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Nutrition and Drug Monitoring > Iron Part 2: Anaemia > Flashcards

Iron Part 2: Anaemia Flashcards

1
Q

What is the definition of Anaemia?

A
  • Hb: <120 g/L in females (<100 g/L during pregnancy due to dilution of blood volume)
  • Hb: <140 g/L in males
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2
Q

What are Risk Factors for Anaemia?

A
  • Extremes of age
  • Female gender
  • Pregnancy
  • Lactation
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3
Q

What are the mechanisms of Anaemia?

A
  • Decreased RBC production
  • Increased RBC destruction
  • Loss of RBC due to bleeding
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4
Q

What are symptoms of Anaemia?

A
  • Pallor
  • Fatigue
  • Weakness
  • Decreased exercise tolerance
  • Shortness of breath with exercise
  • Jaundice (haemolytic anaemias)
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5
Q

What are Aetiologies of Anaemia?

A
  • Blood loss
  • Nutrient deficiency or depletion (Iron, vitamin B12, folate)
  • Acquired bone marrow disease
  • Toxin exposure (Drugs, radiation, lead, alcohol)
  • Chronic systemic disease
  • Immune reactions
  • Infections
  • Genetic disorders
  • Microvascular disease
  • Pregnancy
  • Thermal burns
  • Hospital-acquired anaemia (excessive phlebotomy
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6
Q

What are laboratory assessments of Anaemia?

A

Iron status: ferritin, TIBC

Vitamin B12 & Folate

FBC & Film

  • Total haemogloblin
  • Haematocrit
  • Differential cell count
  • Red cell indices: (Mean cell volume (MCV), Mean cell haemoglobin (MCH), RBC distribution width (RBCDW))
  • Blood film
    • Target cells (liver disease, thalassaemia)
    • Pencil cells (Fe deficiency, thalassaemia)
    • Heinz bodies (oxidatively damaged Hb)
    • Schistoctes (fragmented RBCs)
    • Spherocytes (active haemolysis)
  • Reticulocyte count

Bone marrow aspiration

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7
Q

What are morphological classifications fo Anaemia?

A

Microcytic = MCV <80 fL

Normocytic = MCV 80-100 fL

  • Hyperproliferative = reticulocyte count >2% (increased): Compensatory response to e.g. acute blood loss or haemolysis
  • Hypoproliferative = reticulocyte count <2% (unchanged): Primary disorders of decreased RBC production

Macrocytic = MCV >100 fL

  • Megaloblastic = deficient DNA production or maturation: Large immature RBCs (megaloblasts)
  • Non-megaloblastic = normal DNA synthesis: Megaloblasts and hypersegmented neutrophils are absent
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8
Q

What do iron studies reveal in microcytic anaemia?

A
  • History guides investigation.
  • Low iron and TIBC suggests iron deficiency. Normal ferritin and history of inflammation suggests co-existent anaemia of chronic disease
  • Generalised malnutrition (combined iron/vitamin B12/folate deficiency) may have normocytic anaemia
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9
Q

What is the presentation of Iron Deficiency Anaemia?

A
  • Tiredness
  • Palpitations
  • Angular stomatitis
  • Nail/hair/retinal changes
  • Pica
  • Restless legs
  • Pale complexion
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10
Q

What are aetiologies of Iron Deficiency Anaemia?

A
  • Excessive menstrual losses (transvaginal ultrasound)
  • Upper GI bleeding: coffee-ground vomiting, haematemesis, melaena
  • Lower GI bleeding: fresh red rectal bleeding
  • Haemoptysis may indicate Goodpasture’s syndrome or idiopathic pulmonary haemosiderosis
  • Trauma, excessive phlebotomy, blood donation, self-harm
  • Runner’s anaemia (repetitive mechanical trauma)
  • Malabsorption (silent coeliac disease)
  • Increased iron requirement (pregnancy, growth)
  • Paroxysmal nocturnal haemoglobinuria (flow cytometry if haematuria)
  • Poor diet/absorption/bioavailability: antacids/bran/tannin/phytates/starch
  • Malabsorption, bowel resection
  • Rare genetic defects: DMT1, Glutarodoxin 5
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11
Q

What causes Upper GI bleeding and the investigations for it?

A
  • NSAIDs and corticosteroids are associated with peptic ulcer disease (Helicobacter pylori testing)
  • Alcohol use and cirrhosis are associated with coagulation disorders and oesophageal varices
  • Investigate with Faecal Occult Blood, Upper GI Endoscopy, Colonoscopy
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12
Q

What causes Lower GI bleeding?

A
  • Haemorrhoids
  • Bowel disease,
  • Hookworm/Whipworm/Schistosoma (travel history – stool microscopy)
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13
Q

How is Iron Deficiency Anaemia managed?

A
  • History guides investigation and treatment
  • Establish and correct cause
  • Oral iron supplements
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14
Q

What are causes of Abnormal Iron Distribution?

A
  • Anaemia of Chronic Disease
  • Sideroblastic Anaemia
  • Porphyrias
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15
Q

What causes Anaemia of Chronic Disease?

A

Induction of hepcidin expression by inflammation

  • Macrophages sequester iron that should be recycled
  • Intestinal iron absorption interrupted so decreased availability of iron for erythropoiesis
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16
Q

What causes Sideroblastic Anaemia?

A

Group of blood disorders characterized by impaired erythropoiesis

  • Impaired haemoglobin synthesis despite normal iron
  • Iron accumulates in erythrocytes. Ringed appearance to nucleus (ringed sideroblast)
17
Q

How does Sideroblastic Anaemia present?

A
  • Fatigue
  • Breathing difficulty
  • Weakness
  • Hepato/splenomegaly
18
Q

What causes Porphyrias?

A

Abnormal haem biosynthesis

  • Excessive accumulation of porphyrins and their precursors

Decrease in hepcidin leads to increased iron absorption

  • High iron and transferrin saturation
19
Q

What is the Purpose of Iron Metabolism?

A

Meet demand for iron for growth and repair whilst avoiding iron excess. Involves:

  • Dietary intake
  • Storage and retrieval
  • Recycling
20
Q

How does iron metabolism occur?

A

Regulation of iron entry into plasma circulation

  • Enterocytes – newly absorbed dietary iron
  • Macrophages – recycled iron
  • Hepatocytes – stored iron

Iron homeostasis is maintained through regulation of intestinal absorption controlled by enterocytes in brush border of the duodenum; excretion is not regulated by renal/hepatic excretion

21
Q

What is the purpose of transferrin, ferritin and hepcidin?

A
  • Transferrin = Iron transport protein
  • Ferritin = Soluble form of hepatic iron storage protein
  • Hepcidin = Circulating hepcidin signals high iron status
22
Q

What are features of Hepcidin?

A
  • HAMP gene; 25 amino acid protein produced by liver
  • Rapid renal clearance; regulated at level of production
  • Primary responsibility for modulating availability of circulating iron
23
Q

How does Hepcidin coordinate iron balance?

A

Binds to cell surface Ferroportin

  • Hepcidin triggers lysosomal internalisation and degradation of ferroportin, blocking iron export into circulation
  • Ferroportin is a a cell surface iron efflux channel expressed by all iron-exporting cells such as enterocytes, macrophages and hepatocytes
  • It is facilitated by multicopper ferroxidases which oxidise Fe2+ to Fe3+ for uptake by transferrin.
  • Examples of multicopper ferroxidases are Caeruloplasmin and Hephaestin (membrane-bound homologue)
24
Q

What are the functions of Hepcidin-Ferroportin interaction?

A
  • The release of iron from duodenal enterocytes
  • Recycling macrophages
  • Hepatocyte stores
25
Q

Which proteins in the small intestine are used for regulation of Iron?

A

Ferroreductase

  • Reduces dietary Fe3+ to Fe2+ for absorption. Acidic pH effluent

Divalent metal transporter 1 (DMT1)

  • Proton-coupled transport of Fe2+ across apical membrane
  • Increased in iron deficiency due to increased responsivity to intracellular labile iron pool. Due to increased gene expression and altered mRNA processing
  • Can also be used to transport Mn2+, Zn2+, Co2+, Cd2+, Pb2+
  • Haem iron absorbed separately by efficient receptor-mediated endocytosis

Ferroportin

  • Transports iron across basolateral membrane into circulation
26
Q

How is Ferroportin regulated?

A

Ferritin-bound iron is lost via enterocyte senescence. Ferroportin is responsible for basolateral iron transport:

  • Ferroportin activity is regulated via hepcidin
  • Decreased activity in presence of high iron
  • Ferroportin transcription is regulated via free iron pool
  • Increased protein synthesis in presence of high iron
27
Q

Which proteins are used in the bone marrow for iron regulation?

A
  • Transferrin Receptor: Accepts delivery of transferrin-bound iron via transferrin cycle
  • DMT1: Transports iron out of endosomes
28
Q

What are features of Transferrin Receptor?

A
  • 190 kDA: 2x 95 kDa subunits joined by S-S bond
  • High affinity for diferric and monomeric transferrin at neutral pH
  • High affinity of apo-transferrin at acidic pH
  • Soluble transferrin receptor is a truncated monomer of the tissue receptor that circulates in a complex with transferrin
  • Classical transferrin receptor (TFR1) in all tissues. It is highly expressed on rapidly dividing cells and increased expression in iron deficiency
29
Q

How is Erythropoesis carried out?

A
  • Erythropoiesis uses major portion of body iron to produce new RBCs
  • Controlled by the stromal network, cytokines and erythropoietin
  • Reticulocytes generated in the bone marrow are released after 3 days. After 1 day in the circulation, reticulocytes lose their ribosomal network and become mature RBCs
  • At steady state, rate of RBC production equals rate of loss
30
Q

Describe the Transferrin cycle

A
  • Apotransferrin’ binds Fe3+ at the basolateral surface of enterocytes
  • Transferrin delivers iron to cells expressing transferrin receptors
  • TFR1 selectively binds diferric ‘holotransferrin’. This leads to membrane invagination forming endosomes.
  • H+ influx causes release of HCO3- and Fe3+ from transferrin. Apotransferrin dissociates from TFR1
  • Liberated Fe3+ is reduced to Fe2+ by STEAP3 ferrireducatase
  • DMT1 transports Fe2+ into the cytoplasm of the recipient cell
31
Q

How is Transferrin Cycle regulated?

A

HFE competes with holotransferrin for binding to TFR1

  • Increased iron bioavailability increases saturation of transferrin.
  • More holotransferrin is available to bind TFR1. HFE is released

High labile iron pool increases HFE expression (reciprocally to DMT1

32
Q

Which proteins are used to regulate iron in the Liver?

A
  • Ferroportin: Transports stored iron out of hepatocytes into circulation
  • BMP6
  • HFE: Regulates supply of hepcidin in response to iron
  • Ferritin: Hepatocyte iron storage protein
33
Q

How is Hepcidin production regulated?

A

Regulated By Paracrine Signaling

  • Intercellular crosstalk between different liver cells
  • Hepcidin is positively regulated by plasma holotransferrin, hepatic iron stores and inflammation
  • Iron stores sensed by hepatic sinusoidal endothelial cells: ↑ BMP6
  • Hepcidin transcription upregulated by haemojuvelin, HFE and TFR2
  • Holotransferrin may upregulate hepcidin regulation via release of HFE from TFR1 and increased binding of HFE to TFR2

Hepcidin synthesis is negatively regulated by increased erythropoiesis and hypoxia

34
Q

How does the liver control Hepcidin?

A
  • Hepatic endothelial cells produce BMP6, which binds to the BMP receptors (BMPR) and BMP coreceptor hemojuvelin (HJV) on the hepatocyte cell membrane, activating the BMP-SMAD pathway and inducing hepcidin expression.
  • This can be inhibited by matriptase 2 (MT-2), which cleaves HJV.
  • Hepatic macrophages produce inflammatory cytokines, including IL-6, in response to antigens and infectious agents. IL-6 binds to IL-6 receptors on the hepatocyte membrane, activating the JAK-STAT pathway and inducing hepcidin expression.
35
Q

Which proteins control iron within macrophages?

A
  • Ferroportin: Transports recycled iron out of macrophages for transferrin uptake
  • Ferritin: Excess iron stored in macrophages
36
Q

How is Iron sotred, transported and recycled?

A

RBCs ingested by macrophages after 120 days

  • Macrophages release Fe2+ via ferroportin
  • Fe2+ oxidised to Fe3+ by membrane-bound iron oxidase, allowing uptake and delivery by transferrin

Cytosolic Fe3+ reduced to Fe2+ for uptake into iron core, re-oxidised to Fe3+, stored as ferric oxyhydroxide phosphate

750-2000 mg iron stored in health

  • Ferritin & haemosiderin
  • 1/3 each in liver, macrophages & bone marrow
  • Lysosomes turn over iron pool every few days
37
Q

What are some molecular iron sensors?

A
  • Cytoplasmic iron response proteins (IRPs) sense concentration of chelatable iron in the labile pool
  • IRP1 forms an 4Fe-4S cluster when iron is abundant (clusters cannot bind mRNA)
  • IRP2 degradation is triggered by high iron concentration (not available to bind mRNA)
38
Q

How does cellular iron homeostasis get translationally regulated?

A

Translational regulation

  • mRNA is synthesised by transcription from DNA
  • Proteins are synthesised by translation of mRNA
  • Initiation of protein synthesis requires binding of large cellular enzyme apparatus to the 5’ untranslated region (UTR) of mRNA
  • Synthesis of a complete amino acid chain requires progression of the translational apparatus though to the 3’ UTR of the mRNA

Iron regulatory Proteins bind to hairpin iron response elements (IREs) in mRNA, sterically altering translation and affecting mRNA stability

Increased translation: proteins with IRE in 5’UTR of mRNA, so in presence of high iron there are no functional IRPs to block binding of translational apparatus

  • H- and L-ferritin
  • Ferroportin
  • ALA synthase (haem synthesis)

Decreased translation: proteins with IRE in 3’UTR of mRNA, so in presence of high iron no functional IRPs to stabilise mRNA: DMT1, TFR1

Nutrition and Drug Monitoring (17 decks)

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