Human iron metabolism

Human iron metabolism is the set of chemical reactions that maintain human homeostasis of iron at the systemic and cellular level. Iron is both necessary to the body and potentially toxic, and controlling iron levels in the body is a critically important part of many aspects of human health and disease. Hematologists have been especially interested in systemic iron metabolism because iron is essential for red blood cells, where most of the human body's iron is contained. Understanding iron metabolism is also important for understanding diseases of iron overload, such as hereditary hemochromatosis, and iron deficiency, such as iron deficiency anemia.

Cellular iron homeostasis
Diagram showing a generalized view of cellular iron homeostasis in humans. Iron import can occur via endocytosis of transferrin receptor 1 or via ferrous iron importers DMT1 and ZIP14, which require the activity of iron reductases such as STEAP2, SDR-2 and Dcytb. Intracellular iron can be stored in ferritin, used for protein biosynthesis, generate reactive oxygen species (ROS) and regulate transcription via iron-responsive element-binding proteins (IRP1/2). Export occurs through ferroportin, often aided by hephaestin (Hp) and/or ceruloplasmin (Cp), and repressed by hepcidin.

Importance of iron regulation

Heme b
Structure of Heme b; "Fe" is the chemical symbol of iron, "II" indicates its oxidation state.

Iron is an essential bioelement for most forms of life, from bacteria to mammals. Its importance lies in its ability to mediate electron transfer. In the ferrous state, iron acts as an electron donor, while in the ferric state it acts as an acceptor. Thus, iron plays a vital role in the catalysis of enzymatic reactions that involve electron transfer (reduction and oxidation, redox). Proteins can contain iron as part of different cofactors, such as iron-sulfur clusters (Fe-S) and heme groups, both of which are assembled in mitochondria.

Cellular respiration

Human cells require iron in order to obtain energy as ATP from a multi-step process known as cellular respiration, more specifically from oxidative phosphorylation at the mitochondrial cristae. Iron is present in the iron-sulfur clusters and heme groups of the electron transport chain proteins that generate a proton gradient that allows ATP synthase to synthesize ATP (chemiosmosis).

Heme groups are part of hemoglobin, a protein found in red blood cells that serves to transport oxygen from the lungs to the tissues. Heme groups are also present in myoglobin to store and diffuse oxygen in muscle cells.

Oxygen transport

The human body needs iron for oxygen transport. Oxygen (O2) is required for the functioning and survival of nearly all cell types. Oxygen is transported from the lungs to the rest of the body bound to the heme group of hemoglobin in erythrocytes. In muscles cells, iron binds myoglobin, which regulates its release.

Toxicity

Iron is also potentially toxic. Its ability to donate and accept electrons means that it can catalyze the conversion of hydrogen peroxide into free radicals. Free radicals can cause damage to a wide variety of cellular structures, and ultimately kill the cell.[1]

Iron bound to proteins or cofactors such as heme is safe. Also, there are virtually no truly free iron ions in the cell, since they readily form complexes with organic molecules. However, some of the intracellular iron is bound to low-affinity complexes, and is termed labile iron or "free" iron. Iron in such complexes can cause damage as described above.[2]

To prevent that kind of damage, all life forms that use iron bind the iron atoms to proteins. This binding allows cells to benefit from iron while also limiting its ability to do harm.[1][3] Typical intracellular labile iron concentrations in bacteria are 10-20 micromolar,[4] though they can be 10-fold higher in anaerobic environment,[5] where free radicals and reactive oxygen species are scarcer. In mammalian cells, intracellular labile iron concentrations are typically smaller than 1 micromolar, less than 5 percent of total cellular iron.[2]

Bacterial protection

EscherichiaColi NIAID
Electron micrograph of E. coli. Most bacteria that cause human disease require iron to live and to multiply.

In response to a systemic bacterial infection, the immune system initiates a process known as iron withholding. If bacteria are to survive, then they must obtain iron from their environment. Disease-causing bacteria do this in many ways, including releasing iron-binding molecules called siderophores and then reabsorbing them to recover iron, or scavenging iron from hemoglobin and transferrin. The harder they have to work to get iron, the greater a metabolic price they must pay. That means that iron-deprived bacteria reproduce more slowly. So our control of iron levels appears to be an important defense against most bacterial infections; there are some exceptions however. TB causing bacterium can reside within macrophages which are an iron rich environment and Borrelia burgdorferi utilises manganese in place of iron. People with increased amounts of iron, like people with hemochromatosis, are more susceptible to some bacterial infection.[6]

Although this mechanism is an elegant response to short-term bacterial infection, it can cause problems when inflammation goes on for longer. Since the liver produces hepcidin in response to inflammatory cytokines, hepcidin levels can increase as the result of non-bacterial sources of inflammation, like viral infection, cancer, auto-immune diseases or other chronic diseases. When this occurs, the sequestration of iron appears to be the major cause of the syndrome of anemia of chronic disease, in which not enough iron is available to produce enough hemoglobin-containing red blood cells.[3]

Body iron stores

Gray72-en
Illustration of blood cell production in the bone marrow. In iron deficiency, the bone marrow produces fewer blood cells, and as the deficiency gets worse, the cells become smaller.

Most well-nourished people in industrialized countries have 4 to 5 grams of iron in their bodies (∼38 mg iron/kg body weight for women and ∼50 mg iron/kg body for men).[7] Of this, about 2.5 g is contained in the hemoglobin needed to carry oxygen through the blood, and most of the rest (approximately 2 grams in adult men, and somewhat less in women of childbearing age) is contained in ferritin complexes that are present in all cells, but most common in bone marrow, liver, and spleen. The liver's stores of ferritin are the primary physiologic source of reserve iron in the body. The reserves of iron in industrialized countries tend to be lower in children and women of child-bearing age than in men and in the elderly. Women who must use their stores to compensate for iron lost through menstruation, pregnancy or lactation have lower non-hemoglobin body stores, which may consist of 500 mg, or even less.

Of the body's total iron content, about 400 mg is devoted to cellular proteins that use iron for important cellular processes like storing oxygen (myoglobin) or performing energy-producing redox reactions (cytochromes). A relatively small amount (3–4 mg) circulates through the plasma, bound to transferrin.[8] Because of its toxicity, free soluble iron is kept in low concentration in the body.

Iron deficiency first affects the storage iron in the body, and depletion of these stores is thought to be relatively non-symptomatic, although some vague and non-specific symptoms have been associated with it. Since iron is primarily required for hemoglobin, iron deficiency anemia is the primary clinical manifestation of iron deficiency. Iron-deficient people will suffer or die from organ damage well before cells run out of the iron needed for intracellular processes like electron transport.

Macrophages of the reticuloendothelial system store iron as part of the process of breaking down and processing hemoglobin from engulfed red blood cells. Iron is also stored as a pigment called hemosiderin which is an ill-defined deposit of protein and iron, created by macrophages where excess iron is present, either locally or systemically for example among people with iron overload due to frequent blood cell destruction and transfusions. If the systemic iron overload is corrected, over time the hemosiderin is slowly resorbed by macrophages.

Mechanisms of iron regulation

Human iron homeostasis is regulated at two different levels. Systemic iron levels are balanced by the controlled absorption of dietary iron by enterocytes, the cells that line the interior of the intestines, and the uncontrolled loss of iron from epithelial sloughing, sweat, injuries and blood loss. In addition, systemic iron is continuously recycled. Cellular iron levels are controlled differently by different cell types due to the expression of particular iron regulatory and transport proteins.

Systemic iron regulation

Redbloodcells
Humans use 20 mg of iron each day for the production of new red blood cells, much of which is recycled from old red blood cells.

Dietary iron uptake

The absorption of dietary iron is a variable and dynamic process. The amount of iron absorbed compared to the amount ingested is typically low, but may range from 5% to as much as 35% depending on circumstances and type of iron. The efficiency with which iron is absorbed varies depending on the source. Generally the best-absorbed forms of iron come from animal products. Absorption of dietary iron in iron salt form (as in most supplements) varies somewhat according to the body’s need for iron, and is usually between 10% and 20% of iron intake. Absorption of iron from animal products, and some plant products, is in the form of heme iron, and is more efficient, allowing absorption of from 15% to 35% of intake. Heme iron in animals is from blood and heme-containing proteins in meat and mitochondria, whereas in plants, heme iron is present in mitochondria in all cells that use oxygen for respiration.

Like most mineral nutrients, the majority of the iron absorbed from digested food or supplements is absorbed in the duodenum by enterocytes of the duodenal lining. These cells have special molecules that allow them to move iron into the body. To be absorbed, dietary iron can be absorbed as part of a protein such as heme protein or iron must be in its ferrous Fe2+ form. A ferric reductase enzyme on the enterocytes’ brush border, duodenal cytochrome B (Dcytb), reduces ferric Fe3+ to Fe2+.[9] A protein called divalent metal transporter 1 (DMT1), which can transport several divalent metals across the plasma membrane, then transports iron across the enterocyte’s cell membrane into the cell. It the iron is bound to Heme it is instead transported across the apical membrane by Heme carrier protein 1 (HCP1).[10]

These intestinal lining cells can then either store the iron as ferritin, which is accomplished by Fe3+ binding to apoferritin (in which case the iron will leave the body when the cell dies and is sloughed off into feces), or the cell can release it into the body via the only known iron exporter in mammals, ferroportin. Hephaestin, a ferroxidase that can oxidize Fe2+ to Fe3+ and is found mainly in the small intestine, helps ferroportin transfer iron across the basolateral end of the intestine cells. In contrast, ferroportin is post-translationally repressed by hepcidin, a 25-amino acid peptide hormone. The body regulates iron levels by regulating each of these steps. For instance, enterocytes synthesize more Dcytb, DMT1 and ferroportin in response to iron deficiency anemia.[11] Iron absorption from diet is enhanced in the presence of vitamin C and diminished by excess calcium, zinc, or manganese.[12]

The human body’s rate of iron absorption appears to respond to a variety of interdependent factors, including total iron stores, the extent to which the bone marrow is producing new red blood cells, the concentration of hemoglobin in the blood, and the oxygen content of the blood. The body also absorbs less iron during times of inflammation, in order to deprive bacteria of iron. Recent discoveries demonstrate that hepcidin regulation of ferroportin is responsible for the syndrome of anemia of chronic disease.

Iron recycling and loss

Most of the iron in the body is hoarded and recycled by the reticuloendothelial system, which breaks down aged red blood cells. In contrast to iron uptake and recycling, there is no physiologic regulatory mechanism for excreting iron. People lose a small but steady amount by gastrointestinal blood loss, sweating and by shedding cells of the skin and the mucosal lining of the gastrointestinal tract. The total amount of loss for healthy people in the developed world amounts to an estimated average of 1 mg a day for men, and 1.5–2 mg a day for women with regular menstrual periods. People with gastrointestinal parasitic infections, more commonly found in developing countries, often lose more.[1] Those who cannot regulate absorption well enough get disorders of iron overload. In these diseases, the toxicity of iron starts overwhelming the body's ability to bind and store it.[13]

Cellular iron regulation

Iron import

Most cell types take up iron primarily through receptor-mediated endocytosis via transferrin receptor 1 (TFR1), transferrin receptor 2 (TFR2) and GAPDH. TFR1 has a 30-fold higher affinity for transferrin-bound iron than TFR2 and thus is the main player in this process.[14][15] The higher order multifunctional glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH) also acts as a transferrin receptor.[16][17] Transferrin-bound ferric iron is recognized by these transferrin receptors, triggering a conformational change that causes endocytosis. Iron then enters the cytoplasm from the endosome via importer DMT1 after being reduced to its ferrous state by a STEAP family reductase.[18]

Alternatively, iron can enter the cell directly via plasma membrane divalent cation importers such as DMT1 and ZIP14 (Zrt-Irt-like protein 14).[19] Again, iron enters the cytoplasm in the ferrous state after being reduced in the extracellular space by a reductase such as STEAP2, STEAP3 (in erythrocytes), Dcytb (in enterocytes) and SDR2.[18]

The labile iron pool

In the cytoplasm, ferrous iron is found in a soluble, chelatable state which constitutes the labile iron pool (~0.001 mM).[20] In this pool, iron is thought to be bound to low-mass compounds such as peptides, carboxylates and phosphates, although some might be in a free, hydrated form (aqua ions).[20] Alternatively, iron ions might be bound to specialized proteins known as metallochaperones.[21] Specifically, poly-r(C)-binding proteins (PCBPs) appear to mediate transfer of free iron to ferritin (for storage) and non-heme iron enzymes (for use in catalysis).[19][22] The labile iron pool is potentially toxic due to iron's ability to generate reactive oxygen species. Iron from this pool can be taken up by mitochondria via mitoferrin to synthesize Fe-S clusters and heme groups.[18]

The storage iron pool

Iron can be stored in ferritin as ferric iron due to the ferroxidase activity of the ferritin heavy chain.[23] Dysfunctional ferritin may accumulate as hemosiderin, which can be problematic in cases of iron overload.[24] The ferritin storage iron pool is much larger than the labile iron pool, ranging in concentration from 0.7 mM to 3.6 mM.[20]

Iron export

Iron export occurs in a variety of cell types, including neurons, erythrocytes, macrophages and enterocytes. The latter two are especially important since systemic iron levels depend upon them. There is only one known iron exporter, ferroportin.[25] It transports ferrous iron out of the cell, generally aided by ceruloplasmin and/or hephaestin (mostly in enterocytes), which oxidize iron to its ferric state so it can bind ferritin in the extracellular medium.[18] Hepcidin causes the internalization of ferroportin, decreasing iron export. Besides, hepcidin seems to downregulate both TFR1 and DMT1 through an unknown mechanism.[26] Another player assisting ferroportin in effecting cellular iron export is GAPDH.[27] A specific post translationally modified isoform of GAPDH is recruited to the surface of iron loaded cells where it recruits apo-transferrin in close proximity to ferroportin so as to rapidly chelate the iron extruded.[28]

The expression of hepcidin, which only occurs in certain cell types such as hepatocytes, is tightly controlled at the transcriptional level and it represents the link between cellular and systemic iron homeostasis due to hepcidin's role as "gatekeeper" of iron release from enterocytes into the rest of the body.[18] Erythroblasts produce erythroferrone, a hormone which inhibits hepcidin and so increases the availability of iron needed for hemoglobin synthesis.[29]

Translational control of cellular iron

Although some control exists at the transcriptional level, the regulation of cellular iron levels is ultimately controlled at the translational level by iron-responsive element-binding proteins IRP1 and especially IRP2.[30] When iron levels are low, these proteins are able to bind to iron-responsive elements (IREs). IREs are stem loop structures in the untranslated regions (UTRs) of mRNA.[18]

Both ferritin and ferroportin contain an IRE in their 5' UTRs, so that under iron deficiency their translation is repressed by IRP2, preventing the unnecessary synthesis of storage protein and the detrimental export of iron. In contrast, TFR1 and some DMT1 variants contain 3' UTR IREs, which bind IRP2 under iron deficiency, stabilizing the mRNA, which guarantees the synthesis of iron importers.[18]

Pathology

Iron deficiency

Pregnant Woman With Dumbells
Iron is an important topic in prenatal care because women can sometimes become iron-deficient from the increased iron demands of pregnancy.

Functional or actual iron deficiency can result from a variety of causes. These causes can be grouped into several categories:

  • Increased demand for iron, which the diet cannot accommodate.
  • Increased loss of iron (usually through loss of blood).
  • Nutritional deficiency. This can result due to a lack of dietary iron or consumption of foods that inhibit iron absorption. Absorption inhibition has been observed caused by phytates in bran[31], calcium from supplements or dairy products[32], and tannins from tea[33], although in all three of these studies the effect was small and the authors of the studies cited regarding bran and tea note that the effect will probably only have a noticeable impact when most iron is obtained from vegetable sources.
  • Acid-reducing medications: Acid-reducing medications reduce the absorption of dietary iron. These medications are commonly used for gastritis, reflux disease, and ulcers. Proton pump inhibitors (PPIs), H2 antihistamines, and antacids will reduce iron metabolism [34].
  • Damage to the intestinal lining. Examples of causes of this kind of damage include surgery involving the duodenum, or diseases like Crohn's or celiac sprue which severely reduce the surface area available for absorption.
  • Inflammation leading to hepcidin-induced restriction on iron release from enterocytes (see above).

Iron overload

The body is able to substantially reduce the amount of iron it absorbs across the mucosa. It does not seem to be able to entirely shut down the iron transport process. Also, in situations where excess iron damages the intestinal lining itself (for instance, when children eat a large quantity of iron tablets produced for adult consumption), even more iron can enter the bloodstream and cause a potentially deadly syndrome of iron overload. Large amounts of free iron in the circulation will cause damage to critical cells in the liver, the heart and other metabolically active organs.

Iron toxicity results when the amount of circulating iron exceeds the amount of transferrin available to bind it, but the body is able to vigorously regulate its iron uptake. Thus, iron toxicity from ingestion is usually the result of extraordinary circumstances like iron tablet over-consumption[1][35] rather than variations in diet. The type of acute toxicity from iron ingestion causes severe mucosal damage in the gastrointestinal tract, among other problems.

Excess iron has been linked to some cancers. Of note, a recent study showed that breast cancer patients with low ferroportin expression (leading to higher concentrations of intracellular iron) survive for a shorter period of time on average. Conversely, high ferroportin expression in breast cancer predicts 90% 10-year survival.[36]

Chronic iron toxicity is usually the result of more chronic iron overload syndromes associated with genetic diseases, repeated transfusions or other causes. In such cases the iron stores of an adult may reach 50 grams (10 times normal total body iron) or more. Classic examples of genetic iron overload includes hereditary hemochromatosis (HH) and the more severe disease juvenile hemochromatosis (JH) caused by mutations in either the gene RGMc gene, a member of a three gene repulsive guidance molecule family,[37] (also called hemojuvelin (HJV), and HFE2), Hemojuvelin, or the HAMP gene that encodes (an iron regulatory peptide). The exact mechanisms of most of the various forms of adult hemochromatosis, which make up most of the genetic iron overload disorders, remain unsolved. So while researchers have been able to identify genetic mutations causing several adult variants of hemochromatosis, they now must turn their attention to the normal function of these mutated genes.

References

  1. ^ a b c Conrad ME, Umbreit JN (Apr 2000). "Disorders of iron metabolism". The New England Journal of Medicine. 342 (17): 1293–4. doi:10.1056/NEJM200004273421716. PMID 10787338.
  2. ^ a b Kakhlon O, Cabantchik ZI (2002). "The labile iron pool: characterization, measurement, and participation in cellular processes". Free Radical Biology and Medicine. 33 (8): 1037–1046. doi:10.1016/s0891-5849(02)01006-7.
  3. ^ a b Andrews NC (Dec 1999). "Disorders of iron metabolism". The New England Journal of Medicine. 341 (26): 1986–95. doi:10.1056/NEJM199912233412607. PMID 10607817.
  4. ^ Yan Y, Waite-Cusic JG, Kuppusamy P, Yousef AE (Jan 2013). "Intracellular free iron and its potential role in ultrahigh-pressure-induced inactivation of Escherichia coli". Applied and Environmental Microbiology. 79 (2): 722–724. doi:10.1128/aem.02202-12. PMC 3553779. PMID 23124235.
  5. ^ Yamamoto Y, Fukui K, Koujin N, Ohya H, Kimura K, Kamio Y (2004). "Regulation of the intracellular free iron pool by Dpr provides oxygen tolerance to Streptococcus mutans". Journal of Bacteriology. 186 (18): 5997–6002. doi:10.1128/jb.186.18.5997-6002.2004. PMC 515136. PMID 15342568.
  6. ^ Ganz T (Aug 2003). "Hepcidin, a key regulator of iron metabolism and mediator of anemia of inflammation". Blood. 102 (3): 783–8. doi:10.1182/blood-2003-03-0672. PMID 12663437.
  7. ^ Gropper, Sareen S.; Smith, Jack L. (2013). Advanced Nutrition and Human Metabolism (6th ed.). Belmont, CA: Wadsworth. p. 481. ISBN 978-1133104056.
  8. ^ Camaschella C, Schrier SL (2011-11-07). "Regulation of iron balance". UpToDate. Retrieved 2012-03-11.
  9. ^ McKie AT, Barrow D, Latunde-Dada GO, Rolfs A, Sager G, Mudaly E, Mudaly M, Richardson C, Barlow D, Bomford A, Peters TJ, Raja KB, Shirali S, Hediger MA, Farzaneh F, Simpson RJ (Mar 2001). "An iron-regulated ferric reductase associated with the absorption of dietary iron". Science. 291 (5509): 1755–9. doi:10.1126/science.1057206. PMID 11230685.
  10. ^ Rouault, Tracey A. (2005-09-09). "The Intestinal Heme Transporter Revealed". Cell. 122 (5): 649–651. doi:10.1016/j.cell.2005.08.027. ISSN 0092-8674. PMID 16143096.
  11. ^ Fleming RE, Bacon BR (Apr 2005). "Orchestration of iron homeostasis". The New England Journal of Medicine. 352 (17): 1741–4. doi:10.1056/NEJMp048363. PMID 15858181.
  12. ^ "Iron". Ohio State University Extension Fact Sheet. Ohio State University. Archived from the original on June 16, 2012. Retrieved June 25, 2012.
  13. ^ Schrier SL, Bacon BR (2011-11-07). "Iron overload syndromes other than hereditary hemochromatosis". UpToDate. Retrieved 2012-03-11.CS1 maint: Uses authors parameter (link)
  14. ^ Kawabata H, Germain RS, Vuong PT, Nakamaki T, Said JW, Koeffler HP (June 2000). "Transferrin receptor 2-alpha supports cell growth both in iron-chelated cultured cells and in vivo". The Journal of Biological Chemistry. 275 (22): 16618–25. doi:10.1074/jbc.M908846199. PMID 10748106.
  15. ^ West AP, Bennett MJ, Sellers VM, Andrews NC, Enns CA, Bjorkman PJ (December 2000). "Comparison of the interactions of transferrin receptor and transferrin receptor 2 with transferrin and the hereditary hemochromatosis protein HFE". The Journal of Biological Chemistry. 275 (49): 38135–8. doi:10.1074/jbc.C000664200. PMID 11027676.
  16. ^ Kumar S, Sheokand N, Mhadeshwar MA, Raje CI, Raje M (Jan 2012). "Characterization of glyceraldehyde-3-phosphate dehydrogenase as a novel transferrin receptor". The International Journal of Biochemistry & Cell Biology. 44 (1): 189–99. doi:10.1016/j.biocel.2011.10.016. PMID 22062951.
  17. ^ Sheokand N, Kumar S, Malhotra H, Tillu V, Raje CI, Raje M (Jun 2013). "Secreted glyceraldehye-3-phosphate dehydrogenase is a multifunctional autocrine transferrin receptor for cellular iron acquisition". Biochimica et Biophysica Acta. 1830 (6): 3816–27. doi:10.1016/j.bbagen.2013.03.019. PMID 23541988.
  18. ^ a b c d e f g Hentze MW, Muckenthaler MU, Galy B, Camaschella C (Jul 2010). "Two to tango: regulation of Mammalian iron metabolism". Cell. 142 (1): 24–38. doi:10.1016/j.cell.2010.06.028. PMID 20603012.
  19. ^ a b Lane, D.J.R.; Merlot, A.M.; Huang, M.L.-H.; Bae, D.-H.; Jansson, P.J.; Sahni, S.; Kalinowski, D.S.; Richardson, D.R. (May 2015). "Cellular iron uptake, trafficking and metabolism: Key molecules and mechanisms and their roles in disease". Biochimica et Biophysica Acta. 1853 (5): 1130–1144. doi:10.1016/j.bbamcr.2015.01.021. PMID 25661197.
  20. ^ a b c Yehuda S, Mostofsky DI, eds. (2010). Iron Deficiency and Overload From Basic Biology to Clinical Medicine. New York, NY: Humana Press. p. 230.
  21. ^ Finney LA, O'Halloran TV (May 2003). "Transition metal speciation in the cell: insights from the chemistry of metal ion receptors". Science. 300 (5621): 931–6. doi:10.1126/science.1085049. PMID 12738850.
  22. ^ Philpott, Caroline C.; Ryu, Moon-Suhn (22 July 2014). "Special delivery: distributing iron in the cytosol of mammalian cells". Frontiers in Pharmacology. 5: 173. doi:10.3389/fphar.2014.00173. PMC 4106451. PMID 25101000.
  23. ^ Arosio P, Levi S (Aug 2002). "Ferritin, iron homeostasis, and oxidative damage". Free Radical Biology & Medicine. 33 (4): 457–63. doi:10.1016/s0891-5849(02)00842-0. PMID 12160928.
  24. ^ Rouault TA, Cooperman S (Sep 2006). "Brain iron metabolism". Seminars in Pediatric Neurology. 13 (3): 142–8. doi:10.1016/j.spen.2006.08.002. PMID 17101452.
  25. ^ Ganz T (Mar 2005). "Cellular iron: ferroportin is the only way out". Cell Metabolism. 1 (3): 155–7. doi:10.1016/j.cmet.2005.02.005. PMID 16054057.
  26. ^ Du F, Qian C, Qian ZM, Wu XM, Xie H, Yung WH, Ke Y (Jun 2011). "Hepcidin directly inhibits transferrin receptor 1 expression in astrocytes via a cyclic AMP-protein kinase A pathway". Glia. 59 (6): 936–45. doi:10.1002/glia.21166. PMID 21438013.
  27. ^ Boradia, Vishant Mahendra; Raje, Manoj; Raje, Chaaya Iyengar (1 December 2014). "Protein moonlighting in iron metabolism: glyceraldehyde-3-phosphate dehydrogenase (GAPDH)". Biochemical Society Transactions. 42 (6): 1796–1801. doi:10.1042/BST20140220. PMID 25399609.
  28. ^ Sheokand N, Malhotra H, Kumar S, Tillu VA, Chauhan AS, Raje CI, Raje M (Oct 2014). "Moonlighting cell-surface GAPDH recruits apotransferrin to effect iron egress from mammalian cells". Journal of Cell Science. 127 (Pt 19): 4279–91. doi:10.1242/jcs.154005. PMID 25074810.
  29. ^ Kautz L, Jung G, Valore EV, Rivella S, Nemeth E, Ganz T (Jul 2014). "Identification of erythroferrone as an erythroid regulator of iron metabolism". Nature Genetics. 46 (7): 678–84. doi:10.1038/ng.2996. PMC 4104984. PMID 24880340.
  30. ^ Muckenthaler MU, Galy B, Hentze MW (2008). "Systemic iron homeostasis and the iron-responsive element/iron-regulatory protein (IRE/IRP) regulatory network". Annual Review of Nutrition. 28: 197–213. doi:10.1146/annurev.nutr.28.061807.155521. PMID 18489257.
  31. ^ Hallberg L (1987). "Wheat fiber, phytates and iron absorption". Scand J Gastroenterol Suppl. 129: 73–9. doi:10.3109/00365528709095855. PMID 2820048.
  32. ^ Lynch SR (2000). "The effect of calcium on iron absorption". Nutr Res Rev. 13 (2): 141–58. doi:10.1079/095442200108729043. PMID 19087437.
  33. ^ Disler PB, Lynch SR, Charlton RW, Torrance JD, Bothwell TH, Walker RB, et al. (1975). "The effect of tea on iron absorption". Gut. 16 (3): 193–200. doi:10.1136/gut.16.3.193. PMC 1410962. PMID 1168162.
  34. ^ https://www.uptodate.com/contents/causes-and-diagnosis-of-iron-deficiency-and-iron-deficiency-anemia-in-adults?search=iron%20deficiency%20anemia&source=search_result&selectedTitle=1~150&usage_type=default&display_rank=1
  35. ^ Rudolph CD (2003). Rudolph's pediatrics. New York: McGraw-Hill, Medical Pub. Division. ISBN 978-0-07-112457-7.
  36. ^ Pinnix, Zandra K.; Miller, Lance D.; Wang, Wei; D’Agostino, Ralph; Kute, Tim; Willingham, Mark C.; Hatcher, Heather; Tesfay, Lia; Sui, Guangchao (2010-08-04). "Ferroportin and Iron Regulation in Breast Cancer Progression and Prognosis". Science Translational Medicine. 2 (43): 43ra56. doi:10.1126/scitranslmed.3001127. ISSN 1946-6234. PMC 3734848. PMID 20686179.
  37. ^ Severyn CJ, Shinde U, Rotwein P (Sep 2009). "Molecular biology, genetics and biochemistry of the repulsive guidance molecule family". The Biochemical Journal. 422 (3): 393–403. doi:10.1042/BJ20090978. PMC 4242795. PMID 19698085.

Further reading

  • Andrews S, Norton I, Salunkhe AS, Goodluck H, Aly WS, Mourad-Agha H, Cornelis P (2013). "Chapter 7, Control of Iron Metabolism in Bacteria". In Banci L. Metallomics and the Cell. Metal Ions in Life Sciences. 12. Springer. pp. 203–39. doi:10.1007/978-94-007-5561-1_7. ISBN 978-94-007-5560-4. PMID 23595674. electronic-book ISBN 978-94-007-5561-1 ISSN 1559-0836 electronic-ISSN 1868-0402
  • Andrews NC (May 2004). "Anemia of inflammation: the cytokine-hepcidin link". The Journal of Clinical Investigation. 113 (9): 1251–3. doi:10.1172/JCI21441. PMC 398435. PMID 15124013.
  • Camaschella C (Dec 2005). "Understanding iron homeostasis through genetic analysis of hemochromatosis and related disorders". Blood. 106 (12): 3710–7. doi:10.1182/blood-2005-05-1857. PMID 16030190.
  • Frazer DM, Anderson GJ (Oct 2005). "Iron imports. I. Intestinal iron absorption and its regulation". American Journal of Physiology. Gastrointestinal and Liver Physiology. 289 (4): G631–5. doi:10.1152/ajpgi.00220.2005. PMID 16160078.
  • Insel P, Ross D, McMahon K, Bernstein M (2011). "Iron". Nutrition (4th ed.). Sudbury, Massachusetts: Jones and Bartlett Publishers. pp. 510–514. ISBN 978-0-7637-7663-3. Retrieved June 25, 2012. See esp. pp. 513-514CS1 maint: Uses authors parameter (link)
  • Lammi-Keef CJ, Couch SC, Philipson EH, eds. (2008). "Dietary diversification and modification of iron". Handbook of Nutrition and Pregnancy. Nutrition & Health. Totowa, New Jersey: Humana Press. pp. 350–351. doi:10.1007/978-1-59745-112-3. ISBN 978-1-59745-112-3. Retrieved June 25, 2012.CS1 maint: Uses editors parameter (link)
  • Panel on Micronutrients; Subcommittees on Upper Reference Levels of Nutrients and of Interpretation and Uses of Dietary Reference Intakes; the Standing Committee on the Scientific Evaluation of Dietary Reference Intakes (2001). "Iron". Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc. Washington, D.C: Food and Nutrition Board, Institute of Medicine. pp. 290–393. ISBN 978-0-309-07279-3. Retrieved June 25, 2012.
  • Reilly C (2004). "Iron". The Nutritional Trace Metals. Oxford, UK & Ames, Iowa: Blackwell Publishing. pp. 35–81. ISBN 978-1-4051-1040-2. Retrieved June 25, 2012.

External links

Aceruloplasminemia

Aceruloplasminemia is a rare autosomal recessive disorder in which the liver can not synthesis the protein ceruloplasmin properly, which is needed to transport copper around the blood. Copper deficiency in the brain results in neurological problems that generally appear in adulthood and worsen over time.

.Aceruloplasminemia has been seen worldwide, but its overall prevalence is unknown. Studies in Japan have estimated that approximately 1 in 2 million adults in this population are affected.Aceruloplasminemia belongs to the group of genetic disorders called neurodegeneration with brain iron accumulation (NBIA).

Anemia of chronic disease

Anemia of chronic disease, is a form of anemia seen in chronic infection, chronic immune activation, and malignancy. These conditions all produce massive elevation of Interleukin-6, which stimulates hepcidin production and release from the liver, which in turn reduces the iron carrier protein ferroportin so that access of iron to the circulation is reduced. Other mechanisms may also play a role, such as reduced erythropoiesis.

Anemia of chronic inflammation is the preferred term since not all chronic diseases are associated with this form of anemia.

Hephaestin

Hephaestin, also known as HEPH, is a protein which in humans is encoded by the HEPH gene.

Iron-responsive element-binding protein

The iron-responsive element-binding proteins, also known as IRE-BP, IRBP, IRP and IFR

, bind to iron-responsive elements (IREs) in the regulation of human iron metabolism.

Iron deficiency

Iron deficiency, or sideropaenia, is the state in which a body lacks enough iron to supply its needs. Iron is present in all cells in the human body and has several vital functions, such as carrying oxygen to the tissues from the lungs as a key component of the hemoglobin protein, acting as a transport medium for electrons within the cells in the form of cytochromes, and facilitating oxygen enzyme reactions in various tissues. Too little iron can interfere with these vital functions and lead to morbidity and death.Total body iron averages approximately 3.8 g in men and 2.3 g in women. In blood plasma, iron is carried tightly bound to the protein transferrin. There are several mechanisms that control human iron metabolism and safeguard against iron deficiency. The main regulatory mechanism is situated in the gastrointestinal tract. When loss of iron is not sufficiently compensated by adequate intake of iron from the diet, a state of iron deficiency develops over time. When this state is uncorrected, it leads to iron-deficiency anemia. Before anemia occurs, the medical condition of iron deficiency without anemia is called latent iron deficiency (LID) or iron-deficient erythropoiesis (IDE).

Untreated iron deficiency can lead to iron-deficiency anemia, a common type of anemia. Anemia is a condition characterized by inadequate red blood cells (erythrocytes) or hemoglobin. When the body lacks sufficient amounts of iron, production of the protein hemoglobin is reduced. Hemoglobin binds to oxygen, enabling red blood cells to supply oxygenated blood throughout the body. Children, pre-menopausal women (women of child-bearing age) and people with poor diet are most susceptible to the disease. Most cases of iron-deficiency anemia are mild, but if not treated it can cause problems like fast or irregular heartbeat, complications during pregnancy, and delayed growth in infants and children.

Iron metabolism disorder

Iron metabolism disorders may involve a number of genes including HFE and TFR2.Hepcidin is the master regulator of iron metabolism and, therefore, most genetic forms of iron overload can be thought of as relative hepcidin deficiency in one way or another[1]. For instance, a severe form of iron overload, juvenile hemochromatosis, is a result of severe hepcidin deficiency. The majority of cases are caused by mutations in the hemojuvelin gene (HJV or RGMc/repulsive guidance molecule c). The exceptions, people who have mutations in the gene for ferroportin, prove the rule: these people have plenty of hepcidin, but their cells lack the proper response to it. So, in people with ferroportin proteins that transport iron out of cells without responding to hepcidin's signals to stop, they have a deficiency in the action of hepcidin, if not in hepcidin itself.

But the exact mechanisms of most of the various forms of adult hemochromatosis, which make up most of the genetic iron overload disorders, remain unsolved. So while researchers have been able to identify genetic mutations causing several adult variants of hemochromatosis, they now must turn their attention to the normal function of these mutated genes.

These genes represent multiple steps along the pathway of iron regulation, from the body's ability to sense iron, to the body's ability to regulate uptake and storage. Working out the functions of each gene in this pathway will be an important tool for finding new methods of treating genetic disorders, as well as for understanding the basic workings of the pathway.

So though many mysteries of iron metabolism remain, the discovery of hepcidin already allows a much better understanding of the nature of iron regulation, and makes researchers optimistic that many more breakthroughs in this field are soon to come.

Iron overload

Iron overload (also known as haemochromatosis or hemochromatosis) indicates accumulation of iron in the body from any cause. The most important causes are hereditary haemochromatosis (HHC), a genetic disorder, and transfusional iron overload, which can result from repeated blood transfusions.

Iron supplement

Iron supplements, also known as iron salts and iron pills, are a number of iron formulations used to treat and prevent iron deficiency including iron deficiency anemia. For prevention they are only recommended in those with poor absorption, heavy menstrual periods, pregnancy, hemodialysis, or a diet low in iron. Prevention may also be used in low birth weight babies. They are taken by mouth, injection into a vein, or injection into a muscle. While benefits may be seen in days up to two months may be required until iron levels return to normal.Common side effects include constipation, abdominal pain, dark stools, and diarrhea. Other side effects, which may occur with excessive use, include iron overload and iron toxicity. Ferrous salts used as supplements by mouth include ferrous fumarate, ferrous gluconate, ferrous succinate, and ferrous sulfate. Injectable forms include iron dextran and iron sucrose. They work by providing the iron needed for making red blood cells.Iron pills have been used medically since at least 1681, with an easy-to-use formulation being created in 1832. It is on the World Health Organization's List of Essential Medicines, the most effective and safe medicines needed in a health system. Ferrous salts are available as a generic medication and over the counter. The wholesale cost in the developing world is about US$0.05–0.63 per month. In the United States a typical month of treatment costs less than $25. Slow release formulations, while available, are not recommended. In 2016 ferrous sulfate was the 93rd most prescribed medication in the United States with more than 8 million prescriptions.

Nagasuma Chandra

Nagasuma Chandra is an Indian structural biologist, biochemist and a professor at the department of biochemistry of the Indian Institute of Science. She is known for her studies on Mycobacterium tuberculosis. The Department of Biotechnology of the Government of India awarded her the National Bioscience Award for Career Development, one of the highest Indian science awards, for her contributions to biosciences in 2008.

Pedro Pedrosa Mendes

Pedro Pedrosa Mendes is a Professor of Computational Systems Biology in the School of Computer Science at the University of Manchester. He is a member of the Manchester Centre for Integrative Systems Biology (MCISB), the Machine Learning and Optimization (MLO) group. He is also a Professor at the University of Connecticut Health Center.

Serum iron

Serum iron is a medical laboratory test that measures the amount of circulating iron that is bound to transferrin (90%) and serum ferritin (10%). Clinicians order this laboratory test when they are concerned about iron deficiency, which can cause anemia and other problems.

65% of the iron in the body is bound up in hemoglobin molecules in red blood cells. About 4% is bound up in myoglobin molecules. Around 30% of the iron in the body is stored as ferritin or hemosiderin in the spleen, the bone marrow and the liver. Small amounts of iron can be found in other molecules in cells throughout the body. None of this iron is directly accessible by testing the serum.

However, some iron is circulating in the serum. Transferrin is a molecule produced by the liver that binds one or two iron(III) ions, i.e. ferric iron, Fe3+; transferrin is essential if stored iron is to be moved and used.

Most of the time, about 30% of the available sites on the transferrin molecule are filled. The test for serum iron uses blood drawn from veins to measure the iron molecules that are bound to transferrin, and circulating in the blood.

The extent to which sites on transferrin molecules are filled by iron ions can be another helpful clinical indicator, known as percent transferrin saturation. Another lab test saturates the sample to measure the total amount of transferrin; this test is called total iron-binding capacity (TIBC). These three tests are generally done at the same time, and taken together are an important part of the diagnostic process for conditions such as anemia, iron deficiency anemia, anemia of chronic disease and Haemochromatosis.

Transferrin receptor 1

Transferrin receptor protein 1 (TfR1), also known as Cluster of Differentiation 71 (CD71), is a protein that in humans is encoded by the TFRC gene. TfR1 is required for iron import from transferrin into cells by endocytosis.

General
Energy
metabolism
Specific
paths
Transition metal
Electrolyte

This page is based on a Wikipedia article written by authors (here).
Text is available under the CC BY-SA 3.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.