RED WHITE BLOOD CELLS DR AMINA TARIQ BIOCHEMISTRY

RED &WHITE BLOOD CELLS DR AMINA TARIQ BIOCHEMISTRY

Blood has two distinct parts to it. Plasma, the fluid part of the blood, takes up about 55% of the blood volume. Plasma is 91% water with various other materials in solution and suspension, such as dissolved proteins, nutrients, electrolytes, hormones, and metabolic wastes.

The cellular portion of blood normally makes up about 45% of the blood volume. It consists primarily of white blood cells (WBCs), platelets, and red blood cells (RBCs). The white blood cells are the mobile elements of the body's defense system. Platelets are small cell fragments which play an important part in blood clotting

RED BLOOD CELLS Biomedical Importance Structure of Hb Function of Hb Porphyrias Jaundice Iron metabolism Anemias

STRUCTURE OF RBC A very simple cell. Major function is to transport oxygen to the tissues. And disposal of carbon dioxide and protons formed by the tissue metabolism. Is composed of a membrane surrounding the hemoglobin. Hb forms about 95% of the intracellular protein of the red cell.

There are no intracellular organelles, such as mitochondria, lysosomes or golgi apparatus. Non- nucleated. Metabolically is active. Biconcave shape increases the surface to volume ratio of RBC, thus facilitating the gas exchange. Contain cytoskeletal components that play an important role in determining its shape.

RBC contains certain enzymes of nucleotide metabolism. At the end of their life span, globin is degraded to amino acids which are reutilized in the body. Iron is released from heme and also reutilized, and porphyrins are converted to bilirubin.

Life span of RBC is 120 days. Production of red cells is regulated by erythropoeitin.

Erythropoeitin: It is a glycoprotein of 166 amino acids. It is a major regulator of human erythropoiesis. It is synthesized mainly in the kidney. Is released in response to hypoxia into the blood stream, and travel to bone marrow. There it interacts with the progenitor of red cells -Burst forming unit-erythroid (BFU-E). Recombinant DNA (anemia of renal failure)

MEMBRANE OF RED CELL Membrane is a lipid bilayer. 50% lipids and 50% proteins. Major lipids are phospholipids and cholesterol. Major phospholipids are: PC, PE, PS and sphingomyelin. Choline containing phospholipids are in the outer leaflet(PC, Sph). Amino containing phospholoipids are in the inner leaflet (PE, PS).

Glycosphingolipids constitute about 5 -10%. These constitute neutral GSLs, gangliosides and complex species, including ABO blood group substances. 10 major proteins and 100 minor species. Major proteins include: spectrin, ankyrin, anion exchange proteins, actin and band 4. 1. Many of the proteins are glycoproteins.

ASPECTS OF RBC METABOLISM Glucose dependent (glucose transporters). Anaerobic glycolysis for ATP production. No mitochondria, no oxidative phosphorylation. Transporters on the membrane. Production of 2, 3 BPG. Pentose Phosphate pathway. Methemoglobin reductase. Synthesis of glycogen, fatty acids, proteins and nucleic acids does not occur in the RBC.

Glucose Transporter – GLUT 1 is present on RBC. It is an example of facilitated transport. Not dependent on insulin. It generates a gated pore in the membrane and to permit the passage of glucose.

Transporters maintain the ionic and water balance. It involves the movement of Cl⁻ and HCO 3( anion exchange protein). In RBC it is called band 3. It is important in adjusting the levels of RBC HCO 3 ⁻ concentration in arterial and venous blood.

DISORDERS AFFECTING RBCS Iron deficiency anemia Methemoglobinemia Sickle cell anemia Thalassemias Megaloblastic anemias ( B 12 , folic acid) Hereditary spherocytosis G 6 PD deficiency Pyruvate kinase deficiency Paroxysmal nocturnal hemoglobinemia

G 6 PD deficiency It is an inherited disorder. Characterized by the hemolytic anemia. Caused by the inability to detoxify oxidizing agents. It is the most common disease producing enzyme deficiency in the world. It is X-linked disorder.

Decreased G 6 PD activity impairs the ability of the cell to form NADPH. Which is responsible for the maintenance of reduced glutathione. Glutathione also helps maintain the reduced states of sulfhydryl groups in proteins including Hb. When these proteins are oxidized it leads to the denaturation of these proteins. That form insoluble masses called Heinz Bodies.

These bodies attach to the red cell membrane. Membranes become rigid and deformable. G 6 PD deficiency occurs in all the cells , but is most severe in RBCs. Because other cells are able to produce NADPH by alternate pathway(NADP dependent malate dehydrogenase).

Precipitating Factors: Oxidant drugs(AAA- antibiotics, antimalarials and antipyretics). Favism. Infection. Neonatal jaundice

Caused by Missense point mutations. Variant forms: 1. G 6 PD A⁻ - Moderate form of disease. 2. G 6 PD Mediterranean – Severe form of disease.

PROTECTION OF RBC Several powerful oxidants are produced in the course of metabolism, in both blood cells and other cells of the body. These include superoxide, hydrogen peroxide, peroxyl radicals and hydroxyl radicals. These are known as reactive oxygen species. Superoxide dismutase, Catalase and Glutathione protect red cell from these ROS.

SOD convert O⁻ 2 into H 2 O 2. Catalase detoxify H 2 O 2 to H 2 O. Glutathione also does the same.

NEUTROPHILS

BIOCHEMICAL FEATURES Active glycolysis Active pentose phosphate pathway Moderate oxidative phosphorylation Rich in lysosomes. Unique enzymes and proteins. E. g. myeloperoxidase , NADPH oxidase, Contain CD 11/ CD 18 integrins in plasma membrane.

IMPORTANT ENZYMES & PROTEINS Myeloperoxidase- responsible for the green color of the pus. Deficiency causes chronic infections. NADPH oxidase- responsible for the respiratory burst. Lysosomes- Abundant in macrophages. Defensins- Antibiotic peptide, kills bacteria by causing membrane damage.

Lactoferrin- It is an iron binding protein, inhibits growth of certain bacteria by binding iron. CD 11/ CD 18 - Adhesion molecules. Receptors for the Fc fragment of Ig. Gs- bind Fc fragment of Ig. G molecule. Vasoactive biomolecules (plate activating factor, eicosanoids).

PROTEINASES Elastase Collagenase Gelatinase Cathepsin G Plasminogen activator

ANTIPROTEINASES α-1 antitrypsin α-2 macroglobulin Secretory leukoproteinase inihibitor α-1 antichymotrypsin Plasminogen activator inhibitor-1 Tissue inhibitor of metalloproteinase.

ACTIVATION OF NEUTROPHILS They are activated by specific receptors. By interaction with bacteria, chemotactic factors, antigen -antibody complexes. Intracellular calcium rises and activates protein kinase C.

RESPIRATORY BURST It involves NADPH oxidase and helps kill bacteria. There are two mechanisms – oxygen dependent and oxygen independent for killing bacteria.

Oxygen independent mechanism: These involve p. H changes in phagolysosmes And Lysosomal enzymes to kill bacteria.

Oxygen dependent mechanism: It includes myeloperoxidase system(MPO) and NADPH oxidase system. It is the most potent bactericidal mechanism. Microorganism is internalized. NADPH oxidase converts molecular O 2 into superoxide radical. This rapid conversion is called respiratory burst. Then superoxide is spontaneously converted into hydrogen peroxide.

This product is then neutralized by catalase or glutathione peroxidase. In the presence of Myeloperoxidase which is a lysosomal enzyme, Hydrogen peroxide plus chloride ions are converted to hypochlorous acid. This kills the bacteria. Hypochlorous acid is the major component of household bleach.

Mutations in the genes encoding NADPH oxidase leads to a disease called chronic granulomatosis. In which severe chronic pyogenic infections occur.

LEARNING RESOURCES Harpers Biochemistry Lippincott's Biochemistry