A porphomethene inhibitor of uroporphyrinogen decarboxylase causes 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.

The clinical management of porphyria cutanea tarda: An update

Porphyria cutanea tarda (PCT) is the commonest of the porphyrias (Semin Liver Dis 1998;18:67). It often occurs secondary to an underlying internal disorder, has significant impacts on liver health and longevity, and is a treatable disease. Thus, for the clinician, recognising the disease to make the correct diagnosis, identifying causative underlying diseases, and treating the porphyria and its complications, are crucial. Although reviews on the management of PCT have been written, there have recently been significant advances in the understanding of the factors predisposing to the disease, and of its wider health impacts. This review aims to help the clinician to diagnose and manage patients with PCT, with an emphasis on the impact of recent advances on clinical management.

Update on heme biosynthesis, tissue-specific regulation, heme transport, relation to iron metabolism and cellular energy

Heme is a primordial macrocycle upon which most aerobic life on Earth depends. It is essential to the survival and health of nearly all cells, functioning as a prosthetic group for oxygen-carrying proteins and enzymes involved in oxidation/reduction and electron transport reactions. Heme is essential for the function of numerous hemoproteins and has numerous other roles in the biochemistry of life. In mammals, heme is synthesised from glycine, succinyl-CoA, and ferrous iron in a series of eight steps. The first and normally rate-controlling step is catalysed by 5-aminolevulinate synthase (ALAS), which has two forms: ALAS1 is the housekeeping form with highly variable expression, depending upon the supply of the end-product heme, which acts to repress its activity; ALAS2 is the erythroid form, which is regulated chiefly by the adequacy of iron for erythroid haemoglobin synthesis. Abnormalities in the several enzymes of the heme synthetic pathway, most of which are inherited partial enzyme deficiencies, give rise to rare diseases called porphyrias. The existence and role of heme importers and exporters in mammals have been debated. Recent evidence established the presence of heme transporters. Such transporters are important for the transfer of heme from mitochondria, where the penultimate and ultimate steps of heme synthesis occur, and for the transfer of heme from cytoplasm to other cellular organelles. Several chaperones of heme and iron are known and important for cell health. Heme and iron, although promoters of oxidative stress and potentially toxic, are essential cofactors for cellular energy production and oxygenation.

A thylakoid biogenesis BtpA protein is required for the initial step of tetrapyrrole biosynthesis in cyanobacteria

Biogenesis of the photosynthetic apparatus requires complicated molecular machinery, individual components of which are either poorly characterized or unknown. The BtpA protein has been described as a factor required for the stability of photosystem I (PSI) in cyanobacteria; however, how the BtpA stabilized PSI remains unexplained. To clarify the role of BtpA, we constructed and characterized the btpA-null mutant (ΔbtpA) in the cyanobacterium Synechocystis sp. PCC 6803. The mutant contained only c. 1% of chlorophyll and nearly no thylakoid membranes. However, this strain, growing only in the presence of glucose, was genetically unstable and readily generated suppressor mutations that restore the photoautotrophy. Two suppressor mutations were mapped into the hemA gene encoding glutamyl-tRNA reductase (GluTR) - the first enzyme of tetrapyrrole biosynthesis. Indeed, the GluTR was not detectable in the ΔbtpA mutant and the suppressor mutations restored biosynthesis of tetrapyrroles and photoautotrophy by increased GluTR expression or by improved GluTR stability/processivity. We further demonstrated that GluTR associates with a large BtpA oligomer and that BtpA is required for the stability of GluTR. Our results show that the BtpA protein is involved in the biogenesis of photosystems at the level of regulation of tetrapyrrole biosynthesis.

Update on the Porphyrias

The porphyrias are a group of rare diseases, each resulting from a defect in a different enzymatic step of the heme biosynthetic pathway. They can be broadly divided into two categories, hepatic and erythropoietic porphyrias, depending on the primary site of accumulation of heme intermediates. These disorders are multisystemic with variable symptoms that can be encountered by physicians in any specialty. Here, we review the porphyrias and describe their clinical presentation, diagnosis, and management. We discuss novel therapies that are approved or in development. Early diagnosis is key for the appropriate management and prevention of long-term complications in these rare disorders.

The Hepatic Porphyrias: Revealing the Complexities of a Rare Disease

The porphyrias are a group of metabolic disorders that are caused by defects in heme biosynthesis pathway enzymes. The result is accumulation of heme precursors, which can cause neurovisceral and/or cutaneous photosensitivity. Liver is commonly either a source or target of excess porphyrins, and porphyria-associated hepatic dysfunction ranges from minor abnormalities to liver failure. In this review, the first of a three-part series, we describe the defects commonly found in each of the eight enzymes involved in heme biosynthesis. We also discuss the pathophysiology of the hepatic porphyrias in detail, covering epidemiology, histopathology, diagnosis, and complications. Cellular consequences of porphyrin accumulation are discussed, with an emphasis on oxidative stress, protein aggregation, hepatocellular cancer, and endothelial dysfunction. Finally, we review current therapies to treat and manage symptoms of hepatic porphyria.

Ledipasvir/Sofosbuvir Is Effective as Sole Treatment of Porphyria Cutanea Tarda with Chronic Hepatitis C

BACKGROUND AND AIMS

Chronic hepatitis C [CHC] is a risk factor for porphyria cutanea tarda [PCT]. To assess whether ledipasvir/sofosbuvir is effective for treating both PCT and CHC, we treated patients with CHC + PCT solely with ledipasvir/sofosbuvir and followed them for at least 1 year to assess cure of CHC and remission of PCT.

METHODS

Between September 2017 and May 2020, 15 of 23 screened PCT + CHC patients were eligible and enrolled. All were treated with ledipasvir/sofosbuvir at recommended doses and durations, according to their stage of liver disease. We measured plasma and urinary porphyrins at baseline and monthly for the first 12 months and at 16, 20, and 24 mos. We measured serum HCV RNA at baseline, 8-12, and 20-24 mos. Cure of HCV was defined as no detectable serum HCV RNA ≥ 12 weeks after the end of treatment (EOT). Remission of PCT was defined clinically as no new blisters or bullae and biochemically as urinary uro- plus hepta-carboxyl porphyrins ≤ 100 mcg/g creatinine.

RESULTS

All 15 patients, 13 of whom were men, were infected with HCV genotype 1. 2/15 withdrew or were lost to follow-up. Of the remaining 13, 12 achieved cure of CHC; 1 had complete virological response, followed by relapse of HCV after ledipasvir/sofosbuvir but was subsequently cured by treatment with sofosbuvir/velpatasvir. Of the 12 cured of CHC, all achieved sustained clinical remission of PCT.

CONCLUSIONS

Ledipasvir/sofosbuvir [and likely other direct-acting antivirals] is an effective treatment for HCV in the presence of PCT and leads to clinical remission of PCT without additional phlebotomy or low-dose hydroxychloroquine treatment.

TRIAL REGISTRATION

ClinicalTrials.gov NCT03118674.

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.

A Recap of Heme Metabolism towards Understanding Protoporphyrin IX Selectivity in Cancer Cells

Mitochondria are essential organelles of mammalian cells, often emphasized for their function in energy production, iron metabolism and apoptosis as well as heme synthesis. The heme is an iron-loaded porphyrin behaving as a prosthetic group by its interactions with a wide variety of proteins. These complexes are termed hemoproteins and are usually vital to the whole cell comportment, such as the proteins hemoglobin, myoglobin or cytochromes, but also enzymes such as catalase and peroxidases. The building block of porphyrins is the 5-aminolevulinic acid, whose exogenous administration is able to stimulate the entire heme biosynthesis route. In neoplastic cells, this methodology repeatedly demonstrated an accumulation of the ultimate heme precursor, the fluorescent protoporphyrin IX photosensitizer, rather than in healthy tissues. While manifold players have been proposed, numerous discrepancies between research studies still dispute the mechanisms underlying this selective phenomenon that yet requires intensive investigations. In particular, we wonder what are the respective involvements of enzymes and transporters in protoporphyrin IX accretion. Is this mainly due to a boost in protoporphyrin IX anabolism along with a drop of its catabolism, or are its transporters deregulated? Additionally, can we truly expect to find a universal model to explain this selectivity? In this report, we aim to provide our peers with an overview of the currently known mitochondrial heme metabolism and approaches that could explain, at least partly, the mechanism of protoporphyrin IX selectivity towards cancer cells.

Iron in Porphyrias: Friend or Foe?

Iron is a trace element that is important for many vital processes, including oxygen transport, oxidative metabolism, cellular proliferation, and catalytic reactions. Iron supports these functions mainly as part of the heme molecule. Heme synthesis is an eight-step process which, when defective at the level of one of the eight enzymes involved, can cause the development of a group of diseases, either inherited or acquired, called porphyrias. Despite the strict link between iron and heme, the role of iron in the different types of porphyrias, particularly as a risk factor for disease development/progression or as a potential therapeutic target or molecule, is still being debated, since contrasting results have emerged from clinical observations, in vitro studies and animal models. In this review we aim to deepen such aspects by drawing attention to the current evidence on the role of iron in porphyrias and its potential implication. Testing for iron status and its metabolic pathways through blood tests, imaging techniques or genetic studies on patients affected by porphyrias can provide additional diagnostic and prognostic value to the clinical care, leading to a more tailored and effective management.

Porphyria cutanea tarda precipitated by ovarian stimulation during oocyte retrieval in a genetically susceptible female

We report a case of 33-year-old female with underlying genetic susceptibility for familial porphyria cutanea tarda due to novel UROD variant (c.636 + 2 dupT) unmasked by transient exposure to supraphysiological oestrogen concentrations following a single cycle of successful controlled ovarian stimulation for oocyte retrieval. Use of oral oestrogen in the form of oral contraceptive pills and hormone replacement therapy has been well known to trigger active porphyria cutanea tarda phenotype in susceptible women. However, to date, the emergence of clinically overt porphyria cutanea tarda has not been reported in association with fertility treatment in the literature before.

Nutrients and Porphyria: An Intriguing Crosstalk

Porphyria refers to a group of fascinating diseases from a metabolic and nutritional standpoint as it provides an example of how metabolic manipulation can be used for therapeutic purposes. It is characterized by defects in heme synthesis, particularly in the erythrocytes and liver. Specific enzymes involved in heme biosynthesis directly depend on adequate levels of vitamins and minerals in the tissues. Moreover, micronutrients that are required for producing succinyl CoA and other intermediates in the Krebs (TCA) cycle are indirectly necessary for heme metabolism. This review summarizes articles that describe the nutritional status, supplements intake, and dietary practices of patients affected by porphyria, paying special attention to the therapeutic use of nutrients that may help or hinder this group of diseases.

Resolution of subclinical porphyria cutanea tarda after hepatitis C eradication with direct-acting anti-virals

BACKGROUND

Hepatitis C virus (HCV) is a risk factor for porphyria cutanea tarda (PCT), a rare disease originating in the liver characterised by overproduction of porphyrins. Although hepatitis C infection is highly prevalent among patients with porphyria, only a minority of hepatitis C patients develop PCT.

AIMS

To explore the presence of porphyrin abnormalities in a cohort of asymptomatic hepatitis C-infected patients and the impact of anti-viral therapy.

METHODS

Eighty-four consecutive patients with HCV infection treated with direct-acting antivirals after 1 January 2018 were longitudinally evaluated for the presence of porphyrin abnormalities. Those patients with biochemical abnormalities at baseline were additionally evaluated at follow-up. Porphyrins in urine were screened by fluorometry and isomer separation was performed by liquid chromatography.

RESULTS

In five patients, all of them asymptomatic, porphyrin profile abnormalities were detected: three presented significant increased urinary porphyrins with a typical PCT profile, and two showed normal levels of urinary porphyrins, but abnormal porphyria-like profiles. Urine evaluation after hepatitis C cure showed complete normalisation of the urinary porphyrins in all patients, confirming the biochemical cure of the disease.

CONCLUSIONS

We document the existence of rare cases of hepatitis C-infected patients with significant uroporphyrinuria in the absence of dermatological manifestations. Anti-viral therapy normalises the biochemical disorder, preventing patients from presenting PCT associated complications.

Porphyria cutanea tarda: Recent update

Porphyria cutanea tarda (PCT) is the most common human porphyria, due to hepatic deficiency of uroporphyrinogen decarboxylase (UROD), which is acquired in the presence of iron overload and various susceptibility factors, such as alcohol abuse, smoking, hepatitis C virus (HCV) infection, HIV infection, iron overload with HFE gene mutations, use of estrogens, and UROD mutation. Patients with familial or type II PCT due to autosomal dominant UROD mutation also require other susceptibility factors, as the disease phenotype requires hepatic UROD deficiency to below 20% of normal. PCT clinically manifests with increased skin fragility and blistering skin lesions on sun exposed areas. The common age of presentation is 5th to 6th decade and occurs slightly more commonly in males. Although mild liver biochemical profile are common, advanced fibrosis and cirrhosis with hepatocellular carcinoma (HCC) can occasionally develop. Screening for HCC using ultrasound examination is recommended in PCT patients, especially with cirrhosis and advanced fibrosis. PCT is effectively and readily treatable with the use of either repeated phlebotomy or use of 100 mg hydroxychloroquine orally twice a week, and both the treatments are equally effective and safe. With the advent of new or direct antiviral agents for HCV infection, treatment of concomitant HCV has become safer and effective. Data are emerging on the benefit of these drugs as monotherapy for both PCT and HCV. After the achievement of remission of PCT, there remains a potential for relapse, especially when the susceptibility factors are not adequately controlled. Scanty data from retrospective and observational studies shows the relapse rate to be somewhat higher after remission with low-dose hydroxychloroquine as compared to phlebotomy induced remission. Future studies are needed on exploring mechanism of action of 4-aminoquinolines, understanding interaction of HCV and PCT, and relapse of PCT on long-term follow-up.

Heme biosynthesis and the porphyrias

Porphyrias, is a general term for a group of metabolic diseases that are genetic in nature. In each specific porphyria the activity of specific enzymes in the heme biosynthetic pathway is defective and leads to accumulation of pathway intermediates. Phenotypically, each disease leads to either neurologic and/or photocutaneous symptoms based on the metabolic intermediate that accumulates. In each porphyria the distinct patterns of these substances in plasma, erythrocytes, urine and feces are the basis for diagnostically defining the metabolic defect underlying the clinical observations. Porphyrias may also be classified as either erythropoietic or hepatic, depending on the principal site of accumulation of pathway intermediates. The erythropoietic porphyrias are congenital erythropoietic porphyria (CEP), and erythropoietic protoporphyria (EPP). The acute hepatic porphyrias include ALA dehydratase deficiency porphyria, acute intermittent porphyria (AIP), hereditary coproporphyria (HCP) and variegate porphyria (VP). Porphyria cutanea tarda (PCT) is the only porphyria that has both genetic and/or environmental factors that lead to reduced activity of uroporphyrinogen decarboxylase in the liver. Each of the 8 enzymes in the heme biosynthetic pathway have been associated with a specific porphyria (Table 1). Mutations affecting the erythroid form of ALA synthase (ALAS2) are most commonly associated with X-linked sideroblastic anemia, however, gain-of-function mutations of ALAS2 have also been associated with a variant form of EPP. This overview does not describe the full clinical spectrum of the porphyrias, but is meant to be an overview of the biochemical steps that are required to make heme in both erythroid and non-erythroid cells.

Porphyria cutanea tarda and hepatoerythropoietic porphyria: Identification of 19 novel uroporphyrinogen III decarboxylase mutations

Porphyria Cutanea Tarda (PCT) is a cutaneous porphyria that results from the hepatic inhibition of the heme biosynthetic enzyme uroporphyrinogen decarboxylase (UROD), and can occur either in the absence or presence of an inherited heterozygous UROD mutation (PCT subtypes 1 and 2, respectively). A heterozygous UROD mutation causes half-normal levels of UROD activity systemically, which is a susceptibility factor but is not sufficient alone to cause type 2 PCT. In both Types 1 and 2 PCT, the cutaneous manifestations are precipitated by additional factors that lead to generation of an inhibitor that more profoundly reduces hepatic UROD activity. PCT is an iron-related disorder, and many of its known susceptibility factors, which include infections (e.g. hepatitis C virus, HIV), high alcohol consumption, smoking, estrogens, and genetic traits (e.g. hemochromatosis mutations) can increase hepatic iron accumulation. Hepatoerythropoietic Porphyria (HEP) is a rare autosomal recessive disease that results from homozygosity or compound heterozygosity for UROD mutations and often causes infantile or childhood onset of both erythropoietic and cutaneous manifestations. During the 11-year period from 01/01/2007 through 12/31/2017, the Mount Sinai Porphyrias Diagnostic Laboratory provided molecular diagnostic testing for 387 unrelated patients with PCT and four unrelated patients with HEP. Of the 387 unrelated individuals tested for Type 2 PCT, 79 (20%) were heterozygous for UROD mutations. Among 26 family members of mutation-positive PCT patients, eight (31%) had the respective family mutation. Additionally, of the four unrelated HEP patients referred for UROD mutation analyses, all had homozygosity or compound heterozygosity for UROD mutations, and all eight asymptomatic family members were heterozygotes for UROD mutations. Of the UROD mutations identified, 19 were novel, including nine missense, two nonsense, one consensus splice-site, and seven insertions and deletions. These results expand the molecular heterogeneity of PCT and HEP by adding a total of 19 novel UROD mutations. Moreover, the results document the usefulness of molecular testing to confirm a genetic susceptibility trait in Type 2 PCT, confirm a diagnosis in HEP, and identify heterozygous family members.

Recent advances on porphyria genetics: Inheritance, penetrance & molecular heterogeneity, including new modifying/causative genes

The inborn errors of heme biosynthesis, the Porphyrias, include eight major disorders resulting from loss-of-function (LOF) or gain-of-function (GOF) mutations in eight of the nine heme biosynthetic genes. The major sites of heme biosynthesis are the liver and erythron, and the underlying pathophysiology of each of these disorders depends on the unique biochemistry, cell biology, and genetic mechanisms in these tissues. The porphyrias are classified into three major categories: 1) the acute hepatic porphyrias (AHPs), including Acute Intermittent Porphyria (AIP), Hereditary Coproporphyria (HCP), Variegate Porphyria (VP), and 5-Aminolevlulinic Acid Dehydratase Deficient Porphyria (ADP); 2) a hepatic cutaneous porphyria, Porphyria Cutanea Tarda (PCT); and 3) the cutaneous erythropoietic porphyrias, Congenital Erythropoietic Porphyria (CEP), Erythropoietic Protoporphyria (EPP), and X-Linked Protoporphyria (XLP). Their modes of inheritance include autosomal dominant with markedly decreased penetrance (AIP, VP, and HCP), autosomal recessive (ADP, CEP, and EPP), or X-linked (XLP), as well as an acquired sporadic form (PCT). There are severe homozygous dominant forms of the three AHPs. For each porphyria, its phenotype, inheritance pattern, unique genetic principles, and molecular genetic heterogeneity are presented. To date, >1000 mutations in the heme biosynthetic genes causing their respective porphyrias have been reported, including low expression alleles and genotype/phenotype correlations that predict severity for certain porphyrias. The tissue-specific regulation of heme biosynthesis and the unique genetic mechanisms for each porphyria are highlighted.

Association between hepatitis C virus and porphyria cutanea tarda

Porphyria cutanea tarda (PCT) arises from a deficiency of uroporphyrinogen decarboxylase (UROD) in the liver. Several exogenous risk factors are associated with the acquired form of the disease. In Southern Europe, PCT is strongly linked to hepatitis C virus (HCV) infection to the point that a high prevalence of viral infection in some geographic areas generated an increase of PCT cases as a complication. In spite of the association, PCT is a rare complication of HCV infection, thus suggesting the existence of susceptibility factors operating in only some patients. Investigation of liver specimens of PCT patients showed iron accumulation, which albeit moderate, was higher in comparison with HCV-infected patients without PCT. Measurements of hepcidin in serum of HCV-infected patients with and without PCT and calculation of hepcidin/ferritin ratio were compatible with the hypothesis that HCV induced inadequate response of hepcidin to iron accumulation. Administration of direct-acting antivirals (DAA) to HCV-infected patients with active PCT showed that eradication of the virus was followed by resolution of PCT and rapid disappearance of urinary porphyrins. This suggests a direct participation of the virus in the oxidative mechanism leading to UROD inhibition. If clinical evolution of HCV- PCT-patients is placed within a time-frame, rapid PCT resolution by DAA is in striking contrast with a long-delay (in most cases of decades) between viral infection and appearance of overt porphyria. This could be explained if HCV infection (a): enhanced an oxidative environment in the vicinity of UROD and (b): facilitated iron accumulation through hepdicin down-regulation. Thus, only when iron accumulation reached a threshold, inhibition of UROD attained a critical level. However, the enigma is why only a minority of HCV-infected patients develop PCT. If additional risk factors (i.e. alcohol abuse) are not concurring, it should be concluded that modifier genes or epigenetic mechanisms related to iron homeostasis, facilitate iron progressive accumulation in only a minority susceptible patients.

Murine models of the human porphyrias: Contributions toward understanding disease pathogenesis and the development of new therapies

Mouse models of the human porphyrias have proven useful for investigations of disease pathogenesis and to facilitate the development of new therapeutic approaches. To date, mouse models have been generated for all major porphyrias, with the exception of X-linked protoporphyria (XLP) and the ultra rare 5-aminolevulinic acid dehydratase deficient porphyria (ADP). Mouse models have been generated for the three autosomal dominant acute hepatic porphyrias, acute intermittent porphyria (AIP), hereditary coproporphyria (HCP), and variegate porphyria (VP). The AIP mice, in particular, provide a useful investigative model as they have been shown to have acute biochemical attacks when induced with the prototypic porphyrinogenic drug, phenobarbital. In addition to providing important insights into the disease pathogenesis of the neurological impairment in AIP, these mice have been valuable for preclinical evaluation of liver-targeted gene therapy and RNAi-mediated approaches. Mice with severe HMBS deficiency, which clinically and biochemically mimic the early-onset homozygous dominant AIP (HD-AIP) patients, have been generated and were used to elucidate the striking phenotypic differences between AIP and HD-AIP. Mice modeling the hepatocutaneous porphyria, porphyria cutanea tarda (PCT), made possible the identification of the iron-dependent inhibitory mechanism of uroporphyrinogen decarboxylase (UROD) that leads to symptomatic PCT. Mouse models for the two autosomal recessive erythropoietic porphyrias, congenital erythropoietic porphyria (CEP) and erythropoeitic protoporphyria (EPP), recapitulate many of the clinical and biochemical features of the severe human diseases and have been particularly useful for evaluation of bone marrow transplantation and hematopoietic stem cell (HSC)-based gene therapy approaches. The EPP mice have also provided valuable insights into the underlying pathogenesis of EPP-induced liver damage and anemia.

Current and innovative emerging therapies for porphyrias with hepatic involvement

Porphyrias are rare inherited disorders caused by specific enzyme dysfunctions in the haem synthesis pathway, which result in abnormal accumulation of specific pathway intermediates. The symptoms depend upon the chemical characteristics of these substances. Porphyrins are photoreactive and cause photocutaneous lesions on sunlight-exposed areas, whereas accumulation of porphyrin precursors is related to acute neurovisceral attacks. Current therapies are suboptimal and mostly address symptoms rather than underlying disease mechanisms. Advances in the understanding of the molecular bases and pathogenesis of porphyrias have paved the way for the development of new therapeutic strategies. In this Clinical Trial Watch we summarise the basic principles of these emerging approaches and what is currently known about their application to porphyrias of hepatic origin or with hepatic involvement.

Clinical Guide and Update on Porphyrias

Physicians should be aware of porphyrias, which could be responsible for unexplained gastrointestinal, neurologic, or skin disorders. Despite their relative rarity and complexity, most porphyrias can be easily defined and diagnosed. They are caused by well-characterized enzyme defects in the complex heme biosynthetic pathway and are divided into categories of acute vs non-acute or hepatic vs erythropoietic porphyrias. Acute hepatic porphyrias (acute intermittent porphyria, variegate porphyria, hereditary coproporphyria, and aminolevulinic acid dehydratase deficient porphyria) manifest in attacks and are characterized by overproduction of porphyrin precursors, producing often serious abdominal, psychiatric, neurologic, or cardiovascular symptoms. Patients with variegate porphyria and hereditary coproporphyria can present with skin photosensitivity. Diagnosis relies on measurement of increased urinary 5-aminolevulinic acid (in patients with aminolevulinic acid dehydratase deficient porphyria) or increased 5-aminolevulinic acid and porphobilinogen (in patients with other acute porphyrias). Management of attacks requires intensive care, strict avoidance of porphyrinogenic drugs and other precipitating factors, caloric support, and often heme therapy. The non-acute porphyrias are porphyria cutanea tarda, erythropoietic protoporphyria, X-linked protoporphyria, and the rare congenital erythropoietic porphyria. They lead to the accumulation of porphyrins that cause skin photosensitivity and occasionally severe liver damage. Secondary elevated urinary or blood porphyrins can occur in patients without porphyria, for example, in liver diseases, or iron deficiency. Increases in porphyrin precursors and porphyrins are also found in patients with lead intoxication. Patients with porphyria cutanea tarda benefit from iron depletion, hydroxychloroquine therapy, and, if applicable, elimination of the hepatitis C virus. An α-melanocyte-stimulating hormone analogue can reduce sunlight sensitivity in patients with erythropoietic protoporphyria or X-linked protoporphyria. Strategies to address dysregulated or dysfunctional steps within the heme biosynthetic pathway are in development.

Porphyrin-Induced Protein Oxidation and Aggregation as a Mechanism of Porphyria-Associated Cell Injury

Genetic porphyrias comprise eight diseases caused by defects in the heme biosynthetic pathway that lead to accumulation of heme precursors. Consequences of porphyria include photosensitivity, liver damage and increased risk of hepatocellular carcinoma, and neurovisceral involvement, including seizures. Fluorescent porphyrins that include protoporphyrin-IX, uroporphyrin and coproporphyrin, are photo-reactive; they absorb light energy and are excited to high-energy singlet and triplet states. Decay of the porphyrin excited to ground state releases energy and generates singlet oxygen. Porphyrin-induced oxidative stress is thought to be the major mechanism of porphyrin-mediated tissue damage. Although this explains the acute photosensitivity in most porphyrias, light-induced porphyrin-mediated oxidative stress does not account for the effect of porphyrins on internal organs. Recent findings demonstrate the unique role of fluorescent porphyrins in causing subcellular compartment-selective protein aggregation. Porphyrin-mediated protein aggregation associates with nuclear deformation, cytoplasmic vacuole formation and endoplasmic reticulum dilation. Porphyrin-triggered proteotoxicity is compounded by inhibition of the proteasome due to aggregation of some of its subunits. The ensuing disruption in proteostasis also manifests in cell cycle arrest coupled with aggregation of cell proliferation-related proteins, including PCNA, cdk4 and cyclin B1. Porphyrins bind to native proteins and, in presence of light and oxygen, oxidize several amino acids, particularly methionine. Noncovalent interaction of oxidized proteins with porphyrins leads to formation of protein aggregates. In internal organs, particularly the liver, light-independent porphyrin-mediated protein aggregation occurs after secondary triggers of oxidative stress. Thus, porphyrin-induced protein aggregation provides a novel mechanism for external and internal tissue damage in porphyrias that involve fluorescent porphyrin accumulation.

[The cutaneous porphyrias]

The porphyrias are a group of metabolic disorders resulting from an innate abnormality in haem biosynthesis, and the clinical settings of which vary according to the genetic enzyme abnormality in question. These are genetic disorders with autosomal dominant or recessive inheritance of varying penetrance, and whose clinical expression differs according to the preferential location of haem precursors. Different classifications have been proposed according to genetic inheritance, the enzyme anomaly at issue, and clinical expression. The clinical classification distinguishes between acute porphyria (acute intermittent porphyria, porphyria variegata, hereditary coproporphyria), bullous cutaneous porphyrias (porphyria cutanea tarda, porphyria variegata and hereditary coproporphyria), painful photosensitive acute cutaneous porphyrias (erythropoietic protoporphyria and X-linked dominant protoporphyria), and rare recessive porphyrias (congenital erythropoietic porphyria, Doss porphyria, hepatoerythropoietic porphyria and harderoporphyria). Treatment depends on the clinical expression of the disorder.

Porphyria cutanea tarda: a case report

Background

The porphyrias are a rare group of metabolic disorders that can either be inherited or acquired. Along the heme biosynthetic pathway, porphyrias can manifest with neurovisceral and/or cutaneous symptoms, depending on the defective enzyme. Porphyria cutanea tarda, the most common type of porphyria worldwide, is caused by a deficiency of uroporphyrinogen decarboxylase, a crucial enzyme in heme biosynthesis, which results in an accumulation of photosensitive byproducts, such as uroporphyrinogen, which leads to the fragility and blistering of sun-exposed skin.

Porphyria cutanea tarda is a condition that affects the liver and skin by reduction and inhibition of uroporphyrinogen decarboxylase enzyme in erythrocytes. Areas of skin that are exposed to the sun can generate blisters, hyperpigmentation, and, sometimes, lesions that heal leaving a scar or keratosis. Liver damage might present in a wide range of ways from liver function test abnormalities to hepatocellular carcinoma. The toxic effect of iron plays a role in liver damage pathogenesis.

Case presentation

A 59-year-old Turkish man presented with hyperpigmented skin lesions, fatigue, and elevated ferritin level and liver function tests. He was diagnosed as having porphyria cutanea tarda after a clinical investigation and treated with phlebotomy.

Conclusion

Porphyria cutanea tarda is a rare condition of the liver but it must be remembered in a differential diagnosis of liver disease with typical skin involvement to decrease morbidity and health costs with early treatment.

Porphyrias and photosensitivity: pathophysiology for the clinician

Porphyrias are disorders caused by defects in the biosynthetic pathway of heme. Their manifestations can be divided into three distinct syndromes, each attributable to the accumulation of three distinct classes of molecules. The acute neurovisceral syndrome is caused by the accumulation of the neurotoxic porphyrin precursors, delta aminolevulinic acid, and porphobilinogen; the syndrome of immediate painful photosensitivity is caused by the lipid-soluble protoporphyrin IX and, the syndrome of delayed blistering photosensitivity, caused by the water-soluble porphyrins, uroporphyrin, and coproporphyrin. Porphyrias can manifest with one, or with a combination, of these syndromes, depending on whether one or more types of molecules are being accumulated. Iron plays a significant role in some of these conditions, as evidenced by improvements in both clinical manifestations and laboratory parameters, following iron depletion in porphyria cutanea tarda, or iron administration in some cases of X-linked erythropoietic protoporphyria. While the pathophysiology of a specific type of porphyrias, the protoporphyrias, appears to favor the administration of zinc, results so far have been conflicting, necessitating further studies in order to assess its potential benefit. The pathways involved in each disease, as well as insights into their pathobiological processes are presented, with an emphasis on the development of photosensitivity reactions.

Relapse of porphyria cutanea tarda after treatment with phlebotomy or 4-aminoquinoline antimalarials: a meta-analysis

BACKGROUND

Porphyria cutanea tarda (PCT) is the most common human porphyria. It is caused by hepatic deficiency of uroporphyrinogen decarboxylase activity, which is acquired in the presence of multiple susceptibility factors. PCT presents clinically with cutaneous blistering photosensitivity and is readily treatable with either repeated phlebotomy or 4-aminoquinoline antimalarials.

OBJECTIVES

To perform a systematic review and meta-analysis to compare the effectiveness of these quite different treatment approaches, especially on relapse rates (RRs) after achieving remission.

METHODS

Published studies that included follow-up for at least 1 year after treatment of PCT were included. The primary study outcome was PCT relapse. Pooled data are reported as the RRs per person-year of follow-up with 95% confidence intervals (CIs).

RESULTS

Of 375 articles identified as pertaining to PCT treatment, 12 were eligible for analysis. Of these, five used high-dose 4-aminoquinoline regimens (two combined with phlebotomy and three without phlebotomy), five used low-dose 4-aminoquinoline regimens and three used phlebotomy. RRs during the year after treatment were similar for the high- and low-dose 4-aminoquinoline groups (35-36%) and lower in the phlebotomy group (20%). The pooled RRs with their 95% CIs were 8·6 (3·9-13·3) per 100 person-years in the high-dose 4-aminoquinoline group, 17·1 (8·9-25·3) per 100 person-years in the low-dose 4-aminoquinoline group and 5·1 (0·5-10·6) per 100 person-years in the phlebotomy group. Subgroup and sensitivity analyses showed similar results.

CONCLUSIONS

Clinical or biochemical RRs ranged from 5 to 17 per 100 person-years after remission of PCT. Relapses were somewhat more frequent after remission with 4-aminoquinoline regimens than after remission following phlebotomy. Prospective studies are needed to define better how often relapses occur with these treatments after documenting both clinical and biochemical remission of PCT.

The association between chemical-induced porphyria and hepatic cancer

The haem biosynthetic pathway is of fundamental importance for cellular metabolism both for the erythroid and nonerythroid tissues. There are several genetic variants of the pathway in the human population that cause dysfunction of one or other of the enzymes resulting in porphyrias of varying severity. Serious chronic hepatic and systemic diseases may result. Some of these can be precipitated by exposure to drugs including hormones, barbiturates and antibiotics, as well as alcohol and particular chlorinated aromatic chemicals. In experimental animals some of the steps of this pathway can also be severely disrupted by a variety of environmental chemicals, potential drugs and pesticides, especially in the liver, leading to the accumulation of uroporphyrins derived from the intermediate uroporphyrinogens or protoporphyrin IX, the immediate precursor of haem. With some of these chemicals this also leads to cholestasis and liver cell injury and eventually hepatic tumours. The review evaluates the available evidence linking hepatic porphyria with carcinogenesis in naturally occurring human genetic conditions and in chemically-induced porphyrias in laboratory animals. The existing data showing gender, strain, and species differences in sensitivity to the chemical-induced porphyrias, liver injury and liver tumours are discussed and the role that transgenically altered mouse models have played in defining the varying mechanisms. Finally, the review proposes a novel, unifying hypothesis linking the hepatotoxicity induced by the accumulation of various porphyrins, with the increased risk of developing hepatic cancer as a long term consequence.

Hepatitis C virus core protein triggers abnormal porphyrin metabolism in human hepatocellular carcinoma cells

Porphyria cutanea tarda (PCT), the most common of the human porphyrias, arises from a deficiency of uroporphyrinogen decarboxylase. Studies have shown a high prevalence of hepatitis C virus (HCV) infection in patients with PCT. While these observations implicate HCV infection as a risk factor for PCT pathogenesis, the mechanism of interaction between the virus and porphyrin metabolism is unknown. This study aimed to assess the effect of HCV core protein on intracellular porphyrin metabolism to elucidate the link between HCV infection and PCT. The accumulation and excretion of porphyrins after treatment with 5-aminolevulinic acid, a porphyrin precursor, were compared between cells stably expressing HCV core protein and controls. Cells expressing HCV core protein had lower amounts of intracellular protoporphyrin IX and heme and had higher amounts of excreted coproporphyrin III, the oxidized form of coproporphyrinogen III, compared with controls. These observations suggest that HCV core protein affects porphyrin metabolism and facilitates the export of excess coproporphyrinogen III and/or coproporphyrin III, possibly via porphyrin transporters. Real-time PCR analysis revealed that the presence of HCV core protein increased the mRNA expression of porphyrin exporters ABCG2 and FLVCR1. Western blot analysis showed a higher expression level of FLVCR1, but not ABCG2, as well as a higher expression level of mature ALAS1, which is the rate-limiting enzyme in the heme synthesis pathway, in HCV core protein-expressing cells compared with controls. The data indicate that HCV core protein induced abnormal intracellular porphyrin metabolism, with an over-excretion of coproporphyrin III. These findings may partially account for the susceptibility of HCV-infected individuals to PCT development.

Porphyria cutanea tarda: an intriguing genetic disease and marker

Porphyrias are a group of intriguing genetic diseases of the heme pathway, of which porphyria cutanea tarda (PCT) is the most common. Resulting from a defect in enzymes in the porphyria pathway, PCT has been linked to several conditions. Recent studies have demonstrated a change in thinking regarding the human immunodeficiency virus (HIV) and development of PCT. The exacerbation of PCT with contraction of HIV is now believed to result from coinfection from the hepatitis C virus (HCV). Blistering of sun-exposed skin, a classic presenting sign of PCT, is not exclusive to the condition. Cutaneous findings must also trigger physicians to consider additional types of porphyrias, such as variegate porphyria. The diagnosis of pseudoporphyria, which does not result from enzymatic absence, must be considered in patients with photosensitivity and cutaneous bullae. Recent health food trends, such as chlorophyll, have been linked to pseudoporphyria. PCT is a serious condition in which accurate diagnosis is necessary for appropriate management.

Hepatitis C Treatment in Patients With Porphyria Cutanea Tarda

BACKGROUND

Hepatitis C virus (HCV) infection is a common susceptibility factor for porphyria cutanea tarda (PCT). Experience on HCV treatment in patients with PCT is limited. Recently, HCV treatment has improved with direct-acting antivirals (DAA). We review our experience on HCV treatment in patients with PCT with older and newer regimens.

MATERIALS AND METHODS

A retrospective chart review was conducted. HCV treatment was attempted 22 times in 13 patients with PCT (5 attempts in 1, 2 in 5 and 1 in the other 7 patients).

RESULTS

Before starting HCV treatment, PCT was in complete remission in 16, partial remission in 2, unknown status in 2 and active in 2 instances. PCT relapsed during therapy 6 times (all interferon-based regimens and 2 including telaprevir), 4 requiring treatment interruption. Treatment was interrupted for reasons other than PCT relapse in 2 patients treated with interferon-based regimens. To prevent PCT recurrence, hydroxychloroquine was continued during HCV therapy 6 times (3 interferon regimens, 2 ribavirin regimens without interferon and 1 DAA alone). Twelve patients achieved sustained viral response, 3 with interferon regimens and 9 with DAA. Two patients with active PCT were treated with DAA, with reduction of plasma porphyrins in 1 and normalization in the other at the end of HCV therapy.

CONCLUSIONS

HCV treatment regimens including interferon or ribavirin may precipitate PCT relapse. Hydroxychloroquine may be useful to prevent such relapses. In this limited experience, DAA were not associated with PCT relapse. Studies are needed to examine DAA as a primary PCT treatment in HCV-infected patients.

Beyond the Aryl Hydrocarbon Receptor: Pathway Interactions in the Hepatotoxicity of 2,3,7,8-Tetrachlorodibenzo-p-dioxin and Related Compounds

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is the prototypical ligand for a group of environmental halogenated aromatic hydrocarbon contaminants which elicit hepatotoxicity and other toxic responses through activation of the aryl hydrocarbon receptor (AhR). Despite the conservation of the AhR and its signaling pathway, TCDD-elicited differential gene expression networks are species-specific, consistent with differences in sensitivity and toxic responses between species. This review integrates gene expression studies with complementary phenotypic analyses (e.g., metabolomics, clinical biochemistry, and histopathology) to elucidate the pathways through which TCDD and related compounds cause hepatotoxicity beyond AhR activation. We propose that AhR-mediated toxicity is a collective response to the cumulative burden of metabolic reprogramming across multiple pathways. Consequently, nutrition, health status, and genetic background establish the basis for differences in sensitivity and predisposition to adverse outcomes between species, sub-populations, tissues, and cells.

Hepatic porphyria: A narrative review

Porphyrias are a group of metabolic disorders, which result from a specific abnormality in one of the eight enzymes of the heme biosynthetic pathway. These have been subdivided based on the predominant site of enzyme defect into hepatic and erythropoietic types and based on clinical presentation into acute neurovisceral and cutaneous blistering porphyrias. This review focuses on hepatic porphyrias, which include acute intermittent porphyria (AIP), variegate porphyria (VP), hereditary coproporphyria (HCP), aminolevulinic acid dehydratase deficiency porphyria (ADP), and porphyria cutanea tarda (PCT). Of these, AIP and ADP are classified as acute porphyria, PCT as cutaneous, while VP and HCP present with both acute and cutaneous clinical manifestations. Porphobilinogen levels in a spot urine sample is the initial screening test for the diagnosis of acute hepatic porphyria, and plasma with spot urine porphyrin levels is the initial screening test to approach patients suspected of cutaneous porphyria. Specific biochemical porphyrin profile for each porphyria helps in determining the specific diagnosis. Pain relief and elimination of triggering agents are the initial steps in managing a patient presenting with an acute attack. Intravenous glucose administration terminates the mild episode of acute porphyria, with intravenous hemin needed for management of moderate to severe episodes. Liver transplantation is curative and may be needed for patients with a life-threatening acute porphyria attack or for patients with recurrent acute attacks refractory to prophylactic treatment. Of the cutaneous porphyrias, PCT is the most common and is frequently associated with a combination of multiple susceptibility factors such as alcohol use, smoking, hepatitis C virus infection, HIV infection, estrogen use, and mutations of the hemochromatosis gene. Regular phlebotomy schedule and low-dose hydroxychloroquine are effective and safe treatment options for management of PCT.

The D519G Polymorphism of Glyceronephosphate O-Acyltransferase Is a Risk Factor for Familial Porphyria Cutanea Tarda

Both familial and sporadic porphyria cutanea tarda (PCT) are iron dependent diseases. Symptoms of PCT resolve when iron stores are depleted by phlebotomy, and a sequence variant of HFE (C282Y, c.843G>A, rs1800562) that enhances iron aborption by reducing hepcidin expression is a risk factor for PCT. Recently, a polymorphic variant (D519G, c.1556A>G, rs11558492) of glyceronephosphate O-acyltransferase (GNPAT) was shown to be enriched in male patients with type I hereditary hemochromatosis (HFE C282Y homozygotes) who presented with a high iron phenotype, suggesting that GNPAT D519G, like HFE C282Y, is a modifier of iron homeostasis that favors iron absorption. To challenge this hypothesis, we investigated the frequency of GNPAT D519G in patients with both familial and sporadic PCT. Patients were screened for GNPAT D519G and allelic variants of HFE (both C282Y and H63D). Nucleotide sequencing of uroporphyrinogen decarboxylase (URO-D) identified mutant alleles. Patients with low erythrocyte URO-D activity or a damaging URO-D variant were classified as familial PCT (fPCT) and those with wild-type URO-D were classified as sporadic PCT (sPCT). GNPAT D519G was significantly enriched in the fPCT patient population (p = 0.0014) but not in the sPCT population (p = 0.4477). Both HFE C282Y and H63D (c.187C>G, rs1799945) were enriched in both PCT patient populations (p<0.0001) but showed no greater association with fPCT than with sPCT. Conclusion: GNPAT D519G is a risk factor for fPCT, but not for sPCT.

[Porphyrias and haem related disorders]

The hereditary porphyrias comprise a group of eight metabolic disorders of the haem biosynthesis pathway characterised by acute neurovisceral symptoms, skin lesions or both. Each porphyria is caused by abnormal function of a separate enzymatic step resulting in a specific accumulation of haem precursors. Seven porphyrias are the consequence of a partial enzyme deficiency while a gain of function mechanism has been recently characterised in a novel porphyria. Acute porphyrias present with severe abdominal pain, nausea, constipation, confusion and seizure, which may be life threatening. Cutaneous porphyrias can be present with either acute painful photosensitivity or skin fragility and blisters. Rare recessive porphyrias usually manifest in early childhood with either severe chronic neurological symptoms or chronic haemolysis and severe cutaneous photosensitivity. Porphyrias are still underdiagnosed, but once they are suspected, and depending on the clinical presentation, a specific and simple front line test allows the diagnosis in all symptomatic patients. Diagnosis is essential to institute as soon as possible a specific treatment. Screening families to identify presymptomatic carriers is crucial to prevent chronic complications and overt disease by counselling on avoiding potential precipitants.

Porphyria cutanea tarda associated with HFE C282Y homozygosity, iron overload, and use of a contraceptive vaginal ring

Porphyria cutanea tarda (PCT) is characterized by decreased uroporphyrinogen decarboxylase activity in hepatocytes, uroporphyrin I and heptacarboxyl porphyrin III accumulation, photosensitivity dermatitis, and increased storage iron. In women, estrogen therapy, including oral contraceptives, postmenopausal hormone replacement, and tamoxifen for breast cancer treatment, is a risk factor for PCT. We report the case of a woman who presented with PCT, HFE C282Y homozygosity, and hepatic iron overload and was using a contraceptive vaginal ring containing ethinyl estradiol, an estrogen. We discuss this case in the context of characteristics of other persons with PCT, including common HFE mutations, iron overload, and estrogen exposure.

HFE gene: Structure, function, mutations, and associated iron abnormalities

The hemochromatosis gene HFE was discovered in 1996, more than a century after clinical and pathologic manifestations of hemochromatosis were reported. Linked to the major histocompatibility complex (MHC) on chromosome 6p, HFE encodes the MHC class I-like protein HFE that binds beta-2 microglobulin. HFE influences iron absorption by modulating the expression of hepcidin, the main controller of iron metabolism. Common HFE mutations account for ~90% of hemochromatosis phenotypes in whites of western European descent. We review HFE mapping and cloning, structure, promoters and controllers, and coding region mutations, HFE protein structure, cell and tissue expression and function, mouse Hfe knockouts and knockins, and HFE mutations in other mammals with iron overload. We describe the pertinence of HFE and HFE to mechanisms of iron homeostasis, the origin and fixation of HFE polymorphisms in European and other populations, and the genetic and biochemical basis of HFE hemochromatosis and iron overload.

Porphyrias: A 2015 update

The hereditary porphyrias comprise a group of eight metabolic disorders of the heme biosynthesis pathway. Each porphyria is caused by abnormal function at a separate enzymatic step resulting in a specific accumulation of heme precursors. Porphyrias are classified as hepatic or erythropoietic, based on the organ system in which heme precursors (δ-aminolevulinic acid [ALA], porphobilinogen and porphyrins) are overproduced. Clinically, porphyrias are characterized by acute neurovisceral symptoms, skin lesions or both. However, most if not all the porphyrias impair hepatic or gastrointestinal function. Acute hepatic porphyrias present with severe abdominal pain, nausea, constipation, confusion and seizure, which may be life threatening, and patients are at risk of hepatocellular carcinoma without cirrhosis. Porphyria Cutanea presents with skin fragility and blisters, and patients are at risk of hepatocellular carcinoma with liver iron overload. Erythropoietic protoporphyria and X-linked protoporphyria present with acute painful photosensitivity, and patients are at risk of acute liver failure. Altogether, porphyrias are still underdiagnosed, but once they are suspected, early diagnosis based on measurement of biochemical metabolites that accumulate in the blood, urine, or feces is essential so specific treatment can be started as soon as possible and long-term liver complications are prevented. Screening families to identify presymptomatic carriers is also crucial to prevent overt disease and chronic hepatic complications.

Porphyria Diagnostics-Part 1: A Brief Overview of the Porphyrias

Porphyria diseases are a group of metabolic disorders caused by abnormal functioning of heme biosynthesis enzymes and characterized by excessive accumulation and excretion of porphyrins and their precursors. Precisely which of these chemicals builds up depends on the type of porphyria. Porphyria is not a single disease but a group of nine disorders: acute intermittent porphyria (AIP), hereditary coproporphyria (HCP), variegate porphyria (VP), δ-aminolevulinic acid dehydratase deficiency porphyria (ADP), porphyria cutanea tarda (PCT), hepatoerythropoietic porphyria (HEP), congenital erythropoietic porphyria (CEP), erythropoietic protoporphyria (EPP), and X-linked protoporphyria (XLP). Each porphyria results from overproduction of heme precursors secondary to partial deficiency or, in XLP, increased activity of one of the enzymes of heme biosynthesis. Taken together, all forms of porphyria afflict fewer than 200,000 people in the United States. Based on European studies, the most common porphyria, PCT, has a prevalence of 1 in 10,000, the most common acute porphyria, AlP, has a prevalence of ∼1 in 20,000, and the most common erythropoietic porphyria, EPP, is estimated at 1 in 50,000 to 75,000. CEP is extremely rare, with prevalence estimates of 1 in 1,000,000 or less. Only six cases of ADP are documented. The current porphyria literature is very exhaustive and a brief overview of porphyria diseases is essential in order for the reader to better appreciate the relevance of this area of research prior to undertaking biochemical diagnostics procedures. This unit summarizes the current knowledge on the classification, clinical features, etiology, pathogenesis, and genetics of porphyria diseases.

Mass-spectrometric profiling of porphyrins in complex biological samples with fundamental, toxicological, and pharmacological applications

Rapid, high-throughput, and quantitative evaluations of biological metabolites in complex milieu are increasingly required for biochemical, toxicological, pharmacological, and environmental analyses. They are also essential for the development, testing, and improvement of new commercial chemical products. We demonstrate the application of ultra-high performance liquid chromatography-mass spectrometry (uHPLC-MS), employing an electrospray ionization source and a high accuracy quadrupole time-of-flight mass analyzer, for the identification and quantification of a series of porphyrin derivatives in liver: a matrix of particular relevance in toxicological or pharmacological testing. Exact mass is used to identify and quantify the metabolites. Chromatography enhances sensitivity and alleviates potential saturation issues by fanning out the contents of a complex sample before their injection into the spectrometer, but is not strictly necessary for the analysis. Extraction and sample treatment procedures are evaluated and matrix effects discussed. Using this method, the known mechanism of action of a well-characterized porphyrinogenic agent was verified in liver extracts from treated rats. The method was also validated for use with bacterial cells. This exact-mass method uses workhorse instruments available in many laboratories, providing a highly flexible alternative to existing HPLC- and MS/MS-based approaches for the simultaneous analysis of multiple compounds in biological media.

Synthesis of 21,23-selenium- and tellurium-substituted 5-porphomethenes, 5,10-porphodimethenes, 5,15-porphodimethenes, and porphotrimethenes and their interactions with mercury

The 3+1 condensation of symmetrical 16-Selena/telluratripyrranes with symmetrical selenophene-2,5-diols/tellurophene-2,5-diols in the presence of BF3-etheratre or BF3-methanol followed by oxidation with DDQ gave 5,10-porphodimethenes, whereas the process with unsymmetrical selenophene-2,5-diols/tellurophene-2,5-diols gave 5-porphomethenes. In addition, the reaction of unsymmetrical 16-Selena/telluratripyrranes with symmetrical selenophene-2,5-diols/tellurophene-2,5-diols gave the corresponding porphotrimethenes, whereas the process with unsymmetrical selenophene-2,5-diols/tellurophene-2,5-diols gave the 5,15-porphodimethenes. The structures of different products were characterized by IR, (1)H and (13)C NMR, (1)H-(1)H COSY, CHN analysis, and mass spectrometry. The binding of mercury with the calix[4]phyrins mentioned above had been observed in the decreasing order of porphodimethenes > porphomethenes > porphotrimethenes by UV-vis and (1)H NMR spectroscopy.

Complicity of haem in some adverse drug-reactions

Genetic variants in haem metabolism enzymes can be predisposition factors for adverse reactions in some individuals. New areas of haem biology may also be associated with idiosyncratic effects which are yet to be identified.

Clinically important features of porphyrin and heme metabolism and the porphyrias

Heme, like chlorophyll, is a primordial molecule and is one of the fundamental pigments of life. Disorders of normal heme synthesis may cause human diseases, including certain anemias (X-linked sideroblastic anemias) and porphyrias. Porphyrias are classified as hepatic and erythropoietic porphyrias based on the organ system in which heme precursors (5-aminolevulinic acid (ALA), porphobilinogen and porphyrins) are chiefly overproduced. The hepatic porphyrias are further subdivided into acute porphyrias and chronic hepatic porphyrias. The acute porphyrias include acute intermittent, hereditary copro-, variegate and ALA dehydratase deficiency porphyria. Chronic hepatic porphyrias include porphyria cutanea tarda and hepatoerythropoietic porphyria. The erythropoietic porphyrias include congenital erythropoietic porphyria (Gűnther’s disease) and erythropoietic protoporphyria. In this review, we summarize the key features of normal heme synthesis and its differing regulation in liver versus bone marrow. In both organs, principal regulation is exerted at the level of the first and rate-controlling enzyme, but by different molecules (heme in the liver and iron in the bone marrow). We also describe salient clinical, laboratory and genetic features of the eight types of porphyria.