Download - Iron metabolism final
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IRON
Dr.Riddhi H PatelDr.Khushbu Soni
3rd year Residents Biochemistry
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● Iron is very important in the human body because of its occurance in many hemoproteins such as hemoglobin, myoglobin and cytochromes.
● Other enzymes such as aconitase and ferredoxin have iron co-ordinated with sulfur, forms “Iron sulfur cluster”.
● Enzymes of the krebs cycle like Aconitase, Isocitrate dehydrogenase, Succinate dehydrogenase and citrate synthase modulated by iron.
● Iron modulates the expression of the critical citric acid cycle enzyme aconitase via a translational mechanism involving iron regulatory proteins.
● Iron supplementation results in increased formation of reducing equivalents (NADH) by the citric acid cycle, and thus in increased mitochondrial oxygen consumption and ATP formation via oxidative phosphorylation.
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Distribution of Iron
● Total body iron in healthy adult male: 3-4 gm
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Requirement
● For Adult : 20 mg/day (Only 1 mg is absorbed)
● For Children : 20-30 mg/day
● Pregnant women : 40 mg/day
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Sources of Iron
● Leafy vegetables
● Pulses
● Cereals
● Liver and Meat
● Jaggery
● Cooking in Iron utensil
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Absorption
● Iron is ingested in diet either as nonheme or heme iron.
● Heme Iron Absorption:
- Heme carrier protein present on microvillous surface of absorptive enterocyte.
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● Non heme iron absorption:
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Transferrin
● A glycoprotein playing important role in shuttle of iron between various tissues.
● It is beta-1 globulin.
● Each molecule binds with 2 Fe+3 molecule.
● Glycosylation of transferrin is impaired in :
- Congenital disorder of glycosylation
- Chronic alcoholism.
● TIBC
● Transferrin saturation
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Transferrin Cycle
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Recycling of Iron by macrophage
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Factors influencing Iron absorption
Physical State (bioavailability)
heme > Fe2+ > Fe3+
Inhibitors
phytates, tannins, soil clay, laundry starch, iron overload, antacids
Competitorslead, cobalt, strontium, manganese, zinc
Facilitatorsascorbate, citrate, amino acids, iron deficiency
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Storage of Iron
● Iron is stored as a ferritin
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Serum ferritin
● In serum minute quantities of ferritin present in concentrations proportional to total body stored iron.
● Serum ferritin is glycosylated.
● Contains mostly L- chain.
● Poor in iron.
● So mostly apoferritin.
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● Hemosiderin :
- Aggregated, partially deproteinized ferritin.
- Formed when ferritin is partially degraded in secondary lysosomes.
-Insoluble in aqueous solution.
- Found predominantly in cells of liver, spleen and bone marrow.
- iron is released slowly from aggregates of hemosiderin.
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Intracellular Iron Regulation
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Systemic iron regulation
● Hepcidin is the chief regulator.
● Hepcidin decreases iron absorption in the intestine (Mucosal Block)and also prevents the recycling of iron from macrophages.
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Hepcidin regulation
● Iron Sensing Complex :
-HFE Protein
-TfR1
-TfR2
-HJV● Bone Morphogenetic Proteins
● Erythropoietic Signals
● Inflammation : Interleukin-6
● Hypoxia
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Excretion of Iron
● Iron is one way element and very little of it is excreted.
● Any type of bleeding will cause loss of iron.
● Women up to menopause will loss iron at a rate of about 1 mg/day.
● Male : <0.5 mg/day.
● Almost no iron is excreted through urine.
● Considerable fecal loss.
● Some amount from skin.
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Clinical Significance
Major disorders of iron metabolism
– Iron deficiency -Iron overload● Abnormal iron distribution
● Abnormal production of iron related proteins
-Hereditary Hyperferritinemia-cataract syndrome
-Aceruloplasminemia
-Neuroferritinopathy
-Atransferrinemia
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Iron Deficiency
● One of the most prevalent nutritional deficiency disorder.
● 70% of indians and 85% of pregnant women suffer from it.
● Anemia: a reduction in the oxygen-carrying capacity of the blood caused by a diminished erythrocyte mass.
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Pathophysiology
Increase demands of iron
Increase iron loss
Decrease iron intake
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Stages of Development
● 3 Stages:
1) Negative Iron balance
2) Iron deficient erythropoiesis
3) Iron deficiency Anaemia
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1) Negative Iron balance
● Intestinal iron absorption is insufficient.
● Body's iron stores being mobilized to meet requirements.
● So progressive depletion of iron stores.
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2)Iron deficient erythropoiesis
● Hemoglobin synthesis is impaired.
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3) Iron deficiency Anaemia
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Clinical Presentation
● Iron-deficiency anemia can cause:
brittle nails
cracks in the sides of the mouth
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Extreme fatigue (tiredness)
chest pain
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● Pale skin
● Dizziness or lightheadedness
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● Fast heart rate
● Headache
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● An enlarged spleen
● Cold hands and feet
● frequent infections.
● Irritability
● shortness of breath
● swelling or soreness of the tongue
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Changes in Various laboratory tests
Parameters Normal Negative iron balance Iron deficient erythropoiesis
Anaemia
Serum Ferritin (ug/dl) 50-200 <20 <15 <15
TIBC (ug/dl) 300-360 >360 >380 >400
Serum Iron (ug/dl) 50-150 Normal <50 <30
Transferrin saturation (%)
30-50 Normal <20 <10
RBC Protoporphyrin (ug/dl)
30-50 Normal Increased Increased
Soluble transferrin receptor (ug/l)
4-9 Increased Increased Increased
RBC morphology Normal Normal Normal Microcytic hypochromic
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● Staining of Bone marrow iron with perls' prussian blue to allow visualization of ferric ion is probably most reliable but impractical.
● It may be misleading due to:
-Insufficient sample size
-Patient treated with parentral iron suppliments
-Stainable iron may be present in the phase of deficiency
-Patients with myeloproliferative disorders
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TREATMENT
IRON SUPPLEMENT
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Iron overload conditions
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Hemochromatosis
● Is a Disorder of iron overload :
-Hereditary hemochromatosis (HH)
-Acquired hemochromatosis
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Hereditary hemochromatosis
● HH: genetic defect in iron metabolism
-Excess iron absorbed from the gut
-Symptoms due to pathologic deposition of iron in body tissue = iron overload
● Classic Triad:
-Cirrhosis (hepatic damage)
-Diabetes (type II) (pancreatic damage)
-Bronzing of skin (hyperpigmentation)
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Non-Specific Symptoms and Signs
● Liver: hepatomegaly, elevated liver enzymes
● Cardiac: myocardial infarction, cardiomyopathy
● Endocrine: impotence/amenorrhea, diabetes
● Musculoskeletal: arthritis/arthralgia
● Fatigue: unexplained, severe and chronic
● Generally not evident until 40-60 years of age
● Some patients may present earlier
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HFE hemochromatosis
● HFE– associated Hemochromatosis accounts for > 90% of cases and is the most common adult onset form:
● Autosomal recessive inheritance
● C282Y mutation
● Carrier rate 1 in 7 - 10 Caucasians
● Incidence 1 in 200 - 400
● Penetrance is high
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Bb Bb
BB Bb Bb bb
Unaffected carrier
Unaffected
Autosomal Recessive Inheritance
Unaffectedcarrier
Susceptible genotype for Hemochromatosis
Unaffectedcarrier
Unaffected Carrier
Legend
B: Normal HFE gene
b: HFE gene with mutation
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● HFE gene on chromosome 6p● Involved in iron homeostasis
● HFE protein normally limits amount of iron uptake by gut and regulates amount of iron stored in the tissues
● Mutations in HFE:
C282Y allele
H63D allele
S65C allele
● HFE gene mutations produce altered HFE protein unable to properly regulate iron metabolism - results in an excess of iron storage in tissues
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HJV Hemochromatosis
● Rare disorder
● Early age of onset
● Severe multi organ iron overload
● Most common presentation :
-Testicular Atrophy
-Ammenorhea● Autosomal Recessive
● Mutation : Of HJV on chromosome 1q
● Most common deleterious mutation : G320V
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HAMP Hemochromatosis
● Mutation: HAMP gene of chromosome 19q13.
● Usually associated with HFE C282Y mutation.
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TFR2 Hemochromatosis
● Rare Autosomal Recessive disorder.
● Mutations : TFR2 Y250X and R455Q
● TFR2: encodes Transferrin receptor 2
- It mediates uptake of transferrin bound iron by the liver after the classical TfR1 is down reguated by iron overload .
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Ferroportin(SLC40A1) Hemochromatosis
● Present on the surface of the cell responsible for iron absorption and recycling of iron from macrophage.
● Mutation : SLC40A1 gene
● Autosomal Dominant
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African Iron overload and African american iron overload
● Type of iron overload due to ingestion of large quantities of iron contained in traditional beer.
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Iron overload due to Anaemia with ineffective erythropoiesis
● In this, there is increased GDF 15 expression by erythroblast.
● Lead to down regulation of hepcidin expression.
● Thus increase iron absorption.
● Anemias with increased GDF 15 expression:
-beta-thalassemia major
-Pyruvate kinase deficiency
-Congenital dyserythropoietic anemia
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Secondary Iron Overload
● Acquisition of iron from non dietary sources in amounts that exceeds the body's limited excretory capacity can cause iron overload.
● Causes : Chronic erythrocyte transfusion
-Excessive iron supplements (I.V or I.M)
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Analytical methods
● For measurement of Serum Iron:
1) Iron is released from transferrin by decreasing pH of serum.
2) Reduced from Fe+3 to Fe+2.
3) Complexed with a chromogen like ferrozine.
● Such iron chromogen complexes have an extremely high absorbance in the visible region that is proportional to iron concentration.
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● For measurement of Serum TIBC:
1) Addition of Sufficient Fe+3 to saturate empty iron binding site of transferrin.
2) Excess Fe+3 is removed by adsorption with MgCO3, silica column or ion exchange resin.
3) Assay for iron content is repeated.
● For measurement of Serum Transferrin Saturation :
Transferrin Saturation (%) = (100 X serum iron) / TIBC
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● For measurement of Serum UIBC:
1) Add known excess concentration of iron to the serum.
2) pH should be neutral.
3) Add iron binding chromogen.
4) Measure the absorbance
5) Measure blank with no added serum.
● UIBC = O.D of serum free iron blank – O.D of sample
● Advantage: Can be fully automated
less cumbersome
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Reference Interval
● Differs as much as 35% between commercial methods.
● A generic reference interval is not valid.
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Factors affecting Serum Iron
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● Hemolysis has very little effect on serum iron result because Hb iron is not released from heme by acid treatment.
● Iron is ubiquitous in the environment so care is necessary to ensure that glassware, water and reagents do not become contaminated with extraneous iron.
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serum transferrin receptor
● Under normal conditions TfR1 is highly expressed on the surface of erythroid cells.
● Certain proportion is released into the circulation by proteolytic cleavage. Referred to as “Soluble TfR”.
● Number of transferrin receptor increases in iron deficiency and decreases in iron excess.
● Developing erythroid cells in bone marrow are reach in transferrin receptor.
● Variation in transferrin receptor quantity are reflected in soluble serum TfR.
● Measured by standard immunoassay technique.
● Measurement of STfR is usefull to distinguish between anemia due to iron deficiency and anemia due to chronic disease.
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Red Cell protoporphyrin
● Its level is increased in Iron deficiency.
● The presence of protoporphyrin in erythrocyte reflects impaired ferrochelatase catalyzed incorporation of iron into protoporphyrin IX ring.
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