Inhibition of iron uptake from iron salts and chelates by divalent metal cations in intestinal epithelial cells

Complexed amino acid minerals vs. bis-glycinate chelated minerals: Impact on the performance of old laying hens

The present study was to evaluate the effect of trace minerals (Zn, Mn, and Cu) from complexed amino acid minerals (ZMCAA) and bis-glycinate chelated minerals (ZMCGly) in laying hen diets on performance, internal and external egg quality, yolk mineral deposition, intestinal morphometry, and bone characteristics. From 78 to 98 weeks of age, 400 White LSL-Lite strain laying hens were distributed in a randomized design with 4 treatments with 10 replicates per treatment. Treatments were distributed in a 2 × 2 factorial arrangement using either Zn, Mn, and Cu of ZMCAA or ZMCGly source at 2 levels: low (20, 20, and 3.5 mg/kg of Zn, Mn, and Cu, respectively) or high (40, 40, and 7 mg/kg of Zn, Mn, and Cu, respectively). The analysis of variance was performed, and in cases where differences were observed, the means were compared using Tukey's test (P < 0.05). The source and level of trace mineral supplementation had a significant impact on the performance of laying hens. Hens fed ZMCAA had higher egg production (P = 0.01), egg weight (P = 0.02), egg mass (P = 0.01), and lower feed conversion ratio (P = 0.05) compared to those fed ZMCGly. The ZMCAA supplementation showed higher albumen height (P = 0.01), albumen weight (P = 0.01), and eggshell thickness (P < 0.01). The deposition of Zn (P < 0.01), Mn (P < 0.01), and Cu (P < 0.01) in the egg yolk was greater for hens received ZMCAA. Tibia weight (P = 0.04) and bone densitometry (P < 0.01) in the tibia were higher with ZMCAA supplementation. In the small intestine, ZMCAA resulted in longer villi (P = 0.02) and shorter crypt depth (P = 0.01) in the duodenum. Jejunum and ileum measurements were influenced by the level and source of trace minerals (P < 0.05). Laying hens fed ZMCAA exhibited superior performance, egg quality, deposition of trace minerals in the egg yolk, and bone density compared to hens fed ZMCGly. In this study, older laying hens supplemented with ZMCAA at lower levels demonstrated adequate levels of supplementation.

Characterization of fifteen key genes involved in iron metabolism and their responses to dietary iron sources in yellow catfish Pelteobagrus fulvidraco

BACKGROUND

Iron is an essential metal element for organisms, whose metabolism is regulated by many genes and also dietary iron sources. However, the characterization, distribution and the responses of iron metabolism-related genes to different iron sources were not clear in fish.

METHODS

The full-length cDNA sequences of fifteen iron metabolism-relevant genes (tf, tfr1, hp, fpn1, ho1, ho2, tfr2, hjv, hepcidin, fth, ftl, ftm, irp1, irp2 and hif2α.) were obtained via 3' and 5' RACE PCR from yellow catfish, a widely distributed freshwater teleost in China and other Asian countries. Their molecular characterizations were analyzed via the bioinformatic methods. Real-time quantitative PCR was used to explore their mRNA distribution in nine tissues. Their mRNA expression responses in four tissues (heart, brain, kidney and gill) were explored in yellow catfish fed diets with five iron sources, including ferrous sulfate (FeSO4), ferrous bisglycinate (Fe-Gly), ferrous chloride (FeCl2), ferric citrate (Fe-CA) and ferric oxide nanoparticles (Fe2O3NPs).

RESULTS

Compared with mammals and other teleost, these members shared similar domains. Their mRNAs were expressed in nine tested tissues, but mRNA levels varied. Yellow catfish fed the diets containing Fe-Gly and Fe2O3NPs had higher iron contents in heart, brain, kidney and gill. Meantime, different dietary iron sources addition affected their mRNA expression differentially in brain, heart, kidney and gill. It should be pointed out that only three biological replicate tanks were used in the present feeding treatment, and more biological replicate tanks (more than five) should be emphasized in further researches.

CONCLUSION

Taken together, our study identified fifteen iron metabolism-relevant genes, explored their mRNA expression in nine tissues, and their mRNA expression in the responses to different dietary iron sources in four tissues, indicating their important regulatory function in iron metabolism and homeostasis.

Fe3+ opposes the 1,25(OH)2D3-induced calcium transport across intestinal epithelium-like Caco-2 monolayer in the presence or absence of ascorbic acid

Although iron is an essential element for hemoglobin and cytochrome synthesis, excessive intestinal iron absorption—as seen in dietary iron supplementation and hereditary disease called thalassemia—could interfere with transepithelial transport of calcium across the intestinal mucosa. The underlying cellular mechanism of iron-induced decrease in intestinal calcium absorption remains elusive, but it has been hypothesized that excess iron probably negates the actions of 1,25-dihydroxyvitamin D [1,25(OH)₂D₃]. Herein, we exposed the 1,25(OH)₂D₃-treated epithelium-like Caco-2 monolayer to FeCl₃ to demonstrate the inhibitory effect of ferric ion on 1,25(OH)₂D₃-induced transepithelial calcium transport. We found that a 24-h exposure to FeCl₃ on the apical side significantly decreased calcium transport, while increasing the transepithelial resistance (TER) in 1,25(OH)₂D₃-treated monolayer. The inhibitory action of FeCl₃ was considered rapid since 60-min exposure was sufficient to block the 1,25(OH)₂D₃-induced decrease in TER and increase in calcium flux. Interestingly, FeCl₃ did not affect the baseline calcium transport in the absence of 1,25(OH)₂D₃ treatment. Furthermore, although ascorbic acid is often administered to maximize calcium solubility and to enhance intestinal calcium absorption, it apparently had no effect on calcium transport across the FeCl₃- and 1,25(OH)₂D₃-treated Caco-2 monolayer. In conclusion, apical exposure to ferric ion appeared to negate the 1,25(OH)₂D₃-stimulated calcium transport across the intestinal epithelium. The present finding has, therefore, provided important information for development of calcium and iron supplement products and treatment protocol for specific groups of individuals, such as thalassemia patients and pregnant women.

Iron delivery systems for controlled release of iron and enhancement of iron absorption and bioavailability

Iron deficiency is a global nutritional problem, and adding iron salts directly to food will have certain side effects on the human body. Therefore, there is growing interest in food-grade iron delivery systems. This review provides an overview of iron delivery systems, with emphasis on the controlled release of iron during gastrointestinal digestion, as well as the enhancement of iron absorption and bioavailability. Iron-bearing proteins are easily degraded by digestive enzymes and absorbed through receptor-mediated endocytosis. Instead, protein aggregates are slowly degraded in the stomach, which delays iron release and serves as a potential iron supplement. Amino acids, peptides and polysaccharides can bind iron through iron binding sites, but the formed compounds are prone to dissociation in the stomach. Moreover, peptides and polysaccharides can deliver iron by mediating the formation of ferric oxyhydroxide which is absorbed through endocytosis or bivalent transporter 1. In addition, liposomes are unstable during gastric digestion and iron is released in large quantities. Complexes formed by polysaccharides and proteins, and microcapsules formed by polysaccharides can delay the release of iron in the gastric environment and prolong iron release in the intestinal environment. This review is conducive to the development of iron functional ingredients and dietary supplements.

Perinatal and early-life cobalt exposure impairs essential metal metabolism in immature ICR mice

The objective of the present study was to assess the impact of cobalt (Co) exposure on tissue distribution of iron (Fe), copper (Cu), manganese (Mn), and zinc (Zn), as well as serum hepcidin levels in immature mice (18, 25, 30 days). Pregnant mice were exposed to 75 mg/kg b.w. cobalt chloride (CoCl₂ × 6H2O) with drinking water starting from 3 days before delivery and during lactation. At weaning (day 25) the offspring were separated and housed in individual cages with subsequent exposure to 75 mg/kg b.w. CoCl₂ until 30 days postnatally. Evaluation of tissue metal levels was performed by an inductively coupled plasma-mass spectrometry (ICP-MS). Serum hepcidin level was assayed by enzyme linked immunosorbent assay (ELISA). Cobalt exposure resulted in a time- and tissue-dependent increase in Co levels in kidney, spleen, liver, muscle, erythrocytes, and serum on days 18, 25, and 30. In parallel with increasing Co levels, CoCl₂ exposure resulted in a significant accumulation of Cu, Fe, Mn, and Zn in the studied tissues, with the effect being most pronounced in 25-day-old mice. Cobalt exposure significantly increased serum hepcidin levels only in day18 mice. The obtained data demonstrate that Co exposure may alter essential metal metabolism in vivo.

Growth and Virulence of Salmonella Typhimurium Mutants Deficient in Iron Uptake

The present study investigated the effects of iron, iron chelators, and mutations of tonB or iroN fepA genes on the growth and virulence of Salmonella Typhimurium. Results indicated that organic iron (ferric citrate and ferrous-l-ascorbate) supported better growth of Salmonella compared to inorganic iron. Among tested chelators, 2,2'-bipyridyl at 500 μM showed the highest inhibition of Salmonella growth with 5 μM ferrous sulfate. Deletion of genes (tonB^- and iroN^- fepA^- ) in the iron uptake system attenuated Salmonella invasion of Caco-2 cells and its ability to damage the epithelial monolayer. The expression of all tested host genes in Caco-2 was not affected under the iron-poor condition. However, claudin 3, tight junction protein 1, tumor necrosis factor α (TNF-α), and interleukin-8 (IL-8) were altered under the iron-rich condition depending on individual mutations. In Caenorhabditis elegans, a significant down-regulation of ferritin 1 expression was observed when the nematode was infected by the wild-type (WT) strain.

Iron Transport from Ferrous Bisglycinate and Ferrous Sulfate in DMT1-Knockout Human Intestinal Caco-2 Cells

This experiment was conducted to investigate the transport characteristics of iron from ferrous bisglycinate (Fe-Gly) in intestinal cells. The divalent metal transporter 1 (DMT1)-knockout Caco-2 cell line was developed by Crispr-Cas9, and then the cells were treated with ferrous sulfate (FeSO₄) or Fe-Gly to observe the labile iron pool and determine their iron transport. The results showed that the intracellular labile iron increased significantly with Fe-Gly or FeSO₄ treatment, and this phenomenon was evident over a wide range of time and iron concentrations in the wild-type cells, whereas in the knockout cells it increased only after processing with high concentrations of iron for a long time (p < 0.05). DMT1-knockout suppressed the synthesis of ferritin and inhibited the response of iron regulatory protein 1 (IRP-1) and IRP-2 to these two iron sources. The expression of peptide transporter 1 (PepT1) was not altered by knockout or iron treatment. Interestingly, the expression of zinc-regulated transporter (ZRT) and iron-regulated transporter (IRT)-like protein 14 (Zip14) was elevated significantly by knockout and iron treatment in wild-type cells (p < 0.05). These results indicated that iron from Fe-Gly was probably mainly transported into enterocytes via DMT1 like FeSO₄; Zip14 may play a certain role in the intestinal iron transport.

Estimation of the bioaccessibility and bioavailability of Fe, Mn, Cu, and Zn in Chinese vegetables using the in vitro digestion/Caco-2 cell model: the influence of gut microbiota

The influence of the human gut microbiota on the bioaccessibility and bioavailability of trace elements in vegetables has barely been studied. An in vitro digestion model combining the physiologically based extraction test (PBET) and the Simulator of Human Intestinal Microbial Ecosystem (SHIME) was applied. Results showed that the gut microbiota increased the bioaccessibility of iron (Fe) in ten test vegetables by 1.3-1.8 times, but reduced the bioaccessibility of manganese (Mn), copper (Cu), and zinc (Zn) in vegetables in the colon phase by 3.7% to 89.6%, 24.8% to 100.0%, and 59.9% to 100.0%, respectively. Using the Caco-2 cell model to simulate the human absorption process, the bioavailable contents and the bioavailability of the trace elements were further determined. Swamp cabbage was the best source of Fe and Cu; spinach and lettuce provided the highest amounts of bioavailable Mn and Zn, respectively. Referring to the daily reference intakes of trace elements, the obtained data provide a scientific basis for both reasonable ingestion of vegetables in diets and diversification of diets.

Digital gene expression profiling analysis of duodenum transcriptomes in SD rats administered ferrous sulfate or ferrous glycine chelate by gavage

The absorption of different iron sources is a trending research topic. Many studies have revealed that organic iron exhibits better bioavailability than inorganic iron, but the concrete underlying mechanism is still unclear. In the present study, we examined the differences in bioavailability of ferrous sulfate and ferrous glycinate in the intestines of SD rats using Illumina sequencing technology. Digital gene expression analysis resulted in the generation of almost 128 million clean reads, with expression data for 17,089 unigenes. A total of 123 differentially expressed genes with a |log2(fold change)| >1 and q-value < 0.05 were identified between the FeSO4 and Fe-Gly groups. Gene Ontology functional analysis revealed that these genes were involved in oxidoreductase activity, iron ion binding, and heme binding. Kyoto Encyclopedia of Genes and Genomes pathway analysis also showed relevant important pathways. In addition, the expression patterns of 9 randomly selected genes were further validated by qRT-PCR, which confirmed the digital gene expression results. Our study showed that the two iron sources might share the same absorption mechanism, and that differences in bioavailability between FeSO4 and Fe-Gly were not only in the absorption process but also during the transport and utilization process.

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.

Iron uptake by Caco-2 cells following in vitro digestion: effects of heat treatments of pork meat and pH of the digests

The present in vitro studies report on iron uptake by Caco-2 cells from pepsin and pepsin+pancreatin-digested pork meat proteins at pH values between 4.6 and 7 mimicking conditions in the duodenum and the proximal jejunum, respectively. Heat treatment of the pork meat resulted in increased iron uptake from pepsin-digested samples to Caco-2 cells at pH 4.6. The major enhancing effects on iron uptake by Caco-2 cells were observed after pepsin digestion in the pH range 4.6-6.0, whereas the pepsin+pancreatin-digested samples resulted in negligible iron uptake in Caco-2 cells at pH 7. Thus, the results emphasize the importance of separating pepsin-digested and pepsin+pancreatin-digested proteins during in vitro studies on iron availability. Furthermore, the present results showed the pH dependency of iron uptake anticipated. The enhancing effect of ascorbic acid was verified by increased iron uptake from pepsin-digested pork meat samples at pH 4.6, while no effect of ascorbic acid was observed at pH 7 in pepsin+pancreatin-digested samples.

Titanium(IV) complexes: cytotoxicity and cellular uptake of titanium(IV) complexes on caco-2 cell line

Replacement of the ancillary ligand in titanocene dichloride by amino acids provides titanocene species with high water solubility. As part of our research efforts in the area of titanium-based antitumor agents, we have investigated the cytotoxic activity of Cp(2)TiCl(2) and three water soluble titanocene-amino acid complexes - [Cp(2)Ti(aa)(2)]Cl(2) (aa=L-cysteine, L-methionine, and D-penicillamine) and one water soluble coordination compound, [Ti(4)(maltolato)(8)(micro-O)(4)] on the human colon adenocarcinoma cell line, Caco-2. At pH of 7.4 all titanocene species decompose extensively while [Ti(4)(maltolato)(8)(micro-O)(4)] is stable for over seven days. In terms of cytotoxicity, the [Cp(2)Ti(aa)(2)]Cl(2) and [Ti(4)(maltolato)(8)(micro-O)(4)] complexes exhibited slightly higher toxicity than titanocene dichloride at 24h, but at 72h titanocene dichloride and [Ti(4)(maltolato)(8)(micro-O)(4)] have higher cytotoxic activity. Cellular titanium uptake was quantified at various time intervals to investigate the possible relationship between Ti uptake and cellular toxicity. Results indicated that there was not a clear relationship between Ti uptake and cytotoxicity. A structure-activity relationship is discussed.

The interactions of iron with other divalent metals in the intestinal tract of a freshwater teleost, rainbow trout (Oncorhynchusmykiss)

This study examined the concentration-dependent interactive effects of four essential (Cu(2+), Zn(2+), Ni(2+), Co(2+)) and two non-essential (Pb(2+) and Cd(2+)) divalent metals on intestinal iron (Fe(2+)) absorption in freshwater rainbow trout (Oncorhynchusmykiss) using an invitro gut sac technique. All of the divalent metals except cobalt inhibited the intestinal Fe(2+) absorption in fish, and the magnitude of inhibition followed the order of: Ni(2+)~Pb(2+)>Cd(2+)~Cu(2+)>Zn(2+). The mucosal epithelium of the intestine was found to be the most sensitive to inhibition relative to the mucus or blood compartment, suggesting that these interactions likely occur via the divalent metal transporter-1 (DMT1). In addition, the reciprocal effects of Fe(2+) on intestinal accumulation of lead and cadmium were investigated. Elevated Fe(2+) did not affect lead accumulation in the intestine, indicating a greater affinity of Pb(2+) to the Fe(2+) transport pathway and/or the existence of additional pathways for lead absorption. In contrast, the accumulation of cadmium in the intestine decreased considerably in the presence of excess Fe(2+), indicating the importance of the Fe(2+) absorption pathway in dietary cadmium accumulation in fish. Overall, our study provides important insights into the mechanisms of dietary uptake of several divalent metals in freshwater fish.

Phytate: impact on environment and human nutrition. A challenge for molecular breeding

Phytic acid (PA) is the primary storage compound of phosphorus in seeds accounting for up to 80% of the total seed phosphorus and contributing as much as 1.5% to the seed dry weight. The negatively charged phosphate in PA strongly binds to metallic cations of Ca, Fe, K, Mg, Mn and Zn making them insoluble and thus unavailable as nutritional factors. Phytate mainly accumulates in protein storage vacuoles as globoids, predominantly located in the aleurone layer (wheat, barley and rice) or in the embryo (maize). During germination, phytate is hydrolysed by endogenous phytase(s) and other phosphatases to release phosphate, inositol and micronutrients to support the emerging seedling. PA and its derivatives are also implicated in RNA export, DNA repair, signalling, endocytosis and cell vesicular trafficking. Our recent studies on purification of phytate globoids, their mineral composition and dephytinization by wheat phytase will be discussed. Biochemical data for purified and characterized phytases isolated from more than 23 plant species are presented, the dephosphorylation pathways of phytic acid by different classes of phytases are compared, and the application of phytase in food and feed is discussed.

Comparison of iron uptake from reduced iron powder and FeSO4 using the Caco-2 cell model: effects of ascorbic acid, phytic acid, and pH

The reduced iron powder has considerable potential for use as an iron fortificant because it does not change organoleptically during storage or food preparation for cereal flour, and its bioavailability is scarcely influenced by iron absorption inhibitors in foods. The objective of this article is to study the effects of ascorbic acid, phytic acid, and pH on iron uptake from reduced iron powder (43 microm) and FeSO 4, and to compare iron bioavailability of reduced iron powders among four selected granularity levels. The cell ferritin formation is used as a marker of iron uptake. Obviously, iron uptake of reduced iron powder is increased with decreasing of powder granularity and is much lower than FeSO 4 when the size is above 43 microm, but significantly higher at 40-60 nm. In the presence of ascorbic acid or phytic acid, Caco-2 cell iron absorption from reduced iron powder (43 microm) is significantly higher than that from FeSO 4. And iron uptake of Caco-2 cells is decreased with increasing of pH from 5.5 to 7.5. Moreover, the decrease trend is more obvious for reduced iron powder than for FeSO 4. Our results indicated that iron bioavailability of reduced iron powder by intestinal enterocytes is similar to that of iron salts, and reduced iron powder is more excellent than FeSO 4 as food fortificant, especially at ultramicroscopic granularity.