L7: Introduction to anaemia and Vitamin B12 and Folate Metabolism Flashcards
What is anaemia?
A haemoglobin concentration lower than normal
Normal range–> age, ethnicity, sex etc
What are the signs and symptoms of anaemia?
Insufficient O2 delivery Symptoms - Shortness of breath - Palpitations - Headaches - Claudication (cramping in leg) - Angina - Weakness and lethargy - Confusion Signs - Pallor - Tachycardia - Tachypnoea (rapid short breaths) - Hypotension - Systolic flow murmur
What are the signs related to specific types of anemia?
- Koilonychia –> spoons shaped nail –> Iron deficiency
- Angular Stomatitis –> Inflammation at side of mouth –> Iron deficiency
- Glossitis –> Inflammation and depapillation of tongue –> Vit B12 deficiency
- Abnormal facial development–> Thalassaemia –> screening program so rarely seen nowadays
Why might anaemia develop?
*Affect different stages of RBC life cycle* Bone marrow --> Reduced or dysfunctional erythropoiesis --> Abnormal Haem synthesis --> Abnormal globin chain synthesis Peripheral RBC --> Abnormal structure --> Mechanical damage --> Abnormal metabolism Excessive bleeding Removal --> Increased removal by reticuloendothelial system
How does erythropoiesis normally work?
Low blood O2
Kidney sense hypoxia–> releases erythropoietin
Bone marrow–> erythroblast –> reticulocyte –> erythrocyte
Increase RBC –> high blood O2–> negative feedback
How can reduced or dysfunctional erythropoiesis result in anaemia?
Kidney defects
-Chronic kidney disease–> Hypoxia kidney doesn’t release erythropoietin
Bone marrow defects
-Bone marrow doesn’t respond to erythropoietin e.g. chemotherapy, infection
-Infiltrated by cancer cells, fibrous tissue (myelofibrosis) etc –> stops RBC growing properly
-Anaemia of chronic disease –> iron not available to bone marrow for synthesis
-Rare blood cancer–> myelodysplastic syndromes, abnormal marrow cells limit capacity to make RBC and WBC
How can defects in haemoglobin synthesis result in anaemia?
- Thalassaemia –> α and β, sickle cells disease –> don’t produce correct number of chains to form haemoglobin molecule
- Sideroblastic anaemia –> defect in haem synthesis
- Iron deficiency anaemia–> Not enough iron in diet to make haem
- Anaemia of chronic disease–> functional iron deficiency (enough iron in body but not available for erythropoiesis
How does abnormal structures come about? How does abnormal structure and mechanical damage result in haemolytic anaemia?
Haemolytic anaemic –> RBC destroyed»_space; RBC production
Inherited mutations in genes–> code for proteins
Abnormal proteins –> cytoskeleton of RBC changed
Cell less flexible–> more easily damage in circulation or removed by RES
Acquired damage
-Microangiopathic haemolytic anaemias- mechanical damage caused by
–> e.g. shear stress–> cells passing through stenosed valve
OR cell snagging on fibrin strands –> where clotting cascade has occured
-Heat damage –> destroys RBC
-Osmotic change
Results in schistocyte production (fragments of RBCs)–> Damaged RBC are removed
How does defects in RBC metabolism impact on anaemia?
- Pyruvate kinase deficiency
RBC require glycolysis for energy production
Pyruvate kinase deficiecny –> inhibits final stage in glycolysis–> Phosphoenolpyruvate to Pyruvate–> prevents further ATP production –> RBC depleted of ATP –> haemolysis - G6PDH deficiency
Less NADPH produced (pentose phosphate pathway) –> less oxidised glutathione GSSG) back to reduced glutathione (GSH)–> oxidative stress–> crosslinks haemoglobin –> heinz bodies –> haemolysis
How can excessive bleeding result in anaemia?
Loss of blood–> Less RBC and haemoglobin = anaemia
Acute blood loss (injury, surgery, birth, ruptured BV)
Chronic –> small amount of bleeding over long time–> Loose RBC= Loose iron, amount of iron out»> iron in there no new RBC synthesised
–> mensturation
–> nosebleeds
–> haemorrhoids
–> Gastrointestinal bleeding–> ulcers, diversticulosis, polyps in LI, Intestinal cancer
–> kidney or bladder tumours
How can NSAIDs lead to anaemia?
Chronic use
Aspirin, ibuprofen and naproxen –> treat inflammation
GI bleeding induced via inhibition of COX activity or direct cytotoxic effects on epithelium
How can the reticuloendothelial system lead to anaemia?
Haemolytic anaemias –> RBC damaged so destroyed
Damage occurs internally (intravascular haemolysis) in BV or external (extravascular haemolysis) in RES
Autoimmune haemolytic anaemias –> antibodies to RBC membrane –> macrophages in spleen recognise and destroy–> splenomegaly
In reality what is the most likely cause of anaemias?
Multifactorial –> usually more than one thing
e.g. myelofibrosis–> proliferation of mutated hematopoietic stem cells –> reactive bone marrow fibrosis –> less space for RBC production ↓ low RBC –> progenitor cells migrate into spleen and liver–> extramedullary haemopoiesis –> splenomegaly
Or e.g. Thalassemia
What parameters can be used to help identify the cause of anaemia?
- RBC size–> microcytic (small), macrocytic (large) or normocytic (normal)
- Presence of reticulocytes (immature RBC, no nucleus, eliminate mitochondria)–> presence suggest bone marrow is functioning normally –> Typically 1% of BC and mature in 1 day
What measurements can be used to determine if reticulocytes are present?
Mean Cell Volume–> slightly larger than RBC, Reticulcyte ↑ will increase MCV
Reticulocyte count–> count number
How do you determine the type of anaemia?
1) Increase in reticulocyte count–> yes–> bone marrow functioning properly
–> Evidence of heamolysis? –>
yes –> high biliruin or high LDH–> determine cause e.g. autoimmune, enzyme defects, membrane defects, haemoglobinopathies, microangiopathic haemolytic anaemias (MAHA)
no–> evidence of bleeding? –> acute blood loss, chronic bleeding (NSAID usage, ulcers), Splenic sequestration
2) Increased reticulocyte count –> no –> bone marrow problems
- -> What are the RBC indicies?
- -> microcytic- small <80fl (TAILS, Thalassaemia, Anaemia of chronic disease, Iron deficiency, Lead poisoning, Sideroblastic anaemias)
- -> macrocytic -large >100fl (Vit B12 deficiency, folate deficiency, myelodysplasia, liver disease, alcohol toxicity)
- -> nomocytic - normal 80-100fl (primary bone marrow failure (aplastic anaemia) or secondary bone marrow failure)
What are macrocytic anaemias?
Anaemia where the average RBC size is larger than normal 3 main causes --> megaloblastic anaemias --> macronormoblastic erythropoiesis --> stress erythropoiesis
What are megaloblastic anaemias? What causes it?
Interference with DNA synthesis
Nucleus develops slowly
Cytoplasm continues to develop
Cell division delayed but cell grows–> megaloblasts –> larger RBC
Causes–> VitB12/ folate deficiency, drugs (interfere with DNA synthesis), erythroid leukaemias
What is macronormoblastic erythropoiesis? Causes?
Normal relationship between nucleus development and cytoplasm
Erythroblast are larger than normal
Liver disease, alcohol toxicity, some myelodysplastic syndromes
What is stress erythropoiesis?
Erythropoietin produced high levels
Expanded and accelerate erythropoiesis
High reticulocyte count –> reticulocytes are larger than normal RBC
What is folate? Where does it come from? What is its role?
Synthesised in bacteria and plants
Present in wide variety of animal and vegetable food sources
Abundant in green leafy veg
Absorbed from duodenum and jejunum
Converted to tetrahydrofolate (TH4) stored in the liver (enough for 3-4 months)
Metabolic role–> provide carbons for other reactions , other role–> synthesis of nucleotides and bases required for DNA and RNA
What causes folate deficiency?
Dietary deficiency
Increased requirements (pregnancy, ↑erythropoesis, severe skin disease)
Disease of duodenum and jejunum –> not absorbed
Drug which inhibit dihydrofolate reductase
Alcoholism
Urinary loss of folate –> liver disease and heart failure
What are the symptoms of folate deficiency?
Related to anaemia and reduced sense of taste, diarrhoea, numbness and tingling, muscle weakness, depression
Who needs to take folic acid (synthetic folate)? Why?
Women --> trying to conceive --> pregnant --> 1st 12 weeks 400 micrograms/day Prevents neural tube defects in babies
What is Vitamin B12? What is is needed for?
Water soluble
Produced by bacteria (obtained from animals as commensal bacteria on/in it)
Essential co-factor for DNA synthesis
Required for erythropoiesis
Normal function and development of CNS
Vegan–>foods fortified with Vit B12 or supplements 10 micrograms daily or 2 milligrams weekly
How is Vitamin B12 absorbed?
1) Released from foods–> proteolysis
2) Stomach–> binds to heptocorrin (salivary glands)–> prevents acid degradation
3) Heptocorrin B12 complex–> Duodenum/jejunum–> pancreatic proteases–> release B12
4) B12 binds intrinsic factor (released from paritel cells in stomach)= intrinsic factor B12 complex–> uptake by receptor mediated endocytosis into enterocytes via cubam receptor
5) Lysosomal release inside cell–> B12 exit basolateral membrane via MDR1 into blood
6) Binds to transcobalamin in blood for transport
7) Majority stored in liver (3-6yrs)
What causes vitamin B12 deficiency?
Dietary deficiency
Perinicious anaemia–> lack intrinsic factor
Disease of ileum
Lack of transcobalamin (congential defect)
Chemical inactivation of B12 –> no erythropoiesis
Parasitic infection –> trap B12
Chelate intrinsic factor
What is perinicious anaemia?
Decrease in intrinsic factor
Progressive exhaustion of B12 reserves
Autoimmune disease–> 2 types of antibodies–>
- Blocking Ab–> common, blocks binding of B12 to IF
- Binding Ab–> prevents receptor mediated endocytosis
What are the symptoms of B12 deficiency?
Related to anaemia Glossitis and mouth ulcers Diarrhoea Paraesthersia (pins and needles) Disturbed vision Irritability
How does B12 and folate deficiency affect the nervous system?
Folate–> pregnancy–> neural tube defects
VitB12–> Associated with focal demyelination, reversible peripheral neuropathy
However can result in serious–> subacute combined degeneration of the cord–> degeneration of posterior and lateral columns of spinal cord–> can be irreversible
What are the symptoms of subacute combined degeneration of the cord?
Gradual onset weakness
Numbness
Tingling in arms, legs and trunk –> worsens
Chnage in mental state
How are folate and VitB12 linked?
Lack of B12 traps folate as methyltertrahydrofolate
Prevents use in other reactions e.g. synthesis of thymidine for DNA synthesis
How does B12 and folate deficiency result in megaloblastic anaemia?
Both involved in thiamine production
Required for DNA synthesis
Absence Uracil is incorporated
DNA repair enzymes detect and repair by excision
Asynchondrous maturation between nucleus and cytoplasm
Also both required for nuclear division and maturation
Lags behind–> RBC with inappropriately large nuclei and open chromatin–> RBC large–> macrocytic anaemia
What are the features of megablastic anaemia on blood film?
Anisopoikilocytosis (various size and shapes)
Tear drop red cells
Ovalocytes RC
Hypersegmented neutrophils (>6 lobes)
Macrocytic (larger than normal)
Pancytopenia –> low RBC, WBC and platelets
How is vitamin B12 and folate deficiency treated?
Folate–> oral folic acid
B12–>
Pericinous anaemia (no intrinsic factor)–> hydroxycobalamine intramuscular–> straight into circulation bypass metabolism–> becareful of hypokalaemia (low K+) because suddenly get a massive increase in erythropoiesis so K+ used up
Others–> oral VitB12 (cyanocobalamine)
Blood transfusion for severe cases–> high output cardiac failure
Why? long time to become deficient–> heart become hypertrophied and enlarged to compensate–> increase blood volume too quikly= cardiac failure
What would you expect to see after treatment for B12 or folate deficiency?
2-4 day reticulocyte count rises 10 days Hb rise, MCV fall 14 days hypersegmented neutrophils disappear 2 months resolution of anaemia 3-6 months resolution of neuropathy
