Drugs in porphyria: From observation to a modern algorithm-based system for the prediction of porphyrogenicity

Drug-associated porphyria: a pharmacovigilance study

BACKGROUND

The potentially fatal attacks experienced by porphyria carriers are triggered by various porphyrinogenic drugs. However, determining the safety of particular drugs is challenging.

METHODS

We retrospectively used the U.S. Food and Drug Administration's Adverse Event Reporting System (FAERS) to identify drugs associated with porphyria as an adverse event (AE) extracted from data from January 2004 to March 2022. The associated search terms included "Porphyria," "Porphyria screen," "Porphyria non-acute," "Porphyria acute," "Acquired porphyria," and "Pseudoporphyria." Signal mining analysis was performed to identify the association between drugs and AEs by four algorithms, namely the reporting odds ratio, proportional reporting ratio, Bayesian confidence propagation neural network, and multi-item gamma Poisson shrinker.

RESULTS

FAERS reported 1470 cases of porphyria-related AEs, and 406 drugs were screened after combining trade and generic names. All four algorithms identified 52 drugs with signals. The characteristics of all the reports and signaling drugs were analyzed.

CONCLUSIONS

This is the first report of drug-associated porphyria that provides critical information on drug porphyrogenicity, facilitating rational and evidence-based drug prescription and improving the accuracy of porphyrogenicity prediction based on model algorithms. Moreover, this study serves a reference for clinicians to ensure that porphyrinogenic drugs are not prescribed to carriers of porphyria genetic mutations.

Onset of Acute Intermittent Porphyria After Etonogestrel Implant Insertion: A Case Report

A 17-year-old previously healthy female developed posterior reversible encephalopathy syndrome 1 week after etonogestrel implantation. She had a previous etonogestrel implant removed 4 months prior after unrelenting abdominal pain and hyponatremia with a negative workup for other etiologies, including hypercoagulable disorders and malignancy. This second insertion and resulting hospitalization allowed for the diagnosis of acute intermittent porphyria (AIP) to be confirmed. Progesterone can induce enzymatic activity upstream of porphobilinogen deaminase, the enzyme implicated in AIP, resulting in build-up of toxic metabolites. AIP requires high clinical suspicion for diagnosis but should be considered when hormonal triggers lead to unexplained neurovisceral symptoms.

Update on the diagnosis and management of the autosomal dominant acute hepatic porphyrias

The autosomal dominant acute hepatic porphyrias (AHPs), acute intermittent porphyria, hereditary coproporphyria (HCP) and variegate porphyria (VP), are low penetrance adult onset disorders caused by partial deficiency of enzymes of haem biosynthesis. All are associated with acute neurovisceral attacks, which are a consequence of the increased hepatic demand for haem triggered by hormones, stress, drugs or systemic infections which leads to upregulation of the pathway and overproduction of haem precursors 5-aminolaevulinic acid (ALA) and porphobilinogen (PBG). Acute episodes are characterised by severe abdominal pain, nausea, vomiting, hyponatraemia, hypertension and tachycardia, behavioural disturbance and can progress to include seizures, peripheral motor neuropathy and posterior reversible encephalopathy syndrome if undiagnosed and untreated. VP and HCP may also present with photocutaneous skin lesions either alone or during acute symptoms. Diagnosis involves demonstrating increased excretion of PBG in urine. Treatment focuses on removing or managing triggers, supportive treatment and suppressing the hepatic haem pathway by administering human haemin. Chronic complications include hypertension, chronic kidney disease and hepatocellular carcinoma. A small proportion of symptomatic patients with AHP progress to repeated acute attacks which require preventative therapy. A new RNA interference therapy has recently been licensed and is likely to become the treatment of choice in this situation.

[Anesthesia in patients with acute porphyria]

Porphyrias are a group of rare, mostly inherited metabolic disorders of heme biosynthesis. Each type of porphyria results from a specific deficiency of one of the pathway enzymes, causing a characteristic accumulation and excretion of heme precursors. Diagnosis is confirmed by the biochemical detection of these porphyrins and the precursors in urine, feces and blood. Porphyrias can be classified into acute and non-acute forms. The clinical presentation is unspecific and includes acute neurovisceral and/or cutaneous symptoms. The latent phase can evolve into a potentially life-threatening acute crisis, which is often misdiagnosed. The four acute hepatic porphyrias are relevant for anesthesiologists as precipitating factors are commonly found in the perioperative setting. Safe anesthetic management in cases of known porphyria is possible by adherence to current recommendations. The immediate administration of heme arginate as specific treatment for acute attacks is decisive for the outcome.

Acute hepatic porphyria and maternal health: Clinical and biochemical follow-up of 44 pregnancies

BACKGROUND

Pregnancy in women with acute hepatic porphyria (AHP) has historically been associated with significant morbidity. Clinical outcomes have been the focus of previous reports on porphyria and maternal health, with little data available on the levels of heme precursors during pregnancy. We present the results of a follow-up program for women with AHP in the Swedish cohort who were pregnant between 2001 and 2020.

METHODS

Thirty-three women with AHP were monitored during 44 pregnancies resulting in 44 single births. Seven of 33 women had a clinical history of acute attacks that required hospitalization.

RESULTS

Four women experienced acute porphyria attacks during pregnancy and one during the puerperium. Seven women developed hypertension and four pregnancies ended with pre-eclampsia. There were no maternal or fetal pre- or postnatal deaths. One infant had a congenital cardiac anomaly. In 32 of the 38 pregnancies in which we measured heme precursors in the urine during pregnancy, the levels increased.

CONCLUSION

Our observations align with contemporary reports that pregnancy in patients with AHP is frequently uncomplicated. Excretion of heme precursors increased during pregnancy, but this did not manifest as a higher frequency of clinical porphyria manifestations. The involvement of porphyria specialists in the patients' maternal care is recommended for reducing risk and improving the probability of good pregnancy outcomes.

Multibiomarker approach to assess the magnitude of occupational exposure and effects induced by a mixture of metals

Metals and metalloids including lead (Pb), arsenic (As) and manganese (Mn) can occur as mixtures in occupational contexts, such as mines. These chemicals are all known to be neurotoxic and provoke changes in heme metabolism also known to induce neurotoxicity. The objective of this work was to propose a multi-biomarker (BM) methodology to screen subjects exposed to the mixture of Pb, As and Mn and assess the severity of their exposure/effects, in an individual basis. The urinary levels of the metals, dela-aminolevulinic acid (ALA) and porphyrins were determined in Portuguese miners and in a control group. The combination of Pb and As urinary levels had the highest capability to identify subjects occupationally exposed to this mixture in mines, as evaluated through Receiver Operating Characteristic (ROC) (A = 98.2%; p < 0.05), allowing that 94.2% of 86 studied subjects were properly identified and the generation of an equation indicating the odd of a subject be considered as exposed to the metal mixture. The combination of urinary ALA and porphyrins revealed to be best one to be applied in the assessment of subjects with high, intermediate, and low magnitudes of exposure/effects, with 95.7% of 46 miners classified correctly according to their severity sub-group and allowing to generate equations, which can be applied in new subjects. The proposed methodology showed a satisfactory performance, evaluating in an integrated manner the magnitude of exposure/effects of the exposed workers, may contributing to improve the control of their health.

Treatment with assisted reproduction technologies in women with acute hepatic porphyria

INTRODUCTION

Acute porphyrias are rare disorders of the heme biosynthetic pathway and present with acute neurovisceral symptoms that can be induced by hormonal changes and medications. Women are far more likely to present with clinical symptoms than men, particularly during parts of their lifetime with changes in the level of female sex hormones such as ovulation, menstruation, and pregnancy. Treatment of ovulatory dysfunction and controlled ovarian hyperstimulation require the administration of hormones, which are considered porphyrinogenic. Women with acute hepatic porphyria have therefore been considered unsuitable for such treatments in the past.

MATERIAL AND METHODS

We report on nine women with acute hepatic porphyria who underwent in vitro fertilization (IVF), preceded by ovarian stimulation. Their mean age at the start of IVF was 33.2 years (range 27-38 years). Two women had been diagnosed with polycystic ovarian syndrome, two were treated for hyperprolactinemia, two had hypothyroidism, of which one also had type 1 diabetes, one had a uterus malformation, one had anovulatory cycles, and one used a sperm donor.

RESULTS

All patients were able to undergo fertility treatment without experiencing severe porphyria attacks.

CONCLUSIONS

Women with acute hepatic porphyria considering fertility treatments should be assessed individually for potential risks, treatment should be planned in close collaboration with a porphyria specialist, and biochemical activity should be monitored regularly during ovarian stimulation. As we gather more knowledge, we hope that the porphyrinogenicity of the stimulation agents is re-assessed and that more studies will shed light on the reproductive health of women living with acute hepatic porphyria.

The acute hepatic porphyrias

The acute hepatic porphyrias (AHP) are a group of four inherited diseases of heme biosynthesis. They present with similar severe, episodic, acute neurovisceral symptoms due to abnormally elevated levels of porphyrin precursors delta-aminolevulinic acid (ALA). Recently genetic screening indicates that the prevalence of mutation carrier state is more common than previously thought, occurring in 1 in 1,500, though the clinical penetrance of symptomatic AHP is low at ~1%. Symptomatic attacks occur primarily in females during their reproductive years. In an acute porphyria attack, the primary symptom is abdominal pain, due to intestinal dysmotility from autonomic nerve injury. Other manifestations include seizures, weakness and mood changes, point to injury involving peripheral and central nervous system. Due to the non-specific nature of the symptoms and signs in AHP, the diagnosis is often delayed by many years. The diagnosis of AHP depends on biochemical evidence of elevated ALA and PBG levels in urine during symptomatic attacks. Genetic testing is used for confirmation of the gene involved and the exact mutation. Treatment involves administration of heme, which downregulates production of ALA. Long-term management centers on educating genetic carriers on avoiding triggers that increase the risk of acute attacks and screening family members.

A Pharmacological Chaperone Therapy for Acute Intermittent Porphyria

Mutations in hydroxymethylbilane synthase (HMBS) cause acute intermittent porphyria (AIP), an autosomal dominant disease where typically only one HMBS allele is mutated. In AIP, the accumulation of porphyrin precursors triggers life-threatening neurovisceral attacks and at long-term, entails an increased risk of hepatocellular carcinoma, kidney failure, and hypertension. Today, the only cure is liver transplantation, and a need for effective mechanism-based therapies, such as pharmacological chaperones, is prevailing. These are small molecules that specifically stabilize a target protein. They may be developed into an oral treatment, which could work curatively during acute attacks, but also prophylactically in asymptomatic HMBS mutant carriers. With the use of a 10,000 compound library, we identified four binders that further increased the initially very high thermal stability of wild-type HMBS and protected the enzyme from trypsin digestion. The best hit and a selected analog increased steady-state levels and total HMBS activity in human hepatoma cells overexpressing HMBS, and in an Hmbs-deficient mouse model with a low-expressed wild-type-like allele, compared to untreated controls. Moreover, the concentration of porphyrin precursors decreased in liver of mice treated with the best hit. Our findings demonstrate the great potential of these hits for the development of a pharmacological chaperone-based corrective treatment of AIP by enhancing wild-type HMBS function independently of the patients’ specific mutation.

Lifestyle factors including diet and biochemical biomarkers in acute intermittent porphyria: Results from a case-control study in northern Norway

BACKGROUND

Lifestyle factors, including a low intake of carbohydrates, dieting, alcohol consumption, cigarette smoking and stress are some of the possible triggers of attacks in acute intermittent porphyria (AIP). The influence of lifestyle factors, including energy intake, diet and alcohol consumption on the biochemical disease activity in AIP and biochemical nutritional markers were examined.

METHODS

A case-control study with 50 AIP cases and 50 controls matched for age, sex and place of residence was performed. Dietary intake was registered using a food diary in 46 matched pairs. Symptoms, alcohol intake, stress and other triggering factors of the last AIP attack were recorded on questionnaires. Porphyrin precursors, liver and kidney function markers, vitamins, diabetogenic hormones and other nutritional biomarkers were analyzed by routine methods. The Wilcoxon matched-pairs signed rank test was used to compare the cases vs. controls. The Spearman's rank correlation coefficient was used on the cases.

RESULTS

Increasing total energy intake was negatively correlated with the biochemical disease activity. The intake of carbohydrates was lower than recommended, i.e., 40 and 39% of total energy intake in the AIP cases and controls, respectively. The plasma resistin level was significantly higher (p = .03) in the symptomatic than asymptomatic cases. Plasma insulin was lower in those with high porphobilinogen levels. The intake of sugar and candies were higher in the AIP cases with low U-delta aminolevulinic acid (ALA) levels (p = .04). Attacks were triggered by psychological stress (62%), physical strain (38%), food items (24%) and alcohol (32%) in the 34 symptomatic cases. Alcohol was used regularly by 88% of the cases (3.2 g ethanol/day) and 90% of the controls (6.3 g/day), but the intake was significantly lower in symptomatic than in asymptomatic cases (p = .045).

CONCLUSION

A high intake of energy, sugar and candies and a higher insulin level were associated with a lower biochemical disease activity. The resistin level was higher in the symptomatic than the asymptomatic cases. AIP patients drink alcohol regularly, but the intake was significantly lower in the symptomatic cases.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT01617642.

The essential role of the transporter ABCG2 in the pathophysiology of erythropoietic protoporphyria

Erythropoietic protoporphyria (EPP) is an inherited disease caused by loss-of-function mutations of ferrochelatase, an enzyme in the heme biosynthesis pathway that converts protoporphyrin IX (PPIX) into heme. PPIX accumulation in patients with EPP leads to phototoxicity and hepatotoxicity, and there is no cure. Here, we demonstrated that the PPIX efflux transporter ABCG2 (also called BCRP) determines EPP-associated phototoxicity and hepatotoxicity. We found that ABCG2 deficiency decreases PPIX distribution to the skin and therefore prevents EPP-associated phototoxicity. We also found that ABCG2 deficiency protects against EPP-associated hepatotoxicity by modulating PPIX distribution, metabolism, and excretion. In summary, our work has uncovered an essential role of ABCG2 in the pathophysiology of EPP, which suggests the potential for novel strategies in the development of therapy for EPP.

Porphyrias: A clinically based approach

BACKGROUND

Porphyrias are a group of metabolic diseases, individually rare but with an important combined prevalence. Because of their pathological complexity and clinical heterogeneity, they present a challenging diagnosis. The present review aims to provide a clinically based approach to the recognition and treatment of these disorders.

METHODS

We carried out a search in PubMed, with the keyword "porphyria", for reviews published in English from 2010 until 2017.

RESULTS

The research yielded 196 papers, of which 64 were included in the final narrative review.

CONCLUSIONS

Porphyrias can be divided based on clinical presentation in acute neurovisceral, chronic cutaneous bullous, chronic cutaneous non-bullous and acute neurovisceral/chronic cutaneous bullous. Each individual porphyria presents a characteristic pattern of porphyrins in plasma, urine, stool and red blood cells. As such, diagnosis is easily obtained by following a simple diagnostic algorithm. Early recognition is key in managing these diseases. Neurovisceral porphyrias require acute support therapy and chronic eviction of precipitating factors. Cutaneous prophyrias, as photosensitivity disorders, rely on sunlight avoidance and, in some cases, specific therapeutic interventions. Given the rarity of these conditions, physician awareness is crucial.

Biomarkers of exposure and effect in a working population exposed to lead, manganese and arsenic

Lead (Pb), manganese (Mn) and arsenic (As) are among the major toxicants in mining environments. Miners are commonly and repeatedly exposed to this toxic mixture. Some adverse effects may appear at concentrations below environmental quality guidelines for individual mixture components. Further, Pb, Mn, and As induce common adverse outcomes, such as interferences in the cholinergic system and heme synthesis. It is thus vital to monitor miners through biomarkers (BM), such that subclinical effects may be identified at an early stage. The main objectives of this study were to evaluate the exposure of a mining population to these three metals and determine alterations in cholinergic and heme synthesis parameters. Blood and urine samples of workers (n = 60) were obtained from a Portuguese mining industry and compared with a control population (n = 80). The levels of the metals were determined in biological samples, as well as urinary heme precursor levels, delta aminolevulinic acid (ALA) and porphyrins, and blood acetylcholinesterase (AChE) activity. The miners exhibited significantly higher values of Pb and As in blood and urine compared to control. In the case of Mn near or slightly higher than limit values were found. Our data show that heme precursors may be used simultaneously with metal levels as BMs for multiple metal exposures on an individual basis, resulting in 94.3% and 95.7% accuracy, respectively, in blood and urine, for subjects correctly identified with respect to occupation. This study also revealed that biological monitoring of this working population regarding metal body burden and heme precursor accumulation is advisable.

Update review of the acute porphyrias

Acute porphyrias are rare inherited disorders due to deficiencies of haem synthesis enzymes. To date, all UK cases have been one of the three autosomal dominant forms, although penetrance is low and most gene carriers remain asymptomatic. Clinical presentation is typically with acute neurovisceral attacks characterised by severe abdominal pain, vomiting, tachycardia and hypertension. Severe attacks may be complicated by hyponatraemia, peripheral neuropathy sometimes causing paralysis, seizures and psychiatric features. Attacks are triggered by prescribed drugs, alcohol, hormonal changes, fasting or stress. The diagnosis is made by finding increased porphobilinogen excretion in a light-protected random urine sample. Management includes administration of intravenous human haemin and supportive treatment with non-porphyrinogenic drugs. A few patients develop recurrent attacks, a chronic illness requiring specialist management. Late complications include chronic pain, hepatocellular carcinoma, chronic renal failure and hypertension. In the UK, the National Acute Porphyria Service provides clinical advice and supplies haemin when indicated.

Systemic inflammation in acute intermittent porphyria: a case-control study

This study aimed to examine whether acute intermittent porphyria (AIP) is associated with systemic inflammation and whether the inflammation correlates with disease activity. A case-control study with 50 AIP cases and age-, sex- and place of residence-matched controls was performed. Plasma cytokines, insulin and C-peptide were analysed after an overnight fast using multiplex assay. Long pentraxin-3 (PTX3) and complement activation products (C3bc and TCC) were analysed using enzyme-linked immunosorbent assay (ELISA). Urine porphobilinogen ratio (U-PBG, µmol/mmol creatinine), haematological and biochemical tests were performed using routine methods. Questionnaires were used to register AIP symptoms, medication and other diseases. All 27 cytokines, chemokines and growth factors investigated were increased significantly in symptomatic AIP cases compared with controls (P < 0·0004). Hierarchical cluster analyses revealed a cluster with high visfatin levels and several highly expressed cytokines including interleukin (IL)-17, suggesting a T helper type 17 (Th17) inflammatory response in a group of AIP cases. C3bc (P = 0·002) and serum immunoglobulin (Ig)G levels (P = 0·03) were increased significantly in cases with AIP. The U-PBG ratio correlated positively with PTX3 (r = 0·38, P = 0·006), and with terminal complement complex (TCC) levels (r = 0·33, P = 0·02). PTX3 was a significant predictor of the biochemical disease activity marker U-PBG in AIP cases after adjustment for potential confounders in multiple linear regression analyses (P = 0·032). Prealbumin, C-peptide, insulin and kidney function were all decreased in the symptomatic AIP cases, but not in the asymptomatic cases. These results indicate that AIP is associated with systemic inflammation. Decreased C-peptide levels in symptomatic AIP cases indicate that reduced insulin release is associated with enhanced disease activity and reduced kidney function.

Radiopharmaceuticals in Acute Porphyria

PURPOSE

The acute porphyrias are a group of rare metabolic disorders of the heme biosynthetic pathway. Carriers of the acute porphyria gene are prone to potentially fatal acute attacks, which can be precipitated by drug exposure. It is therefore important to know whether a drug is safe for carriers of the acute porphyria gene. In this study, radiopharmaceuticals were assessed on their porphyrogenicity (ie, the potential of a drug to induce an attack).

METHODS

The assessment was conducted by classifying the drugs according to the Thunell model.

FINDINGS

From 41 radiopharmaceuticals assessed, I-131 norcholesterol, Tc-99m mebrofenin, Tc-99m phytate, Tc-99m sestamibi, and Tl-201 chloride were classified as possibly porphyrogenic.

IMPLICATIONS

I-131 norcholesterol, Tc-99m mebrofenin, Tc-99m phytate, Tc-99m sestamibi, and Tl-201 chloride should not be prescribed for patients experiencing acute porphyria unless an urgent indication is present and no safer alternative is available. In such cases, potential users should seek advice from a porphyria expert. Preventive measures may also be required.

Porphyria: Pathophysiology, diagnosis, and treatment

Porphyrias are inherited metabolic disorders that involve alterations in enzymes utilized in the heme biosynthetic pathway. Most of these conditions are inherited; however, some are believed to be acquired through environmental exposures. Patients with porhyrias often present with a wide range of clinical symptoms, making it difficult to diagnose. Treatments vary depending on clinical presentation. A thorough and detailed history is essential and key to discovering a porphyria diagnosis.

Lead, Arsenic, and Manganese Metal Mixture Exposures: Focus on Biomarkers of Effect

The increasing exposure of human populations to excessive levels of metals continues to represent a matter of public health concern. Several biomarkers have been studied and proposed for the detection of adverse health effects induced by lead (Pb), arsenic (As), and manganese (Mn); however, these studies have relied on exposures to each single metal, which fails to replicate real-life exposure scenarios. These three metals are commonly detected in different environmental, occupational, and food contexts and they share common neurotoxic effects, which are progressive and once clinically apparent may be irreversible. Thus, chronic exposure to low levels of a mixture of these metals may represent an additive risk of toxicity. Building upon their shared mechanisms of toxicity, such as oxidative stress, interference with neurotransmitters, and effects on the hematopoietic system, we address putative biomarkers, which may assist in assessing the onset of neurological diseases associated with exposure to this metal mixture.

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.

Cytochrome P450 expression in mouse brain: specific isoenzymes involved in Phase I metabolizing system of porphyrinogenic agents in both microsomes and mitochondria

Brain cytochrome P450 (CYP) metabolizes a variety of drugs to produce their pharmacological effects within the brain. We have previously observed that porphyrinogenic agents altered CYP levels in brain. The aim of this work was to further study the involvement of mice brain mitochondrial and microsomal Phase I drug metabolizing system when porphyrinogenic agents, such as Enflurane, Isoflurane, allylisopropylacetamide, veronal, ethanol, and Griseofulvin were administered. To this end, CYP2E1, CYP2B1, and CYP3A4 expression were measured. NADPH cytochrome P450 reductase (CPR) expression was also determined. Western Blots were performed in microsomes and mitochondria of whole brain. Some of the drugs studied altered expression mainly in microsomes. Chronic Isoflurane augmented mitochondrial isoform, although this anaesthetic diminished microsomal expression. Ethanol and topical Griseofulvin affected expression in microsomes but not in mitochondria. CYP2E1 mitochondrial activity was induced by acute Enflurane; while the activity of the microsomal protein was enhanced in alcoholised animals. Ethanol also induced CYP2E1 expression in microsomes, although Isoflurane provoked opposite effects in mitochondria and microsomes. Expression of CPR was also induced. Several reports support an emergent role of CYP enzymes in the pathogenesis of neurological disorders, so CYP response in brain could be one of the multiples factors influencing porphyria acute attacks.

Drugs and acute porphyrias: reasons for a hazardous relationship

The porphyrias are a group of metabolic diseases caused by inherited or acquired enzymatic deficiency in the metabolic pathway of heme biosynthesis. Simplistically, they can be considered as storage diseases, because the partial enzymatic defect gives rise to a metabolic "bottleneck" in the biosynthetic pathway and hence to an accumulation of different metabolic intermediates, potentially toxic and responsible for the various (cutaneous or neurovisceral) clinical manifestations observed in these diseases. In the acute porphyrias (acute intermittent porphyria, hereditary coproporphyria, variegate porphyria, and the very rare delta-aminolevulinic acid dehydratase ALAD-d porphyria), the characteristic severe neurovisceral involvement is mainly ascribed to a tissue accumulation of delta-aminolevulinic acid, a neurotoxic nonporphyrin precursor. Many different factors, both endogenous and exogenous, may favor the accumulation of this precursor in patients who are carriers of an enzymatic defect consistent with an acute porphyria, thus contributing to trigger the serious (and potentially fatal) clinical manifestations of the disease (acute porphyric attacks). To date, many different drugs are known to be able to precipitate an acute porphyric attack, so that the acute porphyrias are also considered as pharmacogenetic or toxygenetic diseases. This article reviews the different biochemical mechanisms underlying the capacity of many drugs to precipitate a porphyric acute attack (drug porphyrogenicity) in carriers of genetic mutations responsible for acute porphyrias, and addresses the issue of prescribing drugs for patients affected by these rare, but extremely complex, diseases.

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.

N-alkylprotoporphyrin formation and hepatic porphyria in dogs after administration of a new antiepileptic drug candidate: mechanism and species specificity

A new antiepileptic synaptic vesicle 2a (SV2a) ligand drug candidate was tested in 4-week oral toxicity studies in rat and dog. Brown pigment inclusions were found in the liver of high-dose dogs. The morphology of the deposits and the accompanying liver changes (increased plasma liver enzymes, increased total hepatic porphyrin level, decreased liver ferrochelatase activity, combined induction, and inactivation of cytochrome P-450 CYP2B11) suggested disruption of the heme biosynthetic cascade. None of these changes was seen in rat although this species was exposed to higher parent drug levels. Toxicokinetic analysis and in vitro metabolism assays in hepatocytes showed that dog is more prone to oxidize the drug candidate than rat. Mass spectrometry analysis of liver samples from treated dogs revealed an N-alkylprotoporphyrin adduct. The elucidation of its chemical structure suggested that the drug transforms into a reactive metabolite which is structurally related to a known reference porphyrogenic agent allylisopropylacetamide. That particular metabolite, primarily produced in dog but neither in rat nor in human, has the potential to alkylate the prosthetic heme of CYP. Overall, the data suggested that the drug candidate should not be porphyrogenic in human. This case study further exemplifies the species variability in the susceptibility to drug-induced porphyria.

Alterations of the redox state, pentose pathway and glutathione metabolism in an acute porphyria model. Their impact on heme pathway

A classical acute porphyria model in rats consists of combined treatment with 2-allyl-2-isopropylacetamide (AIA) and 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC). The present work describes the effects of this treatment on the pentose phosphate (PP) pathway, glutahione metabolism and redox state and how they contribute to alter the glucose pool of hepatocytes and modulate porphyria, in Wistar rat livers. Our approach is based on the fact that glucose is a repressor of 5-aminolevulinic synthase (ALA-S), the rate-limiting enzyme of the heme pathway, and treatment with AIA/DCC causes oxidative stress. Different doses of the xenobiotcs were used. The results show that AIA (500 mg/kg body weight [BW])/DDC (50 mg/kg [BW]) treatment increased glutathione peroxidase (GPx) activity by 46%, decreased both glutathione reductase (GR) and glutathione S-transferase (GST) activity by 69% and 52%, respectively, and reduced by 51% reduced glutathione (GSH) and increased by 100% glutathione disulfide (GSSG) concentrations, therefore lowering by four-fold the GSH/GSSG ratio. The activity of glucose-6-phosphate dehydrogenase (G6PD), the rate-limiting enzyme of PP-pathway, was increased by 129% as well as that of 6-phosphogluconate dehydrogenase. NADPH and the NADPH/NADP(+) ratio were increased by 14% and 28%, respectively. These effects could be attributed to the generation of reactive oxygen species (ROS) elicited by the porphyrinogenic treatment, shown by enhanced DNA damage and ROS production. G6PD stimulation would decrease hepatic glucose concentrations and consequently exacerbate the porphyria. A decrease in glucose could stimulate ALA-S and this would add to the effect of drug-induced heme depletion. Since the key role of GST is to inactivate toxic compounds, the drastic fall in its activity together with the accumulation of ALA would account for the symptoms of this hepatic disease model. The present findings show the high metabolic interplay between pathways and constitute a relevant contribution to achieve a better treatment of acute human porphyria.

The potential role of cell penetrating peptides in the intracellular delivery of proteins for therapy of erythroid related disorders

The erythroid related disorders (ERDs) represent a large group of hematological diseases, which in most cases are attributed either to the deficiency or malfunction of biosynthetic enzymes or oxygen transport proteins. Current treatments for these disorders include histo-compatible erythrocyte transfusions or allogeneic hematopoietic stem cell (HSC) transplantation. Gene therapy delivered via suitable viral vectors or genetically modified HSCs have been under way. Protein Transduction Domain (PTD) technology has allowed the production and intracellular delivery of recombinant therapeutic proteins, bearing Cell Penetrating Peptides (CPPs), into a variety of mammalian cells. Remarkable progress in the field of protein transduction leads to the development of novel protein therapeutics (CPP-mediated PTs) for the treatment of monogenetic and/or metabolic disorders. The “concept” developed in this paper is the intracellular protein delivery made possible via the PTD technology as a novel therapeutic intervention for treatment of ERDs. This can be achieved via four stages including: (i) the production of genetically engineered human CPP-mediated PT of interest, since the corresponding native protein either is missing or is mutated in the erythroid progenitor cell (ErPCs) or mature erythrocytes of patients; (ii) isolation of target cells from the peripheral blood of the selected patients; (iii) ex vivo transduction of cells with the CPP-mediated PT of interest; and (iv) re-administration of the successfully transduced cells back into the same patients.