Expression and characterization of six mutations in the protoporphyrinogen oxidase gene among Finnish variegate porphyria patients.

BACKGROUND: Variegate porphyria (VP) is an inherited disorder of heme biosynthesis that results from a partial deficiency of protoporphyrinogen oxidase (PPOX). Patients with VP may experience acute neurovisceral attacks and cutaneous photosensitivity. To date we have characterized 109 VP patients representing 19 VP families in the Finnish population of 5 million, both biochemically and clinically. MATERIALS AND METHODS: Mutations were identified by direct sequencing of the patients' genomic DNA. The effect of the mutations was determined by sequencing the reverse transcriptase polymerase chain reaction (RT-PCR) product amplified from total RNA extracted from the patients' lymphoblast cell lines and expressing the mutations in E. coli and COS-1 cells. RESULTS: Of the six mutations identified in the PPOX gene, three mutations (IVS2-2a-->c, 338G-->C, and 470A-->4C) caused splicing defects, one produced a frameshift (78insC) and two mutations (R152C and L401F) caused amino acid substitutions. In RT-PCR, the IVS2-2a-->c mutation caused a retention of a 36-bp fragment in the 3' end of intron 2, the 338G-->C mutation caused an exon 4 deletion, and the 470A-->C mutation caused an exon 5 deletion with retention of a 19-bp fragment of the 3' end of intron 5. In both prokaryotic and eukaryotic expression systems, the PPOX activities of five mutants were decreased to 0-5% of the normal activity. CONCLUSIONS: This study describes five novel mutations and one earlier described major mutation among Finnish VP patients. All mutations produced detectable transcripts, but resulted in decreased PPOX activity confirming the causality of the mutations and the biochemical defects in these patients.

Homozygous variegate porphyria: 20 y follow-up and characterization of molecular defect.

The long-term follow-up of a homozygous variegate porphyria patient revealed severe photosensitivity accompanied by mild sensory neuropathy and IgA nephropathy. A 35T to C transition in exon 2 (I12T) and a 767C to G transversion in exon 7 (P256R) of the protoporphyrinogen oxidase gene were identified from both alleles of the patient's cDNA and genomic DNA samples. Both prokaryotic and eukaryotic expression studies showed that the first mutation in the evolutionary conserved region resulted in a decrease in the protoporphyrinogen oxidase activity in contrast to the polymorphic substitution in exon 7, which affected the function of the enzyme assayed in Escherichia coli but not COS-1 cells.

Vascular changes in erythropoietic protoporphyria: histopathologic and immunohistochemical study.

BACKGROUND: Erythropoietic protoporphyria (EPP) is an inherited disease caused by deficient activity of ferrochelatase in the heme biosynthetic pathway. Accumulation of protoporphyrins and light exposure results in acute phototoxic skin reactions. The histopathologic findings of the light-exposed skin are thickening of the superficial dermal vessel walls and amorphous deposits around the vessels, but the origin and detailed composition of the perivascular material have been unclear. OBJECTIVE: The vascular morphology and composition of the perivascular material were studied in the skin samples of patients with EPP. METHODS: Skin biopsy specimens of 8 patients with EPP representing 7 Finnish EPP families with different genotypes were studied by means of light and electron microscopy and immunohistochemical methods. RESULTS: The characteristic finding was thickened, periodic acid-Schiff-positive vessel walls caused by concentric reduplication of basal lamina and excess of fine granular material at the basal membrane zone in the superficial dermis. The perivascular deposits in the vicinity of vessel walls had a homogeneous or fine granular appearance without filaments. Direct immunofluorescence showed constant IgG deposits together with IgA, IgM, and C3 in the vessel walls. In immunohistochemistry, collagen IV and laminin could be demonstrated at the vascular basal membrane together with serum amyloid P protein, kappa and lambda light chains, and a 90-kd glycoprotein. CONCLUSION: The vascular involvement indicates that the blood vessel walls in the papillary dermis are the primary tissues affected during an acute photoreaction. The repeated acute damage and repair processes in the basement membrane zone result in thickening of the vessel walls. Perivascular deposits are a secondary and irreversible phenomenon resulting from the leakage and accumulation of different serum components. These changes were not found in the nonexposed skin, indicating that an increased level of erythrocyte protoporphyrin per se is not responsible for the cutaneous manifestations, but the interaction of solar radiation is mandatory. Amorphous deposits distinguish EPP from variegate porphyria and porphyria cutanea tarda; a histopathologic examination may be a helpful tool in differentiating porphyric and nonporphyric photosensitivity.

Acute porphyria: treatment with heme.

The characterization of porphyrias as disorders of heme biosynthesis leading to hepatic heme deficiency and raised formation and secretion of heme precursors laid the basis for heme treatment. Although mild attacks sometimes respond to glucose administration, severe attacks or symptoms that are likely to progress should be treated with heme. The heme compounds used in treatment are hematin and heme arginate. In our opinion, heme arginate is preferable to hematin in the treatment of acute porphyrias because of its better stability, fewer side effects, and better documentation of its benefits.

Four novel mutations in the ferrochelatase gene among erythropoietic protoporphyria patients.

A novel mutation was identified by direct sequencing of genomic polymerase chain reaction products in each of four Finnish erythropoietic protoporphyria families. All four mutations, including two deletions (751delGAGAA and the first de novo mutation, 1122delT) and two point mutations (286C-->T and 343C-->T), resulted in a dramatically decreased steady-state level of the allelic transcript, since none of the mutations could be demonstrated by direct sequencing of the amplified cDNAs synthesized from total RNA extracted from patients' lymphoblast cell lines. Because the assays of the ferrochelatase activity and erythrocyte protoporphyrin identify asymptomatic patients poorly, the DNA-based demonstration of a mutation is the only reliable way to screen individuals for the disease-associated mutation.

Effect of exogenous erythropoietin on haem synthesis in anaemic patients with rheumatoid arthritis.

The effect of recombinant human erythropoietin (rHuEPO) on haem biosynthesis in peripheral red blood cells was evaluated in 12 patients with RA and anaemia (mean haemoglobin concentration 102 g/l, range 90-109 g/l). Before treatment, the serum concentrations of erythropoietin (EPO) were low (mean 13 pmol/l, range 5-32 pmol/l), the activities of haem-synthesizing enzymes within the reference intervals and the erythrocyte protoporphyrin (E-PROTO) concentrations clearly higher than normal. Nine patients responded with an increase in the haemoglobin level of 15 g/l or more. rHuEPO induced a rise in the mean haem synthase (HAEM-S) activity from a baseline of 12.1 to a maximum of 26.8 pmol/h per 10(6) reticulocytes after 20 weeks of treatment (P < 0.002). The mean E-PROTO concentration also rose and reached its maximum at 8 weeks of treatment. We conclude that correction of anaemia in patients with RA using rHuEPO is associated with an activation of HAEM-S, commonly regarded as the rate-limiting enzyme of haem synthesis in erythroid cells. Functional iron deficiency probably explains the simultaneous rise in E-PROTO concentration.

Sustained high plasma 5-aminolaevulinic acid concentration in a volunteer: no porphyric symptoms.

The pathogenesis of the acute porphyric attack is not known. One hypothesis is that porphyrin precursors, especially 5-aminolaevulinic acid (ALA), are toxic for neuronal tissue. This was tested by infusing ALA in a male volunteer after a loading dose at a rate of 50-80 mg h-1 for 92.5 h. During the experiment plasma ALA concentration was 9-11 mumol 1-l and porphobilinogen concentration 3-6 mumol 1-l which are the levels seen during acute attacks. Urinary excretion of these porphyrin precursors was also markedly increased. ALA infusion caused no subjective symptoms and no change in pulse rate, blood pressure, or autonomic nerve function or conduction velocity of peripheral nerves. Photosensitivity was not demonstrable. It is concluded that sustained high plasma ALA concentration does not cause porphyria-like symptoms.

Rapid normalization of antipyrine oxidation by heme in variegate porphyria.

Effects of heme on hepatic xenobiotic drug metabolism were investigated in eight subjects with variegate porphyria. A single infusion of heme arginate (3 mg/kg heme) reversed rapidly the prolonged mean elimination half-life of antipyrine from 27.2 to 12.7 hours (p less than 0.001) and increased total clearance from 0.23 to 0.44 ml/min/kg (p less than 0.001). Excretion of 6 beta-hydroxycortisol and D-glucaric acid increased significantly during heme infusion. Excretion of urinary porphyrin precursors increased during the antipyrine test but was normalized by heme. It is concluded that in variegate porphyria a partial block in heme biosynthesis results in subnormal capacity of P450-associated monooxygenases, but this is easily normalized by exogenous heme.

Effects of haem arginate on variegate porphyria.

Four patients with variegate porphyria (VP) were treated with repeated haem arginate infusions daily for 4 days and then weekly for 4 weeks. After the initial four daily doses of haem arginate (haem 3 mg/kg), the excretion of faecal protoporphyrin (mean 579 nmol/g dry wt) fell to an almost normal level (mean 123 nmol/g dry wt), and that of coproporphyrin (mean 162 nmol/g dry wt) to the normal level (mean 21 nmol/g dry wt) in all patients. However, during the period of the four weekly infusions of haem the excretion of porphyrins increased almost to the pretreatment level. Phototesting showed no changes in the photoreactivity of the skin, and no improvement in skin lesions was seen during the treatment. Except for one case of thrombophlebitis no side-effects occurred. In a child with homozygous VP, four daily infusions of haem arginate (2 mg/kg) normalized the faecal protoporphyrin content, but had no effect on the increased erythrocyte protoporphyrin concentration.

Erythropoietin, aluminium, and anaemia in patients on haemodialysis.

Effects of erythropoietin treatment on haem synthesis in peripheral blood were evaluated in 11 patients on haemodialysis. After 2 weeks of erythropoietin, mean (SEM) uroporphyrinogen-l synthase activity increased significantly from 88 (10) to 116 (9) pmol/h per mg protein. Haem synthase activity, thought to be the rate-limiting step in erythroid haem synthesis, also showed a significant increase from 4.5 (0.8) to 8.4 (1.8) pmol/h per 10(6) reticulocytes. 4 patients, who showed only a partial response to erythropoietin, had significantly higher serum aluminium concentrations than the 7 who responded fully (225 [44] vs 55 [23] micrograms/l); erythrocyte protoporphyrin concentrations in partial responders were also much higher than in responders (973 [120] vs 388 [29] nmol/l). Aluminium intoxication may cause resistance to erythropoietin by interference with haem synthesis, with accumulation of protoporphyrin.

Heme in the treatment of heme deficiency states.

The mechanism of regulation of heme biosynthesis is of great interest for both biological and medical reasons. The hepatic and erythropoietic porphyrias are shown to be hereditary or acquired disorders characterized by defects in specific enzymes of the heme biosynthetic pathway. In addition, several other diseases can be associated with a defect of heme biosynthesis. Heme has become well established in the treatment of acute porphyrias. In recent years, heme has been used increasingly for the treatment of other heme deficiency states as well.

Skin changes in variegate porphyria. Clinical, histopathological, and ultrastructural study.

The skin of 20 patients with variegate porphyria (VP) was studied using light, fluorescent, and electron microscopy. Twelve patients had skin symptoms and markedly increased fecal protoporphyrin excretion. Their sun-exposed skin was characterized by homogeneous PAS-positive thickening and IgG deposition in the vessel walls. The basic ultrastructural change was thickening of the vascular walls caused by reduplication of the basal lamina and perivascular deposition of amorphous material. Qualitatively similar but less prominent histopathological changes occurred in sun-protected skin in some of the patients. Six patients had no skin symptoms but an increased porphyrin excretion. The light microscopical changes were comparable to those in the patients with skin symptoms, but the ultrastructural changes were less severe. No abnormal histopathological changes occurred in two symptomless patients who had low lymphocyte protoporphyrinogen oxidase activity but normal fecal porphyrin excretion. These results show that the primary site of skin damage in VP is the vessel wall, and that histopathological changes of the skin also occur in porphyric patients who have never had skin symptoms. Factors determining the occurrence of skin symptoms in VP are discussed.

Effect of haem arginate on colony formation by haematopoietic progenitors in vitro.

The effect of haem arginate, a new stable haem compound, was studied on colony formation by erythroid (CFU-E, BFU-E) and granulocyte-macrophage (CFU-GM) progenitors from the bone marrow of 12 healthy persons. At the concentration of 10 mumol/l haem arginate significantly (p less than 0.05) increased and at the concentration of 200 mumol/l significantly decreased (p less than 0.005) the colony formation of CFU-E. A similar, though not significant, trend was seen in the BFU-E colony growth, while the CFU-GM colony formation was not influenced at any concentration between 1 and 200 mumol/l. We conclude that the stimulation of erythropoiesis in vitro is seen at lower concentrations with haem arginate than with former haemin preparations.

Effect of exogenous heme on hepatic iron-load and changes induced in hepatic heme metabolism by chronic iron-load.

It has recently been shown that heme arginate treatment can markedly improve blood cell counts in some severely cytopenic patients with a myelodysplastic syndrome (MDS). As MDS is often associated with iron overload, we have now studied in iron-loaded rats the hepatic effects of heme arginate given in a dose of 1.2 mg/100 g intraperitoneally twice a week for a period of 4.5 weeks. The heme injections caused a very marked increase in the mean hepatic iron content of the iron-loaded rats, which was more than twice the total amount of the heme-iron injected per rat. The heme treatment did not significantly affect the activities of the enzymes involved in the heme metabolism. Although no clinical side effects have been found in the MDS patients treated with heme arginate so far, the present study suggests that in iron-load the possible adverse hepatic effects should be taken into account and a minimum therapeutic dose of heme arginate should be used.