Enzyme Deficiency and Anaemia

MADE BY APHRODITE PASCOE ENZYME DEFICIENCY AND ANAEMIA COMPOSITION OF BLOOD I. SOLID PHASE • It comprises or erythrocytes/haematids (red blood cells), leukocytes (white blood cells) and thrombocytes (platelets) II. LIQUID PHASE • Comprises of proteins, metabolites and ions. - Blood with anticoagulant centrifuges supernatant is plasma while blood without anticoagulant centrifuged supernatant is serum. ERYTHROCYTES ✓ They have no nucleus; hence, nucleus. ✓ Its main function in vertebrates is to deliver oxygen from lungs to tissues. ✓ People living at high altitudes with low oxygen partial pressure will have more RBCs. ✓ A typical RBC contains about 270 million Hb molecules. ✓ Erythrocyte production is called erythropoiesis. Erythrocytes are continuously produced in bone marrow of large bones and in high amounts (2 million per second). ✓ In the embryo, liver is the main site of RBC production. ✓ Erythrocyte production is induced by erythropoietin (EPO) which is secreted from kidney. Erythropoietin is used as doping hormone in sports. ✓ Reticulocytes are RBCs which are just before and after leaving the bone marrow. They develop from stem cells and they are enucleated cells but retain the capacity for protein synthesis. ✓ Erythrocytes develop from reticulocytes in 7 days and stays in circulation for about 120 days. ✓ In RBCs there are two metabolic pathways related to carbohydrates: o Glycolysis o Pentose phosphate pathway (ppp) Metabolism: Anaerobic glycolysis ➢ Erythrocytes carry out anaerobic glycolysis and net 2 moles of ATP are synthesized and 2 moles of NAD+ are reduced to 2 moles of NADH per mole of glucose and last product is lactate. ➢ In erythrocytes, there is a lactate export system which pumps lactate to circulation. Then, lactate goes to liver where it is converted to glucose and given to circulation. The glucose comes to erythrocytes or goes to muscles. Each molecule of ATP produced is used to pump 3Na+ out and 2k+ in. Thus; i. The flexibility of membranes is maintained, and ii. The concave form of erythrocytes is preserved. The NADH produced is used; i. NAD+ regeneration: Pyr + NADH → NAD +lactate ii. metHb red: Met-Hb (Fe ) + NADH → Hb (Fe ) + NAD + 3+ 2+ + Metabolism: Glycolysis and PPP Functions of PPP ✓ NADPH production ✓ Production of pentose phosphate ✓ To divert monosaccharides to glycolysis NADPH Production i. Glucose-6-phosphate dehydrogenase ii. 6-phophogluconate dehydrogenase (6PGD) NADPH is used in: a. Biosynthesis: NADPH functions as reducing agent (e.g.; fatty acid biosynthesis etc.) b. Reduction: reduction of GSSG (oxidized glutathione) to GSH (reduced glutathione) occurs by the below reaction; + GSSG + NADPH + H → 2GSH + NADP Glutathione reductase (GR) is the enzyme involves. STRUCTURE GSH AND THIOL BUFFER Thiol buffer has a critical role on the survival of living organisms. GSH plays a central role on the protection of cells against harmful agents. GSH is used in: a. Reduction of vit E and C b. Reduction of thiol groups of erythrocyte proteins c. Detoxification of drugs and chemicals by conjugation d. Protects the functional thiol groups of hemoglobin and other proteins in erythrocytes. e. Essential to keep the erythrocyte membrane intact f. Essential for the detoxification of hydrogen peroxide and other peroxides. Results of Blockage of NADPH production due to enzyme deficiency? ➢ NADH and ATP production decreases ➢ Hb denatures and accumulates as “Heinz bodies” ➢ The decrease in NADH will result in the accumulation of met-Hb ➢ GAL3P dehydrogenase oxidized and glycolysis stops. ANEMIA Anaemia is obtained from greek word “an-haima” meaning without blood. It is a deficiency or RBCs and hemoglobin. Anaemia and clinical consequences Oxygen is required for survival of all human cells. Anaemia causes capacity of blood to transport oxygen to tissues to decrease; hypoxia develops which leads to a wide range of damaging clinical consequences The deficiency of enzymes in erythrocyte metabolism triggers hemolytic anaemia In anaemia, pyruvate kinase, glucose-6-phosphate dehydrogenase (G6PD) and phosphohexoisomerase (PHI) are observed enzyme deficiencies. The deficiency of G6PD results in spherocytic anaemia (Favism) ➢ It is an x-dependent mutation ➢ Clinical manifestation is hemolysis due to low NAPDH ➢ It’s the most common genetic deficiency. ➢ In erythrocytes the major function of NADPH is to reduce GSSG ➢ Normal enzyme homozygotes will die from malaria ➢ Only people with heterozygotes G6PD can survive ➢ G6PD mutation and malaria maps overlap Reaction involved Formation of Oxidative stress and its results ➢ It is formed as a result of infection, drugs or vicia fava. ➢ Oxidative stress results in the formation of reactive oxygen species (ROS) ➢ Oxidative stress will trigger formation of “Heinz bodies” from hemoglobin which will cause extravascular hemolysis. Erythrocytes and Oxidative Stress ➢ Erythrocytes with damaged membranes due to ROS are destroyed by macrophages located in spleen, liver and bone marrow. ➢ Favism (G6PD deficiency) is characterized by acute hemolysis of RBCs following the ingestion of fava beans (vicia fava) by G6PD deficient people. ➢ Fava bean contain high amount of oxidative agents. G6PD deficiency and drug-induced anaemia ➢ Drugs used in malaria treatment such as sulfonamides will cause the hemolysis of erythrocytes. There drugs in absence of GSH produce ROS. ➢ ROS will oxidize lipids found in the RBC membrane and distort membrane structure. Pyruvate Kinase deficiency and Anaemia PEP + ADP → ATP + Pyruvate PK is enzyme involved. ➢ Pyruvate kinase constitutes the second energy production and control step in glycolysis. ➢ There are 3 isozymes: o R-form in erythrocytes o L-form in liver o K(or M2) form in kidney and liver: M- form in muscle. ➢ Pk deficiency is the most common and important form of hemolytic anemia; it is transmitted as an autosomal recessive trait. Its deficiency is characterized by nonspherocytic chronic hemolytic anemia. ➢ PK deficiency results to decrease of ATP in RBCs. ➢ Low ATP interferes with membrane ion gradient and distorts the membrane structure. ➢ Splenomegaly is observed in PK deficient individuals ➢ PK deficiency may cause hemolytic disease (jaundice) in the newborns. ➢ PK deficient patients may tolerate anemia rather well due to high (2,3-BPG) as a result of the block of glycolysis. Therefore, Oxygen dissociates much more easily from Hb in presence of high (2,3-BPG) Phosphohexoisomerase Deficiency ➢ PHI (phosphoglucoisomerase, PGI) catalyzes the following reaction G-6-P ↔ F-6-P ➢ PGI will supply G6P to PPP and Glycolysis ➢ The single gene enzyme, PGI, is a dimer of subunit Mr of 60 kDa. ➢ PGI deficiency is associated with the hemolytic disease of the newborn.