Starry Starry Night - Vincent 2012 - 2013

1. Prayer for New Beginnings
God of new beginnings, we are walking into
mystery.
We face the future, not knowing what the
days and months will bring us or how we
will respond.
Be love in us as we journey.
May we welcome all who come our way.
Deepen our faith to see all life through your
eyes.
Fill us with hope and an abiding trust that
You dwell in us amidst all our joys and
sorrows.
Thank You for the treasure of our faith life.
Thank You for the gift of being able to rise
each day with the assurance of
Your walking through the day with us.
God of our past and future, we praise you.
AMEN

2. NOEL MARTIN S. BAUTISTA, MD, DPPS, MBAH
Department of Biochemistry, Molecular Biology and Nutrition
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3. 3
Road Map
 Understand the metabolism of Iron in the body
 Distribution of iron
 Sources of iron
 Absorption of iron
 Metabolism of iron
 Disorders of iron metabolism
 Understand the chemistry of Porphyrins
 Understand the metabolism of Heme in the body
 Biosynthesis of heme
 Regulation of the synthesis of heme
 Disorders of heme synthesis
 Degradation of heme
 Disorders of heme degradation
share IRON AND HEME METABOLISM

4. 4
METABOLISM
IRON AND HEME METABOLISM

5. 5
Iron
 important trace mineral; essential for
function of numerous proteins in cells
 oxygen transport, electron transfer, xenobiotic
metabolism
 expression of proteins involved in iron
uptake and sequestration carefully
regulated to ensure that iron supplies are
adequate
 meet metabolic needs but not in excess to
cause toxic damage
IRON AND HEME METABOLISM

6. 6
Iron
 exists in two ionic states
 ferrous: reduced form (Fe+2)
 ferric: oxidized form (Fe+3)
 different forms important in
oxidation-reduction reactions
 ETC, oxygen-binding molecules
 excess – damage to cells and tissues by
formation of free radicals (ROS)
IRON AND HEME METABOLISM

7. 7
IRON AND HEME METABOLISM

8. 8
Iron: Forms
 iron exists in a wide range of
oxidation states, −2 to + 6,
 +2 and +3 are the most
common and biologically
important
IRON AND HEME METABOLISM

9. 9
Iron: Functions
 oxidation-reduction reactions of energy
metabolism
 component of many enzyme system that
create ATP and energy
 structural/functional
component of hemoglobin
(blood) and myoglobin
muscle
 carries oxygen
IRON AND HEME METABOLISM

10. 10
Iron: Distribution
 human body: 4–5 g
iron (protein-bound)
 heme proteins
(~72%)
 hemoglobin (2.5 g)
 myoglobin (0.15 g)
 transport and
storage proteins
(~26%)
 transferrin (1.0 g)
 serum ferritin (0.0001 g)
 iron–sulfur clusters
(<1%)
 cofactors in the
respiratory chain, other
redox chains
IRON AND HEME METABOLISM

11. 11
Iron: Dietary Sources
 average American diet: 10-50 mg iron
 heme iron – readily absorbed
 animal source: meat, fish and poultry
 not found in milk or dairy products
 non-heme iron – not readily absorbed
 source: mostly plant products which contains
phytates, tannins, oxalates that chelates /
precipitates iron
 iron supplements
IRON AND HEME METABOLISM

12. Iron: Dietary Sources
IRON AND HEME METABOLISM

13. 13
Iron: Sources of Heme Iron
spinach IRON AND HEME METABOLISM

14. 14
IRON AND HEME METABOLISM

15. 15
Iron: Absorption
 occurs predominantly in the
duodenum and upper
jejunum
 tightly regulated since there is
no physiologic pathway for its
excretion
 feedback mechanism
(“iron guarding”)
 enhances iron absorption in
individuals who are iron
deficient
 dampens iron absorption
people with iron overload
IRON AND HEME METABOLISM

16. 16
Iron: Absorption
 physical state of iron (duodenum) greatly
influences its absorption
 ferrous iron (Fe2+) is better absorbed
 ferric (Fe3+) iron forms large complexes (with anions,
water and peroxides) which have poor solubility
 at physiological pH, ferrous iron (Fe2+) is rapidly
oxidized to the insoluble ferric (Fe3+) form
 gastric acid lowers the pH in the proximal duodenum,
enhancing the solubility and uptake of ferric iron
 when gastric acid production is impaired (acid
pump inhibitors, e.g., prilosec), iron absorption is
reduced substantially
factors IRON AND HEME METABOLISM

17. Iron: Factors Affecting Absorption
Physical State
(bioavailability) heme > Fe2+ > Fe3+
phytates, tannins, soil/clay (pica), laundry
Inhibitors
starch, iron overload, antacids
Competitors lead, cobalt, strontium, manganese, zinc
ascorbate, citrate, amino acids, iron
Facilitators deficiency, stomach acid, high altitude,
exercise, pregnancy
overview IRON AND HEME METABOLISM

18. Iron: Absorption
HT, Heme Transporter; HO, Heme Oxidase; FP, Fe2+ Transporter; HP, Hephaestin; TF,
transferrin; DMT1, Divalent Metal Transporter 1

19. 19
Iron: Absorption
 proximal duodenum
 Incoming Fe3+ is reduced
to Fe2+ by a ferrireductase
 vitamin C in food 
reduction of Fe3+ to Fe2+
 transfer of iron from the
apical surfaces into inside
of enterocytes by a proton-
coupled Divalent Metal
Transporter (DMT1)
IRON AND HEME METABOLISM

20. 20
Iron: Absorption
 inside the enterocyte, iron can either be
stored as ferritin or transferred across the
basolateral membrane into the plasma,
where it is carried by transferrin
IRON AND HEME METABOLISM

21. 21
Iron: Absorption
 passage across the
basolateral
membrane: possibly
iron regulatory
protein 1 (IREG1) or
Fe2+ Transporter
(FP).
 IREG1 (FP) protein
may interact with the
copper-containing
protein hephaestin
 hephaestin: ferroxidase activity  release of iron from
cells
 Fe2+ is converted back to Fe3+, the form in which it is
transported in the plasma by transferrin
regulation IRON AND HEME METABOLISM

22. 22
Iron Absorption: Regulation
 complex and not well understood
 occurs at the level of the
enterocyte
 “mucosal block” - further
absorption of iron is blocked if a
sufficient amount has been taken
up
 “erythropoietic regulation”
– iron absorption appears to be
responsive to the overall
requirement of erythropoiesis
metabolism IRON AND HEME METABOLISM

23. 23
Iron Metabolism: Overview
 iron is absorbed from the diet
 transported in the blood in transferrin
 stored in ferritin
 used for the synthesis of cytochromes,
iron-containing enzymes, hemoglobin, and
myoglobin
 lost from the body with bleeding and
sloughed-off cells, sweat, urine, and feces
IRON AND HEME METABOLISM

24. Iron: Metabolism

25. 25
Iron Metabolism: Overview
 Key proteins
 Transferrin (Tf) - serum Fe+3 transport
protein
 Transferrin Receptor (TfR) - cellular
uptake
 Ferritin - cellular Fe+3 storage protein
 Hemosiderin - denaturated, insoluble
ferritin
IRON AND HEME METABOLISM

26. 26
Iron: Transport
 Transferrin (Tf)
 -globulin with a mass of 80 kDa
 plays a central role: transports iron
 monomeric protein with two similar domains,
each of which binds an Fe3+ ion
 glycoprotein and is synthesized in the liver
 if not bound to iron, it is known as apo-
transferrin, a single chain glycoprotein
composed of 2 homologous lobes which can
independently bind a single Fe3+
IRON AND HEME METABOLISM

27. 27
Iron: Transport
 Lactoferrin (Lf)
 Lactotransferrin
 transfer iron and control the level
of free iron in the blood
 multifunctional protein of the transferrin
family
 globular glycoprotein with 80 kDa MW
 widely represented in various secretory
fluids, such as milk, saliva, tears other
secretions
 better iron retention at low pH
IRON AND HEME METABOLISM

28. 28
Iron: Transport
 Transferrin and Lactoferrin
 maintain the concentration of free iron in body
fluids at values below 10–10 mol L–1
 low level prevents bacteria that require free
iron as an essential growth factor from
proliferating in the body
IRON AND HEME METABOLISM

29. 29
Cellular Iron Uptake
 transferrin (Tf) binds to
transferrin receptors (TfRs) on
the external surface of the cell
 complex is internalized into an
endosome, where the pH ~ 5.5
 iron separates from the
transferrin molecule, moving
into the cell cytoplasm
 iron transport molecule
shuttles the iron to various
points in the cell, including
mitochondria and ferritin
 ferritin molecules accumulate
excess iron
IRON AND HEME METABOLISM

30. 30
Cellular Iron Uptake
 acid pH inside the lysosome
causes the iron to dissociate
from the protein
 unlike the protein component
of LDL, apoTf is not
degraded within the
lysosome but remains
associated with its receptor,
returns to the plasma
membrane, dissociates from
its receptor, re-enters the
plasma, picks up more iron,
and again delivers the iron to
needy cells
IRON AND HEME METABOLISM

31. 31
Iron: Storage
 Ferritin
 where excess iron is stored
(liver, spleen, bone marrow)
 normally, little ferritin in human serum, but
level correlates with total body stores
 450 kDa protein consisting of 24 subunits
(hollow sphere)
 binds Fe2+ ions, which are oxidized to Fe3+
and deposited in the interior of the sphere as
ferrihydrate
 can contain 3000-4500 ferric atoms
balance IRON AND HEME METABOLISM

32. 32
Iron: Homeostasis
 synthesis of the transferrin receptor (TfR) and that of
ferritin are reciprocally linked to cellular iron content
 specific untranslated sequences (iron response
elements, IREs) of the mRNAs for both proteins
interact with a cytosolic protein (iron-responsive
element-binding protein or IRPs) sensitive to variations
in levels of cellular iron
IRON AND HEME METABOLISM

33. 33
Iron: Homeostasis
 when iron levels are low
 IRE-binding protein (IRP) binds to IRE of ferritin
mRNA, so translation of ferritin mRNA is inhibited
 IRE-binding protein (IRP) binds to IRE of TfR
mRNA  synthesis of TfR proceeds
IRON AND HEME METABOLISM

34. 34
Iron: Homeostasis
 when iron levels are high
 IRE-binding protein cannot bind to IRE of ferritin
 translation of ferritin mRNA proceeds
 IRE-binding protein cannot bind to IRE of TfR 
degradation of TfR mRNA (no translation of TfR)
IRON AND HEME METABOLISM

35. 35
Iron: Homeostasis
IRON AND HEME METABOLISM

36. 36
Iron: Storage
 Hemosiderin
 a somewhat ill-defined
molecule
 appears to be a partly
degraded/denatured form of
ferritin but still containing iron
 iron within deposits of
hemosiderin is very poor
source of iron when needed
 detected by histologic stains
(eg, Prussian blue) for iron;
presence is determined
histologically when excessive
storage of iron occurs
DO IRON AND HEME METABOLISM

37. 37
Iron Metabolism: Disorders
 reduced iron level: negatively affects the
function of oxygen transport in red blood
cells
 consequences of reduced iron intake or
absorption
 increased iron level: bind to and form
complexes with numerous
macromolecules  disruption in normal
activities of the affected complexes
 consequences of excess iron intake and
storage
IRON AND HEME METABOLISM

38. 38
Iron Deficiency Anemia (IDA)
 sideropenic anemia
 ↓iron intake and/or ↑iron
excretion (loss)
 ↓ globin protein content in red
blood cells as a consequence
of the heme control of globin
synthesis
 microcytic (small) and
hypochromic (low pigment)
red blood cells
IRON AND HEME METABOLISM

39. 39
IDA: Causes
 decreased iron intake/absorption
 inadequate diet, impaired absorption, gastric surgery,
celiac disease
 increased iron loss
 gastrointestinal bleeding (hemorrhoids, peptic ulcer,
neoplasm, ulcerative colitis, hiatal hernia or the
gastritis associated with chronic alcohol consumption)
 excessive menstrual flow, blood donation, disorders
of hemostasis
 increased physiologic requirements for iron
 infancy, pregnancy, lactation
 idiopathic hypochromic anemia
IRON AND HEME METABOLISM

40. 40
IDA: Symptoms
 attributable to anemia
 fatigue, dizziness, headache,
palpitation, dyspnea, lethargy,
disturbances in menstruation and
impaired growth in infancy
IRON AND HEME METABOLISM

41. 41
IDA: Symptoms
 deficiency of iron
 irritability, poor attention
span, lack interest in
surroundings, poor
academic/work performance,
behavioral disturbances
 pica is the habitual ingestion
of unusual substances like
earth, clay, laundry starch or
ice
 usually a manifestation of iron
deficiency and is relieved when
the deficiency is treated
IRON AND HEME METABOLISM

42. 42
IDA: Treatment
 diagnosis: determine the cause and
source of the excess bleeding
 supplementation: oral ferrous sulfate to
replace iron loss; IV iron therapy may be
necessary
 severe cases: packed red blood cells
transfusion
IRON AND HEME METABOLISM

43. 43
Hereditary Hemochromatosis
 primary or type 1
 siderosis
 excessive iron absorption, saturation of
iron-binding proteins and deposition of
hemosiderin in the tissues
 primary affected tissues are the liver
pancreas and skin
IRON AND HEME METABOLISM

44. 44
Hereditary Hemochromatosis
 iron deposition in the liver,
pancreas and heart leads to
cirrhosis/liver tumors, diabetes
mellitus and cardiac failure
 excess iron deposition leads to
bronze pigmentation of the
organs and skin
 bronze skin pigmentation seen
in hemochromatosis +
resultant diabetes: bronze
diabetes
IRON AND HEME METABOLISM

45. 45
Hereditary Hemochromatosis
 normal HFE: forms
a complex with the
transferrin receptor
(TfR)  regulate
the rate of iron
transfer into cells
 mutation in HFE 
increased iron
uptake and
substitution of Cys 282 by a Tyr
storage
IRON AND HEME METABOLISM

46. 46
Secondary Hemochromatosis
 severe chronic hemolysis of any
cause, including intravascular
hemolysis and ineffective
erythropoiesis (hemolysis within the
bone marrow)
 multiple frequent blood transfusions
for hereditary anemias
 excess dietary iron / iron
supplementation
 other disorders
 cirrhosis (alcohol abuse)
 steatohepatitis of any cause
 porphyria cutanea tarda
 prolonged hemodialysis
IRON AND HEME METABOLISM

47. 47
Hemochromatosis: Treatment
 routine phlebotomy
(bloodletting)
 may be fairly frequent,
perhaps as often as once a
week, until iron levels can be
brought to normal range
 iron chelators
 deferoxamine - binds with
iron in the bloodstream and
enhances its elimination via
urine and feces
 deferasirox, deferiprone
IRON AND HEME METABOLISM

48. 48
porphyrins IRON AND HEME METABOLISM

50. 50
Porphyrins
 cyclic compounds formed by
the linkage of four pyrrole rings
through (=HC-) methenyl
bridges
 characteristic property:
formation of complexes with
metal ions bound to the
nitrogen atom of the pyrrole
rings
 iron porphyrin such as heme of
hemoglobin
 magnesium-containing
porphyrin chlorophyll
 cobalt in cobalamine
IRON AND HEME METABOLISM

51. 51
Porphyrins
 compounds in which
various side chains are
substituted for the eight
hydrogen atoms
numbered in the porphin
 rings are labeled I, II, III,
and IV
 substituent positions on
the rings are labeled 1,
2, 3, 4, 5, 6, 7, and 8
 methenyl bridges (=HC-)
are labeled α, β, γ, and δ
IRON AND HEME METABOLISM

52. 52
Porphyrins
 Fischer proposed a
shorthand formula:
 rings are labeled I,
II, III, and IV
 methenyl bridges
are omitted
 each pyrrole ring is
shown as indicated
with the eight
substituent
positions numbered
IRON AND HEME METABOLISM

53. 53
Porphyrins:
Substituents
 M : methyl : -CH3
 A : acetyl : -CH2COOH
 P : propionyl : -CH2CH2COOH
 V : vinyl : -CH=CH2
IRON AND HEME METABOLISM

54. 54
Porphyrins: Type I
 APAPAPAP
 completely
symmetric
arrangement of
the acetyl (A) and
propionyl (P)
substituents
 uroporphyrins
were first found in
the urine, but they
are not restricted
to urine
IRON AND HEME METABOLISM

55. 55
Porphyrins: Type III
 APAPAPPA
 arrangement of the
acetyl (A) and
propionyl (P)
substituents in the
uroporphyrin is
asymmetric
 in ring IV, the
expected order of the
A and P substituents
is reversed
 type III series is far
more abundant
 it includes heme
IRON AND HEME METABOLISM

56. 56
Coproporphyrin I and III
 substituents are methyl (M) and propionyl (P)
 first isolated in feces but are also found in
urine
IRON AND HEME METABOLISM

57. 57
Protoporhyphyrin III
 precursor of heme
 substituents are methyl
(M) and vinyl (V)
 MVMVMPPM
 position of the methyl
group is reversed on
the fourth ring,
 sometimes considered
as type IX; designated
ninth in a series of
isomers by Fischer
name IRON AND HEME METABOLISM

58. 58
Name That Porphyrin!
Coproporphyrin III Uroporphyrin I
IRON AND HEME METABOLISM

59. 59
Name That Porphyrin!
Uroporphyrin III Coproporphyrin I
IRON AND HEME METABOLISM

60. 60
Name That Porphyrin!
Protoporphyrin III (IX)
IRON AND HEME METABOLISM

61. 61
Name That Porphyrin!!!
Protoporphyrin III (IX)
HM IRON AND HEME METABOLISM

63. Biosynthesis
of Heme

64. 64
Heme: Biosynthesis
 bone marrow – incorporation into Hgb
 liver – requirement for cytochromes
 eight enzymatic steps, first and last
three steps: mitchondrial
 organic portions of heme derived from 8
residues of glycine and succinyl CoA
 porphyrinogens – intermediates
involved in reactions involving the side
groups
IRON AND HEME METABOLISM

65. 65
STEP 1: Biosynthesis of -Aminolevulinic
Acid (ALA)
 Succinyl CoA (TCA) condenses with glycine,
subsequent decarboxylation to yield -aminolevulinate
(ALA)
 catalyzed by ALA synthase
 synthesis of ALA occurs in mitochondria
 pyridoxal phosphate activates glycine
IRON AND HEME METABOLISM

66. 66
STEP 2: Biosynthesis of Phorphobilinogen
 2 molecules of ALA are condensed by the enzyme ALA
dehydratase  porphobilinogen (PBG) and 2
molecules H2O
 catalyzed by ALA dehydratase – very sensitive to
inhibition by heavy metals, e.g., lead poisoning
 occurs in the cytosol
 first pathway intermediate that includes a pyrrole ring
IRON AND HEME METABOLISM

67. 67
STEP 3: Synthesis of Hydroxymethylbilane
 formation of a cyclic
tetrapyrrole (porphyrin)
 condensation of four
molecules of PBG in a
head-to-tail manner to form
a linear tetrapyrrole,
hydroxymethylbilane
(HMB)
 catalyzed by
uroporphyrinogen I
synthase (PBG
deaminase or HMB
synthase), no ring-closing
function
 occurs in the cytosol
structure of HMB IRON AND HEME METABOLISM

68. 68
STEP 3: Synthesis of Hydroxymethylbilane
IRON AND HEME METABOLISM

69. STEP 4. Synthesis of Uroporphyrinogen 69
from Hydroxymethylbilane
 HMB cyclizes
spontaneously to form
uroporphyrinogen I
 HMB converted to
uroporphyrinogen III
by the action of
uroporphyrinogen III
synthase
 under normal
conditions, the
uroporphyrinogen
formed is almost
exclusively the III
isomer
IRON AND HEME METABOLISM

70. 70
STEP 5: Decarboxylation of
Uroporphyrinogens to Coproporphyrinogens
 decarboxylation of
all acetate (A) 
methyl (M) groups
 catalyzed by
uroporphyrinogen
decarboxylase,
also converts
uroporphyrinogen I
to coproporphyrino-
gen I
 porphyria cutanea
tarda
IRON AND HEME METABOLISM

71. STEP 6. Conversion of Coproporphyrinogen III
to Protoporphyrinogen III
 coproporphyrinogen III then enters
the mitochondria
 coproporphyrinogen oxidase
catalyzes the decarboxylation and
6 oxidation of two propionic side
chains (from P to V) to form
protoporphyrinogen III
 enzyme acts only on
coproporphyrinogen III; why type I
protoporphyrins do not generally
occur in nature
COO-
CH2 CH2 + CO2
CH2 CH
propionate vinyl

72. 72
STEP 7. Conversion of
Protoporphyrinogen III to Protophyrin III
 oxidation of
protoporphyrinogen III (IX) to
protoporphyrin III (IX) is
catalyzed by
protoporphyrinogen oxidase
 porphyrinogen converted to
porphyrin;
 methylene (-CH2-) bridges
oxidized to methenyl/methyne
(–CH=) bridges
7
 occurs in the mitochondria
PP IRON AND HEME METABOLISM

73. Porphyrinogen  Porphyrin
H2C N CH 2 HC CH
N
H H
NH HN N N
H -6H
H
H2C N CH 2 N
HC CH
Porphyrinogen
porphyrinogen Porphyrin porphyrin
 no resonance between  methylene bridges oxidized to
pyrrole groups methenyl bridges
 colorless (continuous resonance =
 mostly non-enzymatic, stability)
presence of light  colored
 characteristic absorption
spectrum (visible and UV)
IRON AND HEME METABOLISM

74. 74
Porphyrin: Absorption Spectrum
 sharp absorption near
400 NM
 distinguishing feature
of the porphyrin ring
 characteristic of all
porphyrins regardless
of the side chains
 Soret band
 fluoresce (red) when
illuminated by UV
IRON AND HEME METABOLISM

75. 75
STEP 8. Addition of iron to Protoporphyrin
III to form Heme
 final step in heme synthesis
 incorporation of ferrous iron into protoporphyrin
 catalyzed by ferrochelatase (heme synthase)
 occurs in the mitochondria
IRON AND HEME METABOLISM

76. 76
Compartmentation
 ALA synthase (Step 1) and last
3 (steps 6, 7 and 8) enzymes in
the pathway are located in the
mitochondrion
 whereas the other enzymes are
cytosolic
 all cells except RBC
 bone marrow: ~ 85% of heme
synthesis; the rest in liver
IRON AND HEME METABOLISM

77. 77
Heme Biosynthesis:
Regulation
 ALA synthase is the key
and rate-regulating enzyme
 induced by drugs and other
substances  drug-induced
porphyrias
 glucose (unknown
mechanism): inhibits heme
biosynthesis
IRON AND HEME METABOLISM

78. 78
Heme Biosynthesis:
Regulation
 ALA synthase is the key
and rate-regulating enzyme
 synthesis of ALA synthase is
repressed by heme, the end
product of the pathway
(feedback inhibition)
 heme also affects translation
of the enzyme and its
transfer from the cytosol to
the mitochondrion
IRON AND HEME METABOLISM

79. 79
Heme Biosynthesis: Regulation
 heme regulates the synthesis
of hemoglobin by stimulating
synthesis of the protein
globin
 heme maintains the ribosomal
initiation complex for globin
synthesis in an active state
 usage of heme by other
processes
 cytochrome P450 in xenobiotic
metabolism
DO IRON AND HEME METABOLISM

80. 80
Heme Biosynthesis: Disorders
 Porphyrias
 inherited or acquired diseases that result from
an abnormal metabolism in heme
biosynthesis
 main causes are partial or complete enzyme
deficiencies
 compensatory mechanisms: attempt to make
more heme
 most common
 Acute Intermittent Porphyria (AIP)
 Porphyria Cutanea Tarda (PCT)
 Protoporphyria (PP)
IRON AND HEME METABOLISM

81. 81
 if the enzyme lesion
Porphyrias occurs before
formation of
porphyrinogens,
ALA and PBG
accumulate
 clinically, patients
complain of
neuropsychiatric
symptoms
 abdominal pain
 peripheral
neuropathy
 mental
disturbance
IRON AND HEME METABOLISM

82. 82
 if enzyme blocks
Porphyrias later 
accumulation of the
porphyrinogens
 highly unsaturated
porphyrin rings can
absorb UV/visible
light and become
photoreactive
 porphyrin
derivatives cause
photosensitivity
IRON AND HEME METABOLISM

83. 83
Photosensitivity
 photosensitivity - a reaction
to visible light of about 400 nm
 porphyrins, when exposed to
light of this wavelength 
“excited” and then react with
molecular oxygen to form
oxygen radicals (reactive
oxygen species, ROS)
 species injure lysosomes and
other organelles
 damaged lysosomes release
their degradative enzymes,
causing variable degrees of skin
damage, including scarring
IRON AND HEME METABOLISM

84. 84
Porphyria Photosensitivity
IRON AND HEME METABOLISM

85. 85
Porphyrias
 two major groups of
porphyrias according to the
site of dysfunction:
 Erythropoietic
 Congenital Erythropoietic
Porphyria
 Protoporphyria
 Hepatic
 ALA dehydratase
deficiency
 Acute Intermittent
Porphyria
 Hereditary Coproporphyria
 Variegate Porphyria
 Porphyria Cutanea Tarda
IRON AND HEME METABOLISM

86. 86
Porphyria Cutanea Tarda (PCT)
 most common form of porphyria
 hepatic; uroporphyrinogen decarboxylase
deficiency
 acquired disorder, associated with estrogen, drugs
and alcohol use
 photosensitivity is the only major manifestation
 other cutaneous manifestations: dermal abrasions,
superficial erosions and blister formation after
trivial mechanical trauma
 lesions leave depigmented and pigmented scars
 hypertricosis
 diagnosis: increased urinary uroporphyrin I
symptoms IRON AND HEME METABOLISM

87. 87
Porphyria Cutanea Tarda (PCT)
myths IRON AND HEME METABOLISM

88. 88
Porphyria Cutanea Tarda (PCT)
 PCT is implicated in the origin of
vampire and werewolf myths
(hypertricosis)
 people with the disease tend to avoid
the sun due to blistering and desire
iron rich foods (blood and meat) due
to their enzymatic deficiency
 description of the title character of Bram
Stoker's Dracula:
"His eyebrows were very massive, almost
meeting over the nose, and with bushy
hair that seemed to curl in its own
profusion. The mouth ... was fixed and
rather cruel-looking, with peculiarly
sharp white teeth; these protruded over
the lips, whose remarkable ruddiness
showed astonishing vitality in a man of
his years ... The general effect was one
of extraordinary pallor."
IRON AND HEME METABOLISM

89. 89
Acute Intermittent Porphyria (AIP)
 hepatic; uroporphyrinogen I synthase (PBG
deaminase, hydroxymethylbilane synthase) deficiency
 majority of patients are asymptomatic
 abdominal pain: initial and commonest manifestation
 clinical picture may mimic an acute inflammatory
abdominal disease
 neuropsychiatric symptoms: peripheral neuropathy,
nerve atrophy, CNS abnormalities (confusion,
hallucinations, delirium and seizures)
 precipitating factors are drugs as barbiturates,
sulfonamides, estrogens and dietary restriction of
carbohydrates
 diagnosis: increased erythrocytic and urinary
porphobilinogen (PBG) and aminolevolinic acid (ALA)
levels
vincent IRON AND HEME METABOLISM

90. 90
Acute Intermittent Porphyria (AIP)
VINCENT (Don Mclean)
Starry, starry night.
Flaming flowers that brightly blaze,
Swirling clouds in violet haze,
Reflect in Vincent's eyes of china blue.
Colors changing hue, morning field of amber grain,
Weathered faces lined in pain,
Are soothed beneath the artist's loving hand.
…For they could not love you,
But still your love was true.
And when no hope was left in sight
On that starry, starry night,
You took your life, as lovers often do.
But I could have told you, Vincent,
This world was never meant for one
As beautiful as you.
…Now I think I know what you tried to say to me,
How you suffered for your sanity,
How you tried to set them free.
They would not listen, they're not listening still.
Perhaps they never will...
IRON AND HEME METABOLISM

91. 91
Protoporphyria (PP or EPP)
 erythropoietic protoporphyria
(EPP); ferrochelatase deficiency
 mild photosensitivity occurs after
sunlight exposition,
characterized by painful burning
or stinging sensations, pruritus,
erythema, and occasional
edema
 mild abnormalities in liver, biliary
tract (protoporphyrin gallstones)
and blood may be present
 diagnosis: increased fecal and
red cell protoporphyrin III (IX)
IRON AND HEME METABOLISM

92. 92
Drug-Induced Porphyria
 some drugs can induce
attacks, e.g.:
 barbiturates, griseofulvin, chlor
oquine, dapsone, etc.
 highly lipid-soluble drugs
 induce cytochrome P450
which uses up here  de-
represses (up-regulate) ALA
synthase
 ↑ levels of heme precursors
IRON AND HEME METABOLISM

93. 93
Lead Intoxication
 can mimic symptoms of
porphyrias
 combines with ALA
dehydratase  activity
 ALA accumulates
 lead inhibits
ferrochelatase, accumulate
protoporphyrin III (IX)
IRON AND HEME METABOLISM

94. 94
Porphyrias: Treatment
 symptomatic
 avoid drugs that cause induction of cytochrome
P450
 glucose loading - ingestion of large amounts of
carbohydrates
 administration of hematin (a hydroxide of heme)
to repress ALAS1, resulting in diminished
production of harmful heme precursors
 β-carotene: decrease production of free radicals,
thus diminishing photosensitivity and tissue
damage
 sunscreens that filter out visible light
heme degradation IRON AND HEME METABOLISM

95. 95
Overview
of Heme
Degradation
IRON AND HEME METABOLISM

96. 96
Degradation of Hemoglobin
 ~ 100–200 million
aged RBCs/hr are
broken down in a
person
 a 70-kg human turns
over approximately
6 g/day of hemoglobin
 hemoglobin is destroyed:
 globin  amino acids (reused)
 iron enters the iron pool
 iron-free porphyrin degraded, mainly in the
reticuloendothelial (RES) cells of the liver, spleen,
and bone marrow
IRON AND HEME METABOLISM

97. 97
Heme Degradation
 the tetrapyrrole ring
of heme is
oxidatively cleaved
between rings I and
II by heme
oxygenase
NADPH + requiring O2 and
+ NADP+ NADPH + H+
 produces green
biliverdin, CO and
Fe 2+ (recycled)
IRON AND HEME METABOLISM

98. 98
Heme Degradation
 biliverdin is reduced
by biliverdin
reductase to the
orange colored
bilirubin
 reduction breaks
the system down
into two smaller
separate systems
IRON AND HEME METABOLISM

99. 99
Bilirubin Transport
 bilirubin is transported to the
liver bound to albumin
 antibiotics / other drugs compete
with bilirubin for the high-affinity
binding site on albumin 
displace bilirubin  jaundice
 a transporter moves
dissociated bilirubin into the liver
cells
 inside the cell, cytosolic proteins
(ligandin , protein Y) binds
bilirubin
IRON AND HEME METABOLISM

100. 100
Bilirubin Conjugation
 bilirubin is
conjugated with
UDP-glucuronic
acid into the water-
soluble bilirubin
monoglucuronides
and diglucuronides
 occurs in the
endoplasmic
reticulum
 excreted into the
bile
IRON AND HEME METABOLISM

101. 101
Bilirubin Conjugation
 UDP-glucuronosyltransferase
(bilirubin-UGT) forms ester type bonds
between the OH group at C-1 of glucuronic
acid and the carboxyl groups in bilirubin
IRON AND HEME METABOLISM

102. 102
Bilirubin Conjugation
 rate-determining
step in hepatic
bilirubin
metabolism
 drugs
(phenobarbital,
etc) induce both
conjugate
formation and the
transport process
of bilirubin
B1 vs B2 IRON AND HEME METABOLISM

103. 103
Unconjugated Vs Conjugated
Bilirubin
B1 vs B2
Type Solubility Van den Berg Reaction
Reacts more slowly;
Unconjugated Still produces
Indirect bilirubin Lipid/ Fat Soluble azobilirubin. Alcohol
B1 makes all bilirubin
react promptly
Water Soluble Reacts quickly when
Conjugated dyes (diazo reagent)
(bound to
Direct Bilirubin are added to the blood
glucuronic acid) specimen to produce
B2
azobilirubin
excretion IRON AND HEME METABOLISM

104. 104
Bilirubin
Excretion
 glucuronides are then excreted by active
transport (MRP-2) into the bile as bile
pigments
 bacterial glucuronidases convert bilirubin
in the intestine to urobilinogen and
further reduced to stercobilinogen,
which are oxidized into orange to yellow-
colored stercobilin (feces)
IRON AND HEME METABOLISM

105. 105
Bilirubin Excretion
 end products of bile
pigment metabolism in
the intestine are mostly
excreted in feces, 10%
resorbed (enterohepatic
circulation)
 with excessive heme
degradation,
urobilinogen spills out
into the circulation and
excreted in the urine,
where oxidative
processes darken it to
form urobilin
(urochrome)
DO IRON AND HEME METABOLISM

106. 106
Heme Metabolism: Disorders
 Hyperbilirubinemia
 when bilirubin in the
blood increases
beyond normal and
exceeds 1 mg/dL (17.1
μmol/L)
 when it reaches a
certain concentration
(approximately 2–2.5
mg/dL), it diffuses into
the tissues, which then
become yellow
(jaundice or icterus)
IRON AND HEME METABOLISM

107. 107
Hyperbilirubinemia: Causes
 Pre-Hepatic
 ↑ bilirubin
production
 Hepatic
 ↓ bilirubin
conjugation
 micro-obstruction
 Post-Hepatic
 ↓ bilirubin excretion
IRON AND HEME METABOLISM

108. 108
Hyperbilirubinemia: Pre-Hepatic
 Hemolytic Anemia
 important cause of unconjugated
hyperbilirubinemia
 results from excessive RBC
destruction
 hereditary – sickle cell, thalassemia,
G6PD deficiency
 acquired – hypersplenism, drugs,
poisons
 ↑ indirect bilirubin, urine and fecal
urobilinogen
 absent urine bilirubin (acholuric
jaundice)
 retention hyperbilirubinemia
IRON AND HEME METABOLISM

109. 109
Hyperbilirubinemia: Intra-Hepatic
 Neonatal “Physiologic”
Jaundice
 transient condition, most
common cause of
unconjugated
hyperbilirubinemia
 accelerated hemolysis
 immature hepatic system for
the uptake, conjugation, and
secretion of bilirubin
 reduced synthesis of the
substrate for that enzyme,
bilirubin-UGT
 ↑ indirect bilirubin
 ↓ urine and fecal urobilinogen
photoTx IRON AND HEME METABOLISM

110. 110
Hyperbilirubinemia: Intra-Hepatic
 Pathologic Jaundice
 excessive unconjugated
bilirubin (> (20–25
mg/dL)  penetrates
the blood-brain barrier
 hyperbilirubinemic toxic
encephalopathy, or
kernicterus, which can
cause neurological
deficits, mental
retardation or death
IRON AND HEME METABOLISM

111. 111
Hyperbilirubinemia: Intra-Hepatic
 Criggler-Najar Syndrome
 rare autosomal recessive
disorder, severe congenital
jaundice; Type I and II
 mutations in the gene
encoding for Bilirubin-UGT
 no bilirubin conjugation
 often fatal (before 15 mos)
 ↑ indirect bilirubin
 absent urine bilirubin
 ↓ urine, fecal urobilinogen
IRON AND HEME METABOLISM

112. 112
Hyperbilirubinemia: Intra-Hepatic
 Gilbert Syndrome
 caused by mutations in
the gene encoding
Bilirubin-UGT (~ 30%
enzyme activity)
 harmless jaundice seen
during times of stress,
fasting, drug intake
 most common disorder
affecting bilirubin
metabolism (3-7% of
population)
 no treatment needed
IRON AND HEME METABOLISM

113. 113
Hyperbilirubinemia: Intra-Hepatic
 Toxic
Hyperbilirubinema
 acquired disorders
from hepatic
parenchymal cell
damage; impairs
conjugation
 infection or toxin-
induced liver damage:
hepatitis, chemicals,
toxins
IRON AND HEME METABOLISM

114. 114
Hepatic Jaundice
 Liver damage
(cirrhosis, hepatitis)
:
 less efficient uptake
and conjugation of
bilirubin
 leakage of
unconjugated (and
conjugated) bilirubin
into blood
IRON AND HEME METABOLISM

115. 115
Hyperbilirubinemia: Post-Hepatic
 Biliary Tree Obstruction
 conjugated hyperbilirubinemia
 blockage of biliary ducts
(gallstone, cancer of the head
of the pancreas, etc)
 B2 cannot be excreted;
regurgitated into the hepatic
veins and lymphatics
 regurgitation
hyperbilirubinemia
 B2 appears in the urine
(choluric jaundice)
 cholestatic jaundice
IRON AND HEME METABOLISM

116. 116
Hyperbilirubinemia: Post-Hepatic
 Dubin-Johnson Syndrome
 autosomal recessive disorder
 conjugated hyperbilirubinemia
 mutations in the gene
encoding MRP-2, the protein
involved in the secretion of
conjugated bilirubin into bile
 centrilobular hepatocytes
contain an abnormal black
pigment (derived from
epinephrine)  black liver
IRON AND HEME METABOLISM

117. 117
Hyperbilirubinemia: Post-Hepatic
 Rotor Syndrome –
 rare benign condition
 chronic conjugated
hyperbilirubinemia
 similar to DJS except that the
liver cells are not pigmented
(normal liver)
 cause unknown; impaired biliary
excretion of conjugated BR
 maybe due to an abnormality in
hepatic storage
named after the Filipino internist,
Arturo Belleza Rotor (1907–1988)
??? Dx IRON AND HEME METABOLISM

119. 119
Hyperbilirubinemia: Diagnosis
 pre-hepatic
 ↑ unconjugated bilirubin
 ↑ urine urobilinogen
 ↑ fecal urobilinogen
 unconjugated bilirubin
does not pass into urine
 no bilirubin in urine
(acholuric jaundice)
IRON AND HEME METABOLISM

120. 120
Hyperbilirubinemia: Diagnosis
( )
 intra-hepatic
 ↑ unconjugated (and
conjugated bilirubin)
 ↓ fecal urobilinogen
 ↓ urine, fecal urobilinogen
 + urine bilirubin
IRON AND HEME METABOLISM

121. 121
Hyperbilirubinemia: Diagnosis
 post-hepatic
 ↑ conjugated bilirubin
 bilirubin in the urine
(choluric jaundice)
 absent urine, stool
urobilinogen
TY IRON AND HEME METABOLISM