Porphyrias

A novel 55-basepair deletion of hydroxymethylbilane synthase gene found in a Chinese patient with acute intermittent porphyria and her family: A case report

RATIONALE

Acute intermittent porphyria (AIP) is caused by hydroxymethylbilane synthase (HMBS) gene mutation.

PATIENT CONCERNS

A Chinese female patient with very typical AIP symptoms of severe abdominal pain, seizures, hypertension, and tachycardia, accompanied with hyponatremia, anemia, and hyperbilirubinemia.

DIAGNOSES

She was diagnosed as AIP based on positive result of urine porphobilinogen and her clinical syndrome.

INTERVENTIONS

The proband was treated with intravenous glucose (at least 250 g per day) for 4 days. HMBS mutation was investigated in this family by Sanger sequencing.

OUTCOMES

A heterozygous mutation of the HMBS gene was identified in the proband and 7 other family members. Genetic sequencing showed a deletion of 55 basepairs (C.1078_1132delGCCCATTAACTGGTTTGTGGGGCACAGATGCCTGGGTTGCTGCTGTCCAGTGCCT) including the stop codon position, leading to frameshift mutation. The mutation has not been documented in current gene databases. Further prediction of mutated protein structure suggests that the mutation is likely to produce prolonged peptide with structural change and less stability.

LESSONS

Physicians should pay attention to AIP attack in patients with suspected symptoms and make use of genetic testing to increase identification of mutated HMBS gene carriers for further preventive strategy.

Medical and financial burden of acute intermittent porphyria

INTRODUCTION

A small proportion of patients with acute intermittent porphyria (AIP) suffer from recurrent porphyric attacks, with a severely diminished quality of life. In this retrospective case-control study, the burden of disease is quantified and compared among three AIP patient subgroups: cases with recurrent attacks, cases with one or occasional attacks and asymptomatic carriers.

METHODS

Data from patient records and questionnaires were collected in patients between 1960 and 2016 at the Erasmus Medical Center, Rotterdam, the Netherlands. We collected symptoms related to porphyria, porphyria related complications, attack frequency, hospitalisation frequency, hospitalisation days related to acute porphyric attacks, frequency of heme infusions and medical healthcare costs based on hospitalisations and heme therapy.

RESULTS

In total 11 recurrent AIP cases, 24 symptomatic AIP cases and 53 AIP carriers as controls were included. All recurrent patients reported porphyria related symptoms, such as pain, neurological and/or psychiatric disorders, and nearly all developed complications, such as hypertension and chronic kidney disease. In the recurrent cases group, the median lifelong number of hospitalisation days related to porphyric attacks was 82 days per patient (range 10-374), and they spent a median of 346 days (range 34-945) at a day-care facility for prophylactic heme therapy; total follow-up time was 243 person-years (PYRS). In the symptomatic non-recurrent group the median lifelong number of hospitalisation days related to porphyric attacks was 7 days per patient (range 1-78), total follow-up time was 528 PYRS. The calculated total medical healthcare cost for recurrent cases group was €5.8 million versus €0.3 million for the symptomatic cases group.

Rare Genetic Blood Disease Modeling in Zebrafish

Hematopoiesis results in the correct formation of all the different blood cell types. In mammals, it starts from specific hematopoietic stem and precursor cells residing in the bone marrow. Mature blood cells are responsible for supplying oxygen to every cell of the organism and for the protection against pathogens. Therefore, inherited or de novo genetic mutations affecting blood cell formation or the regulation of their activity are responsible for numerous diseases including anemia, immunodeficiency, autoimmunity, hyper- or hypo-inflammation, and cancer. By definition, an animal disease model is an analogous version of a specific clinical condition developed by researchers to gain information about its pathophysiology. Among all the model species used in comparative medicine, mice continue to be the most common and accepted model for biomedical research. However, because of the complexity of human diseases and the intrinsic differences between humans and other species, the use of several models (possibly in distinct species) can often be more helpful and informative than the use of a single model. In recent decades, the zebrafish (Danio rerio) has become increasingly popular among researchers, because it represents an inexpensive alternative compared to mammalian models, such as mice. Numerous advantages make it an excellent animal model to be used in genetic studies and in particular in modeling human blood diseases. Comparing zebrafish hematopoiesis to mammals, it is highly conserved with few, significant differences. In addition, the zebrafish model has a high-quality, complete genomic sequence available that shows a high level of evolutionary conservation with the human genome, empowering genetic and genomic approaches. Moreover, the external fertilization, the high fecundity and the transparency of their embryos facilitate rapid, in vivo analysis of phenotypes. In addition, the ability to manipulate its genome using the last genome editing technologies, provides powerful tools for developing new disease models and understanding the pathophysiology of human disorders. This review provides an overview of the different approaches and techniques that can be used to model genetic diseases in zebrafish, discussing how this animal model has contributed to the understanding of genetic diseases, with a specific focus on the blood disorders.

Many pitfalls in diagnosis of acute intermittent porphyria: a case report

BACKGROUND

Acute intermittent porphyria is a rare autosomal dominant disorder caused by a deficiency of the enzyme, hydroxymethylbilane synthase. Recognition of acute neurovisceral attacks can be difficult due to the nonspecific nature of symptoms.

CASE PRESENTATION

We report a case of 33-year-old male patient who presented with recurrent episodes of severe abdominal pain, nausea, vomiting, constipation and numbness of bilateral lower limb extremities. These nonspecific neurovisceral attacks were subject to medical and surgical misdiagnoses of acute appendicitis, sinus tachycardia, renal calculi, drug-induced acute interstitial nephritis and two episodes of partial intestinal obstruction. The sixth acute attack raised the suspicion of an acute porphyria. Watson and Schwartz test was positive for porphobilinogen in urine. Mutation analysis by DNA sequencing of the extracted DNA of the proband revealed a previously reported missense mutation, c.517C>T encoding p.R173W in the HMBS gene, confirming the diagnosis of Acute Intermittent Porphyria. Four out of five family members who underwent targeted mutation analyses were mutation-positive.

CONCLUSION

The most common clinical presentation of Acute Intermittent Porphyria is abdominal pain with neurovisceral manifestations which are common to several medical, psychiatric and surgical pathologies. This leads to underdiagnosis and misdiagnosis of this disorder, incorrect management, and severe complications. Therefore, a high index of suspicion and awareness of front line laboratory investigations are important for diagnosis. Definitive diagnosis enables implementation of strategies to prevent acute attacks, and also triggers genetic testing and genetic counseling of at-risk family members.

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.

Recurrent attacks of acute hepatic porphyria: major role of the chronic inflammatory response in the liver

BACKGROUND

Acute intermittent porphyria (AIP) is an inherited disorder of haem metabolism characterized by life-threatening acute neurovisceral attacks due to the induction of hepatic δ-aminolevulinic acid synthase 1 (ALAS1) associated with hydroxymethylbilane synthase (HMBS) deficiency. So far, the treatment of choice is hemin which represses ALAS1. The main issue in the medical care of AIP patients is the occurrence of debilitating recurrent attacks.

OBJECTIVE

The aim of this study was to determine whether chronic hemin administration contributes to the recurrence of acute attacks.

METHODS

A follow-up study was conducted between 1974 and 2015 and included 602 French AIP patients, of whom 46 had recurrent AIP. Moreover, we studied the hepatic transcriptome, serum proteome, liver macrophage polarization and oxidative and inflammatory profiles of Hmbs^-/- mice chronically treated by hemin and extended the investigations to five explanted livers from recurrent AIP patients.

RESULTS

The introduction of hemin into the pharmacopeia has coincided with a 4.4-fold increase in the prevalence of chronic patients. Moreover, we showed that both in animal model and in human liver, frequent hemin infusions generate a chronic inflammatory hepatic disease which induces HO1 remotely to hemin treatment and maintains a high ALAS1 level responsible for recurrence.

CONCLUSION

Altogether, this study has important impacts on AIP care underlying that hemin needs to be restricted to severe neurovisceral crisis and suggests that alternative treatment targeting the liver such as ALAS1 and HO1 inhibitors, and anti-inflammatory therapies should be considered in patients with recurrent AIP.

Characterization and origin of heme precursors in amniotic fluid: lessons from normal and pathological pregnancies

BACKGROUND

Heme is the prosthetic group of numerous proteins involved in vital processes such as oxygen transport, oxidative stress, and energetic mitochondrial metabolism. Free heme also plays a significant role at early stages of development and in cell differentiation processes. The metabolism of heme by the fetal placenta unit is not well-established in humans.

METHODS

In a retrospective study, we measured heme precursors in the amniotic fluid (AF) of 51 healthy women, and 10 AF samples from pregnancies with either upper or lower intestinal atresia or ileus were also analyzed.

RESULTS

We showed that the porphyrin precursors aminolevulinic acid, porphobilinogen, and protoporphyrin IX are present at the limit of detection in the AF. Total porphyrin levels decreased progressively from week 13 to week 33 (p < 0.01). Interestingly, uroporphyrin, initially detected as traces, increased with maturation, in contrast to coproporphyrin. Uro- and coproporphyrins were type I immature isomers (>90%), suggesting a lack of maturity in the fetal compartment of the heme pathway. Finally, the differential analysis of AF from normal and pathological pregnancies demonstrated the predominant hepatic origin of fetal porphyrins excreted in the AF.

CONCLUSION

This study gives the first insight into heme metabolism in the AF during normal and pathological pregnancies.

Acute intermittent porphyria: general aspects with focus on pain

Despite medical advances, the diagnosis and management of acute intermittent porphyria continues to be challenging. Acute pain is one of the most important clinical manifestations in acute intermittent porphyria, but management and pain assessment have been poorly studied in these patients. The lack of information and evidence based recommendations regarding these topics in the medical literature is certainly surprising. Furthermore, pain management is discussed based on extrapolating concepts adopted for other pain syndromes. An important arsenal of medications, including reportedly safe opioid and non-opioid analgesics, is available for use in this type of patient. In addition to conducting an extensive review of the current literature, the present article aims to show the general aspects of a disease that generates a challenge for the clinician, emphasizing what is related to pain as a cardinal symptom and to create awareness about the need for studies supporting the development of guidelines, based on evidence obtained from analgesic management in patients presenting with this disorder. A systematic assessment directed at understanding the physiopathological processes underlying acute pain combined with a stepwise approach to pain management with safe opioid and non-opioid drugs constitutes the fundamental basis for a successful pain management program in patients with acute intermittent porphyria.

Rhodococcus equi Pneumonia in Kidney Transplant Recipient Affected by Acute Intermittent Porphyria: A Case Report

Rhodococcus equi is a gram-positive coccobacillus responsible for severe infections in patients with weakened immune systems. R equi generally causes pnumonia that may evolve into fatal systemic infection if left untreated. Here, we present a case of a 67-year-old woman affected by acute intermittent porphyria (AIP) who developed R equi pneumonia 7 months after kidney transplantation. Although clinical features at presentation were nonspecific, lung computed tomography showed right perihilar consolidation with a mass-like appearance causing bronchial obstruction. Appropriate antibiotic including intravenous meropenem and oral azithromycin that was then switched to oral levofloxacin and oral azithromycin along with reduction of immunosuppressive therapy resolved pneumonia without provoking an acute attack of porphyria. AIP limited the choice of antibiotics for the treatment of R equi infection because some potentially porphyrinogenic antibacterial agents were avoided. Based on this experience, azithromycin and meropenem can be safely administered for the treatment of R Equi infection in patients with AIP.

Anti-Correlation between the Dynamics of the Active Site Loop and C-Terminal Tail in Relation to the Homodimer Asymmetry of the Mouse Erythroid 5-Aminolevulinate Synthase

Biosynthesis of heme represents a complex process that involves multiple stages controlled by different enzymes. The first of these proteins is a pyridoxal 5′-phosphate (PLP)-dependent homodimeric enzyme, 5-aminolevulinate synthase (ALAS), that catalyzes the rate-limiting step in heme biosynthesis, the condensation of glycine with succinyl-CoA. Genetic mutations in human erythroid-specific ALAS (ALAS2) are associated with two inherited blood disorders, X-linked sideroblastic anemia (XLSA) and X-linked protoporphyria (XLPP). XLSA is caused by diminished ALAS2 activity leading to decreased ALA and heme syntheses and ultimately ineffective erythropoiesis, whereas XLPP results from “gain-of-function” ALAS2 mutations and consequent overproduction of protoporphyrin IX and increase in Zn²⁺-protoporphyrin levels. All XLPP-linked mutations affect the intrinsically disordered C-terminal tail of ALAS2. Our earlier molecular dynamics (MD) simulation-based analysis showed that the activity of ALAS2 could be regulated by the conformational flexibility of the active site loop whose structural features and dynamics could be changed due to mutations. We also revealed that the dynamic behavior of the two protomers of the ALAS2 dimer differed. However, how the structural dynamics of ALAS2 active site loop and C-terminal tail dynamics are related to each other and contribute to the homodimer asymmetry remained unanswered questions. In this study, we used bioinformatics and computational biology tools to evaluate the role(s) of the C-terminal tail dynamics in the structure and conformational dynamics of the murine ALAS2 homodimer active site loop. To assess the structural correlation between these two regions, we analyzed their structural displacements and determined their degree of correlation. Here, we report that the dynamics of ALAS2 active site loop is anti-correlated with the dynamics of the C-terminal tail and that this anti-correlation can represent a molecular basis for the functional and dynamic asymmetry of the ALAS2 homodimer.

Sugammadex and amino acid infusion can contribute to safe anesthetic management of variegate porphyria

BACKGROUND

Variegate porphyria (VP) is an inherited type of porphyria characterized by cutaneous manifestations and/or acute neurovisceral attacks. We report successful anesthetic management of VP.

CASE PRESENTATION

A 66-year-old woman with VP was scheduled to undergo distal pancreatectomy for pancreatic cancer. Medical history was unremarkable except for sudden onset of abdominal pain that occurred every few months, possibly due to VP. There was no abnormality in laboratory data except for a mild increase in creatinine levels. General anesthesia was induced and maintained with total intravenous anesthesia using propofol, remifentanil, and rocuronium. Blood glucose levels were measured every hour and glucose administered to prevent hypoglycemia. Amino acids were also infused to treat hypothermia. Upon completion of distal pancreatectomy, sugammadex was administered to reverse neuromuscular blockade. She was neurologically intact and discharged on postoperative day 15 with no acute attack.

CONCLUSIONS

Sugammadex and amino acids can be used safely in patients with VP.

Liver metabolomics in a mouse model of erythropoietic protoporphyria

Erythropoietic protoporphyria (EPP) is a genetic disease that results from the defective mutation in the gene encoding ferrochelatase (FECH), the enzyme that converts protoporphyrin IX (PPIX) to heme. Liver injury and even liver failure can occur in EPP patients because of PPIX accumulation in the liver. The current study profiled the liver metabolome in an EPP mouse model caused by a Fech mutation (Fech-mut). As expected, we observed the accumulation of PPIX in the liver of Fech-mut mice. In addition, our metabolomic analysis revealed the accumulation of bile acids and ceramide (Cer) in the liver of Fech-mut mice. High levels of bile acids and Cer are toxic to the liver. Furthermore, we found that the major phosphatidylcholines (PC) in the liver and the ratio of total PC to PPIX in the bile were decreased in Fech-mut mice compared to wild type mice. A decrease of the ratio of PC to PPIX in the bile can potentiate the accumulation of PPIX in the liver because PC increases PPIX solubility and excretion. These metabolomic findings suggest that the accumulation of PPIX, together with the disruption of the homeostasis of bile acids, Cer, and PC, contributes to EPP-associated liver injury.

Intracellular iron and heme trafficking and metabolism in developing erythroblasts

Vertebrate red blood cells (RBCs) arise from erythroblasts in the human bone marrow through a process known as erythropoiesis. Iron uptake is a crucial hallmark, essential for heme biosynthesis in the differentiating erythroblasts, which are dedicated to producing hemoglobin. Erythropoiesis is facilitated by a network of intracellular transport proteins, chaperones, and circulating hormones. Intracellular iron is targeted to the mitochondria for incorporation into a porphyrin ring to form heme and cytosolic iron-sulfur proteins, including Iron Regulatory Protein 1 (IRP1). These processes are tightly regulated to prevent both excess and insufficient levels of iron and heme precursors. Crosstalk between the heme and iron-sulfur synthesizing pathways has been demonstrated to serve as a regulatory feedback mechanism. The activity of δ-aminolevulinic acid synthase (ALAS), the first and rate-limiting enzyme of heme biosynthesis, is a fundamental node of this regulation. Recently, the mitochondrial unfoldase, ClpX, has received attention as a novel key player that modulates this step in heme biogenesis, implicating a role in the pathophysiology of anemic diseases. This chapter reviews the canonical pathways in intracellular iron and heme trafficking and recent findings of iron and heme metabolism in vertebrate red cells. A discussion of the molecular approaches to studying iron and heme transport is provided to highlight opportunities for revealing therapeutic targets.

Lamins and Lamin-Associated Proteins in Gastrointestinal Health and Disease

The nuclear lamina is a multi-protein lattice composed of A- and B-type lamins and their associated proteins. This protein lattice associates with heterochromatin and integral inner nuclear membrane proteins, providing links among the genome, nucleoskeleton, and cytoskeleton. In the 1990s, mutations in EMD and LMNA were linked to Emery-Dreifuss muscular dystrophy. Since then, the number of diseases attributed to nuclear lamina defects, including laminopathies and other disorders, has increased to include more than 20 distinct genetic syndromes. Studies of patients and mouse genetic models have pointed to important roles for lamins and their associated proteins in the function of gastrointestinal organs, including liver and pancreas. We review the interactions and functions of the lamina in relation to the nuclear envelope and genome, the ways in which its dysfunction is thought to contribute to human disease, and possible avenues for targeted therapies.

Whole Exome Sequencing Identified a Novel Heterozygous Mutation in HMBS Gene in a Chinese Patient With Acute Intermittent Porphyria With Rare Type of Mild Anemia

Acute intermittent porphyria (AIP) is a rare hereditary metabolic disease with an autosomal dominant mode of inheritance. Germline mutations of HMBS gene causes AIP. Mutation of HMBS gene results into the partial deficiency of the heme biosynthetic enzyme hydroxymethylbilane synthase. AIP is clinically manifested with abdominal pain, vomiting, and neurological complaints. Additionally, an extreme phenotypic heterogeneity has been reported in AIP patients with mutations in HMBS gene. Here, we investigated a Chinese patient with AIP. The proband is a 28-year-old Chinese male manifested with severe stomach ache, constipation, nausea and depression. Proband’s father and mother is normal. Proband’s blood sample was collected and genomic DNA was extracted. Whole exome sequencing and Sanger sequencing identified a heterozygous novel single nucleotide deletion (c.809delC) in exon 12 of HMBS gene in the proband. This mutation leads to frameshift followed by formation of a truncated (p.Ala270Valfs^∗2) HMBS protein with 272 amino acids comparing with the wild type HMBS protein of 361 amino acids. This mutation has not been found in proband’s unaffected parents as well as in 100 healthy normal control. According to the variant interpretation guidelines of American College of Medical Genetics and Genomics (ACMG), this variant is classified as “likely pathogenic” variant. Our findings expand the mutational spectra of HMBS gene related AIP which are significant for screening and genetic diagnosis for AIP.

Erythropoietic Protoporphyria: Initial Diagnosis With Cholestatic Liver Disease

The porphyrias are a group of rare metabolic disorders that result from defects in heme biosynthesis. Erythropoietic protoporphyria (EPP) is the most common inherited porphyria in children and is diagnosed in most individuals after the onset of cutaneous manifestations. Hepatobiliary disease affects the minority of individuals with EPP and usually manifests in patients with an established diagnosis of EPP. We report on a classic but rare case of EPP that masqueraded as cholestasis. An 8-year-old boy was referred to the Hepatology Clinic after an abrupt onset of jaundice with a longstanding history of dermatitis. The diagnosis of EPP was established with liver biopsy, which revealed dense, dark-brown pigment in hepatocytes and Kupffer cells that, on polarization, displayed bright-red birefringence and centrally located Maltese crosses. Plasma total porphyrins and erythrocyte protoporphyrin were elevated and confirmed a diagnosis of EPP. We hope to raise awareness of this diagnosis among pediatricians, hepatologists, and pathologists and increase the consideration of EPP in patients with cholestatic liver disease and chronic dermatitis.

Biomarkers for In Vivo Assessment of Transporter Function

Drug-drug interactions are a major concern not only during clinical practice, but also in drug development. Due to limitations of in vitro-in vivo predictions of transporter-mediated drug-drug interactions, multiple clinical Phase I drug-drug interaction studies may become necessary for a new molecular entity to assess potential drug interaction liabilities. This is a resource-intensive process and exposes study participants, who frequently are healthy volunteers without benefit from study treatment, to the potential risks of a new drug in development. Therefore, there is currently a major interest in new approaches for better prediction of transporter-mediated drug-drug interactions. In particular, researchers in the field attempt to identify endogenous compounds as biomarkers for transporter function, such as hexadecanedioate, tetradecanedioate, coproporphyrins I and III, or glycochenodeoxycholate sulfate for hepatic uptake via organic anion transporting polypeptide 1B or N1-methylnicotinamide for multidrug and toxin extrusion protein-mediated renal secretion. We summarize in this review the currently proposed biomarkers and potential limitations of the substances identified to date. Moreover, we suggest criteria based on current experiences, which may be used to assess the suitability of a biomarker for transporter function. Finally, further alternatives and supplemental approaches to classic drug-drug interaction studies are discussed.

The role of ClpX in erythropoietic protoporphyria

Hemoglobin is an essential biological component of human physiology and its production in red blood cells relies upon proper biosynthesis of heme and globin protein. Disruption in the synthesis of these precursors accounts for a number of human blood disorders found in patients. Mutations in genes encoding heme biosynthesis enzymes are associated with a broad class of metabolic disorders called porphyrias. In particular, one subtype - erythropoietic protoporphyria - is caused by the accumulation of protoporphyrin IX. Erythropoietic protoporphyria patients suffer from photosensitivity and a higher risk of liver failure, which is the principle cause of morbidity and mortality. Approximately 90% of these patients carry loss-of-function mutations in the enzyme ferrochelatase (FECH), while 5% of cases are associated with activating mutations in the C-terminus of ALAS2. Recent work has begun to uncover novel mechanisms of heme regulation that may account for the remaining 5% of cases with previously unknown genetic basis. One erythropoietic protoporphyria family has been identified with inherited mutations in the AAA+ protease ClpXP that regulates ALAS activity. In this review article, recent findings on the role of ClpXP as both an activating unfoldase and degrading protease and its impact on heme synthesis will be discussed. This review will also highlight the role of ClpX dysfunction in erythropoietic protoporphyria.

Genetic Variations Associated with Anti-Tuberculosis Drug-Induced Liver Injury

Purpose of this Review

In order to combat the development of drug resistance, the clinical treatment of tuberculosis requires the combined use of several anti-tuberculosis (anti-TB) drugs, including isoniazid and rifampicin. Combinational treatment approaches are suggested by the World Health Organization (WHO) and are widely accepted throughout the world. Unfortunately, a major side effect of the treatment is the development of anti-tuberculosis drug-induced liver injury (AT-DILI). Many factors contribute to isoniazid- and rifampicin-mediated AT-DILI and genetic variations are among the most common factors. The purpose of this review is to provide information on genetic variations associated with isoniazid- and rifampicin-mediated AT-DILI.

Recent Findings

The genetic variations associated with AT-DILI have been identified in the genomic regions within or near genes encoding proteins in the following pathways: drug metabolizing enzymes (NAT2, CYP2E1, and GSTs), accumulation of bile acids, lipids, and heme metabolites (CYP7A1, BSEP, UGTs, and PXR), immune adaptation (HLAs and TNF-α), and oxidant challenge (TXNRD1, SOD1, BACH1, and MAFK).

Summary

The information summarized in this review considers the genetic bases of risk factors contributing to AT-DILI and provides information that may help for future studies. Some of the implicated genetic variations can be used in the design of genetic tests and serve as biomarkers for the prediction of isoniazid- and rifampicin-mediated AT-DILI risk in personalized medicine.

Porphyria: often discussed but too often missed

The diagnosis of acute intermittent porphyria (AIP) is often overlooked. We describe a patient with this condition who had all the 'bells and whistles', in whom the diagnosis was only made after considerable delay. Far from an esoteric condition haunting examination candidates, AIP is an important cause of a broad spectrum of neurological symptoms. Its early recognition allows the astute clinician to prevent potentially devastating sequelae. We provide practical guidance on the investigation and management of this complex disorder. With a 'back to basics' approach to the underlying genetics and biochemistry, we hope to dispel some of the confusion that may obstruct a timely diagnosis.

[Archibald Cochrane: evidence, effectiveness and decision-making in health]

Nowadays, Evidence-Based Medicine plays a fundamental role while making medical decisions, considering that through the methods of science, it attempts to justify the variety of alternatives that may be offered to patients. In order to understand the historical evolution of this way of practicing medicine, it is necessary to review the contribution of one of the main participants in this cultural movement: Archibald Leman Cochrane, who helped to define the theoretical framework that has allowed the integration of science into the practice of medicine. Since he insisted in the need of integrating scientific evidence into clinical experience, his role became a fundamental and decisive element in the development of a new discipline: Evidence-Based Medicine.

Prevention of photosensitivity with action spectrum adjusted protection for erythropoietic protoporphyria

Erythropoietic protoporphyria is a genetic disease characterized by sensitivity to sunlight caused by the accumulation of protoporphyrin IX. Photoprotection against ultraviolet A and visible light is necessary for erythropoietic porphyria patients because the absorption spectrum of protoporphyrin IX lies in both ultraviolet A and visible light region. We developed a novel index, in vitro porphyrin protection factor, based on the protoporphyrin IX absorbance spectrum. We also selected appropriate photoprotective products designed according to protoporphyrin IX absorbance. The porphyrin protection factors of a combination of make-up base with a powder as well as with a liquid foundation were significantly higher than those of a conventional sunscreen product, even at a small application dose. An in-use test carried out for 6 months showed that the efficacy of these products was 78.3%, and no adverse reactions were observed. Male subjects preferred liquid foundation, whereas all female subjects used powder foundation. The preference of the subjects could lead to the long-term use of the tested products. In conclusion, this study provided a new approach to improve photoprotection in erythropoietic protoporphyria patients.

Porphyria and kidney diseases

The kidneys, after the bone marrow and liver, are third in terms of the amounts of haem synthesized daily. Haem is incorporated into haemoproteins that are critical to renal physiology. In turn, disturbances in haem metabolism interfere with renal physiology and are tightly interrelated with kidney diseases. Acute intermittent porphyria causes kidney injury, whereas medical situations associated with end-stage renal disease, such as porphyrin accumulation, iron overload and hepatitis C, participate in the inhibition of uroporphyrinogen decarboxylase and predispose the individual to porphyria cutanea tarda. Even if some of these interactions have been known for a long time, the clinical situations associated with these interrelations have strikingly evolved over time with the advent of new therapeutic strategies for dialysis therapy and a better understanding of the pathophysiological mechanisms of porphyria-associated kidney disease. Physicians should be aware of these interactions. The aim of this review is to summarize the complex interactions between kidney physiology and pathology in the settings of porphyria and to emphasize their often-underestimated importance.

An Inducible Promoter Responsive to Different Porphyrinogenic Stimuli Improves Gene Therapy Vectors for Acute Intermittent Porphyria

Porphobilinogen deaminase (PBGD) gene therapy represents a promising therapeutic option for acute intermittent porphyria (AIP) patients suffering recurrent acute attacks. A first-in-human Phase I clinical trial confirmed the safety and tolerability of adeno-associated virus (AAV)-AAT-PBGD gene therapy, but higher doses and/or more efficient vectors are needed to achieve therapeutic expression of the transgene. This study assayed the insertion into the promoter of a short enhancer element able to induce transgene expression during exposure to endogenous and exogenous stimuli related to the pathology of the disease. The inclusion in tandem of two elements of the minimal functional sequence of human δ-aminolevulinic acid synthase drug-responsive enhancing sequence (ADRES) positioned upstream of the promoter strongly induced transgene expression in the presence of estrogens, starvation, and certain drugs known to trigger attacks in porphyria patients. The inclusion of two ADRES motives in an AAV vector improved therapeutic efficacy, reducing 10-fold the effective dose in AIP mice. In conclusion, the inclusion of specific enhancer elements in the promoter of gene therapy vectors for AIP was able to overexpress the therapeutic transgene when it is most needed, at the time when porphyrinogenic factors increase the demand for hepatic heme and precipitate acute porphyria attacks.

[CME: Acute Intermittent Porphyria: When to Think of It? What Must be Checked? How to Treat?]

Zusammenfassung. Unter dem Begriff «Porphyrie» wird eine Gruppe von acht Stoffwechselerkrankungen zusammengefasst, welche in Folge einer gestörten Hämbiosynthese entstehen. Die Einteilung der verschiedenen Formen erfolgt anhand der klinischen und biochemischen Merkmale. Dieser Artikel fokussiert auf die akuten (hepatischen) Porphyrien (AHP), die durch eine ähnliche Pathophysiologie und klinische Symptomatik gekennzeichnet sind. Typisch sind akute, das autonome Nervensystem betreffende Symptome; starke, kolikartige, teilweise ausstrahlende Oberbauchschmerzen, Übelkeit, Erbrechen, Hypertonie, Tachykardie, Obstipation und Hyponatriämie. Die Diagnose einer AHP wird aufgrund einer mindestens fünffach erhöhten Ausscheidung von Porphobilinogen (PBG) im Urin gestellt. Therapie der Wahl ist die Zufuhr von Kohlenhydraten, die Gabe von humanem Häm, die Elimination und Vermeidung von schubauslösenden Triggerfaktoren und eine begleitende symptomorientierte Therapie, im Besonderen eine suffiziente Analgesie.

Urinary metabolic profiling of asymptomatic acute intermittent porphyria using a rule-mining-based algorithm

INTRODUCTION

Metabolomic profiling combines Nuclear Magnetic Resonance spectroscopy with supervised statistical analysis that might allow to better understanding the mechanisms of a disease.

OBJECTIVES

In this study, the urinary metabolic profiling of individuals with porphyrias was performed to predict different types of disease, and to propose new pathophysiological hypotheses.

METHODS

Urine ¹H-NMR spectra of 73 patients with asymptomatic acute intermittent porphyria (aAIP) and familial or sporadic porphyria cutanea tarda (f/sPCT) were compared using a supervised rule-mining algorithm. NMR spectrum buckets bins, corresponding to rules, were extracted and a logistic regression was trained.

RESULTS

Our rule-mining algorithm generated results were consistent with those obtained using partial least square discriminant analysis (PLS-DA) and the predictive performance of the model was significant. Buckets that were identified by the algorithm corresponded to metabolites involved in glycolysis and energy-conversion pathways, notably acetate, citrate, and pyruvate, which were found in higher concentrations in the urines of aAIP compared with PCT patients. Metabolic profiling did not discriminate sPCT from fPCT patients.

CONCLUSION

These results suggest that metabolic reprogramming occurs in aAIP individuals, even in the absence of overt symptoms, and supports the relationship that occur between heme synthesis and mitochondrial energetic metabolism.

Secret Underlying Unexplained Abdominal Pain, Neurological Symptoms and Intermittent Hypertension: Acute Intermittent Porphyria

A 21-year-old female patient with abdominal pain, vomiting and constipation was admitted to the hospital with the possible diagnosis of diabetic ketoacidosis. Due to increased abdominal pain and constipation the patient underwent a surgery with the diagnosis of ileus. However, no pathological findings were found in the abdominal organs apart from serous fluid in the abdominal cavity. The patient became hypertensive, tachycardic and had an episode of seizures postoperatively. Neurological manifestations with unexplained abdominal pain indicated a diagnosis of acute intermittent porphyria (AIP). Acute intermittent porphyria diagnosis is based on elevated urinary δ-aminolevulinic acid (ALA) and porphobilinogen (PBG) levels as well as hydroxymethylbilane synthase (HMBS) IVS13-2 A>G heterozygous mutation. Familial Mediterranean Fever (FMF) gene mutations were not confirmed. Porphyria should be considered in the differential diagnosis of patients with recurrent abdominal pain, neurological symptoms and lack of FMF gene polymorphism.

A Simple Method for Quantification of Five Urinary Porphyrins, Porphobilinogen and 5-Aminolevulinic Acid, Using Liquid Chromatography Tandem Mass Spectrometry

Analysis of porphyrins and 5-aminolevulinic acid (ALA), porphobilinogen (PBG) in physiological liquids is required for diagnosis and follow-up of porphyrias. High performance liquid chromatography (HPLC) and liquid chromatography tandem mass spectrometry (LC-MS) methods with higher specificity and sensitivity have been developed. The major disadvantage of those methods is that they require longer extraction times due to their matrix effects. The present study suggests a simple, fast, sensitive, and specific assay for determination of Coproporphyrin, 5-carboxylporphyrin, 6-carboxylporphyrin, 7-carboxylporphyrin, Uroporphyrin I and ALA, PBG in urine sample by direct injection without sample pre-treatment using LC-MS. For the purposes of the present study LC-MS device was set to multiple reaction monitoring (MRM) and positive ion mode. Porphyrins and ALA, porphobilinogen were characterized by their MS/MS product ion, spectra. ALA, PBG and 5 porphyrins were detected simultaneously. Limit of detection for Coproporphyrin, 5-carboxylporphyrin, 6-carboxylporphyrin, 7-carboxylporphyrin, Uroporphyrin I were 2 nmol/L, where it was 5 μmol/L for ALA and 2 μmol/L for porphobilinogen. The present study suggests that the present method is very effective compared to many other available methods for it does not require pre-treatment, provides simultaneous results of ALA, PBG and 5 porphyrins quantitatively in a shorter span of time, and has suitable sensitivity and selectivity. LC-MS technique was used clinically for the determination of urine porphyrin levels.

Acute hepatic and erythropoietic porphyrias: from ALA synthases 1 and 2 to new molecular bases and treatments

PURPOSE OF REVIEW

Many studies over the past decade have together identified new genes including modifier genes and new regulation and pathophysiological mechanisms in inherited inborn diseases of the heme biosynthetic pathway. A new porphyria has been characterized: X-linked protoporphyria and the perspective to have innovative treatment at very short-term became a reality. We will summarize how recent data on both ALAS1 and ALAS2 have informed our understanding of disease pathogenesis with an emphasis on how this information may contribute to new therapeutic strategies.

RECENT FINDINGS

The development of clinical and biological porphyria networks improved the long-term follow up of cohorts. The ageing of patients have allowed for the identification of novel recurrently mutated genes, and highlighted long-term complications in acute hepatic porphyrias. The treatment of hepatic porphyrias by an RNAi-targeting hepatic ALAS1 is actually tested and may lead to improve the management of acute attacks.In erythropoietic porphyrias, the key role of ALAS2 as a gate keeper of the heme and subsequently hemoglobin synthesis has been demonstrated. Its implication as a modifier gene in over erythroid disorders has also been documented.

SUMMARY

The knowledge of both the genetic abnormalities and the regulation of heme biosynthesis has increased over the last 5 years and open new avenues in the management of erythropoietic and acute hepatic porphyrias.

Acute hepatic porphyrias: Recommendations for evaluation and long-term management

The acute hepatic porphyrias are a group of four inherited disorders, each resulting from a deficiency in the activity of a specific enzyme in the heme biosynthetic pathway. These disorders present clinically with acute neurovisceral symptoms which may be sporadic or recurrent and, when severe, can be life-threatening. The diagnosis is often missed or delayed as the clinical features resemble other more common medical conditions. There are four major subgroups: symptomatic patients with sporadic attacks (<4 attacks/year) or recurrent acute attacks (≥4 attacks/year), asymptomatic high porphyrin precursor excretors, and asymptomatic latent patients without symptoms or porphyrin precursor elevations. Given their clinical heterogeneity and potential for significant morbidity with suboptimal management, comprehensive clinical guidelines for initial evaluation, follow-up, and long-term management are needed, particularly because no guidelines exist for monitoring disease progression or response to treatment. The Porphyrias Consortium of the National Institutes of Health's Rare Diseases Clinical Research Network, which consists of expert centers in the clinical management of these disorders, has formulated these recommendations. These recommendations are based on the literature, ongoing natural history studies, and extensive clinical experience. Initial assessments should include diagnostic confirmation by biochemical testing, subsequent genetic testing to determine the specific acute hepatic porphyria, and a complete medical history and physical examination. Newly diagnosed patients should be counseled about avoiding known precipitating factors. The frequency of follow-up depends on the clinical subgroup, with close monitoring of patients with recurrent attacks who may require treatment modifications as well as those with clinical complications. Comprehensive care should include subspecialist referrals when needed. Annual assessments include biochemical testing and monitoring for long-term complications. These guidelines provide a framework for monitoring patients with acute hepatic porphyrias to ensure optimal outcomes. (Hepatology 2017;66:1314-1322).

Cimetidine/lactulose therapy ameliorates erythropoietic protoporphyria-related liver injury

A 21-year-old Japanese man was admitted to our hospital because of severe abdominal pain and jaundice. He had been suffering from abdominal pain attacks and liver dysfunction since 18 years of age. Liver histology showed amorphous brown deposits in the sinusoidal space and significant periportal fibrosis without apparent hepatitis. Increased protoporphyrin in serum and feces and ferrochelatase gene mutation confirmed the final diagnosis of erythropoietic protoporphyria (EPP). Since ursodeoxycholic acid (UDCA) intake and glucose infusion are insufficient to ameliorate jaundice and abdominal attacks, cimetidine and lactulose were added in order to suppress hepatic delta-aminolevulinic acid synthase and limit re-absorption of protoporphyrin, respectively. Afterwards, the jaundice, liver dysfunction and abdominal symptoms improved and UDCA, cimetidine, and lactulose administration was continued. A repeat biopsy at 1.5 years after adding cimetidine/lactulose revealed marked attenuation of periportal fibrosis and protoporphyrin deposits. As far as we know, this is the first demonstration of histological improvement of EPP-induced liver abnormalities due to persistent cimetidine/lactulose administration. These treatments may be useful for EPP-related liver injury.

A case of previously undiagnosed acute intermittent porphyria in a 34-year-old primigravida with gestational diabetes mellitus

Porphyrias are very rare and easily overlooked diseases in pregnancy. Among these eight known metabolic disorders, acute intermittent porphyria (AIP) is the most common and most severe type. An enzymatic alteration in the haem biosynthesis pathway causes liver overproduction of neurotoxic toxic metabolites, which cause attacks of acute neurovisceral symptoms, severe abdominal pain and/or skin lesions. Women with AIP can sometimes develop their first acute attack during pregnancy, and because the symptoms are unspecific, the diagnosis is difficult to obtain and often missed. However, prompt diagnosis of AIP during pregnancy is crucial as treatment can significantly improve the pregnancy outcome. The backbone of the therapy is food rich with carbohydrates, complemented by 20% glucose infusion and adequate pain control. We present a case of previously undiagnosed AIP in a 34-year primigravida, whose treatment was especially challenging due to co-existing gestational diabetes mellitus and problems with the central venous catheter.

Mutation in human CLPX elevates levels of δ-aminolevulinate synthase and protoporphyrin IX to promote erythropoietic protoporphyria

Loss-of-function mutations in genes for heme biosynthetic enzymes can give rise to congenital porphyrias, eight forms of which have been described. The genetic penetrance of the porphyrias is clinically variable, underscoring the role of additional causative, contributing, and modifier genes. We previously discovered that the mitochondrial AAA+ unfoldase ClpX promotes heme biosynthesis by activation of δ-aminolevulinate synthase (ALAS), which catalyzes the first step of heme synthesis. CLPX has also been reported to mediate heme-induced turnover of ALAS. Here we report a dominant mutation in the ATPase active site of human CLPX, p.Gly298Asp, that results in pathological accumulation of the heme biosynthesis intermediate protoporphyrin IX (PPIX). Amassing of PPIX in erythroid cells promotes erythropoietic protoporphyria (EPP) in the affected family. The mutation in CLPX inactivates its ATPase activity, resulting in coassembly of mutant and WT protomers to form an enzyme with reduced activity. The presence of low-activity CLPX increases the posttranslational stability of ALAS, causing increased ALAS protein and ALA levels, leading to abnormal accumulation of PPIX. Our results thus identify an additional molecular mechanism underlying the development of EPP and further our understanding of the multiple mechanisms by which CLPX controls heme metabolism.

Clinical, Biochemical Characteristics and Hospital Outcome of Acute Intermittent Porphyria Patients: A Descriptive Study from North India

INTRODUCTION

Acute intermittent porphyria (AIP) is an inherited metabolic disease characterized by disordered heme biosynthesis. There is no recent study reported from India.

MATERIALS AND METHODS

It was a retrospective, observational study. Clinical records of patients of AIP with acute porphyric attacks admitted from April 2008 to December 2016 were analyzed.

RESULTS

Fifteen AIP patients constituted of eight females and seven males were analyzed. Mean age at presentation was 34.33 ± 15.86 years. Thirteen patients (86.67%) had acute flaccid paralysis (AFP). All of them had peripheral neuropathy. These patients concomitantly had abdominal pain, seizure, encephalopathy, autonomic hyperactivity, history of passage of dark urine, and electrolyte abnormality (hyponatremia) in various combinations. Abdominal pain was the presenting symptom in 11 (73.33%) patients. Seven (46.67%) patients had seizure episodes. Five patients (33.33%) had hyponatremia at presentation. Significantly higher percentage of them had seizure at presentation or during hospital stay (P = 0.007). These patients also had evidence of autonomic hyperactivity in the form of higher pulse rate, systolic and diastolic blood pressure at presentation. They had prolonged duration of hospital stay as well (P = 0.016). Eleven patients had partial recovery and rest four patients (26.67%) had in-hospital mortality.

CONCLUSION

Patients had severe neurological involvement manifesting mainly as AFP and seizure episodes. We recommend screening for AIP in patients presenting with features of AFP along with any combination of clinical/laboratory manifestations such as abdominal pain, seizure, encephalopathy, autonomic hyperactivity, passage of dark urine, and hyponatremia. Electrolyte abnormality in the form of hyponatremia was an important severity marker.

Dermatologic Manifestations of Chronic Hepatitis C Infection

Chronic hepatitis C virus (HCV) infection is associated with various extrahepatic manifestations, including dermatologic involvement mostly caused by immune complexes. Mixed cryoglobulinemia has a strong relationship with HCV with 95% of these patients being infected with HCV. Lichen planus is a disease of the squamous epithelium and may affect any part of the skin, with 4% to 24% of patients with lichen planus reported to have chronic HCV infection. Porphyria cutanea tarda is the most common form of porphyria, and it is thought that HCV interferes with iron stores, which can promote porphyria cutanea tarda. Finally, necrolytic acral erythema is a rare, psoriasis-like disease closely associated with HCV.

Photosensitization in Porphyrias and Photodynamic Therapy Involves TRPA1 and TRPV1

Photosensitization, an exaggerated sensitivity to harmless light, occurs genetically in rare diseases, such as porphyrias, and in photodynamic therapy where short-term toxicity is intended. A common feature is the experience of pain from bright light. In human subjects, skin exposure to 405 nm light induced moderate pain, which was intensified by pretreatment with aminolevulinic acid. In heterologous expression systems and cultured sensory neurons, exposure to blue light activated TRPA1 and, to a lesser extent, TRPV1 channels in the absence of additional photosensitization. Pretreatment with aminolevulinic acid or with protoporphyrin IX dramatically increased the light sensitivity of both TRPA1 and TRPV1 via generation of reactive oxygen species. Artificial lipid bilayers equipped with purified human TRPA1 showed substantial single-channel activity only in the presence of protoporphyrin IX and blue light. Photosensitivity and photosensitization could be demonstrated in freshly isolated mouse tissues and led to TRP channel-dependent release of proinflammatory neuropeptides upon illumination. With antagonists in clinical development, these findings may help to alleviate pain during photodynamic therapy and also allow for disease modification in porphyria patients.

SIGNIFICANCE STATEMENT

Cutaneous porphyria patients suffer from burning pain upon exposure to sunlight and other patients undergoing photodynamic therapy experience similar pain, which can limit the therapeutic efforts. This study elucidates the underlying molecular transduction mechanism and identifies potential targets of therapy. Ultraviolet and blue light generates singlet oxygen, which oxidizes and activates the ion channels TRPA1 and TRPV1. The disease and the therapeutic options could be reproduced in models ranging from isolated ion channels to human subjects, applying protoporphyrin IX or its precursor aminolevulinic acid. There is an unmet medical need, and our results suggest a therapeutic use of the pertinent antagonists in clinical development.

Involvement of protoporphyrin IX accumulation in the pathogenesis of isoniazid/rifampicin-induced liver injury: the prevention of curcumin

Combination of isoniazid (INH) and rifampicin (RFP) causes liver injury frequently among tuberculosis patients. However, mechanisms of the hepatotoxicity are not entirely understood. Protoporphyrin IX (PPIX) accumulation, as an endogenous hepatotoxin, resulting from isoniazid and rifampicin co-therapy (INH/RFP) has been reported in PXR-humanized mice. Aminolevulinic acid synthase1 (ALAS1), ferrochelatase (FECH) and breast cancer resistance protein (BCRP) play crucial roles in PPIX synthesis, metabolism and transport, respectively. Herein, this study focused on the role of INH/RFP in these processes. We observed PPIX accumulation in human hepatocytes (L-02) and mouse livers. FECH expression was initially found downregulated both in L-02 cells and mouse livers and expression levels of ALAS1 and BCRP were elevated in L-02 cells after INH/RFP treatment, indicating FECH inhibition and ALAS1 induction might confer a synergistic effect on PPIX accumulation. Additionally, our results revealed that curcumin alleviated INH/RFP-induced liver injury, declined PPIX levels and induced FECH expression in both L-02 cells and mice. In conclusion, our data provide a novel insight in the mechanism of INH/RFP-induced PPIX accumulation and evidence for understanding pathogenesis of INH/RFP-induced liver injury, and suggest that amelioration of PPIX accumulation might be involved in the protective effect of curcumin on INH/RFP-induced liver injury.

Genetic, hematological, and immunological disorders transmissible with liver transplantation

It is well recognized that solid organ transplantation can transmit bacterial infection and chronic viral hepatitis as well as certain cancers. As indications for liver transplantation (LT) have expanded, it has been used to treat and even cure certain genetic cholestatic disorders, urea cycle defects, and coagulation abnormalities; many of these conditions are potentially transmissible with LT as well. It is important for clinicians and transplant patients to be aware of these potentially transmissible conditions as unexplained post-LT complications can sometimes be related to donor transmission of disease and thus should prompt a thorough exploration of the donor allograft history. Herein, we will review the reported genetic, metabolic, hematologic, and immunological disorders that are transmissible with LT and describe clinical scenarios in which these cases have occurred, such as in inadvertent or recognized transplantation of a diseased organ, domino transplantation, and with living related liver donation. Liver Transplantation 23 663-678 2017 AASLD.

Heme Gazing: Illuminating Eukaryotic Heme Trafficking, Dynamics, and Signaling with Fluorescent Heme Sensors

Heme (iron protoporphyrin IX) is an essential protein prosthetic group and signaling molecule required for most life on Earth. All heme-dependent processes require the dynamic and rapid mobilization of heme from sites of synthesis or uptake to hemoproteins present in virtually every subcellular compartment. The cytotoxicity and hydrophobicity of heme necessitate that heme mobilization be carefully controlled to mitigate the deleterious effects of this essential toxin. Indeed, a number of disorders, including certain cancers, cardiovascular diseases, and aging and age-related neurodegenerative diseases, are tied to defects in heme homeostasis. However, the molecules and mechanisms that mediate heme transport and trafficking, and the dynamics of these processes, are poorly understood. This is in large part due to the lack of physical tools for probing cellular heme. Herein, we discuss the recent development of fluorescent probes that can monitor and image kinetically labile heme with respect to its mobilization and role in signaling. In particular, we will highlight how heme gazing with these tools can uncover new heme trafficking factors upon being integrated with genetic screens and illuminate the concentration, subcellular distribution, and dynamics of labile heme in various physiological contexts. Altogether, the monitoring of labile heme, along with recent biochemical and cell biological studies demonstrating the reversible regulation of certain cellular processes by heme, is challenging us to reconceptualize heme from being a static cofactor buried in protein active sites to a dynamic and mobile signaling molecule.