Sickle Cell Anemia

1. Sickle Cell Anemia • Hemoglobin HbA (adult) – α2β2 HbF (fetal) – α2γ2 • Sickle Cell Hemoglobin – a single E6V mutation in the β chain HbA (adult) – α2β2s

2. Normal vs Sickled Erythrocytes

3. DeoxyHb Fibers in Sickle Erythrocyte

4. Inter-molecular Contacts of HbS fibers

5. Defects of Sickled Erythrocytes • More rigid and adhesive – lodged in micro-vasculatures resulting in vascular occlusion • Microinfarction – kidney, impaired its ability to concentrate urine and produce erythropoietin • Altered ability to activate complement and defective granulocyte function - infections • Splenic sequestration of sickled erythrocytes results in hemolytic anemia and splenomegaly

6. Treatments of Sickle Cell Disease • Gene therapy • Prevention of infections - penicillin in children • Supportive managements of vaso-occlusive crises - pain killers, chronic heparin therapy • Hydroxyurea increases HbF levels to 15-20%, reducing frequency of vaso-occlusive crises • Prophylactic use, not for treatments of crises • Cytotoxic, side effects include GI effects (nausea, vomiting, diarrhea), dermatologic effect (macular papular rash, pruritus) and risk of secondary neoplasm (leukemia) with prolonged use • Hydroxyurea + Erythropoietin therapy?

7. REVIEW Anemia

8. Anemia • Caused by impaired rbc production • Hypochromic anemia • Megaloblastic anemia • Aplastic anemia • Sickle Cell anemia

9. Hypochromic Anemia • Microcytic rbc • Iron deficiency • Absorption: • duodenum and jejunuum • transported in blood by transferrin • heme iron >>> non-heme iron • ferrous salts >>> ferric salts • Cause: • dietary insufficiency; blood loss; interference of iron absorption • Treatments: • oral therapy: ferrous sulphate administered under fasting • parenteral therapy: iron dextran injection (im or iv)

10. Megaloblastic Anemia • Macrocytic rbc • Vitamin B12 or folate deficiency • Interrelationship of vitamin B12 and folate metabolism • methyltetrahydrofolate donates its methyl group to vitamin B12 • active metabolite N5,10-methylene tetrahydrofolate supports the conversion of dTMP to dUMP necessary for DNA synthesis

11. Vitamin B12 deficiency • Absorption • released from food and bound to Intrinsic Factor • absorbed through the mucosa of ileum • transferred by transcobalamin II in blood • uptake by liver or target cells • Cause: • dietary insufficiency; deficiency of Intrinsic Factor (Addisonian pernicious anemia); damage to ileal mucosa; deficiency of transcobalamin II (rare) • Treatments: • oral therapy to supplement deficient diet • cyanocobalamin injection (im or sc) for absorption problems

12. Folate deficiency • Absorption • Reduced and methylated • absorbed through the mucosa of duodenum and jejunum • transported in blood to liver or target cells • enterohepatic cycle of folate for reabsorption • Cause: • dietary insufficiency; malnutrition and alcoholism; damage to small intestine • Treatments: • oral preparations • Folic acid injection for absorption problems

13. Aplastic Anemia • Caused by disturbed stem cell kinetics • Erythropoietin • growth factor to stimulate rbc production • produced primarily by the kidney • recombinant erythropoietin for treatment of anemia in anephric patients; administered parenterally • Myeloid Growth Factors • GM-CSF: granulocyte/macrophage colony-stimulating factor • G-CSF: granulocyte colony-stimulating factor • Recombinant forms for treatment of neutropenia

14. Sickle Cell Anemia • Cause: • E6V mutation in the Hb β chain • Treatments: • Hydroxyurea increase the expression of HbF (α2γ2)

15. REVIEW Anti-thrombotic Drugs

16. Hemostasis and Thrombosis • Blood Coagulation • Platelet aggregation • Therapy of thrombosis • Anticoagulants • Anti-platelet drugs • Plasminogen activators • Anticoagulants and anti-platelet drugs for the prevention of the formation of thrombi • Plasminogen activators for lysis of existing thrombi

17. Heparin • Mechanism of action: • negatively charged sugar subunits • binds to lysine residues of anti-thrombin III to activate it • neutralizes thrombin and other clotting factors • Absorption: • highly charged • administered parenterally • crosses membranes poorly; drug of choice for pregnant women • Complications: • hemorrhage • heparin-induced thrombocytopenia

18. Coumarins/Warfarin (Oral anticoagulants) • Mechanism of action: • Vitamin K cycles between the KO and KH2 forms • Vitamin KH2 is required for the conversion of Glu to Gla in some clotting factors • Warfarin blocks the reduction of vitamin KO to vitamin KH2 • Absorption: • Given orally • 99% is albumin free in plasma, only the free form is active • crosses the placenta; cannot be used during pregnancy • Complications: • hemorrhage • drug interactions

19. Anti-platelet drugs • Aspirin • Dipyridamole • ADP receptor antagonists • Clopidogrel and Ticlopidine • GPIIb-IIIa or fibrinogen receptor antagonists • Abciximab, Eptifibatide and Tirofiban

20. Aspirin • Mechanism of action: • In activated platelets, arachidonic acid is released and metabolized by cyclooxygenase to the potent platelet agonists PGH2 and TXA2 • Aspirin acetylates cyclooxygenase, rendering it inactive • Complications: • Gastrointestinal bleeding • It also inhibits cyclooxygenase on endothelial cells to block the formation of PGI2, a natural platelet inhibitor • Recommended Uses: • Low doses

21. Dipyridamole • Mechanism of action: • An increase in cAMP in platelets inhibits platelet function by sequestering calcium into its platelet storage sites • Dipyridamole inhibits cAMP phosphodiesterases and increases platelet cAMP by preventing its breakdown • Complications: • Non-specific and not effective • Recommended Uses: • In combination with warfarin to prevent thromboembolism in patients with artificial heart valves

22. ADP Receptor Antagonists(Clopidogel and Ticlopidine) • Mechanism of action: • Blocks the P2Y12, an ADP receptor on platelets • Complications: • Nausea, dyspepsia, diarrhea, hemorrhage, leukopenia, anemia • Recommended Uses: • In combination with low dose aspirin • In aspirin-intolerant and aspirin-resistant patients

23. GPIIb-IIIa Antagonists(Abciximab, Eptifibatide, Tirofiban) • Mechanism of action: • Blocks fibrinogen binding to GPIIb-IIIa thereby inhibiting platelet aggregation • Complications: • Oral drugs not active • Recommended Uses: • Administered parenterally

24. Plasminogen Activator(t-PA, Urokinase, Streptokinase) • Fibrinolysis: • plasminogen is converted to plasmin which degrades fibrin clots • Tissue-type plasminogen activator (t-PA): • serine protease synthesized by endothelial cells • fibrin specific • Urokinase: • zymogen synthesized by kidney cells • fibrin specific • Streptokinase: • produced by β-hemolytic streptococci • complexed with plasminogen to change its conformation • NOT fibrin specific, degrades both fibrinogen and fibrin

25. REVIEW Anti-atherosclerotic Drugs

26. Atherosclerosis • LDL in blood penetrates into the subendothelium and becomes oxidized. • Oxidized LDL induces transmigration of monocytes and macrophages which ingest oxidized LDL to form foam cells and fatty streaks. • SMC proliferation and deposition of extracellular matrix materials results in atherosclerotic plaque formation. • Affects large and medium size arteries, major cause of heart attack and stroke • Elevated LDL and TG levels are associated with increased risk • HDL levels are inversely related to risk

27. Cholesterol and Triglyceride Metabolism • Exogenous pathway: • Chylomicrons (CM) are degraded by lipoprotein lipase • Uptake of TG by adipose tissue and muscle • Transport of cholesterol in CM remnants to liver • Endogenous pathway: • Liver synthesize and secrete VLDL • VLDL degraded by lipoprotein lipase to form IDL and LDL • Uptake of IDL and LDL by LDL receptor-mediated endocytosis • Transport of TG and cholesterol from liver to target cells

28. Cholesterol and Triglyceride Metabolism • Reverse transport of cholesterol: • As cells die, cholesterol is released and trapped in HDL • Cholesterol in HDL is esterified by LCAT and transferred to VDLD, which eventually is metabolized to IDL and LDL • De novo cholesterol synthesis: • Liver is the major site • HMG-CoA is the rate limiting enzyme • Enterohepatic Circulation: • Bile salt is synthesized from cholesterol in liver • Released to intestine and recycled

29. Drug Therapy • Bile salt sequestrants (colestipol, cholestyramine) • Anion exchange resins bind negatively charged bile acid • Increased cholesterol conversion to bile acid • Increased cholesterol synthesis and LDL receptor in liver • Increased LDL uptake by liver and decreased serum LDL and cholesterol levels • Increased HDL/LDL ratio • Niacin (nicotinic acid) • Inhibits a hormone-sensitive lipase involved in lipolysis in adipose tissue • Decreased free fatty acid available to the liver for TG synthesis • Decreased production and release of VLDL by liver • Decreased serum levels of VLDL, LDL, and TG • Decreased HDL clearance • Increased HDL/LDL ratio

30. Drug Therapy • Lovastatin (statins) • HMG-CoA reductase inhibitors • Cells express more LDL receptor • Decreased cholesterol and VLDL production and release by liver • Decreased HDL clearance • Increased HDL/LDL ratio • Fibrates (gemfibrozil) • Stimulate lipoprotein lipase • Increased VLDL clearance • Decreased serum TG and LDL • Decreased HDL clearance • Increased HDL/LDL ratio

31. Drug Therapy • Ezetimibe • Blocks cholesterol uptake by jejumal enterocytes • Reduced cholesterol incorporation into chylomicrons and delivery to liver • Increased expression of LDL receptor in hepatocytes • Decreased serum LDL levels • Increased HDL/LDL ratio

32. Ezetimibe • Action: inhibits dietary cholesterol uptake by jejunal enterocytes by binding to a key mediator of cholesterol absorption – Neimann-Pick C1-Like1 (NPC1L1). • Results: 1) reduction of cholesterol incorporation into chylomicrons and delivery to hepatocytes; 2) increased synthesis of cholesterol and LDL receptors in hepatocytes; 3) decreased serum LDL and cholesterol levels. • Advantages: clinically safe; effective; used as monotherapy in statin-intolerant patients; also used in combination with statins in statin-tolerant patients for further reduction of serum LDL and cholesterol. • Disadvantages: no effect on TG absorption; a new class of anti-atherosclerotic drug – long term effect not known.