This document summarizes heme metabolism and porphyrias. It begins with an overview of heme synthesis and catabolism. It then discusses the biochemical basis and clinical implications of various porphyrias, including acute intermittent porphyria, porphyria cutanea tarda, erythropoietic protoporphyria, and congenital erythropoietic porphyria. Treatment options are provided for acute and cutaneous porphyrias. The document aims to provide details on heme synthesis, porphyrin metabolism, porphyria types and testing, and management.

1. Heme Metabolism and
Porphyrias
Dr. Abhishek Roy
Junior Resident (3rd Year)
Dept. of Biochemistry,
Grant Govt. Medical College and
Sir J.J. Group of Hospitals, Mumbai
Email: mail@abhishek.ro
Twitter: @abhishekroy

2. Objectives
• To study Heme Synthesis in detail
• To understand the Heme Catabolism
• To study the Biochemical Basis and Clinical Implications of Porphyrias
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3. Biosynthesis of δ-Aminolevulinate
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4. 2nd August, 2015 Dr. A Roy 4
Heme Synthesis, enzymes involved and the
site of synthesis at different steps.

5. Spectral Properties of Hematoporphyrins
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6. 2nd August, 2015 Dr. A Roy 6
Heme Catabolism
Since 1 g of hemoglobin yields about 35 mg of bilirubin,
human adults form 250 to 350 mg of bilirubin per day

7. Bilirubin Metabolism in brief
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Bilirubin Diglucuronide

8. Enzymes of Heme Biosynthesis
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9. 5-Aminolevulinate Synthase (EC 2.3.1.37) (ALAS)
• Catalyzes the formation of ALA from succinyl-CoA and glycine
• Mitochondrial and requires a cofactor of pyridoxal phosphate, which
forms a Schif base with the amino group of glycine at the enzyme
surface.
• The carbanion of the Schiff base displaces CoA from succinyl-CoA with
the formation of α-amino-β-ketoadipic acid, which is then
decarboxylated to ALA
• The activity of ALAS is rate limiting as long as the catalytic capacities
of other enzymes in the pathway are normal.
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10. 5-Aminolevulinic Acid Dehydratase (EC 4.2.1.24)
(ALAD)
• ALAD (also known as porphobilinogen synthase) is a cytoplasmic
enzyme
• Catalyzes the formation of the monopyrrole PBG from two molecules
of ALA with elimination of two molecules of water.
• Requires zinc ions as a cofactor and reduced sulfhydryl groups at the
active site and therefore is susceptible to inhibition by lead.
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11. Hydroxymethylbilane Synthase (EC 2.5.1.61) (HMBS)
• HMBS (also known as PBG deaminase) is a cytoplasmic enzyme
• Catalyzes the formation of one molecule of the linear tetrapyrrole 1-
hydroxymethylbilane from four molecules of PBG with the release of
four molecules of ammonia.
• Has two molecules of its own substrate: PBG, attached covalently to
the apoenzyme as a prosthetic group
• Is susceptible to allosteric inhibition by intermediates farther down
the heme biosynthetic pathway, notably coproporphyrinogen-III and
protoporphyrinogen-IX.
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12. Uroporphyrinogen-III Synthase (EC 4.2.1.75) (UROS)
• Cytoplasmic enzyme that rearranges and cyclizes HMB to form
uroporphyrinogen-III
• By the rotation of zero, one, or two alternate or two adjacent pyrrole
rings, it is possible to arrive at four different isomers.
• The enzyme rotates the D-ring via a spirane intermediate,7 producing
the type III isomer—an essential reaction because only this isomer
contributes to heme biosynthesis.
• HMB is unstable, and in those porphyrias in which excess HMB
accumulates, cyclization occurs nonenzymatically with the formation
of the type I isomer.
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13. Uroporphyrinogen Decarboxylase (EC 4.1.1.37) (UROD)
• Last cytoplasmic enzyme in the pathway
• Catalyzes the decarboxylation of all four carboxymethyl groups to form
the tetracarboxylic coproporphyrinogen.
• Uses I and III isomers of uroporphyrinogen as substrate
• Decarboxylation commences on ring D and proceeds stepwise through
rings A, B, and C with formation of heptacarboxylate, hexacarboxylate,
and pentacarboxylate intermediates at a single active site.
• At high substrate concentrations, decarboxylation occurs by a random
mechanism
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14. Coproporphyrinogen Oxidase (EC 1.3.3.3) (CPOX)
• CPOX, which is located in the intermembrane space of mitochondria
• Catalyzes the sequential oxidative decarboxylation of the 2- and 4-
carboxyethyl groups to vinyl groups to produce the more lipophilic
protoporphyrinogen-IX
• Requires sulfhydryl groups for activity, making it a target for inhibition
by metals
• The enzyme is specific for the type III isomer, so that metabolism of
the I-series of porphyrins does not occur beyond
coproporphyrinogen-I
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15. Protoporphyrinogen Oxidase (EC 1.3.3.4) (PPOX)
• Flavoprotein located in the inner mitochondrial membrane, catalyzes
the removal of six hydrogens to form protoporphyrin-IX.
• This involves a three-step, six-electron flavin adenine dinucleotide
(FAD)-dependent oxidation that consumes molecular oxygen.
• The protoporphyrin produced is the only porphyrin that functions in
the heme pathway.
• Other porphyrins are produced by nonenzymatic oxidation and
represent porphyrinogens that have irreversibly escaped from the
pathway.
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16. Ferrochelatase (EC 4.99.1.1) (FECH)
• FECH (also known as heme synthase) is an iron-sulfur protein located
in the inner mitochondrial membrane.
• Inserts ferrous iron into protoporphyrin to form heme.
• In iron-deficient states, Zn2+ successfully competes with Fe2+ in
developing red cells, so that the concentration of zinc protoporphyrin
in erythrocytes increases.
• Integration of the final stages of erythroid heme
• Biosynthesis may be facilitated by interaction between FEC and
proteins involved in iron import.
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17. Heme biosynthesis is regulated differently in
erythroid and liver cells
• In liver, heme biosynthesis must really be “controlled,” whereas in
erythroid cells, the process is more like breaking a dam.
• In liver, the main control target in heme biosynthesis is ALA synthase.
• Heme, or its Fe(III) oxidation product hemin, controls this enzyme’s
activity through three mechanisms:
feedback inhibition,
inhibition of the transport of ALA synthase (ALAS) from its site of synthesis in
the cytosol to its reaction site in the mitochondrion
repression of ALAS synthesis
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18. Porphyria
• The term porphyria is derived from the Greek πορφύρα, porphyra, meaning
"purple pigment".
• Original descriptions are attributed to Hippocrates
• The disease was first explained biochemically by Felix Hoppe-Seyler in 1871
• Acute porphyrias were described by the Dutch physician Barend Stokvis in 1889.
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19. Porphyrinogen and Porphyrins
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Porphyrinogens are reduced form of Porphyrins
• Porphyrinogens are reduced forms of porphyrins
• Difference- 6 hydrogens
• They are unstable in-vitro
• Spontaneously oxidised to respective porphyrins
• They can serve as intermediates of heme synthesis
in situations of low oxygen tension

20. Heme synthetic pathway and various porphyrias
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21. Genetic Basis of development of Porphyrias
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All Porphyrias are autosomal dominant except CEP and ADADP which are autosomal recessive.

22. Summary of Major findings in Porphyrias
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23. Porphyria Epidemiology
• Based on European studies, the prevalence of the most common
porphyria, porphyria cutanea tarda (PCT), is 1 in 10,000
• The most common acute porphyria, acute intermittent porphyria
(AlP), is about 1 in 20,000
• The most common erythropoietic porphyria, erythropoietic
protoporphyria (EPP), is estimated at 1 in 50,000 to 75,000
• Congenital erythropoietic porphyria (CEP) is extremely rare with
prevalence estimates of 1 in 1,000,000 or less
• Only 6 cases of ALAD-deficiency porphyria (ADP) are documented
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24. Myths and Legends explained
• Vampires- Blood Sucking, Intolerance to night and Act weird.
• Werewolves- Hairy individuals with super human strength and human
killer.
• Porphyrias and explanation-
• Porphyria Cutanea Tarda- The hallmark is photosensitivity causing
photomutilations and thus loss of skin around mouth lips and excessive
sensitivity to light.
• Photomutilation can also cause disfigurement of faces with hypertrichosis in
later stages. Initially it might be less, later on it might lead to hirsutism and
excessive body hair.
• Photosensitivity may also explain scarring of cornea and skin at various parts
of the body.
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25. Acute Porphyrias
•Acute Intermittent Porphyria (AIP)
•Alanine Deaminase Deficiency Porphyria (ADP)
•Hereditary Coproporphyria (HCP)
•Variegate Porphyria (VP)
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26. Clinical Signs and Symptoms
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27. Do drugs and environment play a role?
• Ethanol
• Excessive consumption of Iron
• Smoking
• Sulfonamides
• Barbiturates
• Tranquilizers
• Oral Contraceptives
• Stress
• Even in predisposed individuals- Sun Exposure
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28. Non-Acute Pophyrias
• Porphyria Cutanea Tarda
• Photosensitivity, Skin Burns, Hypertrichosis/Hirsutism, Disfigurement, Scleroderma, Often associated HCV
• Congenital Erythropoietic porphyria
• Much more severe than PCT, often leading to death in Utero, Hydrops fetalis, Severe skin blistering and extensive scarring
• Shortened RBC life span, Hemolysis
• Erythropoietic protoporphyria
• Most common porphyria in childhood (3rd most common overall)
• Caused by mutation in FECH or ALAS2 gene. When ALAS2 (rarely) involved, it’s called X-Linked Protoporphyria.
• Painful photosensitivity to sunlight including light that passes through glasses.
• Swelling, scarring, impaired quality of life.
• Hallmark: PBG and ALA not produced in excess.
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29. Adult Lab Parameters
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31. Types and Epidemiology
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32. Patterns of overproductions of Porphyrins
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33. A Simple SOP for Acute Porphyrias Work Up
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Urine PBG
+_
Urine ALA
Total Fecal
Porphyrins
No Porphyria ADAP
AIP
Plasma HPLC
HCP VP ProtoporphyrinCoproporphyrin
+
_
_ +

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35. Treatment of Acute Porphyria
• Precipitating agents are to be identified and are to be withdrawn
• Pain killers including opioids need to be administered.
• Anti histaminics at times may balance the excessive requirement of
opioids
• Electrolyte correction to counter hyponatremia
• Anti emetics and dextrose if required.
• IV Heme (very specific)
• Orthotopic Hepatic Transplant –Best Treatment Modality
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36. A Simple SOP for Cutaneous Porphyria
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Total
Plasma
Porphyrins
+
_
Plasma
HPLC
No
Porphyria
PCT/HEP EPP CEP
7 and 8 carboxyl Porphyrin Protoporphyrin Uroporphyrin I
Coproporphyrin I

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38. Treatment of Cutaneous Porphyria
• Photoprotection
• High SPF Creams/Gels
• Protection from Infections(Secondary)
• Blood Transfusion also helps but temporarily
• Iron Chelators may be beneficial like Desferrioxamine, Defereprime.
• Oral Activated Charcoal
• Gene Therapy and Allogenic BMT- Best Treatment Modality
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40. Thank You