Decreased citrate improves iron availability from infant formula: application of an in vitro digestion/Caco-2 cell culture model

Iron supplementation and iron-fortified foods: a review

About one-third of the world population is suffering from iron deficiency. Delivery of iron through diet is a practical, economical, and sustainable approach. Clinical studies have shown that the consumption of iron-fortified foods is one of the most effective methods for the prevention of iron deficiency. However, supplementing iron through diet can cause undesirable side-effects. Thus, it is essential to develop new iron-rich ingredients, iron-fortified products with high bioavailability, better stability, and lower cost. It is also essential to develop newer processing technologies for more effective fortification. This review compared the iron supplementation strategies used to treat the highly iron-deficient population and the general public. We also reviewed the efficacy of functional (iron-rich) ingredients that can be incorporated into food materials to produce iron-fortified foods. The most commonly available foods, such as cereals, bakery products, dairy products, beverages, and condiments are still the best vehicles for iron fortification and delivery.Scope of reviewThe manuscript aims at providing a comprehensive review of the latest publications that cover three aspects: administration routes for iron supplementation, iron-rich ingredients used for iron supplementation, and iron-fortified foods.

Uma abordagem dos ensaios in vitro para estimar a absorção dos minerais em fórmulas infantis

Resumo A fórmula infantil é a opção de alimento mais recomendada quando a amamentação não é possível. Para o melhor entendimento do comportamento gastrointestinal e da absorção dos nutrientes presentes nas fórmulas infantis, realizam-se estudos que simulam os processos de digestão. Este trabalho teve como objetivo discutir a evolução das fórmulas infantis com foco na avaliação da absorção de Ca, Cu, Fe, K, Mg, Mn, P e Zn, identificando métodos disponíveis para a avaliação de bioacessibilidade e de biodisponibilidade, de forma a melhor entender a absorção desses nutrientes. Para isto, foi realizada uma revisão bibliográfica sobre fórmulas infantis e os métodos in vitro mais utilizados no estudo de minerais, com foco no consumo, na qualidade e nos aspectos tecnológicos. Foi constatada uma tendência mundial no aumento do consumo de fórmulas infantis e verificou-se que estudos de biodisponibilidade e bioacessibilidade de minerais, mesmo que ainda escassos, colaboram para a evolução e o desenvolvimento deste produto, visando a uma aproximação com a composição do leite materno. A pesquisa mostrou que a composição da fórmula infantil vem sendo constantemente aperfeiçoada por revisões das legislações e pela indústria, e que, para a obtenção de uma fórmula infantil com alta capacidade de absorção de nutrientes, devem ser realizados estudos de bioacessibilidade e/ou de biodisponibilidade, pois estes estudos possibilitam uma melhor compreensão da influência dos diferentes ingredientes na absorção dos nutrientes. Os estudos também mostraram que, para uma ingestão mais equilibrada, nas diferentes fases do lactente, são necessárias diferentes composições dos nutrientes nas fórmulas infantis.

In-vitro bioaccessibility and bioavailability of heavy metals in mineral clay complex used in natural health products

Commercial mineral clays that claim to have healing properties are also known to contain trace amounts of heavy metals, albeit the risk of consuming many of them is not entirely known. The primary objective of this study was to evaluate the in vitro bioaccessibility and bioavailability of Arsenic (As), Cadmium (Cd) and Lead (Pb) in mineral clay samples collected from the Sierra Mountains (USA) using the Unified Bioaccessibility Research Group of Europe (UBM) method and the Caco-2 permeability assay, respectively. After UMB-gastric (UBM-G) digestion, As and Pb bioaccessibility were lower compared to Cd and decreased further in the UMB-gastrointestinal (UBM-GI) assay. Bioavailability estimates using the Caco-2 cell showed very low to non-detectable permeability for all 3 heavy metals. Thus, while initial heavy metal ranged from 3.8–17 ppm, 0.024–0.061ppm, and 5.8–20 ppm for As, Cd, and Pb, respectively, the bioavailability for these metals was reduced to very low levels that followed: non-detectable values of As, <0.007ppm of Cd, and <0.1ppm of Pb. Using UBM-digestion to mimic bioaccessibility, followed by Caco-2 cell bioavailability enabled us to conclude that in vitro assessment of heavy metal exposure associated with mineral clay-based natural health products does not pose a potential hazard to consumers.

In Vitro Iron Bioavailability of Brazilian Food-Based by-Products

Background: Iron deficiency is a public health problem in many low- and middle-income countries. Introduction of agro-industrial food by-products, as additional source of nutrients, could help alleviate this micronutrient deficiency, provide alternative sources of nutrients and calories in developed countries, and be a partial solution for disposal of agro-industry by-products. Methods: The aim of this study was to determine iron bioavailability of 5 by-products from Brazilian agro-industry (peels from cucumber, pumpkin, and jackfruit, cupuaçu seed peel, and rice bran), using the in vitro digestion/ Caco-2 cell model; with Caco-2 cell ferritin formation as a surrogate marker of iron bioavailability. Total and dialyzable Fe, macronutrients, the concentrations of iron-uptake inhibitors (phytic acid, tannins, fiber) and their correlation with iron bioavailability were also evaluated. Results: The iron content of all by-products was high, but the concentration of iron and predicted bioavailability were not related. Rice bran and cupuaçu seed peel had the highest amount of phytic acid and tannins, and lowest iron bioavailability. Cucumber peels alone, and with added extrinsic Fe, and pumpkin peels with extrinsic added iron, had the highest iron bioavailability. Conclusion: The results suggest that cucumber and pumpkin peel could be valuable alternative sources of bioavailable Fe to reduce iron deficiency in at-risk populations.

Higher bioavailability of iron from whole wheat bread compared with iron-fortified white breads in caco-2 cell model: an experimental study

BACKGROUND

Bread, as the staple food of Iranians, with average per capita consumption of 300 g d^-1 , could potentially be a good vehicle for many fortificants, including iron. In this study, iron bioavailability from flat breads (three fortified and one whole wheat unfortified) was investigated using in vitro simulation of gastrointestinal digestion and absorption in a caco-2 cell model.

RESULTS

Despite having a lower ferritin/protein ratio in comparison with fortified breads, whole wheat bread showed higher iron bioavailability than the other three types of bread. Assuming iron bioavailability from the ferrous sulfate supplement used as standard was about 10%, the estimated bioavailability of iron from the test breads was calculated as 5.0-8.0%. Whole wheat bread (∼8%), as compared with the fortified breads (∼5-6.5%), had higher iron bioavailability.

CONCLUSION

Iron from unfortified whole wheat bread is more bioavailable than from three types of iron-fortified breads. © 2016 Society of Chemical Industry.

Impact of Lipid Phase on the Bioavailability of Vitamin E in Emulsion-Based Delivery Systems: Relative Importance of Bioaccessibility, Absorption, and Transformation

A simulated gastrointestinal tract/Caco-2 cell culture model was used to investigate the effects of lipid phase type on vitamin E (VE) bioavailability. Oil-in-water emulsions fortified with α-tocopherol acetate were fabricated using a natural emulsifier (quillaja saponin) and long or medium chain triglycerides (LCTs or MCTs) as lipids. The impact of lipid type on VE bioaccessibility, absorption, and transformation was determined. VE bioaccessibility was greater for LCT (46%) than MCT (19%) due to greater solubilization in mixed micelles assembled from longer fatty acids. VE absorption by Caco-2 cells was similar for LCT (28%) and MCT (30%). The transformation of α-tocopherol acetate to α-tocopherol was higher for LCT (90%) than MCT (75%) due to differences in esterase accessibility to VE. Emulsion-based delivery systems formulated using LCT are therefore more suitable for encapsulating and delivering vitamin E than those formulated using MCT.

Iron mediated toxicity and programmed cell death: A review and a re-examination of existing paradigms

Iron is an essential micronutrient that is problematic for biological systems since it is toxic as it generates free radicals by interconverting between ferrous (Fe²⁺) and ferric (Fe³⁺) forms. Additionally, even though iron is abundant, it is largely insoluble so cells must treat biologically available iron as a valuable commodity. Thus elaborate mechanisms have evolved to absorb, re-cycle and store iron while minimizing toxicity. Focusing on rarely encountered situations, most of the existing literature suggests that iron toxicity is common. A more nuanced examination clearly demonstrates that existing regulatory processes are more than adequate to limit the toxicity of iron even in response to iron overload. Only under pathological or artificially harsh situations of exposure to excess iron does it become problematic. Here we review iron metabolism and its toxicity as well as the literature demonstrating that intracellular iron is not toxic but a stress responsive programmed cell death-inducing second messenger.

Effect of Enzyme Amounts Used in Gastrointestinal Digestion Upon Solubility and Caco-2 Cell Uptake Assays of Minerals from Infant Formulas

The effect of enzyme amounts used in gastrointestinal in vitro digestion upon the solubility and Caco-2 cell uptake of calcium, iron and zinc from infant formulas (IFs) was studied. Different amounts of enzymes (g enzyme/g IF), pepsin (0.002 and 0.048), pancreatin (0.0005, 0.002 and 0.01) and bile extract (0.003, 0.125 and 0.0625) were assayed. Mineral soluble contents and mineral uptakes by Caco-2 cells were affected by the enzyme amounts used in digestion. Although the highest mineral solubility (Ca 98.6 vs 46.2%; Fe 98.1 vs 83.9%; Zn 98.4 vs 83%) was obtained when the lowest enzyme (pepsin 0.002 vs 0.048; pancreatin 0.0005 vs 0.01g/g IF) and bile extract (0.003 vs 0.0625g/g IF) amounts were used, under these conditions uptake decreased with respect to that obtained when the highest amounts were used (Ca 0.4 vs 1.8%; Fe 0.3 vs 4.8%; Zn 1.7 vs 37%), that indicated a lack of relationship between solubility and absorption. Interactions among different products resulting from the proteolytic activity of digestive enzymes and minerals can modify the physicochemical forms in which minerals are available for absorption after gastrointestinal digestion.

Review: Effect of Some Components of Milk- and Soy-Based Infant Formulas on Mineral Bioavailability

Infants’ high nutritional needs are fulfilled by mother’s milk or infant formulas to provide all the necessary nutrients, among them minerals. Minerals uptake depends not only on mineral content but also on their bioavailability which, in turn, is affected by the different components of the infant formulas. An understanding of these effects would help to improve mineral bioavailability. This work reviews the influence of endogenous (proteins and phytates) and added (ascorbic and citric acid) components in infant formulas on the bioavailability of nutritionally important mineral elements (calcium, zinc, iron and copper) and their interactions. Special attention is given to the influence of protein, which is positive for calcium and negative for iron absorption. The marked negative effect of phytates on iron and zinc absorption can be counteracted by a dephytinization process. Of the added compounds, ascorbic acid has a positive effect on iron absorption that depends on the molar ratio between ascorbic acid and iron. In fact, adding ascorbic acid can counteract the negative effect of phytic acid on iron absorption but does not alter the effect of phytic acid on zinc absorption. The null effect of an increase in citric acid content can be ascribed to the fact that the citrate contents of infant formulas are already high. One of the most important element interactions is the negative effect of calcium on zinc and iron intestinal absorption and also the interaction between zinc and iron. These interactions deserve our attention because these minerals are essential to infants’ growth and development.

Electropriming of wheatgrass seeds using pulsed electric fields enhances antioxidant metabolism and the bioprotective capacity of wheatgrass shoots

The influence of pulsed electric field (PEF) (0.5–2 kV/cm) treatment of wheatgrass (Triticum aestivum L.) seeds, with different water contents, on antioxidant metabolism in the resultant seedlings was investigated. Imbibing seeds to a water content of 45% or greater prior to PEF treatment increased the glutathione level and activities of superoxide dismutase, catalase, glutathione reductase, glutathione peroxidase and ascorbate peroxidase in the resultant seedlings, compared to untreated controls. Pre-culture of human intestinal Caco-2 cells with simulated gastrointestinal digests of electrostimulated seedlings enhanced the ability of Caco-2 cells to cope with H₂O₂-induced oxidative damage, determined by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and lactate dehydrogenase (LDH) release assays. The Caco-2 cell MTT and LDH assays correlated better with the increases in seedling glutathione content and antioxidant enzyme activities compared to the 2, 2-diphenyl-1-picrylhydrazyl (DPPH) total antioxidant capacity assay, an assay commonly used to determine the ability of plant extracts to protect cells from oxidative damage. These results demonstrate for the first time that PEF treatment of imbibed seeds can stimulate changes in metabolism in the resultant seedlings, increasing the bioprotective potential of their shoots/sprouts and hence value as functional foods.

Designing food delivery systems: challenges related to the in vitro methods employed to determine the fate of bioactives in the gut

This review discussesin vitroavailable approaches to study delivery and uptake of bioactive compounds and the associated challenges.

Characteristics and behaviour of liposomes when incubated with natural bile salt extract: implications for their use as oral drug delivery systems

The use of liposomes for oral administration of drugs and for food applications is based on their ability to preserve entrapped substances and to increase their bioavailability. Bile salts are one of the agents that affect the liposome structure during intestinal digestion and the main reported studies on liposome/bile salt systems used only one bile salt. The aim of this work is to characterise the interaction of liposomes with a natural bile salt extract (BSE) at physiological pH and temperature. Three types of liposomes (fluid, gel-state and liquid-ordered bilayers) were studied. Phase diagrams were obtained and a very different behaviour was found. Fluid bilayers were completely permeable to an entrapped dye with partial or complete disruption of vesicles (final size 10 nm). Gel-state bilayers released their content but BSE led to the formation of large mixed structures (2000 nm). Liquid-ordered bilayers formed mixed vesicles (1000 nm) and, surprisingly, retained a high percentage of their aqueous content (about 50%). As a consequence, each type of liposome offers singular features to be used in oral applications due to their specific interaction with bile salts.

Citric acid mediates the iron absorption from low molecular weight human milk fractions

Previously, we have demonstrated increased iron absorption from low molecular weight (LMW) human milk whey fractions. In the present study, we investigated the effect of heat denaturation, zinc (a competitor of iron), duodenal cytochrome b (DcytB) antibody neutralization and citrate lyase treatment on LMW human milk fraction (>5 kDa referred as 5kF) induced ferric iron reduction, solubilization, and uptake in Caco-2 cells. Heat denaturation and zinc inhibited the 5kF fraction induced ferric iron reduction. In contrast, zinc but not heat denaturation abrogated the ferric iron solubilization activity. Despite inhibition of ferric iron reduction, iron uptake in Caco-2 cells was similar from both native and heat denatured 5kF fractions. However, iron uptake was higher from native compared to heat denatured 5kF fractions in the cells preincubated with the DcytB antibody. Citrate lyase treatment inhibited the ferric iron reduction, solubilization, and uptake in Caco-2 cells. These findings demonstrate that citric acid present in human milk solubilizes the ferric iron which could be reduced by other heat labile components leading to increased uptake in intestinal cells.

Intracellular uptake and associated toxicity of silver nanoparticles in Caenorhabditis elegans

Silver nanoparticles (AgNPs) are frequently used as antimicrobials. While the mechanism(s) by which AgNPs are toxic are unclear, their increasing use raises the concern that release into the environment could lead to environmental toxicity. We characterized the physicochemical behavior, uptake, toxicity (growth inhibition), and mechanism of toxicity of three AgNPs with different sizes and polyvinylpyrrolidone (PVP) or citrate coatings to the nematode Caenorhabditis elegans. We used wild-type (N2) C. elegans and strains expected to be sensitive to oxidative stress (nth-1, sod-2 and mev-1), genotoxins (xpa-1 and nth-1), and metals (mtl-2). Using traditional and novel analytical methods, we observed significant aggregation and extra-organismal dissolution of silver, organismal uptake and, in one case, transgenerational transfer of AgNPs. We also observed growth inhibition by all tested AgNPs at concentrations in the low mg/L levels. A metallothionein-deficient (mtl-2) strain was the only mutant tested that exhibited consistently greater AgNP sensitivity than wild-type. Although all tested AgNPs were internalized (passed cell membranes) in C. elegans, at least part of the toxicity observed was mediated by ionic silver. Finally, we describe a modified growth assay that permits differentiation between direct growth-inhibitory effects and indirect inhibition mediated by toxicity to the food source.

Nicotianamine, a novel enhancer of rice iron bioavailability to humans

Background

Polished rice is a staple food for over 50% of the world's population, but contains little bioavailable iron (Fe) to meet human needs. Thus, biofortifying the rice grain with novel promoters or enhancers of Fe utilization would be one of the most effective strategies to prevent the high prevalence of Fe deficiency and iron deficiency anemia in the developing world.

Methodology/Principal Findings

We transformed an elite rice line cultivated in Southern China with the rice nicotianamine synthase gene (OsNAS1) fused to a rice glutelin promoter. Endosperm overexpression of OsNAS1 resulted in a significant increase in nicotianamine (NA) concentrations in both unpolished and polished grain. Bioavailability of Fe from the high NA grain, as measured by ferritin synthesis in an in vitro Caco-2 cell model that simulates the human digestive system, was twice as much as that of the control line. When added at 1∶1 molar ratio to ferrous Fe in the cell system, NA was twice as effective when compared to ascorbic acid (one of the most potent known enhancers of Fe bioavailability) in promoting more ferritin synthesis.

Conclusions

Our data demonstrated that NA is a novel and effective promoter of iron utilization. Biofortifying polished rice with this compound has great potential in combating global human iron deficiency in people dependent on rice for their sustenance.

Nutriomic analysis of fresh and processed fruit products. 2. During in vitro simultaneous molecular passages using Caco-2 cell monolayers

Many studies have used Caco-2 cell monolayers as human intestinal absorption models. However, only a few studied digested foods, instead of pure standard compounds. Moreover, beneficial and nutritional molecules (nutriome) have not been investigated simultaneously. The present study explored nutriome passages from digest solution of fresh, dried, and juiced tomato, mango, and papaya using Caco-2 cell monolayers in apical-->basolateral directions. A validation method using complementary TEER and P(app) values or internal standard caffeine is recommended because physiologically passive diffusion is unlikely to happen. Sugars were transported into basolateral sides, resulting in potential glucose equivalent bioavailability of 2.26-75 mg h(-1)/100 g (WB). Using sugar passage rates (DB) of juices as 100% references, the rate order was tomato (49.8% dried; 89.5% fresh) > mango (56.8% dried; 22.8% fresh) > papaya (18.7% dried; 36.7% fresh). Major indications that phytochemical absorption does not occur in the small intestine were obtained from the bioassay condition selected. Apical organic acid levels decreased, which occasionally were transported into basolateral sides, whereas the disappearances of apical carotenoids and phenolics were not. Pectin substances were predicted to be responsible for the disappearances of bioactive compounds in those pectin-rich fruits. Further investigations on the role of pectin substances in intestinal passages are recommended.

Nutriomic analysis of fresh and processed fruit products. 1. During in vitro digestions

Nutriomic analysis is a postgenomic-based study of nutritious components (nutriome). There is a need for an in vitro digestion and absorption model to unravel interactive factors varying nutriome release from various food materials that cannot be directly studied in humans. Effects of processing and in vitro digestion steps on carotenoid, sugar, and organic acid release from tomato, papaya, and mango products were comprehensively studied for the first time in this research. In vivo chewing experiments using 24 healthy adult volunteers was carried out prior to chewing simulation. Microscopy showed that cutting and blending alone were unlikely to mimic chewing at swallowing point. Using general linear model (GLM) ANOVA and principal component analysis (PCA), effects of interaction between digestion steps and processing types on the nutriome release were significant (p < 0.05) when 90% particles of 0.5 (dried) and 1.5 cm (fresh) were digested in vitro. Generally, dried and fresh fruits released lower levels of nutriome components than juices. PCA indicated nutriome release from tomato products was affected by the factors studied more than those from papaya and mango products. Fruit type is the main determinant factor relative to processing and digestion steps because it determines the extent of matrix that breaks down and consequent nutriome diffusion rates. It is predicted that pectin plays a role in determining the rate of nutriome release and absorption, which requires further investigation.

Availability and toxicity of Fe(II) and Fe(III) in Caco-2 cells

The objective of the present study was to compare the toxicity and availability of Fe(II) and Fe(III) to Caco-2 cells. Cellular damage was studied by measuring cell proliferation and lactate dehydrogenase (LDH) release. The activities of two major antioxidative enzymes [superoxide dismutase (SOD) and glutathione peroxidase (GPx)] and differentiation marker (alkaline phosphatase) were determined after the cells were exposed to different levels of iron salts. The cellular iron concentration was investigated to evaluate iron bioavailability. The results show that iron uptake of the cells treated with Fe(II) is significantly higher than that of the cells treated with Fe(III) (P<0.05). Fe(II) at a concentration >1.5 mmol/L was found to be more effective in reducing cellular viability than Fe(III). LDH release investigation suggests that Fe(II) can reduce stability of the cell membrane. The activities of SOD and GPx of the cells treated with Fe(II) were higher than those of the cells treated with Fe(III), although both of them increased with raising iron supply levels. The results indicate that both Fe(II) and Fe(III) could reduce the cellular antioxidase gene expression at high levels.

Screening of iron bioavailability patterns in eight bean (Phaseolus vulgaris L.) genotypes using the Caco-2 cell in vitro model

The common bean ( Phaseolus vulgaris) is an important staple plant food in the diets of people of Latin America, East Africa,and other regions of the developing world. It is also a major source of dietary iron. The primary goal of this research was to use an in vitro digestion/Caco-2 model to study iron bioavailability in eight genotypes (three Mesoamerican and five Andean) that represent the diversity of grain types in this crop. Complementing this goal, we measured the distribution of both iron and phytate in different bean grain tissues (cotyledon, seed coats, and embryos). Seed coats were confirmed to be the exclusive tissue containing polyphenols. The removal of the seed coat and associated polyphenols improved Caco-2 iron bioavailability, and significant differences were observed between genotypes. The addition of ascorbate enhanced iron bioavailability and exposed additional differences in Fe availability among the genotypes. These results indicate that iron accumulation and in vitro iron bioavailability vary among bean genotypes and that polyphenols had greater inhibitory effects on Caco-2 iron bioavailability as compared to phytate.

Copper- and Zinc-Enriched Mycelium of Agaricus blazei Murrill: Bioaccumulation and Bioavailability

Agaricus blazei is an edible mushroom with medicinal properties. To obtain organic combinations of potential utility as a food dietary supplement, the accumulation and potential bioavailability of copper (Cu) and zinc (Zn) on mycelium grown in the presence of these metals were studied. At 400 ppm, the mycelium accumulated 449 and 163 times the basal content of Cu and Zn, respectively. When mycelia cultivated with nonmycotoxic concentrations of Cu or Zn (100 and 200 ppm) were subjected to sequential chemical extraction and simulated gastrointestinal digestion, close to 90% of the metals accumulated in the available nonresidual fraction, which was similar to or better than the values found in two commercial supplements. The solubility in the simulated digestive fluids was 30-34% and 18-33%, i.e., 60-98% and 9-11% of the recommended daily intake for Cu and Zn, respectively, with only 1 g of mycelium.

An approach to As(III) and As(V) bioavailability studies with Caco-2 cells

Foods and drinking water are the main sources of human exposure to inorganic arsenic [As(III) and As(V)]. After oral ingestion, the intestinal epithelium is the first barrier to absorption of these species. A human intestinal cell line (Caco-2) was used to evaluate cell retention and transport of As(III) (15.6-156.0 microM) and/or As(V) (15.4-170.6 microM). Cell monolayer integrity, cell viability, membrane damage and effects on cell metabolism were evaluated. Only the highest concentrations assayed [As(III): 156.0 microM; As(V): 170.6 microM] produced a cytotoxic effect with different cellular targets: As(III) altered the permeability of tight junctions, and As(V) caused uncoupling of the respiratory chain. Retention and transport of As(III) was more efficient than that of As(V). After 4h of exposure to As(III) or As(V), monolayer retention percentages varied between 0.87-2.28% and 0.14-0.39%, respectively. Transepithelial transport was greater for As(III) (5.82-7.71%) than for As(V) (not detectable-1.55%). The addition of As(III) and As(V) jointly produced a transport rate similar to that observed when they were added independently.

Calcium, zinc, and iron bioavailabilities from a commercial human milk fortifier: a comparison study

Adding human milk fortifiers (HMF) to human milk (HM) is one way of overcoming the nutrient deficits found in the latter. In this study, the bioavailabilities of calcium, zinc, and iron in S-26/SMA HMF added to HM were compared with those in HM fortified with various bovine milk proteins: alpha-lactalbumin, colostrum, caseinate, casein phosphopeptides, and whey protein concentrate. The bioavailability of each mineral was assessed using an in vitro digestion/Caco-2 cell culture model. Calcium and zinc uptake by the cells was traced with radioisotopes; iron uptake was assessed via cell ferritin levels. Samples were prepared on an equal protein content basis and with added calcium, but no zinc or iron was added. Results revealed that calcium uptake from HM + S-26/SMA was not different from any of the HM fortified with the bovine milk proteins, except for unfortified HM and HM + colostrum in which calcium uptake was significantly lower (-89 and -38%, respectively). Uptake of zinc and iron were significantly higher for HM + S-26/SMA than for the other HM + fortifiers.

An in vitro digestion/Caco-2 cell culture system accurately predicts the effects of ascorbic acid and polyphenolic compounds on iron bioavailability in humans

We developed a rapid in vitro digestion/Caco-2 cell culture model for assessing relative bioavailabilities of iron in foods and meals. The objective of the present study was to determine how closely our Caco-2 model reflects the human response. Meals described in published reports of studies on effects of varying levels of ascorbic acid (AA) and tannic acid (TA) on iron absorption by human subjects were carefully replicated. Iron absorption ratios (iron absorption from meals containing AA or TA divided by iron absorption from identical meals without these enhancers or inhibitors) were determined using the Caco-2 model. Ferritin formation by the Caco-2 cells was used as an indicator of iron absorption. Response patterns of effects of AA and TA on absorption ratios (AR) calculated from Caco-2 and human data were very similar: AA increased ARs in a dose-response manner and TAs decreased AR. The natural logs of the ARs determined in Caco-2 and human studies were correlated: R = 0.935 (P = 0.012) and 0.927 (P = 0.007) for AA and TA, respectively. When results from meals with AA and TA were pooled, a linear relation between the natural logs of ARs from Caco-2 and human studies was observed (R = 0.968, P < 0.001). We conclude that our Caco-2 model accurately predicts the human response to AA and TA in the meals we tested. If future work reproduces the precision and accuracy shown in this paper for predicting iron bioavailability to humans, then the implications for saving time and resources in iron bioavailability measurements are considerable.

Carbohydrate fractions from cooked fish promote iron uptake by Caco-2 cells

The objective of this study was to isolate and characterize the meat factor(s) that enhances nonheme iron bioavailability using various analytical and in vitro cell culture techniques. Nonheme iron bioavailability was measured via radiolabeled iron uptake or ferritin formation in Caco-2 cells. Fish haddock fillet was cooked and lyophilized to be used as the muscle tissue of choice because of its low intrinsic iron content. It was demonstrated that the low pH of the stomach (pH 2.0) was the primary factor responsible for initiating the enhancing effect of fish on nonheme iron uptake. Subsequently, cooked fish samples were titrated with HCl to pH 2.0 and incubated for 1 h without digestive enzymes to release the factor(s) from the fish. The supernatant of this acidic digest was then used as a starting material for the meat factor isolation procedures. Fractions generated through Sephadex G-25 size exclusion increased Caco-2 cell iron uptake approximately 9-fold. Subsequent chromatography of these fractions via C18 reverse-phase HPLC were conducted, and enhancing activity was observed only in the "injection peak." This observation coupled with protein measurement and amino acid composition analysis revealed that the active fractions contained negligible amounts of proteins or amino acids. Active fractions were highly enriched with carbohydrates. Subsequent chromatography via high performance anion exchange chromatography with pulsed amperometric detection yielded 3 active peaks that increased Caco-2 cell iron uptake 3.4- to 4.9-fold. Our results indicate that specific carbohydrates contribute to the enhancing effect of meat on iron uptake by the enterocyte. These carbohydrates may be oligosaccharides originating from glycosaminoglycans in the extracellular matrix of muscle tissue.

The mechanisms for regulating absorption of Fe bis-glycine chelate and Fe-ascorbate in caco-2 cells are similar

Inorganic iron (Fe) absorption from the diet is controlled mainly in the intestinal tract where apical Fe uptake is inversely related to the Fe content in the enterocyte. Iron bis-glycine chelate is an iron compound that may be absorbed by a mechanism different from the regulated nonheme Fe pathway. Because Fe bis-glycine chelate is used increasingly as an Fe fortificant in foods, the critical question is whether this compound is a safe Fe supplement. We compared apical Fe uptake and transepithelial transport offered either as (59)Fe bis-glycine chelate or a (59)Fe-ascorbate (Fe-AA) complex in Caco-2 cells, as a model of human intestinal epithelia, grown in different Fe concentrations in the media (0.5, 5 and 20 micro mol/L Fe). Apical Fe uptake from (59)Fe-AA and (59)Fe bis-glycine chelate did not differ nor did transepithelial transport rates. The rate of (59)Fe uptake decreased with increasing intracellular Fe concentration (P < 0.001), an indication of a common absorption regulatory mechanism. We also evaluated the effect of an excess of Fe (100 micro mol/L) provided as Fe bis-glycine chelate or Fe-AA on the incorporation of 1 micro mol/L (55)Fe-AA into Fe-replete Caco-2 cells. The inhibition of Fe bis-glycine chelate on the absorption of the extrinsic tag of (55)Fe-AA (87.5%) did not differ from that of Fe added as Fe-AA (86.8%). These results suggest that Fe derived from Fe bis-glycine chelate and Fe-AA have similar regulatory absorption mechanisms.

Iron and ascorbic Acid: proposed fortification levels and recommended iron compounds

An adequate supply of dietary iron during the 1st 24 mo of life is essential for preventing iron deficiency with its attendant negative effects on mental, motor and emotional development as well as later cognitive performance. Iron reserves and the small amount of highly bioavailable iron in human milk are adequate to satisfy the iron requirements of breast-fed infants of adequate birth weight for the 1st 6 mo of life. Thereafter, complementary foods, iron supplements or both are needed to meet this requirement. Complementary foods should not displace the consumption of human milk. The quantities eaten, particularly by younger infants, may therefore be quite small. As a consequence it is essential that the iron be supplied in a highly bioavailable form. This can be achieved by fortifying complementary foods with ferrous sulfate and ascorbic acid provided that the ascorbic acid is not lost during storage or meal preparation. Suggested fortification levels for ferrous sulfate and ascorbic acid for some types of complementary foods are given. The use of ferrous fumarate or an elemental iron powder instead of ferrous sulfate has not been evaluated adequately. There is a need to develop alternative strategies for improving iron bioavailability in complementary foods because it may not be possible to preserve ascorbic acid activity in many of them.

Breast milk fractions solubilize Fe(III) and enhance iron flux across Caco-2 cells

Why breastfed infants absorb extrinsic iron (EFe) exceptionally well is an unexplained phenomenon. Our objective was to identify effects of human milk fractions (HMF) on bioavailability of EFe. HMF were prepared by centrifugation followed by successive ultrafiltration using 10-, 3- and 1-kDa molecular weight cutoff membranes. EFe was added to HMF before and after treatment with digestive enzymes. Solubilization of EFe by HMF was characterized by scintillation counting of radioiron and by size exclusion chromatography/inductively coupled plasma mass spectrometry (SEC/ICPMS) of stable iron. Effects of HMF on EFe uptake and basolateral transfer were assessed by using confluent Caco-2 cells in bicameral chambers. Whey fractions of low molecular weight (MW) derived from 10-kDa filtrate, except the 1-kDa filtrate, were as effective as ascorbate and nitrilotriacetate in solubilizing EFe at intestinal pH. Basolateral radioiron transfer from Caco-2 cell monolayers was greater in the presence of low MW whey fractions than in the presence of ferrous ascorbate. The 3-kDa filtrate and 3-kDa retentate fractions promoted basolateral transfer of cellular radioiron taken up previously. SEC/ICPMS of the 1-kDa retentate fraction revealed a UV-absorbing peak of MW approximately 4.2 kDa that contained iron and that solubilized added ferric iron both before and after in vitro digestion with pepsin, pancreatin and bile extract. Our results suggested that a low MW component of breast milk whey enhances iron bioavailability. Because the iron solubilization activity is resistant to in vitro digestion, it is plausible that the component is active in vivo and may explain the excellent absorption of EFe by breastfed infants [corrected].