The enzymatic defect in variegate prophyria. Studies with human cultured skin fibroblasts

Protoporphyrinogen oxidase and ferrochelatase in porphyria variegata

Protoporphyrinogen oxidase activity and ferrochelatase activity were measured in leucocytes from patients with porphyria variegata. The mean activity of protoporphyrinogen oxidase (PPO) in porphyria variegata (PV) was about 50% of normal (P less than 0.05). The mean activity of ferrochelatase with 59Fe2+ sulphate and protoporphyrin as substrates (in the presence of ascorbic acid) was reduced by 40% (P less than 0.009). The mean activity of ferrochelatase with 59Fe3+ chloride and protoporphyrin as substrates (in the presence of reduced glutathione) was increased by 65% (P less than 0.005). Both are statistically highly significant. The findings are interpreted as follows: (a) The occurrence of a low level of protoporphyrinogen oxidase in PV is confirmed. (b) The findings indicate a concurrent structural change in ferrochelatase (this may be structurally related to (a) but no evidence of this is at present available).

Acute variegate porphyria following a Scarsdale Gourmet Diet

Symptoms of porphyria developed in a 34-year-old woman following 3 weeks of a low carbohydrate diet. Reversal of a comatose state was obtained following multiple infusions of hematin. The diagnosis of variegate porphyria was made from the pattern of quantitative urine and stool porphyrins and a plasma fluorescence that was maximal at 626 nm. This fluorescence wavelength maxima also was found in the plasma of two family members screened for latent porphyria.

The inherited enzymatic defect in porphyria variegata

Protoporphyrinogen oxidase activity and ferrochelatase activity have been measured in blood lymphocytes from patients with prophyria variegata, and from some members of the family of one patient; the mean activity of protoporphyrinogen oxidase from patients was about 50% of that in lymphocytes from normal subjects; similar results were obtained from asymptomatic carriers in two generations of the patient's family. This finding confirms that a protoporphyrinogen oxidase decreased activity reflects the primary genetic defect in Porphyria Variegata. Data of ferrochelatase activity have been found usually in the normal range and these results are discussed.

Treatment of the porphyrias: mechanisms of action

The porphyrias are diseases that result from inherited or acquired abnormalities of porphyrin-heme synthesis in the liver and the bone marrow. Only the hepatic porphyrias are known to be aggravated by exposure to a variety of exogenous drugs and chemicals. Simple avoidance of these agents will reduce the risk of developing hepatic porphyria and may lead to clinical improvement in patients with active disease. Some types of therapy of the hepatic porphyrias are effective because of their ability to modulate the activity of delta-aminolevulinic acid synthetase, the rate-limiting enzyme for heme synthesis. Most of the porphyrias are associated with cutaneous photosensitivity, the treatment of which centers about either reducing the excessive production of porphyrins or of inhibiting the photobiological response to these photosensitizing chemicals in the skin.

Enzyme defects in the porphyrias and their relevance to the biochemical abnormalities in these disorders

Defects in enzymes of the heme biosynthesis pathway underlie the biochemical abnormalities which occur in the porphyrias. Porphyrins and porphyrin precursors are accumulated and excreted in excessive amounts because of the enzyme defects. This is illustrated by studies in protoporphyria and variegate porphyria, disorders in which the biochemical abnormalities indicate a defect(s) in the terminal part of the heme biosynthesis pathway. The activity of heme synthease (ferrochelatase), which catalyzes the chelation of ferrous iron to protoporphyrin, is deficient in tissues of patients with protoporphyria. This causes protoporphyrin to be accumulated and excreted excessively. In variegate porphyria protoporphyrinogen oxidase, which catalyzes the oxidation of protoporphyrinogen to protoporphyrin, appears to be defective. As a result, protoporphyrinogen may be excreted in increased amounts in bile, where it is subsequently auto-oxidized to protoporphyrin. The following questions have arisen as a result of the demonstrations of enzyme defects in tissues of patients with porphyria: (1) Will different defects in the same enzyme be found among patients who fulfill the clinical and biochemical criteria for diagnosis of a specific porphyria? That is, does genetic heterogeneity exist in each of the porphyrias? (2) Why do some patients with an enzyme defect not have biochemical abnormalities? (3) Why is one type of tissue, usually the liver, the major site of expression of the biochemical abnormality, when the enzyme defect can be demonstrated in all tissues?

The "glucose effect" in acute hepatic porphyrias and in experimental porphyria

The "glucose effect" was investigated in human acute hepatic porphyrias (acute intermittent porphyria, variegate porphyria, coproporphyria and porphobilinogen synthase defect porphyria) and in avian liver cells. 8 patients (7 women) with acute abdominal-neurological porphyria syndrome and 3 patients (2 women) in the remission phase were treated with high carbohydrate intake (approximately 500 g/24 h), mainly in form of intravenous glucose infusions. The biochemical response with a decrease of metabolites of porphyrin biosynthesis was highly significant, accompanied by clinical improvement in 10 courses of 9 patients. Two patients with delayed detection of the disease under the condition of Landry paralysis died after temporary clinical improvement due to ventricular arrythmias in one case and septicemia in the other. The importance of early diagnosis and therapy, and omission of drugs and alcohol cannot be overemphasized. Complementary studies show the "glucose effect" in drug -mediated induction of porphyrin synthesis in liver cells grown in culture: delta-Aminolevulinic acid synthase and protoporphyrin synthesis are repressed.

Hepatoerythropoietic porphyria: a new uroporphyrinogen decarboxylase defect or homozygous porphyria cutanea tarda?

Uroporphyrinogen decarboxylase levels were measured in haemolysed whole blood or fibroblasts from 3 unrelated patients with hepatoerythropoietic porphyria (HEP) and in 4 unrelated patients with familial porphyria cutanea tarda, a condition in which the enzyme is defective. In HEP patients enzyme activities were 7% of normal in erythrocytes and 8% of normal in cultured skin fibroblasts. All the features of HEP, including the characteristic accumulation of protoporphyrin in erythrocytes, are secondary to this enzyme defect. The father of 1 HEP patient was heterozygous for the same enzyme defect. He also had uroporphyrinuria and was therefore indistinguishable from patients with subclinical familial porphyria cutanea tarda. It is suggested that patients with HEP are homozygous for the gene that causes porphyria cutanea tarda.