Iron overload in porphyria cutanea tarda

BACKGROUND AND OBJECTIVE: Porphyria cutanea tarda (PCT) is a disorder of porphyrin metabolism associated with decreased activity of uroporphyrinogen decarboxylase (URO-D) in the liver. The relevance of iron in the pathogenesis of PCT is well established: iron overload is one of the factors that trigger the clinical manifestations of the disease and iron depletion remains the cornerstone of therapy for PCT. A role for genetic hemochromatosis in the pathogenesis of iron overload in PCT has been hypothesized in the past but only after the recent identification of the genetic defect causing hemochromatosis has the nature of this association been partially elucidated. This review will outline current concepts of the pathophysiology of iron overload in PCT as well as recent contributions to the molecular epidemiology of hemochromatosis defects in PCT. EVIDENCE AND INFORMATION SOURCES: The authors of the present review have a long-standing interest in the pathogenesis, etiology and epidemiology of iron overload syndromes. Evidence from journal articles covered by the Science Citation Index(R) and Medline(R) has been reviewed and collated with personal data and experience. STATE OF THE ART AND PERPECTIVES: Mild to moderate iron overload plays a key role in the pathogenesis of PCT. The recent identification of genetic mutations of the hemochromatosis gene (HFE) in the majority of patients with PCT confirms previous hypotheses on the association between PCT and hemochromatosis, allows a step forward in the understanding of the pathophysiology of the disturbance of iron metabolism in the liver of PCT patients, and provides an easily detectable genetic marker which could have a useful clinical application. Besides the epidemiological relevance of the association between PCT and hemochromatosis, however, it remains to be fully understood how iron overload, and in particular the cellular modifications of the iron status secondary to hemochromatosis mutations, affect the activity of URO-D, and how the altered iron metabolism interacts with the other two common triggers for PCT and etiological agents for the associated liver disease: alcohol and hepatitis viruses. The availability of a genetic marker for hemochromatosis will allow some of these issues to be addressed by studying aspects of porphyrins and iron metabolism in liver samples obtained from patients with PCT, liver disease of different etiology and different HFE genotypes, and by in vitro studies on genotyped cells and tissues.     

Hepatic pathology in porphyria cutanea tarda

We examined clinical and laboratory data and the liver pathology of 48 patients in whom porphyria cutanea tarda was related to alcohol ingestion, estrogen use and pregnancy, or was idiopathic. Biochemical test results, when abnormal, tended to be mild in most cases, with less than two-fold elevations of serum aminotransferases and alkaline phosphatase and mild hyperbilirubinemia. Fatty change, liver cell and Kupffer cell hemosiderosis and glycogenation of hepatocyte nuclei were frequent histologic findings in the 58 liver specimens studied. Alcoholic hepatitis, chronic hepatitis and cirrhosis were uncommon. Granuloma-like lobular aggregates consisting of iron- and ceroid-laden Kupffer cells, chronic inflammatory cells and fat droplets ("lobular lesions of porphyria cutanea tarda") were found in nearly two-thirds of specimens and appeared to be the most characteristic form of parenchymal damage in this form of porphyria. These lesions may be associated with pericentral fibrosis in alcoholic as well as estrogen-treated patients and may remit following therapeutic phlebotomy.     

Insulin resistance in porphyria cutanea tarda

It has been reported that patients with porphyria cutanea tarda (PCT) develop carbohydrate (CHO) intolerance and manifest diabetes melitus (DM) more frequently than the normal population. In order to verify whether this is due to insulin resistance we studied 5 patients with PCT and 5 normal subjects matched for age, sex and weight. In all the patients an evaluation consisted of the glycemic curve and insulin response to an iv glucose tolerance test (IVGTT: 0.33 g/kg) as well as of an evaluation of the circulating monocyte insulin receptors. Blood samples were drawn in the basal state to measure plasma levels of NEFA, glycerol, and intermediate metabolites. The patients with PCT showed normal glucose tolerance which was obtained, however, at the expense of the elevated insulin levels: therefore a condition of insulin resistance was demonstrated in these subjects. An involvement of the lipid metabolism, observed by the raised levels of plasma NEFA and glycerol, was also evident. The insulin binding to circulating monocytes was reduced but not enough to justify the degree of insulin resistance observed. Therefore, it could be hypothesized, in agreement with similar studies, that a postreceptor defect is responsible for the insulin-resistance observed in patients with PCT and that the reduction of insulin receptors is determined by the down regulation in response to elevated insulinemic levels. An alteration of the porphyrin metabolism might be responsible for this disorder.     

Treatment of hemodialysis-related porphyria cutanea tarda with plasma exchange

A patient with hemodialysis-related porphyria cutanea tarda was treated with plasma exchange. A rapid clinical response occurred coincidentally with a significant fall in the plasma porphyrin level. The level fell further over the following few months without additional therapeutic intervention, whereafter a slow rise occurred without recurrence of skin disease. We suggest that this form of treatment may be ideal for the patient with porphyria cutanea tarda and chronic renal failure in whom no alternative therapy is available for the cutaneous problem.     

The HLA system and porphyria cutanea tarda

Familiar occurrence of porphyria cutanea tarda (P. C. T.) has led to search for genetic markers of this disease. One of the three contradictory studies in literature showed significant increased frequencies of HLA-A3 and -B7 in the P. C. T. These results are important for the hypothesis that a disorder of iron metabolism linked to the HLA system (HLA-A3) supports a manifestations of the disease. Our investigations don't support generally this hypothesis. In 90 P. C. T.-patients significantly higher frequencies of any HLA-A, -B and -C-locus were not to be found. But we found a statistic guaranteed higher frequency of HLA-A9 in the subgroup (n = 34) of alcoholic induced P. C. T. An association between HLA-A9 and liver diseases is reported somewhere else. The higher percentage of HLA-A3 incidence in this group was not significant. Significant higher frequency of HLA-A9 possibly refers to liver diseases by P. C. T. HLA-A3--association is imagineable with iron-over loaded disorder in this group.     

Genetic aspects of porphyria cutanea tarda

Porphyria cutanea tarda (PCT) is caused by disruption of heme biosynthesis at the step catalyzed by uroporphyrinogen decarboxylase. The patients present with photosensitive cutaneous lesions, hepatic pathology (including elevated porphyrin levels), and increased excretion of porphyrins. Therapy consists of removing the exacerbating factors of PCT (reduced sunlight exposure, abstinence from alcohol use, decreased estrogen exposure, and treatment for viral infections), decreasing body iron stores (by therapeutic phlebotomy or by the use of the new orally active iron chelators), and, in some instances, the use of low-dose antimalarials. Recent advances in genetics and genomics have allowed DNA testing for porphyria cutanea tarda and are likely to be instrumental in developing improved, gene-based treatments and in finding genetic loci (in addition to uroporphyrinogen decarboxylase) involved in the clinical expression of this disease.     

Australia antigen and porphyria cutanea tarda]

In 40 patients suffering from porphyria cutanea tarda the sera were examined for the existence of HBAg and HBAb. Hepatitis was known in the history of 6 patients, in 3 of 23 bioptically examined livers a chronic aggressive hepatitis could be proved. When the transmigration electrophoresis after Pesendorfer and coworkers was used, in no case HBAg and HBAb could be proved.     

Down-regulation of hepcidin in porphyria cutanea tarda

Hepatic siderosis is common in patients with porphyria cutanea tarda (PCT). Mutations in the hereditary hemochromatosis (hh) gene (HFE) explain the siderosis in approximately 20% patients, suggesting that the remaining occurrences result from additional genetic and environmental factors. Two genes known to modify iron loading in hh are hepcidin (HAMP) and hemojuvelin (HJV). To determine if mutations in or expression of these genes influenced iron overload in PCT, we compared sequences of HAMP and HJV in 96 patients with PCT and 88 HFE C282Y homozygotes with marked hepatic iron overload. We also compared hepatic expression of these and other iron-related genes in a group of patients with PCT and hh. Two intronic polymorphisms in HJV were associated with elevated serum ferritin in HFE C282Y homozygotes. No exonic polymorphisms were identified. Sequencing of HAMP revealed exonic polymorphisms in 2 patients with PCT: heterozygosity for a G-->A transition (G71D substitution) in one and heterozygosity for an A-->G transition (K83R substitution) in the other. Hepatic HAMP expression in patients with PCT was significantly reduced, regardless of HFE genotype, when compared with patients with hh but without PCT with comparable iron overload. These data indicate that the hepatic siderosis associated with PCT likely results from dysregulated HAMP.     

Does paraneoplastic porphyria cutanea tarda exist?

Our investigations in 134 patients showed corresponding to literature porphyria cutanea tarda (PCT) diagnosed by biochemical methods not to be a paraneoplastic dermatosis (but one possible exception acquainted). Relations between PCT and extrahepatic non-porphyrin producing tumours are improbable. Nevertheless but extremely seldom an irregular urinary porphyrin excretion associated with cutaneous changes of hepatic porphyria should lead to the presumption of a porphyrin producing hepatoma. PCT lasting for decades apparently presents a higher frequency of hepatocellular carcinoma in patients suffering from liver cirrhosis than in cirrhotics without PCT. It is supposed that this possible progredience of liver disease in PCT into hepatocellular carcinoma may be prevented by chloroquine phosphate therapy.     

Sporadic porphyria cutanea tarda due to haemochromatosis

Haemochromatosis is a hereditary iron-overload syndrome caused by increased intestinal iron absorption and characterised by accumulation of potentially toxic iron in the tissues. Sometimes this disease presents as a cutanea porphyria. We describe a patient with joint complaints and blistering skin lesions on sun-exposed skin. After identifying the porphyria cutanea tarda by urine analysis we found that the serum activity of uroporphyrinogen decarboxylase (UROD) was normal, meaning a partial inactivation of UROD in liver tissue due to external factors. Further investigation showed the homozygous Cys282Tyr missense mutation and high levels of serum ferritin. It is important to recognise the symptoms of iron overloading at an early stage because hereditary haemochromatosis needs to be treated immediately. We therefore advocate routine sampling of ferritin levels in patients with unexplained joint complaints.     

Hepatitis B virus infection in porphyria cutanea tarda

Serum markers of hepatitis B virus (HBV) infection were determined in 82 patients with porphyria cutanea tarda (PCT). Pathogenetic factors (alcohol, thalassemia minor, drugs) and clinical and histologic findings of PCT were taken into account. The prevalence of HBV infection was very high (70.7%). Hepatitis B surface antigen (HBsAg) was positive in 14 patients (17%). Eight patients had HBV infection as the only documented acquired factor. The clinical picture and histologic findings were aggravated by HBV infection; primary hepatic carcinoma occurred in four patients with HBV infection. Liver siderosis was histologically documented in 82.6% of cases, serum ferritin was pathologically increased in 91%, confirming the role of iron overload in PCT. A correlation (p less than 0.02; chi-squared method) was found between increased serum ferritin levels and HBV infection, suggesting a possible relationship between liver siderosis and HBV clearance. HBV infection appears to be a relevant additional factor in the pathogenesis of PCT liver disease.     

HLA-linked hemochromatosis alleles in sporadic porphyria cutanea tarda

We tested the hypothesis that the hepatic siderosis that characterizes sporadic porphyria cutanea tarda is due to the presence of HLA-linked hemochromatosis alleles. We studied 21 probands with sporadic porphyria cutanea tarda and 135 of their relatives by determining HLA haplotypes and measuring transferrin saturation and serum ferritin concentration. Liver biopsies were performed in all probands and in relatives when appropriate. Seventeen pedigrees were available and were studied by both likelihood analysis and by a gene counting method. We estimated that 10 of the 17 probands with available living relatives possessed at least one hemochromatosis allele. Thirteen of the 21 probands (62%) possessed at least one HLA-A3 alloantigen. Eighteen of 69 relatives who shared an HLA haplotype with a proband (26%) had an elevation of transferrin saturation or serum ferritin concentration. Only one first-degree relative not sharing an HLA haplotype with a proband had an elevated transferrin saturation or serum ferritin concentration. These findings indicate that HLA-linked hemochromatosis alleles are far more common in patients with sporadic porphyria cutanea tarda than in individuals in the general population and may be responsible for the hepatic siderosis associated with most cases of sporadic porphyria cutanea tarda.