwater flocs are expected to remain an effective sink for trace elements.

Iron assimilation by the clam Laternula elliptica: Do stable isotopes (δ⁵⁶Fe) help to decipher the sources?

Iron stable isotope signatures (δ(56)Fe) in hemolymph (bivalve blood) of the Antarctic bivalve Laternula elliptica were analyzed by Multiple Collector-Inductively Coupled Plasma-Mass Spectrometry (MC-ICP-MS) to test whether the isotopic fingerprint can be tracked back to the predominant sources of the assimilated Fe. An earlier investigation of Fe concentrations in L. elliptica hemolymph suggested that an assimilation of reactive and bioavailable Fe (oxyhydr)oxide particles (i.e. ferrihydrite), precipitated from pore water Fe around the benthic boundary, is responsible for the high Fe concentration in L. elliptica (Poigner et al., 2013 b). At two stations in Potter Cove (King George Island, Antarctica) bivalve hemolymph showed mean δ(56)Fe values of -1.19 ± 0.34‰ and -1.04 ± 0.39 ‰, respectively, which is between 0.5‰ and 0.85‰ lighter than the pool of easily reducible Fe (oxyhydr)oxides of the surface sediments (-0.3‰ to -0.6‰). This is in agreement with the enrichment of lighter Fe isotopes at higher trophic levels, resulting from the preferential assimilation of light isotopes from nutrition. Nevertheless, δ(56)Fe hemolymph values from both stations showed a high variability, ranging between -0.21‰ (value close to unaltered/primary Fe(oxyhydr)oxide minerals) and -1.91‰ (typical for pore water Fe or diagenetic Fe precipitates), which we interpret as a "mixed" δ(56)Fe signature caused by Fe assimilation from different sources with varying Fe contents and δ(56)Fe values. Furthermore, mass dependent Fe fractionation related to physiological processes within the bivalve cannot be ruled out. This is the first study addressing the potential of Fe isotopes for tracing back food sources of bivalves.

[Study on efficiency of iron utilization in prepubertal female children]

OBJECTIVE

To investigate the iron utilization of prepubertal female children.

METHODS

27 female children from 10 to 12 years old were selected and given 57Fe as a tracer, in conventional diet mode, the blood samples in 1 day before test, 14 days and 28 days after tracer given were taken, and were conducted into red blood cell sample. The iron content and changes of isotope abundance in samples were analyzed and combined with blood volume to get the utilization of iron in RBC.

RESULTS

The erythrocyte incorporation rate( of dose) in 14 days and 28 days were (19.84 +/- 0.53)% and (18.75 +/- 0.40)% (P > 0.05). The erythrocyte incorporation rate( of absorption) were (93.49 +/- 2.27)% and (88.73 +/- 0.43)% respectively, and there was a significantly difference (P < 0.05).

CONCLUSION

It is feasible and accurate to evaluate the iron utilization using erythrocyte incorporation rate, which is tested by single stable isotopes tracer technique. Prepubertal female children has a higher utilization of iron, and the 14 days after tracer given is a effective entry point in erythrocyte incorporation study.

Mössbauer spectroscopy

Given its ability to detect all iron centers, to identify their electronic structures, and to quantify the ratios of the different iron forms present in a sample, many researchers turn to Mössbauer spectroscopy when wanting to address structural and mechanistic questions involving iron proteins. Yet, this technique applied to biochemistry is provided by only a few dedicated teams in the world. Technical difficulties ranging from sample preparation to data analysis and interpretation make necessary the collaboration between biochemists and Mössbauer spectroscopists. This chapter will be confined to iron Mössbauer. It will focus on giving biologists and biochemists the keys to understand what essential information Mössbauer spectroscopy can yield, and how to engage in successful collaborations with spectroscopists. After introducing the basic principles of a Mössbauer experiment, we will describe first how to prepare a suitable Mössbauer sample, then how this technique is applied to the identification of different iron species inside proteins.

Inclusion of guava enhances non-heme iron bioavailability but not fractional zinc absorption from a rice-based meal in adolescents

Assessing the bioavailability of non-heme iron and zinc is essential for recommending diets that meet the increased growth-related demand for these nutrients. We studied the bioavailability of iron and zinc from a rice-based meal in 16 adolescent boys and girls, 13-15 y of age, from 2 government-run residential schools. Participants were given a standardized rice meal (regular) and the same meal with 100 g of guava fruit (modified) with (57)Fe on 2 consecutive days. A single oral dose of (58)Fe in orange juice was given at a separate time as a reference dose. Zinc absorption was assessed by using (70)Zn, administered intravenously, and (67)Zn given orally with meals. The mean hemoglobin concentration was similar in girls (129 ± 7.8 g/L) and boys (126 ± 7.1 g/L). There were no sex differences in the indicators of iron and zinc status except for a higher hepcidin concentration in boys (P < 0.05). The regular and modified meals were similar in total iron (10-13 mg/meal) and zinc (2.7 mg/meal) content. The molar ratio of iron to phytic acid was >1:1, but the modified diet had 20 times greater ascorbic acid content. The absorption of (57)Fe from the modified meal, compared with regular meal, was significantly (P < 0.05) greater in both girls (23.9 ± 11.2 vs. 9.7 ± 6.5%) and boys (19.2 ± 8.4 vs. 8.6 ± 4.1%). Fractional zinc absorption was similar between the regular and modified meals in both sexes. Hepcidin was found to be a significant predictor of iron absorption (standardized β = -0.63, P = 0.001, R(2) = 0.40) from the reference dose. There was no significant effect of sex on iron and zinc bioavailability from meals. We conclude that simultaneous ingestion of guava fruit with a habitual rice-based meal enhances iron bioavailability in adolescents.

Real sample temperature: a critical issue in the experiments of nuclear resonant vibrational spectroscopy on biological samples

There are several practical and intertangled issues which make the experiments of nuclear resonant vibrational spectroscopy (NRVS) on biological samples difficult to perform. The sample temperature is one of the most important issues. In NRVS the real sample temperatures can be very different from the readings on the temperature sensors. In this study the following have been performed: (i) citing and analyzing various existing NRVS data to assess the real sample temperatures during the NRVS measurements and to understand their trends with the samples' loading conditions; (ii) designing several NRVS measurements with (Et(4)N)[FeCl(4)] to verify these trends; and (iii) proposing a new sample-loading procedure to achieve significantly lower real sample temperatures and to balance among the intertangled experimental issues in biological NRVS measurements.

Impact of head-only iron ion radiation on the peripheral LPS response

Although there is a large body of evidence indicating that radiation can have a dramatic impact on both immune and brain function, there is very little known about its effect on communication between these critical two systems. In this study, mice were exposed to head-localized irradiation with 5 Gy (56)Fe(26+) ions and assessed for immune function. Mice were inoculated with lipopolysaccharide 37-38 days post-irradiation. Subsets of mice were euthanized 1, 7, or 14 days later. Radiation significantly impacted the response to an immune challenge in terms of splenic and circulating leukocyte counts and lymphocyte distributions; the effect was especially pronounced on granulocytes and B-cells (p<0.05). However, there were no interactions in spontaneous or mitogen-induced blastogenesis of activated T-cell proportions, brain interleukin-1β, or circulating corticosterone levels. These data demonstrate that head-localized iron ion radiation modified the peripheral response to a potent bacterial component associated with septic shock.

Use of the stable isotope (57) Fe to track the efficacy of the foliar application of lignosulfonate/Fe(3+) complexes to correct Fe deficiencies in cucumber plants

BACKGROUND

During the last decade, environmental concerns regarding the use of recalcitrant synthetic chelates to overcome iron chlorosis has increased and new ligands such as lignosulfonates (LS) have been evaluated. However, the efficacy of these products is variable. In this work a hardwood (eucalyptus) and softwood (spruce) LS were compared to try to relate their physico-chemical characteristics and their efficacy. Also two more products derived from the eucalyptus lignosulfonate were tested.

RESULTS

All the LS tested presented a good ability to complex Fe, but only the spruce LS was capable to maintain significant amounts of soluble Fe above pH 8. According to the FTIR data, structural changes related to the Fe source (Fe(2+) or Fe(3+) ) used to form the complex occurred in the LS molecule and might influence their efficacy. Cucumber (Cucumis sativus L. cv Ashley) chlorotic plants were used to test lignosulfonate efficacy when applied through foliar sprays in comparison with FeSO(4) and EDTA/(57) Fe(3+) . The (57) Fe content of plants sprayed with LS was very low in respect to the EDTA treatment, but this was not reflected in the biomass and re-greening rates. Eucalyptus LS modifications improve its efficacy for iron chlorosis recovery to levels similar to those found for the spruce LS. Two applications of the LS are recommended.

CONCLUSIONS

Lignosulfonates did not require surfactants for their application; they did not burn the leaves, and had a stimulating effect on the vegetative growth of the plants. So these by-products could be a good alternative when applied through foliar sprays for cucumber plants.

Fe isotope fractionation during equilibration of Fe-organic complexes

Despite the importance of Fe-organic complexes in the environment, few studies have investigated Fe isotope effects driven by changes in Fe coordination that involve organic ligands. Previous experimental (Dideriksen et al., 2008, Earth Planet Sci. Lett. 269:280-290) and theoretical (Domagal-Goldman et al., 2009, Geochim. Cosmochim. Acta 73:1-12) studies disagreed on the sense of fractionation between Fe-desferrioxamine B (Fe-DFOB) and Fe(H(2)O)(6)(3+). Using a new experimental technique that employs a dialysis membrane to separate equilibrated Fe-ligand pools, we measured the equilibrium isotope fractionations between Fe-DFOB and (1) Fe bound to ethylenediaminetetraacetic acid (EDTA) and (2) Fe bound to oxalate. We observed no significant isotope fractionation between Fe-DFOB and Fe-EDTA (Delta(56/54)Fe(Fe-DFOB/Fe-EDTA) approximately 0.02 +/- 0.11 per thousand) and a small but significant fractionation between Fe-DFOB and Fe-oxalate (Delta(56/54)Fe(Fe-DFOB/Fe-Ox(3)) = 0.20 +/- 0.11 per thousand). Taken together, our results and those of Dideriksen et al. (2008) reveal a strong positive correlation between measured fractionation factors and the Fe-binding affinity of the ligands. This correlation supports the experimental results of Dideriksen et al. (2008). Further, it provides a simple empirical tool that may be used to predict fractionation factors for Fe-ligand complexes not yet studied experimentally.

Iron isotope fractionation during Fe uptake and translocation in alpine plants

The potential of stable Fe isotopes as a tracer for the biogeochemical Fe cycle depends on the understanding and quantification of the fractionation processes involved. Iron uptake and cycling by plants may influence Fe speciation in soils. Here, we determined the Fe isotopic composition of different plant parts including the complete root system of three alpine plant species (Oxyria digyna, Rumex scutatus, Agrostis gigantea) in a granitic glacier forefield, which allowed us, for the first time, to distinguish between uptake and in-plant fractionation processes. The overall range of fractionation was 4.5 per thousand in delta(56)Fe. Mass balance calculations demonstrated that fractionation toward lighter Fe isotopic composition occurred in two steps during uptake: (1) before active uptake, probably during mineral dissolution and (2) during selective uptake of Fe at the plasma membrane with an enrichment factor of -1.0 to -1.7 per thousand for all three species. Iron isotopes were further fractionated during remobilization from old into new plant tissue, which changed the isotopic composition of leaves and flowers over the season. This study demonstrates the potential of Fe isotopes as a new tool in plant nutrition studies but also reveals challenges for the future application of Fe isotope signatures in soil-plant environments.

Influence of magnetite stoichiometry on Fe(II) uptake and nitrobenzene reduction

Magnetite (Fe3O4) is a common biomineralization product of microbial iron respiration and is often found in subsurface anoxic environments, such as groundwater aquifers where aqueous Fe(II) is present We investigated the reaction between aqueous Fe(II) and magnetite using the isotopic selectivity of 57Fe Mössbauer spectroscopy and revisited the reduction of nitrobenzene by magnetite. Similar to our previous findings with Fe3+ oxides, we did not observe the formation of a stable sorbed Fe(II) species; instead, we observed oxidation of the Fe(II) to a partially oxidized magnetite phase. Oxidation of Fe(II) was accompanied by reduction of the octahedral Fe3+ atoms in the underlying magnetite to octahedral Fe2+ atoms. The lack of a stable, sorbed Fe(II) species on magnetite prompted us to reevaluate what is controlling the extent of Fe(II) uptake on magnetite, as well as contaminant reduction in the presence of magnetite and Fe(II). Uptake of Fe(II) by magnetite appears to be limited by the stoichiometry of the magnetite particles, rather than the surface area of the particles. More oxidized (or less stoichiometric) magnetite particles take up more Fe(II), with the formation of stoichiometric magnetite (Fe2+/Fe3+ = 0.5) limiting the extent of Fe(II) uptake. We also showthat stoichiometric magnetite, in the absence of aqueous Fe(II), can rapidly reduce nitrobenzene. Based on these results, we speculate that contaminant reduction that was previously attributed to Fe(II) sorbed on magnetite is due to a process similar to negative (n) doping of a solid, which increases the stoichiometry of the magnetite and alters the bulk redox properties of the particle to make reduction more favorable.