به نام یگانه هستی بخش

1. به نام یگانه هستی بخش

2. MODERN INSIGHTS INTO ANEMIA

3. Hepcidin,the key regulator of iron metabolism • Dr.Hossein Ghaziasgar

4. IRON • An essential element ,must be precisely regulated • Intestinal absorption is essential for the iron balance ,but the precise mechanism of its regulation was unknown

5. Conservation of iron • Recycling from Hb .(about 20 mg/day) • Iron absorption in the duodenum • Deposition in the liver (hepatocytes) The coordination is essential and vital

6. BUT • Humans and other mammals lack effective mechanisms to excrete excess iron (the daily loss of iron from the body is 1-2mg/day) Intestinal iron absorption is the sole means of iron balance

7. Excess iron • Is deposited in the liver, endocrine glands ,the heart and the skin Tissue damage (in hereditary hemochromatosis)

8. Question • Who is playing the central role in “orchestration” on iron metabolism? ?

9. Answer • Hepcidin ,the key regulator of iron metabolism

10. What is Hepcidin? • Was first identified in human urine and plasma in June 2000 • A 25-amino acid disulfide-rich peptide • Molecular weight about 2 KDa • Is highly folded and cationic amphipathic

11. What is Hepcidin? • It was recognized as an antimicrobial peptide ( Defensin-like) and is produced in the liver and excreted in urine. • Of course recent studies detected Hepcidin synthesis in bacteria-activated neutrophils and macrophages (at a lower level)

12. What is Hepcidin? • In addition to the 25-amino acid form ,the urine also contains 20- and 22-amino acid forms (but the role is not identified) • Hence the bioactive form is the 25-amino acid form which contains 4 disulfide bands (Hepcidin 20- has been found in serum too, in 2007 )

13. Hepcidin gene • Is named HAMP • Contains 3 exons : • produces 84-amino acid preprohepcidin 60-amino acid prohepcidin 25-amino acid hepcidin • Has also been identified in other vertebrates like mice , rats , pigs and several species of fish.

15. Hepcidin • Controls extracellular iron by regulating: • Intestinal absorption • Recycling by macrophages • Releasing from stores • Placental transport

16. The Mechanism The major mechanism of Hepcidin function is “the regulation of transmembrane iron transport”.

17. HOW? • Hepcidin binds to its receptor, protein FERROPORTIN , which serves as a transmembrane iron channel enabling iron efflux from cells.

18. THEN • The Hepcidin-Ferroportin complex is degraded in lysosomes and iron is locked inside the cells (mainly enterocytes, hepatocytes and macrophages)

19. So • Hepcidin lowers iron absorption in the intestine ,lowers iron releasing from hepatocytes and macrophages Serum iron is decreased.

20. Ferroportin • The sole protein exporter is located on: • the intestinal cells • hepatocytes • macrophages • placental cells

21. The second role • Hepcidin is an acute phase protein type 2 and is increased in inflammation.

22. Hormonal activity of Hepcidin • Lack of Hepcidin results in Hemochromatosis (iron deposition in the liver ,pancreas and macrophages) • Hepcidin excess results in severe iron –deficiency (blocking intestinal iron uptake and iron releasing from hepatocytes and macrophages and inhibiting the placental transport of iron too)

23. Continue • Injected synthetic 25-amino acid Hepcidin causes 75% decrease in serum iron levels within 1 hour persisting for more than 2 days. • By a decrease in Hepcidin level , erythroid regulation can increase iron uptake 40mg/day(normal 1-2 mg/day).

24. Regulation of Hepcidin synthesis by iron • Dietary iron induces Hepcidin synthesis • Urinary Hepcidin concentrations are greatly increased within less than 1 day after iron ingestion.

25. But • The mechanism is not known completely yet: • In the liver the proteins: • HFE • Transferrin receptor 2 • Hemojuvelin may be involved in mediating this signal

26. Regulation of Hepcidin synthesis by anemia and hypoxia • Oxygen Hepcidin Uptake of diet iron Iron release from hepatocytes Iron release from macrophages

27. Continue • Erythropoietic signal Hepcidin • Tissue iron differic transferrin Hepcidin

28. Regulation of Hepcidin synthesis by inflammation • Interleukin-6 Hepcidin iron anemia of chronic disease

29. The role of Hepcidin in hereditary hemochromatosis • Hereditary hemochromatosis: -excessive intestinal iron absorption -Saturation of transferrin -Iron deposition in vital organs

30. Continue • Mutations in: -HFE gene: most common form -TfR2 gene: much rarer -HAMP gene: Severe phenotype -HJV gene: Severe phenotype

31. The role of Hepcidin in anemia of inflammation • This anemia results from: -Chronic infections -Noninfectious generalized inflammatory disorders -Some cancers -Sepsis

32. Continue IL-6 Hepcidin Hypoferremia anemia of inflammation

33. The role of Hepcidin in iron-loading anemias • Ineffective erythropoiesis • Increased intestinal iron absorption • Increased ferritin • Decreased Hepcidin

34. Hepcidin in differential diagnosis

35. Hepcidin assays • Immunoassay (urine ,UCLA) • Mass spectrometry (urine ,serum) • Elisa (for Prohepcidin)

36. Hepcidin assays • Serum Prohepcidin:50-150 ng /mL • Serum Hepcidin :1-500 ng/mL (based on 2007 findings)

37. Continue • Hepcidin in urine is affected by multiple freeze/thaw cycles. Serum is more stable. • High diurnal variation of especially serum Hepcidin. • Use of internal standard:Hepcidin-24 to control for matrix influences and instrumental settings.

38. Overall summary • Hepcidin -Is a recently discovered liver produced 25 amino-acid peptide -Is a regulator of iron metabolism that controls iron absorption and macrophage iron release. -Is regulated by erythropoietic needs( ) ,body iron stores( ) and inflammation( )

39. Overall summary • MS Hepcidin assay for urine and serum: -Precludes the need for Hepcidin specific antibodies -Will provide: -information on etiology of iron metabolism disorders -leads for new therapeutic strategies -novel diagnostic approaches

40. BEST REGARDS Dr.Ghaziasgar