Transcript Mechanisms of induction & prevention of iron induced

Iron Toxicity and Clinical
Sequelae
John B. Porter, MA, MD, FRCP
Professor
Department of Haematology
University College London
London, United Kingdom
Learning Objectives
• Analyze the mechanisms contributing to
the development of iron overload and the
clinical consequences of iron overload on
the liver, heart, and endocrine system.
• Utilizing an understanding of the factors
contributing to the development of iron
overload, identify patients at risk in the
practice setting.
Topics
• Causes of iron overload
• Mechanisms of iron-overload–mediated toxicity
–
–
–
–
Molecular level
Non–transferrin-bound iron—extracellular
Labile iron pool—intracellular
Free radical formation
 Microscopic level
 Macroscopic level
• Clinical impact consequences of iron overload
Conditions Associated with Iron Overload
Transfusional
Nontransfusional
Complications
Age of onset
Thalassaemia major1
Blackfan Diamond Anaemia1
Fanconi’s Anaemia1
Early stroke with HbSS1
Type 2 haemochromatosis (rare)2
2a hemojuvelin2
2b hepcidin2
Childhood
(Risks from HH)
Type 1 haemochromatosis1
Thalassaemia intermedia1
Typically adult
Severe haemolytic anaemias1
Aplastic anaemia1,2
Other transfusion in HbSS1
Myelodysplasia (MDS)3
Repeated myeloablative
chemotherapy1
Slide courtesy of Dr. J. Porter.
1. Porter JB. Br J Haematol. 2001;115:239. 2. Brittenham G. In Hoffman R, et al, ed. Hematology: Basic
Principles and Practice, 4th ed. Philadelphia, PA: Churchill Livingstone, 2004. 3. Taher A, et al. Semin
Hematol. 2007;44:S2.
Acquired, Nontransfusional
Forms of Iron Overload
• Chronic liver disease
– Hepatitis C
– Alcoholic liver disease
– Nonalcoholic steatohepatitis
• Porphyria cutanea tarda
• Portacaval shunting
• Inappropriately high dietary intake
– Latrogenic (eg, treatment of microcytosis)
– African (Bantu) siderosis*
*Dietary and hereditary components.
Bacon BR. In Goldman L, ed. Cecil’s Textbook of Medicine, 23rd ed. Philadelphia, PA: SaundersElsevier, 2008.
Rare Abnormalities of Iron Distribution
Condition
Cause
Aceruloplasminaemia Plasma reductase
AR1,2
Iron Distribution Effects
Retina
Basal ganglia
Pancreas
Retinopathy
Extrapyramidal
Diabetes
Hallervorden-Spatz
AR3
Pantotenate kinase
Basal ganglia
cysteine accumulation
Extrapyramidal
Neuroferritinopathy
AD4
Ferritin light chain
Basal ganglia
Forebrain
Cerebellum
Extrapyramidal
Parkinsonian
Freidrich’s Ataxia5,6
AR
Frataxin
oxidative stress
Mitochondrial
Sensory neurons
Spinal cord
Dorsal root ganglia
Myocardium
Ataxia
Cardiomyopathy
AR = autosomal recessive; AD = autosomal dominant.
1. Mariani R, et al. Gut. 2004;53:756-8. 2. Hellman NE, et al. Gut. 2000;47:858-60. 3. Hayflick SJ. Curr
Opin Pediatr. 2003;15:572-7. 4. Crompton DE, et al. Blood Cells Mol Dis. 2002;29:522-31. 5. Koepen A,
et al. Acta Neuropahtol. 2007;114:163-73. 6. Michael, et al. Cerebellum. 2007;5:257-67.
How Does Transfusional
Iron Loading Develop?
Simplified Iron Turnover and Storage
Erythron
2g
20–30 mg/day
20–30 mg/day
Other
parenchyma
0.3 g
Red
Transferrin
Macrophages
0.6 g
20–30 mg/day
Hepatocytes 2–3 mg/day
1g
1–2 mg/day
Gut
Porter J. Hematol/Oncol Clinics. 2005;19(suppl 1):7.
Rate of Iron Loading from Transfusion
• Simple estimation1
– 1 unit contains 200 mg of iron
– Adult may receive 4–10 g/y from transfusion
• More-precise method2
– Volume of blood transfused x mean haematocrit of
processed blood obtained from the transfusion centre
x 1.08
• For exchange transfusion need to know
– Volume and haematocrit transfused
– Volume and haematocrit removed
1. Taher A, et al. Semin Hematol. 2007;44:S2.
2. Porter JB. Br J Haematol. 2001;115:239.
Transfusional Iron Overload
Transfusion
Erythron
Parenchyma
20–40 mg/day
(0.3–0.7 mg/kg/day)
Parenchyma
NTBI
Hepatocytes
Hepatocytes
Red
Transferrin
Macrophages
Gut
NTBI = non–transferrin-bound iron.
Adapted from Porter JB. Hematol/Oncol Clinics. 2005;19(suppl 1):7-12.
Liver Iron and Risk from Iron Overload
250
Thalassaemia major
40
200
30
HH homozygote
150
20
Threshold for cardiac
disease and early death
100
Increased risk of
complications
50
10
HH heterozygote
Normal
0
0
10
HH = hereditary haemochromatosis.
Olivieri N, Brittenham G. Blood. 1997;89:739.
20
30
Age (years)
0
40
50
Hepatic Iron (mg/g, dry weight)
Hepatic Iron (µmol/g wet weight)
50
How Do Inherited Nontransfusional
Forms of Iron Loading Develop?
Effect of Hepcidin on Iron Turnover
Erythron
20–30 mg/day
Hepatocytes
IL6
Iron
20–30 mg/day
Hypoxia
+
Macrophages
Transferrin
2–3 mg/day
20–30 mg/day
Prohepcidin
1–2 mg/day
Hepcidin
Gut
Adapted from Porter JB. Hematol/Oncol Clinics. 2005;19(suppl 1):7.
Factors Affecting Hepcidin
Expression?
Hepcidin
+
•
•
•
•
•
•
•
TfR21
HJV2
Oral iron1
Iron stores1,2
LPS2
IL-62
HFE1
•
•
•
•
-
Erythropoiesis1
Anaemia1
Hypoxia1
NTBI?
Tf = transferrin; TfR = transferrin receptor; HJV = hemojuvelin; LPS = lipopolysaccharide;
IL = interleukin; NTBI = non–transferrin-bound iron.
1. Leong W, Lönnerdal B. J Nutr. 2004;134:1.
2. Lee P, et al. Proc Natl Acad Sci U S A. 2004;101:9263.
Classification of Haemochromatosis
Type 1
Type 2A
Type 2B
Type 3
Type 4
Gene
HFE
HJV
HAMP
(hepcidin)
TFR2
Ireg1
Ferroportin 1
Function
Interact with
TfR1
Unknown
Regulates
iron export
Iron uptake Iron export
Inheritance
Incidence
Recessive
Common
Recessive
Rare
Recessive
Rare
Recessive
Rare
Liver
hepatocyte
Liver
Duodenum
hepatocyte Macrophage
Tissues affected Liver;
Skeletal
hepatocytes
muscle,
macrophages heart,
liver
Clinical
presentation
Late variable
Early onset Early onset
Severe
Severe
Hepcidin levels
With permission from Worwood M. Blood Rev. 2005;19:69.
Severe
Dominant
Rare
Variable
??
Why Is Iron Overload Toxic?
Redox Cycling of Iron
Fe 2+
+
e
- eFe
Slide courtesy of Dr. J. Porter.
3+
Hydroxyl Radical (HO.) Generation
Haber Weiss Reaction
O2.- +
H2O2
----->
O2 + OH- + HO.
Catalysed by Iron in two steps; (Fenton reaction)
Fe3+ +
O2.-
----->
Fe2+ + O2
Fe2+ +
H2O2
----->
Fe3+ + OH- + HO.
Porter J. Hematol/Oncol Clinics 2005;19(suppl 1):7.
Lipid Peroxidation by HO.
.
Hydrogen abstraction ( H.)
H 2O
Molecular rearrangement
.
O
O
.
+ O2 Oxygen uptake
Peroxyl radical
propagates peroxidation by abstracting H.
from another fatty acid
Lipid hydroperoxide
O
O
H
Decomposition
eg, to MDA
Porter J. Hematol/Oncol Clinics 2005;19(suppl 1):7.
With permission from Gutteridge JM, Halliwell B. Baillieries Clin Haematol. 1989;2:195.
Consequences of Iron-Mediated
Toxicity
Increased free iron
Hydroxyl radical generation
Lipid peroxidation
Organelle damage
TGF-b1
Lysosomal fragility
Enzyme leakage
Collagen
synthesis
Cell death
Fibrosis
Gutteridge JMC, Halliwell B. Bailleres Clin Haematol. 1989;2:195-256. Bacon BR, et al, J Clin Invest. 1983;71:429-439.
Myers BM, et al. J Clin Invest. 1991;88:1207-1215. Tsakamota H, et al. J Clin Invest. 1995;96:620-630.
Houglum K, et al. Hepatology.1997;26:605-610.
20
Nature of NTBI
• Nature of NTBI
– Citrate iron




Polymeric
Oligomeric
Dimeric
Monomeric
Slowly chelated
Rapidly chelated
• Protein-bound iron
– Binds weakly to albumin
– As citrate oligomers bound to albumin
• Other
NTBI = non–transferrin-bound iron.
Evans R et al. J Biol Inorg Chem. 2007;13:57.
Uptake of NTBI
Receptors
• Divalent metal transporter (DMT1)1
– Enterocytes
– Erythron (negatively regulated by iron loading)
– ? Other
• L-type calcium-dependent channels2
– Myocardium (positively induced by iron loading)
– Anterior pituitary (positively induced by iron loading)
• T-type calcium channels3
– Hepatocytes (positively induced by iron loading)
1.Bacon BR. In Goldman L, ed. Cecil’s Textbook of Medicine, 23rd ed. Philadelphia, PA: SaundersElsevier, 2008. 2. Oudit GY, et al. Circulation. 2004;109:1877. 3. Rafique et al. Blood. 2006;108:1542a.
Antioxidant Capacity in Iron Overload
• 48 thalassaemia major (age 11–22 years)
• Vitamin E and NTBI negatively correlate (r = -0.81)
• No correlation with serum ferritin
Lycopene
Ubiquinol
Vitamin E
Ubiquinone
Vitamin A
B-carotene
Vitamin C
0
20
40
60
% Decrease of Control
Slide courtesy of Dr. J. Porter.
De Luca C, et al. Free Radic Res. 1999;30:453.
80
Intracellular Iron-Mediated Toxicity
from Labile Intracellular Iron
Ferritin
Nontransferrin
iron
Labile
iron pool
(LIP)
Transferrin
iron
Free-radical generation
Organelle damage
LVDCC = L-type voltage-dependent calcium channel.
Porter JB. Am J Hematol. 2007;82:1136.
Lysosomal
degradation
Iron
proteins
Where Is Iron Toxic ?
Transfusional Iron Overload
Transfusion
Erythron
Parenchyma
20–40 mg/day
(0.3–0.7 mg/kg/day)
Parenchyma
Hepatocytes
Hepatocytes
NTBI
Transferrin
Gut
NTBI = non–transferrin-bound iron.
Adapted from Porter JB. Hematol/Oncol Clinics 2005;19(suppl 1):7.
Macrophages
Iron Distribution in
Transfusional Overload
• Transfusional overload distribution differs from
absorption distribution at early stages1
• Why great variability in iron distribution in
different tissues?
– Liver, endocrine glands, anterior pituitary1
– Very little in brain, skeletal muscle1
– Liver iron correlates with units transfused2
1. Porter JB. Hematol/Oncol Clinics 2005;19(suppl 1):7.
2. Taher A, et al. Semin Hematol. 2007;44:S2.
Distribution of Body Iron at Postmortem
in TM in Prechelation Era
Skeletal muscle
Testes
Kidney
Heart
Adrenal
Salivary gland
Minimum
Maximum
Thyroid
Pancreas
Liver
Parathyroid
0
2
4
Fe % d.w.
Tm = thalassaemia major; d.w. = dry weight.
Adapted from Modell B, Mathews R. Birth Defects Orig Artic Ser. 1976;12:13.
6
8
Liver and Iron Content Postmortem in
Thalassaemia Major
Liver
Heart
Causes of Death in Thalassaemia
Age (years)
0–4
5–9
10–14
15–19
>20
Total
Heart disease
0
6
39
35
16
96
Infection
2
6
9
3
0
20
Liver disease
0
0
2
7
1
10
Malignancy
2
2
1
1
2
8
Endocrine disease
0
0
2
1
1
4
Accident
0
0
2
2
0
4
Thromboembolism
0
0
2
1
1
4
Anaemia
2
0
0
0
0
2
Other
0
1
1
0
1
3
Unknown
0
1
3
3
1
8
Total
6
16
61
53
n = 1078
Zurlo MG, et al. Lancet. 1989;2:27.
23
159
Blood Transfusion and Cardiac Iron Deposits
at Postmortem in the Prechelation Era
Patients with Cardiac Iron (%)
131 transfused adult patients
100
• 101 leukaemias
•
30 other anaemias
80
60
40
20
0
0–25
26–50 51–75 76–100 101–200 201–300
Units of Blood Transfused
Slide courtesy of Dr. J. Porter.
Buja LM, Roberts WC. Am J Med. 1971;51:209.
20
18
16
14
12
10
8
Upper
Normal
Limit
6
4
Blood Units Transfused
Slide courtesy of Dr. J. Porter.
Jensen PD, et al. Blood. 2003;101:4632.
150
125
100
75
0
50
2
25
Estimated Heart Iron (µmol/g)
Blood Transfusion Predicts Heart Iron
in Unchelated Patients
Is the Heart Equally at Risk of Iron Loading
in All Forms of Transfusional Iron?
UCLH patients with cardiac MRI
Sickle (n = 37)
Myelodysplasia (n = 7)
Diamond Blackfan (n = 7)
PK deficiency (n = 9)
Congenital sideroblastic (n = 4)
Thalassaemia intermedia (n = 23)
Thalassaemia major (n = 108)
0
20
40
60
Patients (%, n) with T2* < 20 ms
Glanvillle J, et al. Presented at ASH 2006. Blood. 2006;108:abstract 1553.
80
NTBI in Sickle Cell or Thalassaemia Major
Matched for Liver Iron Concentration
8
Patients Treated at UCLH
P = 0.0001
7
NTBI (µM)
6
5
4
3.38 ± 2.4
3
2
1
0
0.17 ± 1.8
-1
-2
HbSS
Thalassaemia major
LIC = 4.34
LIC = 4.22
Slide courtesy of Dr. J. Porter.
Shah F. Presentation at ASH Dec 2002. Blood 2002;100:668a.
Which Forms of Iron Are Most Toxic?
Labile Toxic Iron Pools?
• NTBI in plasma?
– Correlates with antioxidant depletion
– Promotion of lipid peroxidation in vitro
– BUT which species?
• Labile iron pools (LIP) in cells?
– In vitro: clear evidence linking free iron to lipid peroxidation and
organelle damage
• Clinical evidence?
– Improvement in cardiac performance with intravenous
desferrioxamine precedes changes in cardiac iron
– BUT direct link of NTBI or LIP to clinical damage not established
Porter J. Hematol/Oncol Clinics. 2005;(suppl 1):S7.
Absolute Tissue Levels?
• Evidence (serum ferritin) >2500 µg/L & cardiac
disease-free survival1
• Liver iron association with cardiac death2
 Of 15/53 thalassaemia major patients with cardiac disease,
all had liver iron >15 mg/g dry weight3
– Association or causation?
• But
– Iron in different tissues at postmortem does not
correlate with damage to those organs3
– Link of cardiac iron to damage & death not known3
1. Olivieri NF, et al. N Engl J Med. 1994;331:574.
2. Brittenham GM, et al. N Engl J Med. 1994;331:567.
3. Porter JB. Hematol/Oncol Clinics. 2005;19(suppl 1):S7.
Intracellular Iron Levels and Toxicity
• Concepts
– “Safe iron”
 No toxicity in heterozygotes of hereditary haemochromatosis
where liver levels < 7mg/g dry weight.1
– “Dangerous iron”
 High risk of cardiac death if liver >15 mg/g dry weight.1
• Limitations
– Uneven distribution within and between tissues2
– Relationship between heart iron and mortality
unknown2
1. Porter JB. Br J Haematol. 2001;115:239.
2. Porter J. Hematol/Oncol Clinics. 2005;19(suppl 1):7.
Functional Consequences
of Transfusional Iron Overload
• Liver1
• Heart1
• Endocrine system1
• Cancer
• Other potential sequelae
– Arthropathy2
– Hyperpigmentation2
1. Porter JB. Hematol/Oncol Clinics. 2005;19(suppl 1):S7.
2. Brittenham G. In Hoffman R, et al, ed. Hematology: Basic Principles and Practice, 4th ed.
Philadelphia, PA: Churchill Livingstone, 2004.
Organ Systems Affected by Iron Overload
Organ
Consequences
Pituitary
Hypogonadotrophic hypogonadism1
Thyroid
Hypothyroidism1
Parathyroid
Heart
Liver
Pancreas
Hypoparathyoidism1
Cardiomyopathy1
Skin
Cirrhosis, carcinoma1
Diabetes1
Pigmentation2
Gonads
Hypogonadotrophic hypogonadism1
Joints
Arthropathy2
1. Taher A, et al. Semin Hematol. 2007;44:S2.
2. Brittenham G. In Hoffman R, et al, ed. Hematology: Basic Principles and Practice, 4th ed.
Philadelphia, PA: Churchill Livingstone, 2004.
Conclusions
• Conditions associated with iron overload include transfusional iron
overload as well as hereditary and acquired nontransfusional iron
overload
• Because the body has no mechanism for excretion of excess iron,
iron can accumulate
• Iron accumulation results in
– Increased free iron
– Hydroxyl radical generation
– Lipid peroxidation
• This results in cell death and fibrosis, with impact on a variety of
organ systems and functional consequences
– Heart
– Liver
– Endocrine system