L.11 Red Cell Metabolism & Enzyme Deficiencies Flashcards
1
Q
What do mature red blood cells (RBCs) lack that affects their metabolism?
A
Mitochondria
This absence prevents RBCs from performing oxidative phosphorylation and metabolizing fatty acids or ketone bodies.
2
Q
How do RBCs generate ATP?
A
Anaerobic glycolysis
This process involves the breakdown of glucose to lactate.
3
Q
Why is ATP critical for red blood cells?
A
It maintains biconcave shape and regulates ion transport
ATP is essential for gas exchange, deformability in capillaries, and osmotic balance.
4
Q
What are the three key areas of RBC metabolism essential for survival?
A
- RBC Membrane Integrity
- Haemoglobin Structure and Function
- Cellular Energy Generation
5
Q
What is the primary metabolic pathway used by mature red blood cells?
A
Anaerobic Glycolysis (Embden-Meyerhof Pathway)
This pathway accounts for approximately 90% of RBC metabolism.
6
Q
What are the main products of anaerobic glycolysis in RBCs?
A
- ATP
- NADH
7
Q
What is the secondary metabolic pathway used by RBCs?
A
Pentose Phosphate Pathway (Hexose Monophosphate Shunt)
This pathway accounts for about 10% of RBC metabolism.
8
Q
What is the main product of the Pentose Phosphate Pathway in RBCs?
A
NADPH
NADPH is crucial for maintaining glutathione in a reduced state.
9
Q
What role does ATP play in the synthesis of reduced glutathione (GSH)?
A
It is indispensable for GSH synthesis and maintenance
GSH is a key antioxidant for RBCs.
10
Q
What does ATP help reduce in hemoglobin for oxygen transport?
A
Iron from ferric (Fe³⁺) to ferrous (Fe²⁺) state
11
Q
Fill in the blank: ATP is critical for the initiation and sustenance of _______.
A
glycolytic enzymes
12
Q
True or False: RBCs can perform oxidative phosphorylation.
A
False
13
Q
What is essential for protecting RBCs against oxidative damage?
A
NADPH
It helps maintain glutathione in a reduced state.
14
Q
How does glucose enter the RBC?
A
Glucose enters the RBC via GLUT-1 transporters (facilitated diffusion)
GLUT-1 is a glucose transporter that facilitates the transport of glucose across the plasma membranes of cells, particularly in the brain and red blood cells.
15
Q
What is glucose phosphorylated to form early in glycolysis?
A
Glucose-6-phosphate (G6P)
This phosphorylation is a crucial first step in the glycolytic pathway, allowing glucose to be trapped in the cell and further metabolized.
16
Q
What percentage of G6P continues through the glycolytic pathway?
A
Approximately 90%
The remaining 10% is shunted into the Pentose Phosphate Pathway.
17
Q
What are the end products of glycolysis in RBCs?
A
Pyruvate and lactate
Pyruvate is reduced to lactate in the anaerobic conditions present in red blood cells.
18
Q
What is the net ATP yield from one molecule of glucose metabolized in glycolysis?
A
2 molecules of ATP
This yield is essential for the energy-dependent processes in RBCs.
19
Q
What is produced by the Pentose Phosphate Pathway (PPP)?
A
NADPH
NADPH is critical for maintaining cellular antioxidants like glutathione.
20
Q
What is the role of reduced glutathione (GSH) in RBCs?
A
Neutralizes hydrogen peroxide (H₂O₂) and other harmful oxidants
This action prevents oxidative injury to hemoglobin and the RBC membrane.
21
Q
What is the function of the methemoglobin reductase enzyme system?
A
Reduces Fe³⁺ back to Fe²⁺
This restoration is vital for maintaining hemoglobin’s oxygen-carrying ability.
22
Q
What happens to hemoglobin when methemoglobin reductase activity is impaired?
A
Methemoglobin accumulates, impairing oxygen transport
This can lead to cyanosis and, if severe, tissue hypoxia.
23
Q
What is the Luebering-Rapoport shunt?
A
A specialized diversion within anaerobic glycolysis unique to red blood cells
This shunt facilitates the synthesis of 2,3-diphosphoglycerate (2,3-DPG).
24
Q
What does the Luebering-Rapoport shunt synthesize?
A
2,3-diphosphoglycerate (2,3-DPG)
This synthesis occurs at the expense of one molecule of ATP.
25
How does 2,3-DPG influence hemoglobin?
Binds to hemoglobin (Hb) in a 1:1 ratio
## Footnote
This binding influences hemoglobin's ability to bind and release oxygen.
26
Fill in the blank: The Pentose Phosphate Pathway is vital for generating reduced _______.
NADPH
## Footnote
NADPH plays a key role in antioxidant defense within red blood cells.
27
True or False: The majority of G6P is converted to lactate in RBCs.
True
## Footnote
This conversion is part of the anaerobic glycolytic pathway.
28
What is the primary function of NADPH in RBCs?
Maintains glutathione (GSH) in its reduced form
## Footnote
This maintenance is crucial for protecting RBCs from oxidative damage.
29
What does 2,3-DPG bind to?
Haemoglobin
## Footnote
2,3-DPG competes with oxygen at the haemoglobin binding sites.
30
What effect does 2,3-DPG have on the oxygen affinity of haemoglobin?
Reduces oxygen affinity
## Footnote
This adaptation facilitates oxygen release to peripheral tissues.
31
What happens to 2,3-DPG levels in stored blood?
Progressively loses 2,3-DPG
## Footnote
This leads to increased oxygen affinity in stored RBCs.
32
How long does it take for depleted RBCs to restore normal 2,3-DPG levels after transfusion?
Approximately 6–24 hours
## Footnote
This is critical for restoring tissue oxygenation.
33
What is the maximum storage duration for blood under refrigeration?
21–42 days
## Footnote
This duration is significant for blood bank practices.
34
What physiological conditions stimulate increased production of 2,3-DPG?
High-altitude exposure and chronic hypoxia
## Footnote
These conditions enhance oxygen unloading.
35
How does foetal haemoglobin (HbF) interact with 2,3-DPG?
Binds 2,3-DPG weakly
## Footnote
HbF has a higher oxygen affinity compared to adult haemoglobin (HbA).
36
What percentage of glucose metabolism in RBCs proceeds through the oxidative Pentose Phosphate Pathway (PPP)?
Approximately 10%
## Footnote
This pathway is important for generating NADPH.
37
What is a critical byproduct of the Pentose Phosphate Pathway?
NADPH
## Footnote
NADPH is a potent reducing agent essential for cellular protection.
38
What is the role of NADPH in red blood cells?
Regenerating reduced glutathione (GSH)
## Footnote
GSH protects haemoglobin and membrane proteins from oxidative damage.
39
How can the activity of the Pentose Phosphate Pathway change during oxidative stress?
Increase to up to 30%
## Footnote
This occurs during infections, inflammation, or drug exposure.
40
What are sources of oxidative stress that can affect RBCs?
* Natural metabolic processes
* Exposure to drugs
* Chemicals
* Infections
## Footnote
These factors lead to the production of reactive oxygen species.
41
What happens if the Pentose Phosphate Pathway is compromised?
Oxidants accumulate within RBCs
## Footnote
This can lead to denaturation of globin chains and formation of Heinz bodies.
42
What are Heinz bodies?
Intracellular inclusions formed from denatured globin chains
## Footnote
These damaged RBCs are removed by the mononuclear phagocyte system.
43
What are the consequences of oxidative stress in RBCs?
* Damage to haemoglobin and lipid peroxidation of the cell membrane
* Heinz body formation inside RBCs
* Reduced membrane deformability
* Increased permeability and instability of the RBC membrane
* Extravascular haemolysis
## Footnote
Oxidative stress can lead to significant structural and functional impairments in red blood cells, ultimately resulting in their premature destruction.
44
What historical events are associated with enzyme deficiencies in red cells?
* 1926: Acute haemolytic episodes in Panama plantation workers
* 1953: Dacie's description of drug-induced haemolytic anaemia
* Hereditary non-spherocytic haemolytic anaemia characteristics:
* No evidence of abnormal haemoglobin
* Negative antiglobulin tests
* Normal osmotic fragility tests
## Footnote
These historical observations helped identify the role of inherited enzyme deficiencies in red blood cell disorders.
45
What is G6PD deficiency?
The most common RBC enzyme defect globally leading to episodic acute haemolysis under oxidative stress
## Footnote
G6PD deficiency is a significant public health concern in various regions due to its association with certain foods and infections.
46
What triggers episodic acute haemolysis in G6PD deficiency?
* Drugs (e.g., antimalarials, sulfonamides)
* Certain foods (e.g., fava beans)
* Infections
## Footnote
These triggers can lead to oxidative stress, exacerbating the condition in affected individuals.
47
What are the clinical signs and symptoms of G6PD deficiency?
* Jaundice
* Confusion and reduced concentration
* Tachycardia
* Dark-coloured urine
* Splenomegaly in severe cases
## Footnote
These symptoms are indicative of hemolytic events and may vary in severity among individuals.
48
How is G6PD deficiency inherited?
Inherited in an X-linked recessive pattern
## Footnote
This inheritance pattern explains why males are more frequently and severely affected, while females may act as carriers.
49
Where is G6PD deficiency highly prevalent?
* Central Africa
* Mediterranean regions
* Middle East
* Indian subcontinent
* Southeast Asia
## Footnote
The prevalence in these regions is often linked to a selective advantage against malaria.
50
Fill in the blank: G6PD deficiency is encoded by the _______ gene located on the X chromosome.
G6PD
51
True or False: Females with G6PD deficiency are always symptomatic.
False
## Footnote
Females are typically carriers and may only show symptoms in specific genetic circumstances such as homozygosity or skewed lyonization.
52
What is the role of G6PD enzyme in the PPP?
Catalyzes the first, rate-limiting step by removing a hydrogen atom from glucose-6-phosphate
## Footnote
G6PD facilitates the production of NADPH, which is essential for keeping glutathione reduced.
53
What happens to RBCs without sufficient G6PD?
RBCs become vulnerable to oxidative injury, Heinz bodies form, and RBCs are destroyed prematurely, leading to haemolytic anaemia
## Footnote
This vulnerability is due to the inability to produce sufficient NADPH.
54
How many G6PD variants are known?
Over 400 variants
## Footnote
Most variants differ based on electrophoretic mobility and kinetic properties.
55
What percentage of enzyme-related haemolytic anaemias is accounted for by G6PD deficiency?
Over 90%
## Footnote
This indicates the significance of G6PD deficiency in the context of haemolytic anaemias.
56
What does FBC reveal in cases of G6PD deficiency?
Hb ↓ (70-100 g/l), MCV N, MCH N
## Footnote
FBC stands for Full Blood Count.
57
What are some findings on a blood film for G6PD deficiency?
* Bite cells
* Hemighosts
* Polychromasia
* NRBC
## Footnote
NRBC stands for Nucleated Red Blood Cells.
58
What does a Heinz Body Stain detect?
Precipitates of oxidatively denatured Hb stained by crystal violet or methylene blue
## Footnote
This test is used to identify the presence of Heinz bodies in RBCs.
59
What is the MetHb reduction test used for?
To determine if G6PD erythrocytes fail to reduce metHb in the presence of methylene blue
## Footnote
A failure indicates a deficiency in G6PD activity.
60
What does a fluorescent spot screening test involve?
Mixing G6P and NADP with the patient's blood and spotting onto filter paper
## Footnote
G6PD should reduce NADP to NADPH, causing fluorescence.
61
What laboratory test directly measures G6PD activity?
G6PD enzyme assay
## Footnote
This test quantifies the activity of the G6PD enzyme in the sample.
62
What are the expected laboratory findings in G6PD deficiency?
* LDH ↑
* Bilirubin ↑
* Haptoglobin ↓
* Haemoglobinuria
## Footnote
Elevated LDH and bilirubin indicate hemolysis, while decreased haptoglobin suggests binding of free hemoglobin.
63
What is the first step in the G6PD Testing Procedure?
Add 1 ml of G6PD Assay Reagent into a labeled test tube
## Footnote
This is the preparation phase of the testing procedure.
64
What volume of the patient sample is added to the G6PD Assay Reagent?
10 µl (microliters)
## Footnote
This is crucial for the reaction to occur.
65
How long should the initial incubation last?
10 minutes
## Footnote
During this time, the contents should be gently mixed.
66
What is used to seal the test tube during the initial incubation?
Parafilm
## Footnote
This prevents contamination or evaporation.
67
What temperature should the substrate solution be pre-warmed to?
30°C
## Footnote
This is necessary for the substrate reaction.
68
What instrument is used for the spectrophotometric measurement?
Thermo Spectronic Helios γ spectrophotometer
## Footnote
This instrument measures absorbance.
69
At what wavelengths should absorbance readings be recorded?
At 5 minutes and 10 minutes after placement
## Footnote
These readings are crucial for calculating G6PD activity.
70
What does the reaction measure in the G6PD testing procedure?
Enzymatic activity converting G6P to 6-phosphogluconate + NADPH
## Footnote
NADPH is fluorescent and measurable at 340 nm.
71
What reflects the amount of NADPH produced in the reaction?
Increase in absorbance (ABS) at 340 nm
## Footnote
This indicates G6PD activity.
72
How is the Total Absorbance Change calculated?
Final ABS – Initial ABS
## Footnote
A larger change indicates higher G6PD enzymatic activity.
73
How often are External Quality Assurance (EQA) samples received?
Bi-monthly (every two months)
## Footnote
These samples are sent from the UK NEQAS.
74
What do the EQA shipments include?
Two blinded samples
## Footnote
This is for comparison and external validation.
75
What is the purpose of running internal controls alongside patient samples?
To validate test performance
## Footnote
This ensures accuracy in results.
76
What are the three levels of G6PD Controls?
* G6PD Control Normal (expected high activity)
* G6PD Control Intermediate (moderate reduced activity)
* G6PD Control Deficient (severely reduced or absent activity)
## Footnote
These controls help assess the test's reliability.
77
True or False: All control materials should be treated as potentially infectious.
True
## Footnote
Standard biohazard safety protocols should be followed.
78
What types of infections can trigger haemolysis in G6PD deficiency?
Bacterial, viral, or parasitic infections generate oxidative stress
## Footnote
Illnesses like diabetic ketoacidosis (DKA) also induce oxidative environments.
79
Name a class of drugs that can precipitate haemolytic crises in G6PD deficiency.
Certain classes of drugs, including:
* Sulfa drugs (e.g., sulfamethoxazole)
* Nitrofurantoin
* Aspirin (in high doses)
* Dapsone
* Some antibiotics like chloramphenicol
## Footnote
These drugs can lead to oxidative stress and trigger haemolysis.
80
Which antimalarial drug is historically important for triggering haemolysis in G6PD deficiency?
Primaquine
## Footnote
Chloroquine can also trigger haemolysis, but to a lesser extent.
81
What food is known to cause severe haemolytic episodes in G6PD deficiency?
Fava beans (broad beans)
## Footnote
They contain high levels of oxidants (vicine and convicine) that can cause favism.
82
What is the first step in the treatment of haemolysis due to G6PD deficiency?
Stop the offending drug
## Footnote
This is crucial to prevent further haemolytic episodes.
83
What is maintained to help manage G6PD deficiency-related haemolysis?
A high urine output
## Footnote
This helps in the excretion of hemolytic products.
84
What treatment may be necessary for severe anaemia in G6PD deficiency?
Blood transfusion
## Footnote
This may be required in cases of severe anaemia.
85
What condition are G6PD-deficient babies prone to?
Neonatal jaundice
## Footnote
In severe cases, phototherapy and exchange transfusion may be needed.
86
What is the cause of jaundice in G6PD-deficient babies?
Deficiency of G6PD affecting neonatal liver function
## Footnote
It is usually not caused by excess haemolysis.
87
What risk is associated with treating Plasmodium vivax malaria with primaquine in G6PD deficiency?
Significant risk of triggering acute haemolytic anaemia
## Footnote
The severity of haemolysis can range from mild to life-threatening.
88
Is there a global consensus on routine G6PD deficiency testing before prescribing primaquine?
No, there remains no global consensus
## Footnote
Despite the known risk associated with primaquine in G6PD deficiency.
89
What are radical cure regimens used for in the context of Plasmodium vivax?
To eliminate dormant liver stages of P. vivax
## Footnote
These regimens are highly effective but can endanger G6PD-deficient individuals without prior screening.
90
What is the primary function of anaerobic glycolysis in mature RBCs?
Production of ATP and NADH
## Footnote
Mature RBCs lack mitochondria and rely on anaerobic glycolysis for energy.
91
What are the consequences of enzyme deficiencies in anaerobic glycolysis?
Reduced ATP and NADH levels, impaired RBC survival, accumulation of metabolic intermediates
## Footnote
Key intermediates include 2,3-Diphosphoglycerate (2,3-DPG) and Methemoglobin (MetHb).
92
Which enzyme deficiency is the most common in anaerobic glycolysis?
Pyruvate Kinase (PK) Deficiency
## Footnote
It is a major cause of hereditary non-spherocytic haemolytic anaemia.
93
What is the second most frequent enzyme deficiency in anaerobic glycolysis?
Glucose-6-Phosphate Isomerase Deficiency
94
How common is Glyceraldehyde-3-Phosphate Dehydrogenase Deficiency?
Rare
95
When was Pyruvate Kinase (PK) Deficiency first identified?
1961
96
What inheritance pattern does Pyruvate Kinase (PK) Deficiency follow?
Autosomal recessive
97
In which regions is Pyruvate Kinase (PK) Deficiency notably distributed?
Northern Europe, Japan, USA, Amish in Pennsylvania
98
What are the clinical presentations of Pyruvate Kinase (PK) Deficiency?
Varies from asymptomatic compensated haemolysis to severe disease requiring medical intervention
## Footnote
Includes severe neonatal jaundice, chronic haemolytic anaemia, moderate worsening during infections or pregnancy, and mild compensated haemolysis.
99
What biochemical consequence results from reduced ATP production in PK Deficiency?
Impaired RBC membrane stability
100
What happens to NADH levels in Pyruvate Kinase (PK) Deficiency?
Decreased NADH levels lead to increased oxidative stress vulnerability
101
What type of haemolysis predominates in PK Deficiency?
Extravascular haemolysis
## Footnote
Intravascular haemolysis can occur under oxidative stress.
102
What common condition is associated with chronic haemolysis in PK Deficiency?
Gallstones
103
What effect does increased 2,3-DPG levels have on oxygen delivery?
Causes a rightward shift in the oxygen dissociation curve, reducing haemoglobin oxygen affinity
104
What is the result of the rightward shift in the oxygen dissociation curve?
Improved oxygen delivery to tissues even at lower haemoglobin concentrations
105
What haematological finding is often observed in PK Deficiency?
Moderately raised reticulocyte count
106
What gene is associated with Pyruvate Kinase Deficiency?
PKLR gene
## Footnote
Over 150 different mutations in the PKLR gene have been identified.
107
What is the estimated global prevalence of Pyruvate Kinase Deficiency?
Approximately 51 cases per million
## Footnote
Observed prevalence in Northern England is closer to 3.3 cases per million.
108
What inheritance pattern is associated with Pyruvate Kinase Deficiency?
Autosomal recessive inheritance
## Footnote
Strong family history often noted.
109
What does FBC stand for in the context of lab diagnosis for PK deficiency?
Full Blood Count
## Footnote
Key indicators include Hb ↓, MCV N, MCH N.
110
What are the common findings in a blood film for PK deficiency?
* Echinocytes
* Polychromasia
* NRBCs
## Footnote
NRBCs refer to nucleated red blood cells.
111
What is the significance of reticulocyte count in PK deficiency diagnosis?
Reticulocytes positive
## Footnote
Indicates increased red blood cell production.
112
What biochemical markers are elevated in PK deficiency?
* LDH
* Bilirubin
## Footnote
Haptoglobin is typically decreased.
113
What does the fluorescence screening test indicate in PK deficiency?
Fluorescence persists beyond 30 min
## Footnote
This is due to the PK enzyme's activity.
114
What is the outcome of the PK enzyme assay in PK deficiency?
Reduced PK enzyme activity
## Footnote
DNA analysis is often performed as part of the diagnosis.
115
What is a common supportive care strategy for mild-to-moderate PK deficiency?
Monitoring and folic acid supplementation
## Footnote
Supportive care is essential for managing symptoms.
116
When are blood transfusions indicated in PK deficiency?
For severe anemia, especially in infants or during crisis periods
## Footnote
Helps manage acute complications.
117
What is the potential benefit of splenectomy in PK deficiency?
May reduce transfusion needs
## Footnote
However, hemolysis persists post-splenectomy.
118
What is Bone Marrow Transplant (BMT) in the context of PK deficiency?
Potential curative treatment
## Footnote
Mouse models have shown complete cure post-transplant.
119
What risk is associated with splenectomy in PK deficiency patients?
Thromboembolic disease
## Footnote
Portal and splenic vein thrombosis have been reported.
120
What did the case report by Van Straaten et al., 2018 demonstrate about BMT?
Full engraftment and normalization of PK enzyme activity 3 years post-BMT
## Footnote
Indicates successful outcomes in human cases.
