10/19/2006 Yuka Mitsuhashi -Scandinavian “Iarn"

NUTR 650, 10/19/ History 2.Fact - chemistry 3.Function 4.Distribution 5.Functional and storage iron 6.Absorption 7.Homeostasis 8.Fe - mineral interaction 9.Storage Status Overview

NUTR 650, 10/19/2006 The ancient Greeks administered iron to their injured soldiers to improve muscle weakness 18th century - Menghini shows that blood contains iron by lifting dried blood with a magnet hemoglobin iron content was determined to be 0.35% – Chlorosis was defined by low level of iron in the blood and reduced number of red cells Boussingault first described the nutritional essentiality of iron History

NUTR 650, 10/19/ Bunge describes special vulnerability of infants to iron deficiency and notes that milk is a particularly poor source of iron Mackay shows that infantile anemia can be avoided by use of iron fortified formula By 1960 ’ s - Physiology and clinical nutrition largely completed 1990 ’ s-present - molecular details of how iron metabolism is regulated History

NUTR 650, 10/19/ th element in the periodic table –Chemical Symbol: Fe –MW = –Electron Configuration: 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 6 –Fourth most abundant mineral O > Si > Al –Oxidation states = -2 to +6 Readily interconverted, i.e. redox active –very useful for redox chemistry in the body –very dangerous chemistry ADP - Fe 3+ + O >ADP - Fe 2+ + O 2 ADP - Fe 2+ + H 2 O 2 ---> HO + OH - Facts

NUTR 650, 10/19/2006 Flavoproteins Hemeproteins Fe-sulfur Nzms Other Fe Nzms Other Fe Proteins Fe-Containing Proteins Transferrin & Others Ferritin & Hemosiderin Other Nzms Heme Flavoproteins Hemoglobin Other Nzms Iron Activated Nzms 2Fe-2S 4Fe-4S Nzms MyoglobinCytochromes Other NzmsFunction

NUTR 650, 10/19/2006 Function Oxygen Transport & Storage –Hemoglobin –Myoglobin Electron Transport & Energy Metabolism –Cytochromes –Fe-S proteins Substrate Oxidation & Reduction – Iron dependent enzyme- –Ribonucleotide reductase –Amino acid oxidases –Fatty acid desaturases –Nitric oxide synthetase –Peroxidases Regulation of intracellular iron

NUTR 650, 10/19/2006 Distribution CompoundMale (mg/kg)Female (mg/kg) FunctionalHemoglobin3126 Myoglobin43 Heme Nzm11 Nonheme Nzm11 Transferrin Iron0.05 Total37 (74%)33 (87%) StorageFerritin94 Hemosiderin41 Total13 (26%)5 (13%) Body Total mg/kg5038 Handbook of Nutritionally Essential Mineral Elements

NUTR 650, 10/19/2006 Distribution Iron Requirement mg/day Body Iron Loss Fetus Menstruation Lactation Red Cells Non gravid 1st2nd3rd Trimester Postpartum

NUTR 650, 10/19/2006 Whole body fluxes Hemoglobin (~2500mg) Plasma Iron (transferrin ) Iron Intake (10-14mg → 0.5-2mg) Stores (1500mg) Myoglobin (200mg) Enzyme Iron (5mg) Iron Loss (1-2mg) FerritinHemosiderin Liver, Spleen Bone marrow Erythrocyte

NUTR 650, 10/19/2006 Functional iron Transferrin: Transport iron Single polypeptides composed of two iron binding half-site motifs, ~679 aas, ~80 kD MW Carbohydrate-rich globular proteins Bind 2 Fe 3+ and 2 HCO 3 Normally 25-50% saturated with iron –Lactoferrin is iron binding protein in milk,plasma and mucus secretion such as tears –Ovotransferrin is iron binding protein in bird’s egg white

NUTR 650, 10/19/2006 Storage Iron Ferritin Major iron storage protein Apoferritin 24polypeptide units in raspberry-like cluster Surrounds spherical cluster of hydrated ferric phosphate within its hollow center Can contain up to 4000 Fe atoms Liver contains ~60% of ferritin in the body ~40% are found in muscles and the reticuloendothelial cells Two isoforms - H subunit: 22kDa, 182aas, predominant in heart - L subunit: 20kDa, 174aas, predominant in liver

NUTR 650, 10/19/2006 Storage Iron Hemosiderin ~50% liver iron stores Reacts to ferritin antibodies - likely a degradation product Insoluble, ~30% iron by weight Less available for mobilization

NUTR 650, 10/19/2006 Iron forms in diets Heme –Iron-porphyrin prosthetic group –Hemoglobin, myoglobin, cytochromes –Other iron-containing enzymes are ~3% body iron Aconitase, peroxidases –5-25% are absorbed –Exist as Fe 2+ Nonheme –>85% of iron in foods is non heme iron –2-5% are absorbed –Exist as Fe 3+

NUTR 650, 10/19/2006 Absorption Nonheme 1. Iron solublized and ionized by stomach acid 2. Chelation with small molecular weight compounds and mucin 3. Iron chelates pass through unstirred water layer bind to surface proteins and are internalized 4. Absorption all along the small intestine, but highest in duodenum Heme 1. Protein digestion of hemoglobin and myoglobin releases heme 2. Heme transported as such into the cell

NUTR 650, 10/19/2006 Absorption Ferrous, Fe 2+, most soluble = most absorbable Each mechanism has 3 phases –Iron uptake –Intraenterocyte transport –Storage and extraenterocyte transfer

NUTR 650, 10/19/2006 Absorption Duodenal LumenDuodenal MucosaPlasma B2-microglobulin HFE DMT1 B 3 integrin Mucin Fe ++ Fe 2+ Fe 3+ Mobilferritin Heme- Protein Heme + Polypeptides Heme Biliverdin Bilirubin Bilirubin Heme Oxigenase CO paraferritin Fe 2+ Fe 3+ Transferritin Ceruloplasmin Ferroportin

NUTR 650, 10/19/2006 Absorption Factors affecting Iron Absorption –Dietary Iron Content –Bioavailability of ingested iron –Body Iron Stores –Erythrocyte production rates –Iron Form Heme - from animal sources 2-3x more available Non-heme - solubility key, ~85% of dietary iron –Gender, Men = 6% absorption; Women = 13% Iron uptake - Duodenal lumen to Duodenal mucosa

NUTR 650, 10/19/2006 Absorption Promotors –Amino Acids –Animal Proteins(for heme) –Ascorbic Acid –Hydrochloric Acid –Organic Acids –Sugars –Mucin Inhibitors –Carbonates –Calcium (for heme) –Egg yolk phosvitin –Fiber –Oxalates –Phosphates –Phytates –Plant polyphenols –Soy proteins Iron uptake phase - Duodenal lumen to Duodenal mucosa

NUTR 650, 10/19/2006 Transferrin Receptor Transferrin Receptor (Tf r ) –Mechanism for most cellular iron uptake –180-kDa glycoprotein 2 identical subunits –Multiple regulators of transcription & translation Several metals (++), retinoic acid (-), & 1,25 Vit D 3 Phosphorylation –Binds 1 transferrin High affinity binding Prefers diferric Tf > > apoTf Usually saturated due to normal Tf plasma concentration Storage and extraenterocyte transfer phase

NUTR 650, 10/19/2006 Intracellular iron metabolism and homeostasis Handbook of Nutritionally Essential Mineral Elements

NUTR 650, 10/19/2006 Homeostasis Low IronHigh Iron Iron-Responsive Element(IRE) bound by IRP? YesNO Ferritin mRNA translation Ferritin Synthesis RepressedActivated TfR mRNA stability TfR synthesis IncreasedDecreased 5’ AAA n 3’ Ferritin mRNA Transferrin Receptor (TfR) mRNA 5’ AAA n 3’ Iron Regulatory Proteins - Regulate iron storage and metabolism - Bind to iron response elements and regulate the synthesis of specific proteins

NUTR 650, 10/19/2006 Mineral Interactions Mn Fe Cu Zn (-) (+) (-)

NUTR 650, 10/19/2006 Mineral Interactions Cu deficiency causes iron accumulation because iron can’t mobilize from tissues (Textbook) Cu-deficient male rats absorbed less Fe than Cu-adequate rats and were severely anemic (J. Nutr. 134: , 2004) Dietary Copper Deficiency Reduces Iron Absorption and Duodenal Enterocyte Hephaestin Protein in Male and Female Rats (J. Nutr. 135:92-98, January 2005) Current theory of Fe-Cu interactions 4Fe 2+ + O 2 + 4H + 4Fe H 2 O (Plasma Cu-containing enzyme ceruloplasmin (ferroxidase1), Hephaestin) Fe-Cu interactions

NUTR 650, 10/19/2006 Mineral Interactions High doses of iron supplements taken together with zinc supplements on an empty stomach can inhibit the absorption of zinc. When takne with food, supplemental iron does not appear to inhibit zinc absorption. Iron- fortified foods have no effect on zinc absorption. (Textbook) When given to adults in solution in ratios of Zn: Iron is >2:1 was found to compete for absorption with zinc. (J. Nutr.116: , 1986) Divalent metal transporter 1 (DMT1) has an affinity for both Fe and Zn Recent studies have shown Zn has a specific transporter, Zn transporter (ZIN), in the apical membrane and ZIP is the primary transporter of Zn because Fe disrupt Zn absorption, not vice versa. (J. Nutr. 134: , 2004, Am J Clin Nutr. 78 (5): 1018, 2003 ) Fe-Zn interactions

NUTR 650, 10/19/2006 Mineral Interactions When iron intake was minimal, a small excess of Mn causes anemia and low serum iron in a lamb. (Textbook) Nonheme iron antagonizes manganese, but not heme iron. (Am J Clin Nutr. 56: , 1992) Absorption of Mn from a meal is reduced as the meal’s iron content is increased. Intestinal absorption of Mn is increased during iron deficiency, and increased ferritin levels are associated with decreased Mn absorption. Fe-Mn interactions

NUTR 650, 10/19/2006 Iron Deficiency –Subtle symptoms unless anemia is severe (hemoglobin <70g/L) –Mainly three identified (from least to most severe)  Storage iron depletion Only iron store is depleted  Early functional iron deficiency Iron store is depleted and functional iron is low but not low enough to cause measurable anemia  Iron deficiency anemia Impaired tissue oxygenation, reduced work ability Responsible for many maternal death at parturition Impaired oxidative metabolism in muscle shift to gluconeogenesis and lactate utilization (acidosis) Behavioral and Intellectual Defects Body temperature regulation impaired Storage Status

NUTR 650, 10/19/2006 Deficiency Signs Koilonychia “Spoon Nails” Glossitis Angular Stomatitis

NUTR 650, 10/19/2006 Iron Excess & Toxicity –Acute toxicity - overload transferrin, strong acids produced by Fe/HCl in stomach kill GI tract Bloody vomit and stools Systemic effects from conversion of ferrous to ferric and release of protons Storage Status

NUTR 650, 10/19/2006 Iron Excess & Toxicity –Chronic Iron Toxicity Hemosiderosis - excess iron in hemosiderin Hemochromotosis - excess iron in fibrotic tissue damage –common causes = excess ingestion or transfusion –Genetic hyper absorption - Hemochromatosis »3-4/100 of European descent »Cirrhosis, diabetes, heart failure, arthritis, sexual dysfunction »Transferrin saturation good screening test Storage Status

NUTR 650, 10/19/2006 Thank you -Arigato gozaimashita- Iron man – Japanese version