L9: Iron and Anemia

Hemoglobin structure: What does each protein subunit contain?

1 heme

absorption of NON-HEME iron: 1) what is non-heme iron present as? 2) what releases iron from ligands in the food? (2) 3) Fe2+ may rapidly oxidize in the stomach to ____ 4) _____ aids in the intestinal absorption of iron by reducing ____ to ____ on the brush-border

1) Fe2+ and Fe3+ 2) - low pH in the stomach and - digestive enzymes 3) Fe3+ 4) ascorbate aids in the intestinal absorption of iron by reducing Fe3+ (ferric iron) to Fe2+ (ferrous iron) on the brush-border

When Fe2+ is transported out of enterocyte into the circulation it is oxidized to Fe3+ by ceruloplasmin &/or hephaestin. -Why? (3)

1) Fe3+ is bound to transferrin 2) transferrin transports iron to cells 3) transferrin Fe3+ complex binds to transferrin receptors on cell surfaces

what are the symptoms of severe iron deficiency? (4)

1) fainting 2) chest pain 3) angina 4) heart attack

What does the assessment of iron status include? (3)

1) ferritin levels 2) iron-transferrin saturation 3) hematocrit

What are the two transferrin receptors? What are the characteristics of each? (Where are they typically and

1. Transferrin receptor-1 (TfR-1) - all dividing cells - particularly enriched on erythrocyte precursor cells (RBC) 2. TfR-2 - primarily in the liver - low affinity - binds the transferrin Fe3+ complex at a much lower affinity than TfR-1

Hemoglobin structure: 1. What makes up the structure of heme? A ____ ring coordinated with ____ 2. Within this structure, what is iron coordinated with? 3. When the protein is oxygenated, what is in the 6th (coordinated) position?

1. a porphyrin ring that is coordinated with Fe2+ 2. iron is coordinated to 4 N atoms of the porphyrin ring and 1 N of histidine residue 3. The 6th position is occupied by O2 (each heme carries 1 O2 so each hemoglobin contains 4 O2)

What are the dietary sources of the two types of iron? How much is provided/what influences absorption?

1. heme iron: - meat, poultry, fish - 10-15% intake, but provide ~30% total absorbed iron due to high bioavailability 2. non-heme iron: - plants, dairy, salts that are enriched/fortified - absorption affected by food matrix

What are the two forms of iron in the diet and what are their characteristics (2 each)?

1. non heme iron: - free or in complexes - affected by food components, e.g. spinach 2. heme iron: - iron incorporated into the porphyrin complex - not affected by other food components

absorption of HEME iron: 1) enters cell through unknown transporter 2) which type of cell does it enter? 3) once in the cell, what does it split into? 4) which enzyme is used? 5) ___ exits into portal ____ via which transport? ____-____ _____ transport

2) enterocytes 3) Fe2+ and bilirubin 4) heme oxygenase 5) Fe2+ exits into portal circulation via ferroportin-mediated basolateral transport

How much iron is recycled daily? with what % efficiency?

35 mg of iron is recycled daily with at least 90% efficiency.

Hemoglobin structure: What is the globin component made up of?

4 protein subunits: 2 alpha 2 beta

How much iron is recycled and from where?

90% from erythrocytes

Certain tissues/organelles may experience a functional lack of iron ______ a significant change in hematological parameters occur

BEFORE

Hepcidin --> iron removal (draw out)

By binding to ferroportin on the basolateral membrane of enterocytes, hepcidin induces ferroportin internalization and degradation, thus trapping the absorbed iron in the enterocyte. Within a day or two, the short-lived enterocytes are shed into the intestine, removing the iron from the body.

Our cells _____ excrete iron.

CANNOT

Describe hemoglobin activity 2: 2. deoxyhemoglobin binds and transports _____ to the ______ in the form of ________________________

Deoxy-hb binds and transports CO2 to the lungs in the form of carbaminohemoglobin

What happens to Fe2+ outside the cell? What 2 things make this happen?

Fe2+ outside the cell is immediately oxidized to Fe3+ by either plasma ceruloplasmin or by hephaestin

How does Fe2+ change to Fe3+ and what are the names of these compounds?

Fe2+: Ferrous Fe3+ Ferric

movement of iron from lumen of duodenum into enterocyte: lumenal iron Fe3+ is reduced to Fe2+ by ____ with ____ as a cofactor

Fe3+ is reduced to Fe2+ by DcytB with ascorbate as a cofactor

Draw out iron absorption in the duodenum and explain:

Ferroportin and hephaestin (Hp) work together in the enterocyte. In other cell types, ferroportin may work with ceruloplasmin (Cp), a soluble ferroxidase, to load iron onto transferrin

what are the clinical parameters of iron deficiency? - functional iron (3) - tissue iron supply (1) - iron stores (1)

Functional iron: 1. hemoglobin concentration 2. red blood cells: MCV (average RBC size), MCH (amount of Hb per RBC) 3. hematocrit Tissue iron supply: 1. saturation of TIBC/transferrin Iron stores: 1. serum ferritin

Hemoglobin structure: Where is heme made? [What happens here?]

Heme is made in the mitochondria Here protoporphryin IX is synthesized and Fe2+ is inserted

There is relatively little iron received from breast milk. Iron content of milk ___ ___ depend on maternal iron ____ or ______

Iron content of milk does not depend on maternal iron deficiency or supplementation.

Iron is an ____ ____. What are the four categories of metalloproteins and their functions?

Iron is an essential mineral 1. non-enzymatic globin-heme ferroproteins 2. heme enzymes involved in electron transfer 3. iron-sulfate clusters in electron transfer for energy production 4. enzymes using iron as a cofactor

control of transferrin receptor mRNA by iron status (draw out)

LOW IRON = IRP1 and 2 bind 3' IRE = stabilize TfR mRNA = increase TfR translation

control of ferritin mRNA by iron status (draw out)

LOW IRON = IRP1 and IRP2 bind IRE = block ferritin

What does ferroportin do? What are two other names for ferroportin? What is it? What is it regulated by? Where is it abundant? (6)

- Ferrportin transfers Fe2+ from the enterocyte into the circulation - Ferroportin is also known as FPN or MTP1 - Ferrportin is a protein regulated by iron - It is abundant in the 1) liver 2) spleen 3) kidney 4) heart 5) placenta 6) duodenum

Cellular iron control: When iron is low: - IRP binding to 5' UTRs represses translation of : (4) - General message about when IRPs bind to 5' UTRs - IRP binding to 3' UTRs sustains production of: (3) - General message about what happens when IRPs contain IREs (multiple) in the 3' noncoding region (from other slide: what happens when IRP binds to IRE)

- IRP binding to 5' UTRs represses translation of [ferratin synthesis]: (when IRP binds to IRE, it prevents the translation of the message) 1) two appoferritin chains --> stops iron sequestration 2) ferroportin --> stops iron export 3) HIF 2 alpha --> reduces iron use 4) alpha-levulinic acid synthase --> reduces iron use - IRP binding to 3' UTRs sustains production of: 1) transferrin receptor 1 2) DMT1 3) organizing molecule for endocytosis When IREs stabilize the message and translation is increased. All these keep the production of components for iron uptake

What is Dcytb?

- ascorbate dependent reductase that is highly expressed in the duodenal enterocyte - it reduces dietary ferric (Fe3+) iron to ferrous iron (Fe2+)

What is hephaestin? Where is it highly expressed?

- copper dependent oxidase - highly expressed in the small intestine

what is DMT1?

- divalent metal transporter - transporter of ferrous iron (Fe2+) into the enterocyte

- HFE: regulates ____ ____ expression. - HFE binds to ____, when displaced by transferrin, binds to ____ - HFE-_____ complex activates the membrane complex of ____ and ____ which co-stimulate ____ and ____ factor of expression of ____

- hepatic hepcidin - binds to TfR1, when displaced binds to TfR2 - HFE-TfR2 complex activates the membrane complex of BMP6 and haemojuvelin which co-stimulatee phosphorylation and transcription factor for expression of hepcidin

fate of iron inside cells: - it is a ____ for enzymes/proteins - OR is it bound to _____ - ferritin is a large molecular weight protein that functions as a storage for protein where? (2) - How is ferritin controlled? - how much of iron storage capacity is occupied?

- iron is a co-factor for enzymes/proteins - OR is bound to ferritin - Ferritin is a large molecular weight protein that functions as a storage for iron both in cytosol and in mitochondria - ferritin is transcriptionally controlled by iron levels (notes: transcription regulation controls the total amount of ferritin mRNA produced. Translational regulation is the second major level of control for ferritin expression) - 20-50%

myoglobin: (stared slide) What kind of protein? ____meric Where is it found? What is in the center? How many O2 can it bind? Where in the cell is it found? It increases the rate of _______ of O2 from capillary red cells to _____ and _____

- monomeric protein - found in the muscle - heme center - can only bind one oxygen for storage - found in the cytoplasm of the cell - It increases the rate of diffusion of O2 from capillary red cells to cytoplasm and mitochondria

Non red slide: - hepcidin reduces the ____ activity - iron is lost in the gut lumen when ____ are shed - plasma levels of hepcidin are regulated by ____ and ____/____ - dysregulation of hepcidin or its receptor ferroportin results in a spectrum of ____ ____

- reduces the DMT1 activity - iron is lost in the gut lumen when enterocytes are shed - plasma levels of hepcidin are regulated by iron and anemia/hypoxia - dysregulation of hepcidin or its receptor ferroportin results in a spectrum of iron disorders

What are the two forms of IRP and what does it stand for? What does these act as and how? What happens to each IRP under high iron conditions? Under low iron conditions?

- the two forms of IRP are IRP1 and IRP2 - IRP is iron response protein - they act as iron response proteins by binding to iron-recognition-elements (IREs) in UTRs of mRNA. (5' noncoding region - before the coding region) - High iron conditions: 1) IRP-1 binds cytosolic Fe, forms Fe-S clusters and acquires aconitase activity. Thus, the IRP (IRE binding) activity is lost. 2) IRP-2 degraded by the proteasome. - Low iron conditions 1) IRP-1 loses Fe-S cluster/aconitase activity and gains IRP activity (binds IRE) 2) IRP-2 stabilized (IRP-1 also can be stabilized)

Iron is ___ controlled. Iron homeostasis is controlled at both a ____ and ____ level

- tightly - cellular and systemic

a clinical parameter of iron deficiency is abnormally ____ circulating Fe and ____ levels

abnormally low circulating Fe and hemoglobin levels

What happens to the Fe3+-Transferrin complex after it binds to the the receptor? Which receptor is this? What are two additional steps that happen after? (not in red)

afte binding to the TfR-1 receptor, the Fe3+-transferrin complex is internalized by receptor-mediated endocytosis through clathrin-coated pits - internalized complex is acidified, and a conformational change causes release of the iron - Fe3+ is reduced to Fe2+ by a ferrireductase named STEAP3

iron overload: what is hemochromatoses?

all forms of iron storage disease

Iron is absorbed in the ____ and ____ part of the intestine

duodenum and jejunum

What is 1 enhancer and 1 inhibitor of iron absorption?

enhancer: vitamin C: reduces Fe3+ to Fe2+ inhibitor: phytic acid: (legumes/corn), polyphenols, tannins, Ca2+, soy protein

What treats anemia from CKD? Is CKD iron sensitive?

erythropoietin treats CKD anemia. CKD anemia is NOT sensitive to iron

How does hepcidin block the export of iron from enterocytes into the circulation? (What does it bind? What does it target for?) An increase in iron increases hepatic ____ _____ expression

hepcidin blocks the export of iron from enterocytes into the circulation by binding to ferroportin and targeting it for degradation - an increase in iron increases hepatic hepcidin mRNA expression

Fetal Hb has a _______ affinity for oxygen than adult Hb which helps to acquire oxygen from ______ Hb

higher affinity maternal Hb

Hereditary Hemochromatosis (HH)

inherited genetic defect that causes people to absorb too much iron

iron balance is maintained by ___ ___

iron acquisition

Homeostatic settings of mucosa to absorb iron and transfer it to the body adapt to the body's needs for _____and to ______

iron and to inflammation

Why is iron highly toxic and what minimizes this risk?

iron is highly toxic due to radical generation tight regulation minimizes the risk of oxidative damage

what do erythrocytes look like in iron-deficiency anemia?

microcytic-small pale cells

risk of iron overload from dietary sources is ____

negligible

iron excretion? forms? (4)

no known regulated form of iron excretion. - enterocyte excretion - mentruation - child birth - leeches

What does transferrin bind?

one or two Fe3+ atoms

What is cooperative binding?

oxygenation of a single heme leads to protein conformational changes which then makes it easier for the other three heme groups to oxygenate as well. Cooperative binding: when conformational changes facilitate the oxygenation of remaining heme groups

Describe hemoglobin activity 2: 1. peripheral tissues have higher ____ and lower _____. Because of this, ____ is displaced from heme and is made into _________

peripheral tissues have higher CO2 and lower O2. Because of this, O2 is displaced from heme and is made into deoxyhemoglobin

How many CO2 does Hb carry to the lungs? What happens when Hb changes back to the oxyhemoglobin form?

- 4 CO2 - CO2 are released when deoxy changes back to oxy

What is hepcidin? - family? - product of? Produced by? Circulates to? - regulated by? (5)

a peptide hormone - defensine family - product of HAMP gene Produced by hepatocytes (liver) & circulates to the small intestine - regulated by 1) iron 2) HFE 3) TfR2 4) haemojuvelin 5) infection

What is ceruloplasmin?

a soluble ferroxidase

hepcidin provides a way to ____ iron from the body

remove iron