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Iron Overload and Iron Chelation: the Inside Story

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Iron Overload and Iron Chelation: the Inside Story Iron Overload and Iron Chelation: The Inside Story Jerry L. Spivak, MD Professor of Medicine and Oncology Johns Hopkins University School of Medicine Baltimore, Maryland [email protected] Iron as a Prosthetic Group • Oxygen transport - Hemoglobin, myoglobin • Cell proliferation - Ribonucleotide reductase • Electron transport - Flavoproteins • Respiratory enzymes - Cytochromes • Oxidases - Catalase • Reductases - Cytochromes Body Iron Stores (♂) Hemoglobin 2.5 gm Myoglobin/heme and nonheme 0.4 gm enzymes Ferritin/hemosiderin 1.0 gm(2/1ratio) Transferrin 0.005 gm There is no normal mechanism for iron excretion above physiologic losses “Tales From the Crypt” Iron Absorption and the Mucosal Iron Block Stomach Sugars, Duodenum pHamino acids pH and Vitamin C Fe++ Heme-Fe Fe +++ Dctyd (ferri-reductase) Heme-Fe Mature enterocyte DMT1 HCP-1 Ferritin Fe++ Fe+++ Mitochondria Hephaestin FPN (Hepcidin) Other processes Plasma transferrin Enterocyte precursor Enterocyte precursor (Macrophage) (Macrophage) Noniron-loaded Iron-loaded FPN (Ceruloplasmin) Ferritin/Fe++ Fe+++ Fe++ Hepcidin Other cells Iron Balance in Adults Gastrointestinal Absorption 1-2 mg/day Storage Iron Functional iron Liver cells and 18 mg Plasma transferrin Bone marrow Macrophages 4 mg Red cell hemoglobin 1000 mg Myoglobin Cytochromes 2500 mg Physiologic daily iron loss 1-2 mg/day Natural Modifiers of Iron Absorption Iron Absorption Inhibitors Spinach ,whole grains such as buckwheat and amaranth, other vegetables such as chard and rhubarb, as well as beans and nuts, all contain significant levels of oxalic acid, which binds with iron, inhibiting its absorption. Soy beans contain phytic acid, which also bind iron. Tea and coffee contain tannins, which block iron absorption. Clay and heavy metals also inhibit iron absorption. Iron Absorption Enhancers •Meat/fish/poultry •Vitamin C-rich fruits: oranges, cantaloupe, strawberries, grapefruit •Vegetables: broccoli, brussel sprouts, tomato, tomato juice, potato, green & red peppers •White wine Iron Turnover in the Anemia of Chronic Disease Gastrointestinal Absorption <1 mg/day Hepcidin Storage Iron Hepcidin Functional iron Liver cells and Plasma transferrin Bone marrow RES 2 mg Red cell hemoglobin 1500 mg Myoglobin Cytochromes 2000 mg Physiologic daily iron loss 1 mg/day Hepcidin Regulation* *IL-6 and LPS also activate hepcidin expression Semin Liver Dis 31:280, 2011 Preservation of the MCHC at the Expense of the MCV Blood 20: 173, 1962 Iron Regulatory Proteins •HFE • Senses cellular iron uptake • Tfr-2 Iron overload • Senses cellular iron uptake • Hemojuvelin No anemia • Upregulates Hepcidin (with Tfr-2 (HJV) and HFE) • Hepcidin • Downregulates Ferroportin • DMT1 • Imports GI iron Iron overload • Ferroportin (FPN) • Exports intracellular iron to Tf anemia • Tfr-1 • Receptor for Tf-bound iron • Hephaestin and • Iron oxidases (cellular and ceruloplasmin circulating) Essential Factors in Erythropoiesis and the Effect of Cancer, Inflammation or Infection • Intensity of the stimulus • Erythropoietin production is suppressed by cytokines and iron overload • Functional capacity of the • Erythroid progenitor cell bone marrow proliferation is suppressed by cytokines and erythropoietin lack • Iron is sequestered and its • Available nutrients absorption is inhibited by hepcidin • Red cell survival • Red cell survival is reduced and blood loss is increased due to diagnostic testing Role of Iron Sequestration in the Anemia of Chronic Disease • There is no impairment of utilization of absorbed iron • There is no impairment of plasma transferrin iron uptake by erythroid cells • Reduced transferrin receptor expression and decreased iron utilization are primarily consequences of EPO deficiency • Iron therapy cannot correct the anemia of chronic disease in the absence of tissue iron deficiency • Pharmacologic concentrations of EPO can correct the anemia of chronic disease but not iron deficiency anemia • Correction of the anemia of chronic disease with EPO can occur without a change in the serum iron abnormalities • Correction of the anemia of chronic disease with EPO is associated with mobilization of iron stores and sometimes iron deficiency Hypoxic Regulation of Erythropoietin Production N Engl J Med 348:1282, 2003 Effect of Iron Administration on the Serum Erythropoietin Level 1600 10 sEpo, mU/mL 1400 Hb, g/dL 9 1200 1000 8 800 7 Hgb, g/dL 600 Serum Epo (mU/ml) 400 6 200 Fe Rx 0 5 –2 0 2 4 6 8 10 12 Time (days) Blood 91:2139, 1998 Br J Haematol 94:288, 1996 Hepcidin Expression is Subordinate to Tissue Hypoxia Increased storage iron J Clin Invest 110:1042, 2002 Serum Immunoreactive Erythropoietin in Iron Deficiency Anemia 100 80 60 P <.005 40 sEPO (mU/ml) 20 0 9.5–9.9 10.0–10.4 10.5–10.9 11.0–11.4 Hgb (g/dL) Transfusion According to the Hemoglobin Level in MDS Hemoglobin gm % Time (months) B J Haematol 94:288, 1996 Blood Transfusion – Bypassing a Natural Barrier Body Iron Homeostasis • After intake, iron is normally sequestered in complexes: – Serum transferrin • Iron transport protein in blood/extracellular fluid • Capacity can be exceeded resulting in Nontransferrin-Bound Iron (NTBI) – NTBI is the most toxic form of iron – Ferritin • Binds intracellular iron • High levels in the serum reflect iron overload but can be affected by NASH, inflammation (Still’s disease and cancer) infection (hematophagocytosis, hepatitis) • A transferrin saturation < 45 % with a high serum ferritin (>400 ng/mL) is characteristic of inflammation or liver disease, not iron overload, where the transferrin saturation is always > 50 % and often > 95 % Iron excess as a Toxin Increased transferrin saturation (>50 %) leads to deposition of iron in nonerythroid tissues such as the heart, liver and pancreas leading to: Congestive heart failure Hepatic fibrosis Diabetes mellitus and other endocrinopathies Increased susceptibility to infection Increased transferrin saturation leads to the accumulation of nontransferrin-bound iron (NBTI), labile or bound to other proteins, and free radical formation. (Fenton reaction) The generation of free hydroxyl radicals causes tissue damage through oxidative reactions with proteins, lipids and nuclei acids. Potential Mechanisms for Iron-induced Cellular Injury Int J Hematol 76:219, 2002 Measures of Body Iron Content • Serum iron • Diurnal variation, affected by diet inflammation and infection • Serum transferrin • Affected by nutrition, liver disease, inflammation, infection and FPN and ceruloplasmin mutations • Serum ferritin • An acute phase reactant, specific only if low. Correlation with LIC = 0.63 • Liver biopsy • Defines iron storage site and liver histology. May not correlate with cardiac iron burden • Liver iron by MRI • May not correlate with cardiac iron status • Cardiac MRI (T2*) • Correlates with cardiac function • Bone marrow aspirate • Considered the “gold standard” but is invasive and not always technically adequate Serum Ferritin: Disadvantages LIC Predicts Total Body Iron Liver MRI Correlation With Biopsy Correlation between Plasma Ferritin (Pl Fer) and Hepatic Iron Concentration LIC Pl Fer Months of chelation therapy R = 0.63 Brit J Haematol 89:880, 1995 Am J Hematol 42:81, 1993 Causes of Extreme Hyperferritinemia (>1500 µg/L) World J Gastroenterol 12:5866, 2006 BBA 1763:700, 2006 Hereditary (HFE) Hemochromatosis • An autosomal recessive disorder due to a C282Y mutation and rarely an H63D mutation in Northern Europeans (0.3-1.2 % prevalence) with variable penetrance • Serum ferritin is elevated in 84 % of men and 65 % of female C282Y homozygotes • Serum ferritin is > 1000 µg in 37 % of men and 3% of female C282Y homozygotes • If baseline ferritin is < 1000 µg , < 50 % of men and 20 % of females exceeded 1000 µg after 12 years • If baseline ferritin is < 1000 µg at age 55, < 15 % progressed to > 1000 µg in 12 years • Iron overload was present in 28 % of men and 1 % of women at age 65. • Iron overload with C282Y/H63D is rare without other risk factors such as liver disease • C282Y homozygosity doubles the colon cancer risk in everyone and the breast cancer risk in women’ • H63D homozygosity triples the hereditary nonpolyposis colon cancer risk • Environmental cofactors are alcohol, hepatic steatosis and viral hepatitis • Non-citrus fruits are protective • An elevated transferrin saturation (> 45 %) is the earliest clue • Phlebotomy should start if the ferritin is if there is evidence of iron overload to achieve a ferritin of 50 µg • Liver biopsy is indicated for a ferritin >1000 µg and abnormal liver function Major Complications of Iron Overload • Cirrhosis • Hepatic fibrosis (reversible with phlebotomy) • Hepatocellular cancer • Diabetes mellitus • Arthritis • Cardiomyopathy • Hypogonadism • Hypothyroidism • Pituitary-adrenal axis impairment • Increased susceptibility to infection (MDS) • Increased risk of leukemic transformation (MDS) • Impaired survival post BMT Terminal Heart Failure due to Cardiac Iron Overload Circulation 30: 698,1964 Cardiac Disease is the Major Cause of Death in β-Thalassemia Lancet 334:27, 1989 Correlation Between NTBI and Transferrin Saturation Am J Hematol 84:29, 2009 Survival in MDS According to Diagnosis (WHO criteria) J Clin Onc 23:7594, 2005 Survival of MDS patients by transfusion dependence (N = 467) Overall survival Leukaemia-free survival (HR = 1.91; p < 0.001) (HR = 1.84; p = 0.001) 1.0 Transfusion independent 1.0 Transfusion independent 0.9 Transfusion dependent 0.9 Transfusion dependent 0.8 0.8 0.7 0.7 0.6 0.6 0.5 0.5 0.4 0.4 0.3 0.3 0.2 0.2 0.1 0.1 Cumulative proportion surviving
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