Glycolysis produces energy for the red blood cells mainly through two main mechanisms. The two glycolysis routes are as follows:
• Embden-Meyerhof pathway: the primary energy source (ATP synthesis) that supplies high energy phosphate for the upkeep of salt and potassium as well as membrane lipids.
The route of hexose monophosphate (HMP) shunt: This route catabolizes just 10% of glucose, yet it is crucial for protecting red blood cells from oxidative damage.
One of the mechanisms that scavenge free radicals is glucose-6-phosphate dehydrogenase (G6PD), an enzyme implicated in HMP shunt.
The metabolism of red blood cells will be impacted by abnormalities if any of the enzymes in these pathways are lacking or impaired.
Hemolytic Illness caused by Imperfect Red Cell Enzymes
Defects in red cell enzymes make red blood cells more vulnerable to hemolysis and less able to defend against oxidative damage. Because the RBC shape is hardly changed, the hemolysis linked to glycolysis abnormalities is referred to as congenital nonspherocytic hemolytic anemia. Deficiencies in red cell enzymes that occur are:
• Deficiencies in the hexose monophosphate shunt enzymes, such as glutathione synthetase and G6PD.
• Pyruvate kinase and hexokinase deficits are examples of glycolytic (Embden-Meyerhof pathway) enzyme deficiencies.
• Deficiency in pyrimidine-5' nucleotidase is one of the other enzymes.
Insufficiency of glucose-6-phosphate dehydrogenase
Both endogenous and external oxidants have the potential to harm red blood cells. It must defend itself against this oxidative harm caused by damage from free radicals. Glutathione levels are lowered to accomplish this (GSH).
G6PD's function
• Normal red blood cells are protected against oxidative damage by the high quantity of reduced glutathione (GSH), which catalyzes the conversion of substances like H2O2 to H2O.
• The hexose monophosphate shunt produces reduced glutathione. The reduced form of nicotinamide adenine dinucleotide (NADPH), which changes oxidized glutathione (GSSG) into reduced glutathione, maintains an adequate quantity of reduced glutathione (GSH). The housekeeping enzyme G6PD oxidizes glucose-6-phosphate while reducing nicotinamide adenine dinucleotide phosphate (NADP) to NADPH.
Events in the G6PD Deficiency Sequence
Oxidants in G6PD deficiency can result in extravascular hemolysis as well as intravascular hemolysis, but the latter is more common. The order in which they happened is:
• G6PD deficiency results in lower glutathione levels and increased oxidative damage susceptibility in red blood cells. • When red blood cells are subjected to circumstances that produce oxidative stress, hemolysis occurs.
The following circumstances have the potential to produce these oxidants:
- Infections: They cause active leukocytes to produce free radicals produced from oxygen. These infections include typhoid fever, pneumonia, and viral hepatitis.
- Medication or chemical exposure: This includes sulfonamides, nitrofurantoin, antimalarials (such as primaquine and chloroquine), and other substances.
- Specific foods: When digested, fava beans produce oxidants that can lead to hemolysis.
• Hemolytic anemia is caused by the accumulation of H2O2 in red blood cells lacking G6PD, which destroys hemoglobin and the erythrocyte membrane.
Hemolysis releases hemoglobin, which is then oxidized by oxidants to generate methemoglobin, which is then ferric (Fe3+) ions made of Fe2+ ions. Because methemoglobin is unstable and unable to carry oxygen, it precipitates in the cytoplasm as membrane-bound precipitates called Heinz bodies. When red blood cells have supravital staining (as in the reticulocyte preparation, Heinz bodies are visible as dark inclusions.
• Macrophages remove the Heinz bodies from these red blood cells as they travel through the spleen. Red blood cells with this membrane damage have an atypical form as if someone had taken a bite out of them. These arise in the peripheral circulation and are referred to as "bite cells."
• The spleen's erythrophagocytosis process is quite effective at capturing and eliminating bite cells as well as spherocytes.
G6PD Variants: There are known to be over 400 different G6PD genetic variations, most of which are benign. The activity, stability, and electrophoretic mobility of these variations vary. Depending on the level of hemolysis and deficiency, these are divided into five classes. Different categories (A+, A–, or B) or geographic names (Mediterranean) are assigned to these variants. G6PD-B is the standard designation for normal G6PD. Red blood cells typically exhibit the maximum G6PD activity while they are young and this activity declines with age.
Because of this, older red blood cells are more vulnerable to hemolysis than younger ones. As red blood cells age, G6PD A- or G6PD Mediterranean, which have a moderate to severe enzyme deficiency, are unable to defend against oxidative damage. • G6PD A–: The negative symbol denotes the lack of G6PD enzyme activity. Hemolysis occurs
when using medicines that cause oxidation or sickness. Only the elder RBCs exhibit mild to moderate hemolysis.
• G6PD Mediterranean: It is common throughout the Middle East and has significantly decreased stability and activity of enzymes.
The prevalence of malaria
Lack of G6PD protects against Plasmodium falciparum malaria because it prevents the availability of ribose products needed for the parasite's nucleic acid synthesis.
G6PD's genetic makeup
The X-linked recessive condition known as G6PD deficiency only manifests fully in males. Homozygous females may sporadically develop the illness. Because they have two populations of red blood cells—normal cells and G6PD deficient cells—heterozygous females will not exhibit any symptoms. Lyon's hypothesis states that the X-chromosome inactivation phenomenon is the cause of the dual population of cells seen in heterozygous females.
Presentation of Clinical Data
G6PD deficiency presents with multiple unique clinical presentations. They are: (4) favism; (5) newborn hyperbilirubinemia; (6) chronic hemolytic anemia; and (1) acute hemolytic anemia.
Hemolytic Acute Anemia
Acute hemolysis following exposure to oxidative stress, such as medications and infections previously stated, is the most typical manifestation. Male patients tend to acquire this kind of appearance. results from the lab auxiliary blood
• Hemoglobin levels are lower. Following hemolysis, there is an abrupt drop to 6–10 g/dL when an acute hemolytic episode is accompanied with:
• Pallor as a result of anemia developing suddenly.
• Dark urine passage brought on by hemoglobinuria.
Jaundice resulting from hemolysis.
• Reticulocyte count: Depending on the extent of hemolysis, it can rise to 20–25%. After hemolysis, reticulocytosis is a hallmark of the recovery phase.
• RBCs in a peripheral smear: They exhibit bite cells, polychromatophilia, bite spherocytes, and a moderate degree of anisopoikilocytosis.
- WBCs: Display a little leukocytosis.
- Platelets: Seem sufficient.
• Self-limited hemolysis: Hemolysis is self-limited because it mostly affects aged red blood cells. Hemoglobin levels begin to rise after around 10 days, and they may reach their normal level again in two months.
urinate
Hemolysis will result in hemoglobinuria, which could last for one to six days.
G6PD deficiency tests
The G6PD deficiency test results are positive. A few weeks following the acute hemolytic episode, G6PD levels should be evaluated due to elevated reticulocytes, which have high G6PD levels and may conceal G6PD insufficiency. The production of NADPH from NADP, as shown by quantitative spectrophotometric measurement or a quick fluorescence screening test, is the basis for the diagnosis of G6PD deficiency. Additional tests include the quantitative G6PD assay, the BCB declorization test, the methemoglobin reduction test (MRT), and PCR DNA analysis.
Non-spherocytic chronic hemolytic anemia
Patients with significant enzyme deficiencies will always have chronic hemolysis. This minor case of hemolytic anemia occurs when there is no known environmental trigger or infection.
Hyperbilirubinemia in neonates
Uncommonly, G6PD deficiency appears as newborn jaundice. A baby could get kernicterus.
Favism
Hemolysis can also happen after consuming fava beans (favism), which when digested, produce oxidants.
DEFICIENCY IN PYRUVATE KINASE
The most prevalent enzyme deficiency in the Embden-Meyerhof pathway is pyruvate kinase (PK) deficiency. The condition is autosomal recessive and results in congenital chronic hemolytic anemia. Increased reticulocytes and normocytic normochromic anemia are visible on the peripheral blood film.
• Red cell enzyme deficiencies that result in hemolytic anemias include PK and G6PD deficiency.
Glycolytic processes entail the involvement of these enzymes.
• By use of glutathione, glucose-6-phosphate dehydrogenase indirectly guards against oxidative damage to red blood cells.
• G6PD deficiency is an X-linked condition that manifests as neonatal jaundice or favism, chronic nonspherocytic hemolytic anemia, or acute hemolytic anemia (due to medication exposure or infection).
• Although it is not recommended to carry out the quantitative assay of red blood cell G6PD enzyme activity right away following the hemolysis episode, it will establish the diagnosis.
An autosomal recessive condition called pyruvate kinase (PK) deficiency results in congenital chronic hemolytic anemia.
