Dietary gelatin enhances non-heme iron absorption possibly via regulation of systemic iron homeostasis in rats

Iron is an essential trace metal in human metabolism. However, imbalances in iron homeostasis are prevalent worldwide and have detrimental effects on human health. Humans do not have the ability to remove excess iron and therefore iron homeostasis is maintained by regulating the amount of iron entering the body from the diet. Iron is present in the human diet in number of different forms, including heme (from meat) and a variety of non-heme iron compounds. While heme is absorbed intact, the bioavailability of non-heme iron varies greatly depending on dietary composition. A number of dietary components are capable of interacting with iron to regulate its solubility and oxidation state. Interestingly, there is an emerging body of evidence suggesting that some nutrients also have direct effects on the expression and function of enterocyte iron transporters. In addition to dietary factors, body iron status is a major determinant of iron absorption. The roles of these important dietary and systemic factors in regulating iron absorption will be discussed in this review.

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The Precision of in vitro Methods and Algorithms for Predicting the Bioavailability of Dietary Iron

International Journal for Vitamin and Nutrition Research ◽

10.1024/0300-9831.75.6.436 ◽

2005 ◽

Vol 75 (6) ◽

pp. 436-445 ◽

Cited By ~ 10

Author(s):

Sean Lynch

Keyword(s):

Iron Absorption ◽

Heme Iron ◽

Iron Bioavailability ◽

Cell Uptake ◽

In Vitro Tests ◽

Cellular Iron ◽

Non Heme Iron ◽

Human Volunteers ◽

Dialyzable Iron

Three factors determine how much iron will be absorbed from a meal. They are the physiological mechanisms that regulate uptake by and transfer through the enterocytes in the upper small intestine, the quantity of iron in the meal, and its availability to the cellular iron transporters. Established methods exist for predicting the effect of physiological regulation and for measuring or estimating meal iron content. Three approaches to estimating bioavailability have been advocated. Two are in vitro screening procedures: measurement of dialyzable iron and Caco-2 cell uptake, both carried out after in vitro simulated gastric and pancreatic digestion. The third is the use of algorithms based on the predicted effects of specific meal components on absorption derived from isotopic studies in human volunteers. The in vitro procedures have been very useful for identifying and characterizing factors that affect non-heme iron absorption, but direct comparisons between absorption predicted from the in vitro tests and measurements in human volunteers have only been made in a limited number of published studies. The available data indicate that dialysis and Caco-2 cell uptake are useful for ranking meals and single food items in terms of predicted iron bioavailability, but may not reflect the magnitudes of the effects of factors that influence absorption accurately. Algorithms based on estimates of the amounts of heme iron and of enhancers and inhibitors of non-heme iron absorption in foods make it possible to classify meals or diets as being of high, medium, or low bioavailability. The precision with which meal iron bioavailability can be predicted in a population, for which a specific algorithm has been developed, is improved by measuring the content of the most important enhancers and inhibitors. However, the accuracy of such predictions appears to be much lower when the algorithm is applied to meals eaten by different populations.

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Alternative pathways for absorption of iron from foods

Pure and Applied Chemistry ◽

10.1351/pac-con-09-06-04 ◽

2010 ◽

Vol 82 (2) ◽

pp. 429-436 ◽

Cited By ~ 3

Author(s):

Bo Lönnerdal

Keyword(s):

Iron Absorption ◽

Iron Status ◽

Age Groups ◽

Heme Iron ◽

Dietary Factors ◽

Iron Binding ◽

Alternative Pathways ◽

Non Heme Iron ◽

Lactoferrin Receptor ◽

Iron Binding Proteins

Iron is known to be absorbed from foods in two major forms, heme iron and non-heme iron. Iron status as well as dietary factors known to affect iron absorption has limited effect on heme iron absorption, whereas inhibitors and enhancers of iron absorption have pronounced effects on non-heme iron absorption. The enterocyte transporter for non-heme iron, DMT1, is strongly up-regulated during iron deficiency and down-regulated during iron overload. A transporter for heme iron, HCP1, was recently characterized and is present on the apical membrane of enterocytes. Two other pathways for iron absorption have been discovered and may serve to facilitate uptake of iron from two unique iron-binding proteins, lactoferrin and ferritin. Lactoferrin is an iron-binding protein in human milk and known to survive proteolytic digestion. It mediates iron uptake in breast-fed infants through endocytosis via a specific lactoferrin receptor (LfR). Recently, lactoferrin has become popular as a food additive and may enhance iron status in several age groups. Ferritin is present in meat, but also in plants. The ferritin content of plants can be enhanced by conventional breeding or genetic engineering, and thereby increase iron intake of populations consuming plant-based diets. Ferritin is a bioavailable source of iron, as shown in recent human studies. Ferritin can be taken up by intestinal cells via endocytosis, suggesting a receptor-mediated mechanism.

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The Serine Protease Tmprss6 Regulates Hepcidin Expression, but Its Loss Does Not Cause Systemic Iron Deficiency In the Fetal and Neonatal Periods

Blood ◽

10.1182/blood.v116.21.4258.4258 ◽

2010 ◽

Vol 116 (21) ◽

pp. 4258-4258

Author(s):

Ramsey M. Wehbe ◽

Rebecca L. Whittlesey ◽

Nancy C. Andrews ◽

Karin E. Finberg

Keyword(s):

Iron Deficiency ◽

Iron Homeostasis ◽

Iron Concentration ◽

Fold Increase ◽

Heme Iron ◽

Hepcidin Expression ◽

Non Heme Iron ◽

Iron Parameters ◽

Maternal Iron ◽

Hepcidin Mrna

Abstract Abstract 4258 Mutations in TMPRSS6 (matriptase-2), a transmembrane serine protease expressed by the liver, result in the clinical phenotype of iron refractory iron deficiency anemia (IRIDA). Additionally, common polymorphisms in TMPRSS6 have been associated with variation in laboratory parameters of iron homeostasis in healthy populations. TMPRSS6 increases iron absorption by reducing expression of the hepatic hormone, hepcidin, via down-regulation of a BMP/SMAD signaling cascade. Hepcidin promotes the internalization and degradation of the duodenal iron transporter, ferroportin, thereby inhibiting iron absorption. Previous studies have demonstrated that adult mice with Tmprss6 deficiency exhibit elevated hepatic hepcidin mRNA levels that are associated with decreased hepatic iron stores. In one study, genetic loss of Tmprss6 was shown to result in significant elevation of hepatic hepcidin expression in mice at birth; however, whether this hepcidin elevation was associated with abnormalities in iron homeostasis was not reported. We therefore asked if the elevated hepcidin levels present in newborn Tmprss6-/- pups correlate with abnormal parameters of iron homeostasis in the fetal or neonatal periods. To answer this question, we intercrossed Tmprss6+/− mice to generate Tmprss6+/+, Tmprss6+/−, and Tmprss6-/- progeny for phenotypic characterization at either gestational day 17.5 (E17.5) or postnatal day 0 (P0). Consistent with prior observations, Tmprss6-/- pups at P0 showed a 4.6-fold increase in hepatic hepcidin mRNA compared to Tmprss6+/+ littermates (p=.006). However, despite this elevation in hepcidin expression, Tmprss6-/- pups were not pale, and they showed no significant differences in body mass or hepatic non-heme iron concentration compared to Tmprss6+/+ and Tmprss6+/− littermates. At E17.5, Tmprss6-/- fetuses showed a 50-fold increase in hepatic hepcidin mRNA compared to Tmprss6+/+ littermates (p=.005). However, Tmprss6-/- fetuses also were not pale, and they showed no significant difference in body mass compared to Tmprss6+/+ and Tmprss6+/− littermates. Surprisingly, hepatic non-heme iron concentration at E17.5 was significantly higher in Tmprss6-/- fetuses than in Tmprss6+/+ fetuses (p=.003). To determine if the increased hepcidin expression of Tmprss6-/- fetuses might affect iron homeostasis in their pregnant mothers, we measured iron parameters in Tmprss6+/− females gestating E17.5 litters that were enriched for either Tmprss6+/+ or Tmprss6-/- fetuses. No significant effects of fetal genotype on maternal iron parameters were observed. In summary, our results demonstrate that Tmprss6 regulates hepcidin expression in the fetal and neonatal periods in mice. However, Tmprss6 deficiency does not appear to be associated with systemic iron deficiency at these stages of development, and fetal Tmprss6 expression does not have a significant effect on maternal iron homeostasis in late gestation. These results may have implications for understanding the maintenance of iron homeostasis in early development, and may provide insight into the evolution of IRIDA as well as other disorders of iron homeostasis. Disclosures: No relevant conflicts of interest to declare.

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Inhibitory Effect of Calcium on Non-heme Iron Absorption May Be Related to Translocation of DMT-1 at the Apical Membrane of Enterocytes

Journal of Agricultural and Food Chemistry ◽

10.1021/jf101388z ◽

2010 ◽

Vol 58 (14) ◽

pp. 8414-8417 ◽

Cited By ~ 31

Author(s):

Ben A. V. Thompson ◽

Paul A. Sharp ◽

Ruan Elliott ◽

Susan J. Fairweather-Tait

Keyword(s):

Iron Absorption ◽

Apical Membrane ◽

Inhibitory Effect ◽

Heme Iron ◽

Non Heme Iron

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Non-heme Iron as Ferrous Sulfate Does Not Interact with Heme Iron Absorption in Humans

Biological Trace Element Research ◽

10.1007/s12011-012-9496-4 ◽

2012 ◽

Vol 150 (1-3) ◽

pp. 68-73 ◽

Cited By ~ 1

Author(s):

Diego Gaitán ◽

Manuel Olivares ◽

Bo Lönnerdal ◽

Alex Brito ◽

Fernando Pizarro

Keyword(s):

Ferrous Sulfate ◽

Iron Absorption ◽

Heme Iron ◽

Non Heme Iron

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Abstract 12425: Sirt2 Mediated-Deacetylation Regulates Cellular Iron Homeostasis

Circulation ◽

10.1161/circ.130.suppl_2.12425 ◽

2014 ◽

Vol 130 (suppl_2) ◽

Author(s):

Xiaoyan Yang ◽

Athanassios Vassilopoulos ◽

Seong-Hoon Park ◽

David Gius ◽

Hossein Ardehali

Keyword(s):

Iron Content ◽

Iron Homeostasis ◽

Underlying Mechanism ◽

Heme Iron ◽

Iron Storage ◽

Cellular Iron ◽

Non Heme Iron ◽

Ferroportin 1 ◽

Cellular Iron Homeostasis ◽

Iron Export

Background: Sirtuins (SIRTs) are NAD+-dependent deacetylases and critical regulators of energy metabolism and response to oxidative stress in the heart. Iron is essential for these processes but is toxic when present in excess. Thus, SIRTs may regulate iron levels to ensure adequate supply of this element for their biological functions. SIRT2 is among the least characterized SIRTs and is mainly present in the cytoplasm. We hypothesized that SIRT2 might be required for cellular iron homeostasis. Methods and Results: Iron content was significantly lower in SIRT2-/- mouse embryonic fibroblasts (MEFs) compared to SIRT2+/+ MEFs (non-heme iron: 0.073 vs. 0.060 nmol/μg protein, p=0.02). Gene expression of ferroportin-1 (FPN1), the major cellular iron exporter, was significantly increased in SIRT2-/- MEFs. Similarly, silencing SIRT2 in HepG2 cells decreased cellular iron levels and increased FPN1 expression, indicating that enhanced FPN1 in SIRT2 knockout or knockdown condition increases iron export and reduces cellular iron. To investigate the underlying mechanism, we focused our studies on nuclear factor (erythroid-derived 2)-like 2 (Nrf2), a known regulator of FPN1. Our results demonstrated that Nrf2 is upregulated and translocates into the nucleus in SIRT2-/- MEFs and knocking down Nrf2 in SIRT2-/- MEFs reverses iron deficiency and FPN1 expression. Furthermore, Nrf2 is acetylated by P300/CBP and can be deacetylated by SIRT2. Finally, to confirm the role of SIRT2 in iron regulation, cellular heme and non-heme iron in the heart (major iron-consuming organ) and liver (major iron-storage organ) were measured in wild type (WT) and SIRT2-/- mice. Heme and non-heme iron content were significantly decreased in SIRT2-/- mouse livers compared to WT livers (heme: 2.25 vs. 1.65 nmol/mg protein, p=0.002; non-heme iron: 0.073 vs. 0.064 nmol/μg protein, p=0.03). Furthermore, heme levels were also significant decreased in the heart, while non-heme iron was not significantly altered. Conclusions: Our results suggest that SIRT2 regulates cellular iron homeostasis by deacetylating NRF2 and altering iron export through FPN1.

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Abstract 92: Sirtuin 2 mediated-deacetylation regulates cellular iron homeostasis

Circulation Research ◽

10.1161/res.115.suppl_1.92 ◽

2014 ◽

Vol 115 (suppl_1) ◽

Author(s):

Xiaoyan Yang ◽

Athanassios Vassilopoulos ◽

Seong-Hoon Park ◽

David Gius ◽

Hossein Ardehali

Keyword(s):

Iron Content ◽

Hepg2 Cells ◽

Iron Homeostasis ◽

Underlying Mechanism ◽

Heme Iron ◽

Iron Storage ◽

Cellular Iron ◽

Non Heme Iron ◽

Cellular Iron Homeostasis ◽

Iron Export

Background: Sirtuins (SIRTs) are NAD+-dependent deacetylases, which regulate energy metabolism and response to oxidative stress in the heart. Iron is essential for these processes but is toxic when present in excess. However, whether SIRTs are involved in maintaining cellular iron homeostasis is not known. SIRT2 is among the least characterized SIRTs and is mainly present in the cytoplasm. We hypothesized that SIRT2 is required for cellular iron homeostasis. Methods and Results: Iron content was significantly lower in SIRT2-/- mouse embryonic fibroblasts (MEFs) compared to SIRT2+/+ MEFs (non-heme iron: 0.073 vs. 0.060 nmol/μg protein, p=0.02), andlevels of ferroportin-1 (FPN1), the major cellular iron exporter, was significantly increased in SIRT2-/- MEFs. Similarly, silencing SIRT2 in HepG2 cells decreased cellular iron levels and increased FPN1 expression, indicating that enhanced FPN1 with SIRT2 downregulation drove iron export and caused a reduction in cellular iron levels. Furthermore, iron export assays showed that iron export was increased in HepG2 cells with SIRT2 knockdown. To investigate the underlying mechanism, we focused our studies on nuclear factor (erythroid-derived 2)-like 2 (Nrf2), a known regulator of FPN1. Our results demonstrated that Nrf2 is upregulated and translocates into the nucleus in SIRT2-/- MEFs and knocking down Nrf2 in SIRT2-/- MEFs reverses iron deficiency. Furthermore, Nrf2 is acetylated by P300/CBP and can be deacetylated by SIRT2. Finally, to confirm the role of SIRT2 in iron regulation, cellular heme and non-heme iron in the heart (major iron-consuming organ) and liver (major iron-storage organ) were measured in wild type (WT) and SIRT2-/- mice. Heme and non-heme iron content were significantly decreased in SIRT2-/- mouse livers compared to WT livers (heme: 2.25 vs. 1.65 nmol/mg protein, p=0.002; non-heme iron: 0.073 vs. 0.064 nmol/μg protein, p=0.03). Furthermore, heme levels were also significant decreased in the heart, while non-heme iron was not significantly altered. Conclusions: Our results suggest that SIRT2 regulates cellular iron homeostasis by deacetylating NRF2 and altering iron export through FPN1.

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Algorithms to Assess non-Heme Iron Bioavailability

International Journal for Vitamin and Nutrition Research ◽

10.1024/0300-9831.75.6.405 ◽

2005 ◽

Vol 75 (6) ◽

pp. 405-412 ◽

Cited By ~ 7

Author(s):

Manju B. Reddy

Keyword(s):

Iron Absorption ◽

Iron Status ◽

Interactive Effect ◽

Population Level ◽

Heme Iron ◽

Iron Bioavailability ◽

Dietary Factors ◽

Interactive Effects ◽

Sufficient Information ◽

Non Heme Iron

While sufficient information exists on the effect of individual factors on iron absorption, their net effect in a mixed meal is less well characterized, being dependent on the combination and quantity of the factors present in the meal. Over a period of more than 25 years, several models have been developed to estimate non-heme iron bioavailability, either to assess iron absorption from a meal or iron sufficiency in populations. Initially, a model was developed to calculate iron absorption in individuals with varying iron status that included only enhancers. This model was useful in classifying the diets but has limited value for accurale assessment. Later models were modified and improved by including inhibitors in the calculations. However, some included either phytate or tea but not in combination. The models that included all the factors in calculations assumed their effect was independent and additive rather than interactive, which is an important issue in addressing iron bioavailability. Although some of the models correlated estimated bioavailability with iron status of the population, the accuracy of the estimations is of concern due to lack of quantitative measurements of bioavailability modifiers, inability to consider interactive effects, and the use of non-iron status measurements. Recent research has led to the development of refined models to assess iron bioavailability of complex meals by comprehensively taking into consideration the interactive effect among enhancers and inhibitors. However, the models are based on single-meal studies and their application to whole diets at a population level is not clear. Accurate measurements of dietary factors and independent validation are needed before using these models. To date, no single model is applicable to all diets and additional studies are needed to develop new models to predict bioavailability of whole diets accurately, in addition to addressing dietary adequacy in all populations.

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Oral Administration of Ginger-Derived Lipid Nanoparticles and Dmt1 siRNA Potentiates the Effect of Dietary Iron Restriction and Mitigates Pre-Existing Iron Overload in Hamp KO Mice

Nutrients ◽

10.3390/nu13051686 ◽

2021 ◽

Vol 13 (5) ◽

pp. 1686

Author(s):

Xiaoyu Wang ◽

Mingzhen Zhang ◽

Regina R. Woloshun ◽

Yang Yu ◽

Jennifer K. Lee ◽

...

Keyword(s):

Iron Overload ◽

Iron Absorption ◽

Hereditary Hemochromatosis ◽

Heme Iron ◽

Dietary Iron ◽

Iron Loading ◽

Body Iron ◽

Iron Restriction ◽

Sirna Treatment ◽

Non Heme Iron

Intestinal iron transport requires an iron importer (Dmt1) and an iron exporter (Fpn1). The hormone hepcidin regulates iron absorption by modulating Fpn1 protein levels on the basolateral surface of duodenal enterocytes. In the genetic, iron-loading disorder hereditary hemochromatosis (HH), hepcidin production is low and Fpn1 protein expression is elevated. High Fpn1-mediated iron export depletes intracellular iron, causing a paradoxical increase in Dmt1-mediated iron import. Increased activity of both transporters causes excessive iron absorption, thus initiating body iron loading. Logically then, silencing of intestinal Dmt1 or Fpn1 could be an effective therapeutic intervention in HH. It was previously established that Dmt1 knock down prevented iron-loading in weanling Hamp (encoding hepcidin) KO mice (modeling type 2B HH). Here, we tested the hypothesis that Dmt1 silencing combined with dietary iron restriction (which may be recommended for HH patients) will mitigate iron loading once already established. Accordingly, adult Hamp KO mice were switched to a low-iron (LFe) diet and (non-toxic) folic acid-coupled, ginger nanoparticle-derived lipid vectors (FA-GDLVs) were used to deliver negative-control (NC) or Dmt1 siRNA by oral, intragastric gavage daily for 21 days. The LFe diet reduced body iron burden, and experimental interventions potentiated iron losses. For example, Dmt1 siRNA treatment suppressed duodenal Dmt1 mRNA expression (by ~50%) and reduced serum and liver non-heme iron levels (by ~60% and >85%, respectively). Interestingly, some iron-related parameters were repressed similarly by FA-GDLVs carrying either siRNA, including 59Fe (as FeCl3) absorption (~20% lower), pancreatic non-heme iron (reduced by ~65%), and serum ferritin (decreased 40–50%). Ginger may thus contain bioactive lipids that also influence iron homeostasis. In conclusion, the combinatorial approach of FA-GDLV and Dmt1 siRNA treatment, with dietary iron restriction, mitigated pre-existing iron overload in a murine model of HH.

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