Eric Niederhoffer SIU-SOM What affects the normal functions of an erythrocyte? A 4-year-old African boy is brought in by his adoptive parents who say that he has pain in his limbs and does not want to walk

Red Blood Cell: Biochemistry and Sickle Cell Disease RBC structure size, spectrin, channels Metabolism glycolysis (2,3-BPG), pentose phosphate pathway (G6PDH, NADPH), glutathione Hemoglobin genes, heme, Mb/Hb (normal), HbS (defect), fibers (sickling and inflammation), thalassemia

An Erythrocyte (RBC) Reference Ranges RBCs, male x 10 6 /µL female x 10 6 /µL Hb, male g/dL female g/dL Hct, male41-53% female36-46% MCH pg MCV fL MCHC31-36 % Practical Values 65% of Fe in Hb 1 g Hb = 3.46 mg Fe 1 mL blood at 15 g/dL Hb = 0.5 mg Fe RBC x 3 = Hb Hb x 3 = Hct Microcytic < 80 fL Macrocytic > 100 fL

Erythrocyte Membrane Composition

RBC Metabolic Pathways 2,3-BPG BPG mutase 2,3-BPG phosphatase PPP NADPH 6PG 3-7 C metabolites (R5P, F6P, G3P) G6PDH lactonase 6PGDH CO 2 NADP + + H + GSH GSSG GR GP H2O2H2O2 H2OH2O Glc Pyr G6P 1,3-BPG 3PG HK PGI PK F6P G3P PFK aldolase F16BP DHAP 2PG PEP PGK PGM enolase G3PDH Glycolysis Lactate No O 2 LDH

Hemoglobin Genes and Gene Products

Hemoglobin Gene Product Production Mehta, A. B., and A. V. Hoffbrand Haematology at a glance, Blackwell Science, Malden, Mass. HbF: 2α and 2γ HbA1: 2α and 2β HbA2: 2α and 2δ HbE: 2ζ and 2ε Yolk sacLiverSpleenBone marrow

Myoglobin and Hemoglobin Structure deoxyHb deoxyMb     oxyHb (HbO 2 ) O2O2 O2O2 O2O2 O2O2 Glu6→Val6 oxyMb (MbO 2 ) O2O2

Hemoglobin Structure Changes

Sickle Cell Disease Rare combinations of HbS with HbD Los Angeles, HbO Arab, G-Philadelphia, among others (>6 major genotypes) at least 1 sickle gene, hemoglobin S (HbS) ≥ 50% Hb present. homozygotic HbSS (sickle cell anemia) - HbS = 100% Hb present HbSbeta-0 thalassemia - Severe double heterozygote for HbS and beta-0 thalassemia; almost indistinguishable from sickle cell anemia phenotypically (MCV low) HbSC disease - Double heterozygote for HbS and HbC, with intermediate clinical severity HbS/hereditary persistence of fetal hemoglobin (S/HPHP) - Mild form or symptom free HbS/HbE syndrome - Rare and generally mild clinical course

Hemoglobin Electrophoresis Homozygous HbS Normal neonate Normal adult HbSC Heterozygous HbS Relative protein charge

Molecular Changes of HbS Daniel J. Harrington, D. J., K. Adachi, and W. E. Royer, Jr J. Mol. Biol. 272(3): Heme Val

Molecular and Cellular Changes of HbS Decreased P O 2 Permanent damage to RBC Cellendothelium interactions

Effects of Therapy with Hydroxyurea ★★★

Thalassemias α-thalassemia β-thalassemia HbH (β 4 ) Hb Barts (γ 4 )

Review Questions What proteins compose the membrane of erythrocytes? What metabolic pathways are used in erythrocytes? What is hemoglobin; what changes with sickle cell disease? What clinical observations would you make concerning patients with SCD? What are the thalassemias?