Studies of the clinical and metabolic effects of phlebotomy treatment in porphyria cutanea tarda

From chemistry to genomics: A concise history of the porphyrias

We describe developments in understanding of the porphyrias associated with each step in the haem biosynthesis pathway and the role of individuals whose contributions led to major advances over the past 150 years. The first case of erythropoietic porphyria was reported in 1870, and the first with acute porphyria in 1889. Photosensitisation by porphyrin was confirmed by Meyer-Betz, who self-injected haematoporphyrin. Günther classified porphyrias into haematoporphyria acuta, acuta toxica, congenita and chronica. This was revised by Waldenström into porphyria congenita, acuta and cutanea tarda, with the latter describing those with late-onset skin lesions. Waldenström was the first to recognise porphobilinogen's association with acute porphyria, although its structure was not solved until 1953. Hans Fischer was awarded the Nobel prize in 1930 for solving the structure of porphyrins and the synthesis of haemin. After 1945, research by several groups elucidated the pathway of haem biosynthesis and its negative feedback regulation by haem. By 1961, following the work of Watson, Schmid, Rimington, Goldberg, Dean, Magnus and others, aided by the availability of modern techniques of porphyrin separation, six of the porphyrias were identified and classified as erythropoietic or hepatic. The seventh, 5-aminolaevulinate dehydratase deficiency porphyria, was described by Doss in 1979. The discovery of increased hepatic 5-aminolaevulinate synthase activity in acute porphyria led to development of haematin as a treatment for acute attacks. By 2000, all the haem biosynthesis genes were cloned, sequenced and assigned to chromosomes and disease-specific mutations identified in all inherited porphyrias. These advances have allowed definitive family studies and development of new treatments.

Iron Metabolism in the Disorders of Heme Biosynthesis

Given its remarkable property to easily switch between different oxidative states, iron is essential in countless cellular functions which involve redox reactions. At the same time, uncontrolled interactions between iron and its surrounding milieu may be damaging to cells and tissues. Heme—the iron-chelated form of protoporphyrin IX—is a macrocyclic tetrapyrrole and a coordination complex for diatomic gases, accurately engineered by evolution to exploit the catalytic, oxygen-binding, and oxidoreductive properties of iron while minimizing its damaging effects on tissues. The majority of the body production of heme is ultimately incorporated into hemoglobin within mature erythrocytes; thus, regulation of heme biosynthesis by iron is central in erythropoiesis. Additionally, heme is a cofactor in several metabolic pathways, which can be modulated by iron-dependent signals as well. Impairment in some steps of the pathway of heme biosynthesis is the main pathogenetic mechanism of two groups of diseases collectively known as porphyrias and congenital sideroblastic anemias. In porphyrias, according to the specific enzyme involved, heme precursors accumulate up to the enzyme stop in disease-specific patterns and organs. Therefore, different porphyrias manifest themselves under strikingly different clinical pictures. In congenital sideroblastic anemias, instead, an altered utilization of mitochondrial iron by erythroid precursors leads to mitochondrial iron overload and an accumulation of ring sideroblasts in the bone marrow. In line with the complexity of the processes involved, the role of iron in these conditions is then multifarious. This review aims to summarise the most important lines of evidence concerning the interplay between iron and heme metabolism, as well as the clinical and experimental aspects of the role of iron in inherited conditions of altered heme biosynthesis.

Hepatic porphyrin concentration and uroporphyrinogen decarboxylase activity in hepatitis C virus infection

Previous studies have shown a high prevalence of hepatitis C virus (HCV) infection in patients with porphyria cutanea tarda (PCT). The aim of this study was to assess hepatic porphyrin concentrations (HPC) and hepatic uroporphyrinogen decarboxylase (UROD) activity in HCV-infected patients free of PCT. Thirty-two HCV-infected patients (20 M, 12 F, mean age 51 years) and seven control patients (4 M, 3 F, mean age 59 years) free of liver disease, were studied. Knodell's score was determined on liver biopsy by two independent anatomopathologists. Measurement of HPC and hepatic UROD activity levels were carried out on liver biopsy. Relative to controls, HCV-infected patients had high HPC levels (mean +/- SD: 47 +/- 20 vs. 17 +/- 6 pmol/mg protein, P < 0.001) and low hepatic UROD activity levels (514 +/- 95 vs. 619 +/- 125 pmol Copro/h/mg protein, P < 0.05). HPC was not correlated with hepatic UROD activity and the increase was due to coproporphyrin accumulation. No correlation was observed between HPC or hepatic UROD activity values and HCV-RNA concentrations, Knodell's score, hepatic fibrosis, periportal necrosis, periportal inflammation or hepatic iron content in HCV-infected patients. Hepatocellular necrosis was significantly correlated with HPC value (P < 0.005). Hence, in HCV-infected patients, HPC is significantly increased and hepatic UROD activity is very slightly decreased as compared to controls. HPC values and UROD activity are not correlated with HCV-RNA concentrations, hepatic iron content and hepatic fibrosis. The small increase in HPC values in hepatitis C infection is linked with hepatic injury and not with a direct effect on hepatic UROD enzyme.

Hemochromatosis genes and other factors contributing to the pathogenesis of porphyria cutanea tarda

Inherited and acquired factors have been implicated in the pathogenesis of porphyria cutanea tarda (PCT), a disorder characterized by a photosensitive dermatosis and hepatic siderosis. This study, comprising 108 patients with PCT, was intended to define the role of hemochromatosis gene (HFE) mutations in the expression of PCT and to determine the contribution of acquired factors including alcohol, hepatitis C virus (HCV), and estrogen. The 2 known HFEmutations, cysteine 282 tyrosine (Cys282Tyr) and histidine 63 asparagine (His63Asp), were detected by polymerase chain reaction, and anti-HCV immunoglobulin G was detected serologically. Liver biopsies were graded for iron content, inflammation, and fibrosis. Estimates of alcohol and estrogen use were based on a questionnaire. Of the PCT patients tested, 19% were homozygous for the Cys282Tyr mutation; controls were equal to 0.5%. The compound heterozygous genotype was detected in 7% of the PCT patients; controls were less than 1%. The transferrin saturation, serum ferritin, and liver iron burden of all PCT patients were higher than those of nonporphyric controls. The highest values were found in PCT patients homozygous for the Cys282Tyr mutation. Of the patients studied, 59% were HCV positive (compared with 1.8% of the population), and 46% consumed more than 70 g of alcohol daily. Of the female patients, 63% were ingesting estrogens. Hepatic damage was most marked in patients with the Cys282Tyr/Cys282Tyr genotype who had HCV and drank heavily. Homozygosity for the Cys282Tyrmutation and HCV are the greatest risk factors for expression of PCT, and in most patients, more than 1 risk factor was identified. It was common for patients with HCV to consume alcohol. Patients with PCT should be screened for HFE mutations and for HCV.

The role of iron in experimental porphyria and porphyria cutanea tarda

Porphyria cutanea tarda (PCT) and experimental porphyria are characterized by a decreased activity of the enzyme uroporphyrinogen decarboxylase, and accumulation of uroporphyrins and heptacarboxylporphyrins in the liver. Iron (Fe) plays an important role in PCT and experimental porphyria. Biochemically and electron microscopically, we examined the relationship between Fe and porphyrins in liver tissue of C57BL/10 mice made porphyric by administration of iron dextran as Imferon (IMF), and in liver biopsies of patients with symptomatic PCT. Accumulation of uroporphyrins and heptacarboxylporphyrins, and an increased amount of Fe were observed in livers of mice treated with IMF and in liver biopsies of patients with PCT. In mice treated with IMF, the activity of uroporphyrinogen decarboxylase was decreased. Both in livers of mice treated with IMF and in livers of patients with PCT, needle-like structures, representing uroporphyrin crystals, were observed by electron microscopy. Uroporphyrin crystals and Fe (as ferritin) were observed in the same hepatocyte. Moreover, there was a striking morphological correlation between uroporphyrin crystals and ferritin-Fe, suggesting a role for (ferritin-)Fe in the pathogenesis of porphyria.

Hepatocellular carcinoma in porphyria cutanea tarda: frequency and factors related to its occurrence

Thirty-eight patients with porphyria cutanea tarda (PCT) have been seen in the last 18 years. Five of these patients (13%) developed hepatocellular carcinoma (HCC) during follow-up. We analyzed the differences in clinical, laboratory and liver histology findings at presentation, between patients who developed HCC during follow-up (HCC-group, n = 5) and those who did not (PCT-group, n = 33). Of the clinical features the duration of skin-symptoms was longer in the HCC-group (mean: 10.4 +/- 1.1 years) than in the PCT-group (mean: 1.4 +/- 1 years) (p less than 0.001). No differences in routine laboratory findings were found. Although 11/38 (29%) patients had serologic evidence of a past hepatitis B virus infection and 7/38 (18%) patients had antibodies against hepatitis C virus, no differences in these parameters were found between the PCT-group and the HCC-group. In all 34 liver biopsies a variable degree of siderosis was found (PCT-group vs. HCC-group: NS). Only piecemeal necrosis (p less than 0.01) and advanced fibrosis or cirrhosis (p less than 0.001) were more common in liver biopsies in the HCC-group. In conclusion, factors related to an increased risk of HCC in PCT are: a) a long symptomatic period before start of treatment and b) the presence of chronic active hepatitis and/or advanced fibrosis or cirrhosis in liver biopsies.

Hepatic mitochondrial oxidative metabolism and lipid peroxidation in experimental hexachlorobenzene-induced porphyria with dietary carbonyl iron overload

Both human porphyria cutanea tarda and experimental hexachlorobenzene-induced porphyria are associated with hepatic injury and are potentiated by excess hepatic iron. The mechanisms whereby cellular injury occurs and the synergistic role of iron overload are unknown. In the present experiments, we studied hepatic mitochondrial function and lipid peroxidation in rats with hexachlorobenzene-induced porphyria in which iron loading was achieved by dietary carbonyl iron supplementation. Female rats were treated for 8 weeks, receiving a chow diet supplemented with hexachlorobenzene (0.2%, w/w), carbonyl iron (1.0%, w/w) or hexachlorobenzene + iron. Hepatic total porphyrins were increased 100-fold in rats receiving hexachlorobenzene (hexachlorobenzene alone and hexachlorobenzene + Fe), and total hepatic iron was increased approximately 10-fold in rats receiving iron supplementation (Fe alone and hexachlorobenzene + Fe). There was a significant increase in mitochondrial lipid peroxidation in rats treated with hexachlorobenzene alone and hexachlorobenzene + Fe. A significant reduction in mitochondrial respiratory control ratios and in oxidative phosphorylation (ADP/O ratios) using glutamate and succinate as substrates was demonstrated when rats were treated with hexachlorobenzene + iron. The reductions in respiratory control ratios were due to a combination of an inhibitory defect in electron transport as evidenced by an irreversible decrease in State 3 respiration and an uncoupling effect as evidenced by an increase in State 4 respiration. These findings suggest that lipid peroxidation and mitochondrial dysfunction may contribute to the hepatotoxicity seen in hexachlorobenzene-induced porphyria.

A potential biochemical explanation for the genesis of porphyria cutanea tarda. Studies on the inherent biochemical defect in highly purified human erythrocyte uroporphyrinogen decarboxylase and its amplification by iron

Familial porphyria cutanea tarda (PCT) is a photocutaneous disease in which subnormal activity of uroporphyrinogen decarboxylase is observed both in the liver and red cells. Hepatic iron plays a key role in the genesis of overt biochemical and clinical PCT. In this report, we have studied the properties of 10 000-fold purified erythrocyte uroporphyrinogen decarboxylase preparations from two familial PCT patients and a non-porphyric control subject. The apparent Michaelis constants (Km), determined by using uroporphyrinogen III substrate, were approx. 3.2-times higher for the enzyme from the diseased subjects (Km = approximately 1.0 microM) as compared to the normal (Km = 0.3 microM). Though both abnormal and normal enzymes were inhibited progressively with increasing concentrations of iron, the enzymes from diseased subjects exhibited greater susceptibility e.g. 0.1 mM Fe2+ inhibited the former about 50% and the latter about 20%. These observations suggest that the inherent biochemical defect in PCT is the reduced enzyme-substrate affinity and the intrinsic abnormal conformation renders the PCT enzyme particularly susceptible to inhibition by iron.

Hematologic and hepatic manifestations of the cutaneous porphyrias

This chapter has dealt with five photocutaneous forms of human porphyria. The forms are a diverse group of disorders with many different hematologic, hepatologic, and neurologic manifestations. In essence, most photocutaneous porphyrias occurring in childhood will relate to congenital erythropoietic porphyria or protoporphyria. The nature of the skin lesions and a study of the heme precursor profile in red cells, plasma, urine, and feces should easily distinguish these two conditions. CEP is a disease wherein photomutilation is a dominant concern and aggressive new approaches of therapy also have been discussed. In protoporphyria, the dermatologic problem is less severe and the dermatologist should be aware that a subset of patients could develop active liver disease that may lead to fatal cirrhosis. Novel approaches of therapy have been briefly alluded to. With regard to postpubertal photocutaneous porphyria, the classic porphyria cutanea tarda syndrome is associated with liver disease, usually alcoholic with siderosis, and the treatment by phlebotomy to reduce hepatic iron is highly effective. The potential danger of liver carcinoma has been discussed. In subsets of porphyria cutanea tarda, this can be an endemic disease relating to environmental factors, ie, ingestion of polyhalogenated hydrocarbons. The biochemical diagnosis can be attained by fairly straight-forward solvent extraction analyses of urine and feces, showing the dominance of uroporphyrin excretion in the urine and coproporphyrin in the feces. Chromatographic techniques in plasma, bile, and feces reveal a PCT-specific porphyrin: isocoproporphyrin. Rare subtypes with hematologic manifestations, ie, hepatoerythropoietic porphyria and CEP, indicate the wide spectra of disorders that might be associated with a spontaneous deficiency of uroporphyrinogen decarboxylase activity. These latter syndromes are, however, rare. Two hereditary hepatic porphyrias, ie, autosomal dominantly inherited VP and HCP, have been briefly discussed. The hepatic lesion is metabolic, not morphologic, and its expression by the liver relates to its adaptive response to induction of microsomal hemoproteins by a variety of exogeneous and endogeneous compounds, eg, drugs and hormones. Photocutaneous lesions of HCP and VP are identical to PCT, the latter having no neurologic sequelae. In the former two, however, exposure of persons to drugs, such as the hydantoins and barbiturates, can lead to potentially fatal acute porphyric attacks.(ABSTRACT TRUNCATED AT 400 WORDS)

The pathology of the liver in porphyria cutanea tarda

We report the findings in 53 biopsies from 45 patients with porphyria cutanea tarda (PCT). Red autofluorescence and birefringent acicular cytoplasmic inclusions were constant findings in all untreated cases. Autofluorescence occurs in other hepatic porphyrias, but acicular inclusions appear to be specific for PCT; we have seen them in subclinical porphyria and before development of cutaneous symptoms. They are probably uroporphyrins and they trend to disappear during rinsing by water during most staining procedures. We recommend unstained paraffin sections for their demonstration. Liver damage in PCT has features distinct from other liver diseases, including alcoholic liver disease. These include constant but mild periportal siderosis, focal lipofuscin deposition, focal lobular hepatocyte necrosis associated with groups of pigment-laden macrophages, focal steatosis, marked hepatocyte hyperplasia and the presence of periductal lymphocyte aggregates. The latter have not been previously described in PCT and were present in 43% of our cases. There is a direct relationship between increasing age and progressive distortion of liver architecture, with fibrosis present at a mean age of 48 years, cirrhosis at 57 and hepatocellular carcinoma at 66. The characteristic liver histology and the natural history of PCT are against this being the result of any non-specific liver damage and favour instead a specific liver disease whose pathogenesis may be mainly the result of the metabolic defect of PCT.

Effects of iron-loading and ethanol treatment on rat porphyrin metabolism

Rats were fed for 50 weeks with a standard diet containing 5.9% ferric ammonium sulphate. Half of these animals drank normal water, and the other half water containing 5% ethanol (groups 1 and 2). Two other groups received normal food, but drank water containing 5 or 10% ethanol (groups 3 and 4) for 40 weeks. Histologic examinations revealed that the iron-loading resulted in only mild hepatic siderosis in groups 1 and 2, the degree of siderosis not differing appreciably in the two groups. The ethanol led to fatty degeneration too in the liver of animals in group 2. Both iron-loading and ethanol treatment, either separately or in combination, increased the porphyrin excretion, but the distribution of the various porphyrins in the urine and faeces showed merely the symptoms of an aspecific poisoning. A significantly elevated uroporphyrin excretion was not observed in any of the groups, and thus the results support the view that dietary iron-loading and ethanol consumption can not be regarded as direct aetiologic factors in the pathomechanism of porphyria cutanea tarda. At the same time, the results suggest that vitamin E therapy, frequently employed effectively in porphyria cutanea tarda, can not be considered a causal intervention as regards the mechanism of action.

Decreased activity of hepatic uroporphyrinogen decarboxylase in sporadic porphyria cutanea tarda

To investigate the role of uroporphyrinogen decarboxylase in the pathogenesis of the sporadic form of porphyria cutanea tarda, we measured this enzyme in liver, erythrocytes and cultured skin fibroblasts, and also measured coproporphyrinogen oxidase and the total iron concentration in liver. The mean uroporphyrinogen decarboxylase activity was lower in liver from seven male patients (9.0 pmol of coproporphyrin per minute per milligram of protein) than in 12 controls, including seven with alcoholic liver disease (22.3 pmol per minute per milligram; P less than 0.05). Coproporphyrinogen oxidase activities were the same in each group. Liver iron concentrations were lower during remission, but uroporphyrinogen decarboxylase activities were not related to clinical activity for uroporphyrin excretion. Erythrocyte and fibroblast enzyme activities were the same as in normal subjects. A hepatic uroporphyrinogen decarboxylase defect is a prerequisite for the development of porphyria cutanea tarda, but other factors, which probably do not alter uroporphyrinogen decarboxylase activity, determine the clinical onset. In sporadic porphyria cutaneous tarda, the enzyme defect appears to be restricted to the liver.

The role of iron in the pathogenesis of porphyria cutanea tarda. An in vitro model

Porphyria cutanea tarda (PCT) is characterized biochemically by excessive hepatic synthesis and urinary excretion of uroporphyrin I. Clinical evidence has implicated iron in the pathogenesis of PCT. The synthesis of the normally occurring isomer of uroporphyrin, namely uroporphyrin III, from porphobilinogen (PBG) requires two enzymes; uroporphyrinogen I synthetase and uroporphyrinogen III cosynthetase (COSYN). In the absence of COSYN only uroporphyrinogen I is formed. These experiments were designed to study the effect of iron on porphyrin biosynthesis in porcine and human crude liver extracts and to measure COSYN activity in the presence of iron.Mitochondria-free crude liver extracts were prepared in 0.25 m sucrose at pH 7.4 by centrifugation at 37,000 g. Preparations were incubated with either 0.2 mm amino-levulinic acid (ALA) or 0.1 mm PBG. The addition of ferrous ion (either from ferritin iron [4 mug/ml] and cysteine [6.7 mm] or ferrous ammonium sulfate [0.3 mm Fe] and cysteine) significantly increased the rate of uroporphyrin synthesis from either ALA or PBG. The predominant porphyrin synthesized in the presence of ferrous ion was uroporphyrin I whereas coproporphyrin III predominated in its absence. Orthophenanthroline blocked these effects of ferrous ion.To investigate the effect of ferrous ion on COSYN, crude liver extracts were incubated with ferrous ammonium sulfate (0.3 mm Fe) and cysteine (6.7 mm) and the COSYN activity of the incubates was assayed directly. In both porcine and human extracts ferrous ion caused marked inhibition of COSYN activity. Orthophenanthroline blocked the inhibitory effect.Inactivation of COSYN by heating resulted in marked enhancement of porphyrin synthesis from PBG. The sole product was uroporphyrin I.Thus, inactivation of COSYN results in accelerated synthesis of uroporphyrin I. This effect of ferrous ion provides a possible biochemical explanation for the excess production and excretion of uroporphyrin I in patients with PCT and the reversal of this defect by phlebotomy.

Hepatic fluorescence in porphyria cutanea tarda studied in fine needle aspiration biopsy smears

Fine needle aspiration biopsy smears from 19 patients with porphyria cutanea tarda were studied by fluorescence microscopy. Fluorescence was arbitrarily graded from 0 to 4. All patients-those with clinically manifest as well as those with latent disease-showed bright red fluorescence of porphyrin type in the liver cells, though in latent cases the fluorescence commonly was of a low grade. In patients with manifest disease fluorescence of grade 3 or 4 was present. In patients with fluorescence of grades 1 or 2 the uroporphyrin excretion in urine was normal or slightly increased. At higher grades all levels of porphyrin excretion were encountered. Of 22 control subjects, only one showed hepatic fluorescence of a porphyrin character. The control patient with a positive finding was found to have definitely increased urinary uroporphyrin excretion and probably has latent porphyria cutanea tarda. The procedure described should be useful as a screening test for hepatic cutaneous porphyria.