L8: Iron metabolism and microcytic anaemias Flashcards

1
Q

What are microcytic anaemias?

A

Erythrocytes are smaller
Reduced rate of haemoglobin synthesis
Cells paler (hypochromic)

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2
Q

What causes microcytic anaemias?

A

Reduced haem synthesis
-Anaemia of chronic disease –> Hepcidin result in functional iron deficiency (plenty of it but cant be used)
-Iron deficiency–> required for haem synthesis
-Lead poisoning–> acquired defect
-Sideroblastic anaemia–> inherited defect in haem synthesis
Reduced globin chain synthesis
- Thalassaemia –> α and β
–> α –> deletion or loss of one or more of α globin genes
–> β –> mutation in β globin genes leading to reduction or absence of the β globin

Mnemonic –> TAILS

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3
Q

What is iron? Whats its function?

A

Element
Essential in all living cells
Free iron–> potentially toxic to cells
Complex regulatory system–> safe utilisation, absorption and transport
Required for:
- O2 carriers –> haemoglobin in red cells
–> myoglobin in myocytes
-Cofactor in many enzymes–> cytochromes (OP), Krebs cycle enzymes, cytochrome P450 enzymes (detoxification), catalase
Body has no mechanism for excreting iron

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4
Q

What is the difference between ferrous and ferric?

A

Ferrous Fe2+ –> reduced form–> absorbed from diet in this form
Ferric Fe3+ –> oxidised form

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5
Q

How is ferric reduced to ferrous and vice versa?

A

Ferric (Fe3+) + e- –> Ferrous (Fe2+) reduction low pH (acid)
Ferrous (Fe2+) –> Ferric (Fe3+) + e- oxidisation high pH (alkaline)

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6
Q

What is the difference between haem and non-haem iron?

A

Haem–> associate with globin–> haemoglobin
Come from animals–> liver, kidney, steak, beef burgers etc
Easily/readily absorbed
Non-haem –> Ferrous or ferric form–> fortified cereals, raisins, beans, figs, barely, oats, rice and potatoes
Converted to ferrous for absorption

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7
Q

How much iron is needed in the diet and where is it absorbed?

A

10-15 mg/day

Absorbed in the duodenum and upper jejunum

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8
Q

How is iron absorbed into the bloodstream?

A
  1. Chyme enter duodenum/ upper jejunum
  2. a) Haem–> readily absorbed by the enterocytes
    - inside Fe2+ released by haem oxygenase
    b) Non Haem–> Fe3+ –> Fe2+ via reductase enzymes in brush border
    –> Requires Vit C as electron donor
    –> Fe2+ –> enters enterocyte through DMT1 (divalent metal transporter 1)- H+ ion out
  3. Fe2+ stored- storage protein ferritin in Fe3+ form
    OR
  4. Enters bloodstream through ferroportin
  5. Transported- Fe3+ form- converted by Hephaestin
  6. Fe3+ binds to transferrin—> transported around the blood
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9
Q

What inhibits the role of ferroportin?

A

Hepcidin
Peptide hormone
Produced by liver
Bind to ferroportin–> degradation

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10
Q

What factors affect the absorption of non-haem iron from food?

A

Negative influences–> Tannis (in tea), phytates (pulses), fibre and antacids (gavison)

  • -> bind to non-heam iron in the intestine reduce absorption
  • -> need acidic environment to convert Fe3+–> Fe2+

Positive influences–> Vit C and citrate–> prevent formation of insoluble iron compounds
VitC require for conversion of Fe3+–> Fe2+

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11
Q

What is the difference between functional and stored iron?

A

Functional iron–> available

  • Heamoglobin (2000mg)
  • Myoglobin (300mg)
  • Enzymes- cytochromes (50mg)
  • Transported iron (transferrin) (3mg)

Stored iron (1000mg)

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12
Q

How can iron be stored?

A

Ferritin–> soluble form

  • -> stored in enterocyte
  • -> globular protein complex with hollow core–> pores allow iron to enter and be released

Haemosiderin –> insoluble form

  • -> Aggregates of clumped ferritin particles, denatured protein and lipid
  • -> Accumulates in macrophages, particular in liver and spleen
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13
Q

How is iron taken up into cells?

A

1- Fe3+ bound trasferrin binds transferrin receptor and enters the cytosol receptor-mediated endocytosis
2- Fe3+ within the endosome released by acidic microenvironment and reduced to Fe2+
3- The Fe2+ transported to the cystol via DMT1
4- Once in cystol Fe2+ can be:
- stored in ferritin
-exported by ferroportin (FPN1) or
-taken up by mitochondria - cytochrome enzymes

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14
Q

What is meant by iron recycling?

A
Small intake in diet
Most (>80%) - recycled from damaged or senescent RBC
Phagocytosis by macrophages
Splenic macrophages and kupffer cells - Liver
Catabolise haem released from RBC
AA reused and iron:
- exported to blood - transferrin 
- stored - Ferritin - macrophages
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15
Q

How is iron absorption regulated?

A

Determined by: dietary factors, iron stores, erythropoiesis
Sensed by enterocytes
Controlled mechanisms
- Regulation of transporter- ferroportin
- Regulation of receptors- Transferrin receptor and HFE protein (homeostatic iron regulator)
- Hepcidin and cytokines
- Crosstalk between the epithelial cells and other cells like macrophages

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16
Q

How does hepcidin regulate iron absorption?

A

Negative regulator
Synthesis increased in iron overload
Decreased by high erythropoietic activity
Induces the internalisation and degradation of ferroportin

17
Q

What is meant by anaemia of chronic disease?

A

Anaemia caused by inflammation
Inflammatory condition–> cytokine release (IL-6)
Main effect–> increased hepcidin production–> inhibition of ferroportin–> decreased iron released from reticuloendothelial cells and reduced absorption from diet–> plasma iron reduced–> inhibition of erythropoiesis in bone marrow–> anaemia (less RBC)
Minor pathway–> Inhibition of erythropoietin production and inhibition of erythropoeisis–anaemia

18
Q

What type of deficiency is anaemia of chronic disease?

A

Functional deficiency

enough iron in body but cannot utilise it

19
Q

How much iron is lost from the body each day and how? Is iron excretion regulated?

A
1-2 mg/day
- desquamation of epithelia
- menstural bleeding
- sweat 
- pregnancy--> 3.5mg/day
No--> no mechanisms to control excretion
20
Q

What is significant about iron deficiency?

A

Most common nutritional disorder
1/3rd population anaemic- 1/2 iron deficient
Sign not a diagnosis

21
Q

What are the causes of iron deficiency?

A
Insufficient iron in diet
Malabsorption 
Bleeding
Increased requirement (pregnancy)
Anaemia of chronic disease
22
Q

Why is the iron requirement for females 19-50 greater than males of similar age?

A

Females of this age lose lots of blood during menstruation each month

23
Q

What groups are at risk?

A

Children
Infants
Women of child bearing age
Geriatric age group (elderly)

24
Q

What are the signs and symptoms of anaemia?

A
  • Tiredness, pallor, reduced exercise tolerance, cardiac (angina, palpitations, development of HF), increased resp rate, headache, dizziness, light-headedness
  • Pica (unusual cravings)–> non-nutritive substances
  • Cold hands and feet
  • Epithelial changes (angular cheilitis, glossy tongue with atrophy of linguinal papillae), Koilonychia (spoon nails)
25
Q

What are the features on a blood film?

A

Low mean corpuscular volume (MCV)
Low mean corpuscular haemoglobin concentration (MCHC)
Elevated platelet count (>45,000/microlitres)
Normal or elevated WBC count
Low serum ferritin, serum iron and %transferrin saturation, raised total iron binding capacity
Low reticulocyte haemoglobin content (CHr)

26
Q

What would a blood smear look like in iron deficiency?

A

RBC are microcytic and hypochromic in chronic cases
Anisopoikilocytosis: change size and shape
Sometimes pencil and target cells

27
Q

How do you test for iron deficiency?

A

Plasma ferritin commonly used marker of total iron status (predominantly a cystolic protein- small amounts secreted into blood)
–> reduced= iron deficiency
Normal or increased does NOT exclude iron deficiency (increase in cancer, infection, inflammation, liver disease, alcoholism)
CHr (reticulocyte haemoglobin content)–> test for functional iron deficiency–> remains low during inflammatory response
Low for thalassaemia pt too

28
Q

How is iron deficiency treated?

A

Dietary advice
Oral iron supplements (potential GI side effects)
Intramuscular iron injections
Intravenous iron
Blood transfusion (only used for severe anaemia with imminent cardiac compromise)

29
Q

What should be the response to treatment?

A

Improvement in symptoms

20g/L rise in Hb in 3 weeks

30
Q

Why is iron excess dangerous?

A

Exceed binding capacity of transferrin
Excess iron deposited in organs–> haemosiderin (insoluble- denatures proteins/lipids)
Iron promoted free radical formation and organ damage

31
Q

What is the fenton reaction? Why is it damaging?

A
Creation of free radicals from iron
Fe2+ + H2O2--> Fe3+ + OH• + OH-
Fe3+ + H2O2--> Fe2+ + OOH• + H+
Hydroxyl and hydroperoxyl radicals cause damage:
- Lipid peroxidation 
- Damage to proteins 
- Damage to DNA
32
Q

What is Transfusion Associated Haemosiderosis?

A

Repeated transfusion–> gradual accumulation of iron
400ml blood= 200mg iron
Problem with transfusion dependent anaemias such as thalassaemias and sickle cell anaemia
Iron chelating agents such as desferrioxamine can delay but not stop effects of overload

33
Q

What are the effects of transfusion associated haemosiderosis with iron overload?

A
Liver cirrhosis
Diabetes mellitus 
Hypogonadism 
Cardiomyopathy
Arthropathy
Slate grey colour of skin
34
Q

What is Hereditary Haemochromatosis?

A

Autosomal recessive disease–> mutation in HFE gene (Chr 6)
HFE protein–> Interacts with transferrin receptor –> reduce affinity for iron bound transferrin
HFE also has increases hepcidin production
Mutated HFE cannot bind to transferrin–> negative influence on uptake is lost
AND –> underproduciton of hepcidin–> increased iron uptake
Iron accumulates in end organs causing damage
Treated with venesection –> removal of blood (1-2pints)

35
Q

What are the features of hereditary haemochromatosis?

A
Liver cirrhosis
Diabetes mellitus 
Hypogonadism 
Cardiomyopathy
Arthropathy
Increased skin pigmentation