Hepcidin,the key regulator of iron metabolism Dr.Hossein Ghaziasgar
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
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
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
Excess iron Is deposited in the liver, endocrine glands,the heart and the skin Tissue damage (in hereditary hemochromatosis)
Question Who is playing the central role in “orchestration” on iron metabolism? ?
Answer Hepcidin, the key regulator of iron metabolism
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
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)
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 )
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.
Hepcidin Controls extracellular iron by regulating: 1. Intestinal absorption 2. Recycling by macrophages 3. Releasing from stores 4. Placental transport
The Mechanism The major mechanism of Hepcidin function is “the regulation of transmembrane iron transport”.
HOW? Hepcidin binds to its receptor, protein FERROPORTIN, which serves as a transmembrane iron channel enabling iron efflux from cells.
THEN The Hepcidin-Ferroportin complex is degraded in lysosomes and iron is locked inside the cells (mainly enterocytes, hepatocytes and macrophages)
So Hepcidin lowers iron absorption in the intestine,lowers iron releasing from hepatocytes and macrophages Serum iron is decreased.
Ferroportin The sole protein exporter is located on: 1. the intestinal cells 2. hepatocytes 3. macrophages 4. placental cells
The second role Hepcidin is an acute phase protein type 2 and is increased in inflammation.
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)
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).
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.
But The mechanism is not known completely yet: In the liver the proteins: 1. HFE 2. Transferrin receptor 2 3. Hemojuvelin may be involved in mediating this signal
Regulation of Hepcidin synthesis by anemia and hypoxia Oxygen Hepcidin Uptake of diet iron Iron release from hepatocytes Iron release from macrophages
Continue Erythropoietic signal Hepcidin Tissue iron differic transferrin Hepcidin
Regulation of Hepcidin synthesis by inflammation Interleukin-6 Hepcidin iron anemia of chronic disease
The role of Hepcidin in hereditary hemochromatosis Hereditary hemochromatosis: -excessive intestinal iron absorption -Saturation of transferrin -Iron deposition in vital organs
Continue Mutations in: -HFE gene: most common form -TfR2 gene: much rarer -HAMP gene: Severe phenotype -HJV gene: Severe phenotype
The role of Hepcidin in anemia of inflammation This anemia results from: -Chronic infections -Noninfectious generalized inflammatory disorders -Some cancers -Sepsis
Continue IL-6 Hepcidin Hypoferremia anemia of inflammation
The role of Hepcidin in iron- loading anemias Ineffective erythropoiesis Increased intestinal iron absorption Increased ferritin Decreased Hepcidin
Hepcidin in differential diagnosis Decreased HepcidinIncreased Hepcidin Iron deficiency Increased and/or ineffective erythropoiesis Classical,,juvenile and TfR2 HH High iron stores Anemia of chronic disease Ferroportin disease(?)
Hepcidin assays Serum Prohepcidin:50-150 ng /mL Serum Hepcidin :1-500 ng/mL (based on 2007 findings)
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.
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( )
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