Porphyrins, Porphobilinogen

Sample

1. Collect fresh urine.
2. Random urine can be used.
3. Protect the sample from light.
   1. Add 5 g Na₂CO₃.
4. Store the sample at 4 to 8 °C.

Purpose of the test (Indications)

1. This test will quantitate porphyrins and porphobilinogen.
2. This can be used to find various forms of porphyria.

Definition

• The porphyrias are a group of disorders characterized by a deficiency of or defect in the enzymes involved in porphyrins metabolism and heme synthesis.

Pathophysiology

1. The term “porphyria” is derived from the Greek word porphyria, meaning “purple pigment.”
2. A porphyria is a group of disorders that result in an accumulation of chemicals called porphyrins in the body.
3. This is a group of genetic abnormality with associated enzyme deficiency involved in the porphyrin synthesis or metabolism.’
4. The porphyrins are building blocks in the synthesis of heme.
   1. Porphyrins are a byproduct of heme synthesis.

5. Porphyrins are the main precursors of heme, an essential constituent of hemoglobin, myoglobin, catalase, peroxidase, respiratory, and P450 liver cytochromes.
6. Accumulation of porphyrins, the heme precursors, is toxic to tissue in high concentrations.
   1. The primary porphyrins of RBC are :
      1. Protoporphyrin.
      2. Uroporphyrin.
      3. Coproporphyrin.

7. Then heme combine with globin in the RBC, and hemoglobin is formed.
8. Porphyrias are classified according to the location of the accumulation of porphyrins and precursors.
9. In most porphyrias, there is an increased level of porphyrins and porphobilinogen in the urine.
   7. Classification of porphyrias:
      1. Symptomatically, acute porphyrias.
         1. Primarily present with nervous system involvement.
         2. Often with severe abdominal pain, vomiting.
         3. Neuropathy and mental disturbances.
      2. Cutaneous porphyrias present with :
         1. Skin manifestations often after exposure to the sun due to the accumulation of excess porphyrins near the skin’s surface.
      1. Physiological classification is based on the accumulation of heme precursors, either in the liver or bone marrow and red blood cells.
         1. Hepatic porphyria has S/S of :
            1. Acute neurological attacks (seizures, psychosis).
            2. Extreme back and abdominal pain.
            3. Acute polyneuropathy.
         2. Erythropoietic porphyria has S/S of :
            1. Skin problems, usually a light-sensitive blistering rash and increased hair growth.
      2. Erythropoietic porphyria shows the following signs and symptoms :
         1. Photosensitivity of eyes and skin.

10. Clinical classification:

    1. Porphyria that produces skin manifestation without the presence of neurological symptoms are:
       1. Porphyria cutanea tarda.
       2. Congenital erythropoietic porphyria.
       3. Erythropoietic porphyria.
    2. Porphyria that is manifested by neurological symptoms (cutaneous symptoms are absent) are:
       1. Acute intermittent porphyria.
    3. Porphyria that has both cutaneous and neurological manifestations are:
       1. Hereditary coproporphyria.
       2. Variegate porphyria.

Excretion of Porphyrins:

1. 1. 1. Aminolevulinic acid and porphobilinogens are excreted in the urine.
      2. Uroporphyrins are also excreted in the urine, and a minimal amount is excreted in the feces.
      3. Most of the coproporphyrins are eliminated in the feces and a small amount in the urine.
      4. Protoporphyrins are eliminated through bile, and the average fecal content is 1 mg/day.
      5. Coproporphyrins’ urinary excretion is increased in obstructive jaundice, liver diseases, lead poisoning, and hemolytic anemias.

Disease	Substrate	Enzyme deficiency
Acute Intermittent Porphyria	Porphobilinogen	Hydroxymethylbilane synthase
Porphyria Cutanea Tarda	Uroporphyrinogen III	Uroporphyrinogen decarboxylase
Hereditary coproporphyria	Coproporphyrinogen III	Coproporphyrinogen Oxidase
Erythropoietic Protoporphyria	protoporphyrin	Ferrochelata

Signs and Symptoms

1. The following factors may initiate an acute attack:
   1. Some of the drugs.
   2. Smoking may initiate the attack.
   3. Use of alcohol.
   4. By some surgical procedures.
   5. Emotional upset.
   6. In females by the menstrual cycle.
   7. In females during pregnancy.
   8. Some time infection may give rise to attack.
   9. The acute attack may start with anxiety, restlessness, and difficulty in sleeping.
2. The patient may develop a painful abdomen, and this may be very severe.
3. There may be nausea and vomiting.
4. The patient may develop constipation.
5. There may be tachycardia and hypertension.
6. Urine is dark or reddish.
7. Rarely there may be sudden death, which may be due to cardiac arrhythmias.

Normal

Source 1

Porphobilinogen

• Fresh urine or 24 hours sample = Negative
• Spectrophotometric method (24 hours of urine)
  • <2.0 mg/L
  • <3.4 mg/day
  • ≤2.0 mg/day
    • To convert into SI unit x 4.42 = µmol/L

Porphyrins 

•  Urine fresh random = Negative
• Total porphyrin (whole blood) = <60 µg/dL

Total porphyrins

• 20 to 320 nmol/L (urine)

Uroporphyrin fraction = <33 µg/24 hours urine

= 17 to 52 µg/24 hours urine

Coproporphyrins fraction = <183 µg/24 hours urine

= <294 µg/24 hours urine

= 52 to 163 µg/24 hours urine

Source 2

Urine 24 hours or fresh:

1. Negative or trace.
2. Total porphyrin:
   • Male = 8 to 149 mcg/24 hours of the urine
   • Female = 3 to 78 mcg/24 hours of the urine
3. Uroporphyrin:
   • Male = 4 to 46 mcg/24 hours of urine
   • Female = 3 to 22 mcg/24 hours of the urine
4. Coproporphyrin:
   • Male = <96 mcg/24 hours of the urine
   • Female = <60 mcg/24 hours of the urine
5. Porphobilinogen = 0 to 2 mg /24 hours of the urine
   1. another source <1 mg/24 hour of the urine
6. δ-Aminolevulinic acid = 1.5 to 7.5 mg/day of the urine

Source 4

• Porphobilinogen 
  • Random  specimen = 0 to 2.0 mg/L
  • 24 hours sample = 0 to 1.5 mg/24 hours
• Δ-aminolevulinic acid 
  • Random specimen = 0. to 4.5 mg/L
  • 24 hour specimen = 1.5 to 7.5 mg/24 hours

Test	µg/24 hours  Urine
	Male	Female
Random sample	Negative	Negative
Uroporphyrin	8 to 44	4 to 22
Coproporphyrin	10 to 109	3 to 56
Heptacarboxyporphyrin	0 to 12	0 to 9
Pentacarboxy porphyrin	0 to 4	o to 3
Hexacarboxyporphyrin	0 to 5	0 to 5

Diagnosis

1. 1. 1. A urine sample is not as accurate as the plasma concentration.
         1. Urine is suitable as a screening test for porphyria.

Treatment

1. 1. 1. Treat to relieve the symptoms.
      2. Drug-like heme arginate is given to stop the process.

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